Embed Size (px)
Citation preview
2 MR 82-5
Floating Bieakwater
Field Experience, West Coast
by
Eugene P. Richey
MISCELLANEOUS REPORT NO. 82-5
JULY 1982
COIaFS 0~'r
_Ap'pr~o~ved_ fo-r -public -release; 0 ~V I. 8 98distribution unlimited.
Prepared for JA
U.S. ARMY, CORPS OF ENGINEERS
>.. COASTAL ENGINEERINGC> RESEARCH CENTERC..)
Kingman Building
Fort Stlvoir, Va. 22060
LA.~
,,7
Reprint or republication of any of this materialshall give appropriate credit to the U.S. Army CoastalEngineering Research Center.
Limited free distribution within the United Statesof single copies of this publication has been made bythis Center. Additionai copies are available from:
4 :.ationaZ Technical I,.ornmation Service4: TTN: Operations Diviaior
.5285 Foy't RoyaZ Reoc.d17p Fp ngqfield, Vir•gi•nia 22162
Contents of Litis rt.port are not to be used foradvertising, publicat ot!, or prumotional purposý.s.Citatioli uf trade names does trot constitute ar: uEficial"endorsemtent or approva. of the use of isuch commercialproducts.
The fittdings in thit report ire nut to be construedas an ofticial epartmen. of the Army poiition unles6so destat4d by other authorized documunts.
LIJCLASS IFIE1VSECURITY CLASSIPICATION OFF THIS PAGE (0lo00 Doea fftn~rnoE) ________________
ION PAGEREAD INSTRUCTIONSREPORT DOCUMENTATINPG BEFORE COMPLETING FORMREPORT7 NUMBE; 12. 1OVY ACCESSION 1,10 2. 04 IP1 jT'S CATALOG NUMBER
fll'. 82- .~
4. ITLE it (j !I. TYPE OF REPORT 4 PERIO0) COVERED
FLOATING BREAKWATER FIELD EXPERIENCE, Miscellaneous ReportWEST COAST *. PERFORMIN ORG, RE PORT NUMBERt
7. AUTHOR(s) 11. 4RACT OR GRAiNTHMUER~O)
Eiugene P1. rzeichy
*S. PERPONM#NG ORGANIZATION NAME AND AOORESS 10. PROGRAM ELEMENT. PROJECT. TASK
Depatmet o Citl Etitcarvi;AREA A *JRK UNiT NUMBERS
Unive rs ity of Wa~shtington 1)31671)Seareic',, Washiington
it. CONTROLLING OFFICE NAME ANtO ADDRESS I2. REPORT DATE
Departnene of the Army July 1982-'Coastal iEhgir'eering Researchi Center (CERPE-CS) 1). NUMBER OF PAGES
Kingman fluildiny,, Fort Belvoir, Virginia 22960) 64IS. N-loSSYiNG AGENCY NAME a AOONE5Sit dIove mnI tem CoatUa 3oW.) IS. SECURITY CLASS. (at the anon)
I I5. OEKCLASSIPI-cA-TION/o-wdtAIrSCHEDOULE
* to. DISTRIBUTION STATEMENT (at Wei 8.flJ)
Approved for public release, distribution unlit-ite'i.
17. GIST RSBUTION STATEMENT (at t IA." ebaatefle to 640 WO. It 4hftrns Am.. LtOgof)
10. SUPLECMVOTARY NOTES
194 wEv noi (Coaslas. an ey** #e si$ It ea*o" ada 14t0sy Or b49 Ouhemuf) -
Fhdld evaluation pertormAnee Floating breakwaters
ki tatotf lwjittoatugo an flcaitma breakwotora to lacqhtag ftied tnkftosntýf ea the eaaotruettcnt tad aubeoqueaipeftatoaatofa these structure*. Ihtt COP0at Partially a&iuooons this dettetaacy by evaluattng AI eutettat
floattng breakwaersa loc~a tedI the ratctle Mrtheioes. The breakiatotao Coas~tat ct flee cCoutset eatioqo unit*,throO £AAkaa&-eoeanraa 09 lodder-tyieo breakatese eonotrgcto at pctea cd connte a11gnsto, a"e Com-atrugtsd at surplus Oll ?trholl" aecttcat. Sea (ke4jear floatitn-tlre W4419e bffaakwateg. OWsad#e with catteecaalatstg ot teats row ot plaone petaloes. The repor4tlacluites a dorptc at ach ait. and breske'uo
* attvLeturo. a diocumulco at the beoakwaser'a paatowaace based c& stotelepnctteas awl dleeotusaoji with osAlrs,"Aettae epovetov*ate., &ad a set at eeselusatc toe tho oenroll snaleatloa, of eta etuettaeo.
DOD Pjg oft 3 EWIOO 9MO hOMOUT LUCLASSIFIEP
Sccumrv CLAWPSCAIIO*l OP T*01 i'AGE (9bo Dee. Iaead)
PREFACE
This report is published to provide coastal engineers recent field expe-rience with the design and construction of floating breakwaters on the westcoast of the United States. A similar report will be published on field expe-rience with floating breakwaters on the east coast; both reports should pro-vide practical guidance for coastal engineers. The work was carried out underthe U.S. Army Coastal Engineering Research Center's (CERC) Design of FloatingBreakwaters work unit, Coastal Structure Evaluation and Design Prugram, Coast-al Engineering Area of Civil Works Research and Development.
MTe report was prepared by Professor Eugene P. Richey, Department of CivilEngineering, University of Washington, Seattle, Washingt'on, under contra:twith the U.S. Army Engineer District, Seattle. J W. Heavner, Graduate Sta-dent, Department of Civil Engineering, University of Washington, assisted withfield surveys and data collection.
W.N. Seelig was the CERC monitor for this effort, under the general super-vision of Dr. R.M. Sorensen, Chief, Coastal Processes and Structures Branch,and Mr. R.P. Savage, Chief, Research Division.
Technical Director of CERC was Dr. Robert W. .4halin, P.E., upon publica-tion of the report.
Comments on this publication are invited.
Approved for pabltcation in accordance with Public Law 166, 79th Congress,&ýQproved 31 July 1945, as supplemented by Public Law 172, 68th Congress,approved 7 Novembcr 1963.
Colonel, Corps of i er.Comiaa'der and Direc~dr
roll• • 19i 1 1. !-4 i _
3~
CONTENTSPage
CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI)......,............. 6
II FLOATING BREAKWATER SITES................... .. *........ 8
12. KS'tckan, Alaska, .... 15 . . ...... ec00* .
3. Tenakee Springs, A .. 234. Auke Bay, Alaska ........ 295. Friday Harbor, Washington (Port of Friday Hataor).............. 336. Friday Harbor, Washington (University of Washington
Oceanographic Laboratory) ... *.... .* ...... ..... g... ............ 397. Blaine, Washington .... ........ ..... .. , ........ . . ....... 428. Langley, Washingt7on. ...... o...... .... . . . . g....
9. Everett , Washington.......... .......................... ... 5010. Port Orchard, Washington.......... ....e.....o.e o . ..... OO.*. . o.... 5311. Camas-Washougal, Washington......... ,..... ....... . ....... 56
III SUMMARY AND CONCLUSIONS ......................... .............. .... 60
TABLE
Winds at Japonski Airport, Sitka, Alaska........ ................. 20
FIGURES
1. Ketchikan, Alaska 9
2 Photos of floating breakwater, Ketchikan, Alaska...................... 10
3 Typical breakwater module.................. ........ 0 . ...... .... c 12
* 4 Layout for Ketchikan floating breakwater..e.....o.oeo.......,o.......o 13
5 Photos of gaps at both north and south of harbor, Ketchi•:an, Alaska... 16
6 Sitka Lwreakwater,.. . , . , . ...... ........... 17
7 Sitka, Alaska. ...... ......o ... . .... ........ . .. ,....0.. 18
8 Photos of facilities at Thomsen Harbor, Sitka, Alaska ....... c.....e.... 19
9 Photos of module connections, Thomsen Harbor.e...e.......o..... ... 22
10 Tenakee Springs, Alaska.......,..,..... 0 .... c . .0 . .... 0 . 0 0 • *, 24
11 Floating breakwater layout, Tenakee Springs, Alaska.e... ... e....g.... 26
12 Photos of floating breakwater, Tenakee Springs, Alaska....e,..... 27
13 Replacement module connector for floating breakwaterTenakee Springs, Alaska...... . ..... . . . • • ... . •. • Ce 0 000 .. 28
14 Photos of deterioration and patching, Tenakee Springs, Alaska...oo..., 30
4
. . . . .... . .. .. ........ . ... i -o .°,,,,,,,., , r -•= i_
CONTENTS
FIGURES-ContinuedPage
15 Auke Bay, Alaska ...... ..*...*..... ........................... 31
16 Photos of floating breakwater sections, Auke Bay, Alaska............,. 32
17 Friday Harbor, Washington......... ..... .. .......... .................. 34
18 Windspeed-duration curves, Friday Harbor, Washington................ 35
19 Cross section of Port of Friday Harbor breakwater.........,........... 36
20 Layout of Port of Friday Harbor breakwater......... ................... 37
21 Photos of the Port of Friday Harbor floating breakwater............... 38
22 Photos of University of Washington Oceanographic Laboratory,Y'r day aro......... .................... ... 41
23 Semriahmoo Spit Marina, Blaine, Washington.. .......................... 43
24 Module connection, Semiahmoo Spit floating breakwater.. .... ,6.... .... 44
25 Semiahmoo Spit Marina anchor detail .................................. 45
26 Photos of the module detail of the Semiahmoo breakwater............... 46
27 Floating tire breakwater, Langley, Washington......... .............. .. 48
28 Windspeed-duration curves, Puget Sound.............................. 49
29 Photo of floating tire breakwater, Langley, Washington..............., 50
30 Port of Everett, Washington, iloating breakwater site.............,.. 51
31 Photos of the floating breakwater at the Port of Everett
32 Port Orchard floating breakwater site................................ 54
33 Floating breakwater and marina, Port Orchard, Washington.............. 55
34 Schematic drawing of module connection, Port Orchard floatingbreakwater.. .,. . . .... ... .... ... °....... ..... ........ ... ... .... $55
35 Photos of anchor chains ut the Port Orchard floating breakwater....,.. 57
36 Camas-Washougal floating breakwater5.................................. 58
37 Photos of the Port of Cams-Washougal floating breakwater..........,. 59
38 Photos of the main section of the Port of Camas-Washougalfloating b. .
, 4d.4j..-' • * •.. •*". s.W• '.'t * • .D .0'.' * .' ,
CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI) UNITS OF MEASUREMENT
U.S. customary units of measurement used in this report can bo converted tometric (SI) units as follows:
Multiply by To obtain
inches 25.4 millimeters2.54 centimeters
square inches 6.452 square centimeterscubic inches 1.39 cubic centimeters
feet 30.48 centimeters0.3048 meters
square feet 0.0929 square meterscubic feet 0.0283 cubic meters
yards 0.9144 meterssquare yards 0.836 square meterscubic yards 0.7646 cubic meters
miles 1.6093 kilometers
square miles 259.0 hectares
knots 1.852 kilometers per hour
acres 0.4047 hectares
foot-pounds 1.3558 newton meters
millibars 1.0197 x 10- 3 kilograms per square centimeter
ounces 28.35 grams
pounds 453.6 grams0.4536 kilograms
ton, long 1.0160 metric tons
ton, short 0.9072 metric tons
degrees (angle) 0.01745 radians
Fahreheit degrees 5/9 Celsius dearees or Kelvins1
ITo obtain Celetus (C) temperiture readings from Fahrenheit (F) readings,
use formWla: C - (5/9) (F -32).To obtain Kelvin (K) readings, use formula: K , (519) (F -32) + 273.15.
-------.... . .. ...- -
FLOATING BREiAKWATER FIELD EXPERIENCE, WEST COASTby
Eugene P. Riohey
I. INTRODUCTION
The increased demand by the boating public and industry for more mooragefacilities challenges the planners and designers of small-craft harbors toexplore all alternatives in developing harbors that have adequate protectionfrom wind waves and boat wakes. Most of the naturaC harbors developed nearpopulation centers, where boating demands are greatest, are ov'vcrcowded.Floating breakwaters have become an alternative with an active potential infuture harbor-marina design. The floating breakwater has been adopted at anumber of sites where water depth or other constraints render a fixed struc-ture too costly, and is proposed for countless others. Although there areother uses for floating breakwaters, such as in waterfront construction andoperation, log rafting in the timber harvesting industry, beach erosion con-trol, etc., the most prominent applications relate to the small-craft harboror marina.
On location, the floating breakwater is subject to random wave loadingswhich can induce motions with components in all directions. The intended jobof the breakwater is to reduce the incident wave system to an acceptablelevel. The transmission characteristics of this reduction capability arevery sensitive to the period (or length) of the incide:.t wave field. Numerousreports on model tests of transmission characteristics are available, butreports on actual field experiences with floating breakwaters are few.Although several floating breakwaters have been in use for as long as8 years, there has been little information excharged as to the type of break-water, the anchorages, and the connections between units. These are con-sidered major points of interest in improving the design of floating break-waters.
To cover these points, the following questions were established as achecklist for eialuating field experience with construction and subeequentperformatce of floating breakwaters:
(1) What were the site conditions and why wac the fioatingbreakwater chosen?
(2) Now was it deployed?
(3) Were there any unusual installatton problems?
(4) What anchoring and connector systems were used?
(5) have there been any fouling, corrosion, or fatigoaig prob-* lems!
(6) What maintenance has been carried out?
(7) Have any environmental problems (shoreline changes, icing,stability) been encountered?
7
(8) Does the structure serve functions other than wave attenua-tion?
(9) What, changes in any step from design to operition would be
done differently now?
(10) Has the structure served its intended purpose?
This report picovides an evaluation of 11 floating breakwater installaLionslocated in the Pacific Northwest--the thrust of the evaluation being the ques-tions listed above. The results of each site evaluation are ,resented, anda list of conclusions summarizes the overall field performance of floatingbreakwaters.
II. FLOATING BREAKW.iTER SITES
1. Ketchikan, Alaska.
a. Location. The Bac Point Harbor breakwater is located on the northside of Tongass Narrows, a fjordlike waterway, at Ketchikan, Alaska (Figs. 1and 2). There are 390 moorage spaces planned for both pleasure and fishingcraft. Most of the boating activity occurs in the period 15 June to I Novem-
,t ber, which spans the seasons for tourism, pleasure craft) and fishing.
b. Site Conditions. The fetch toward the southeast is about 8 miles,about a half-mile across the waterway and practically unlimited toward thenorthwest. Structures along the shoreline shield the breakwater along thesoutheast-northwest line. The wind waves travel neirly parallel to the break-
. water, and sustained wiridspeeds of 45 to 50 miles per hour with gusts to 70miles per 1our are to be expected most winters.
Tide data are as follows:
•ighest (estimated): 19.5 feet
Mean higher high water (MMUW): 15.4 feet
Mean: 3.0 feet
"Mean lower low water (MLLW): 0.0 fot
Lowest (estimated): -5.0 feet
Tidal currents are frea south to qortli on both flood and ebb, with ~iatuumabout 6 knota according to harbormaster; National ceanic and UmosphericAdministration (NOAA) tidl current data report only 1.2 knots. Bottom ele-vations are as follows:
Along tater row of uchor4 -20 to -60 feet
Alotg breakwater: -50 to -70 feet
A o- orteor ei', isf 'vtchoras: -100 to -110 feet!8
0,1.
. 4 2/ !'\
"41'POW•f, \ Ii, 2."
2'' , , o ioo , 4 ,, 1
22 Bar HarvborP ' Flooling Breokwoter 'It
*14 1 *- ~ 24
S•Mar
I?~~ KET CH MIAN v~ 3
1" I',,14
1 $.. .L .. .I" t'{ ' . .. . . . . . . - • Lx, S,
19 4
60
-X \At
1. t'tclk t Alta(r il 73)
a. Utain entraacu to gar Ularboor.
b. KUlc iloatttt breiskwtter,, Mjouch to QtbCtt view.
VIt~uve 2. ftotoou it tkoatt brcjksatear, £etehik.A#.Ats4
No recordings of wave conditions have been made. boat wake loadings arefrequent, because boat traffic Is heavy, with vessils ranging in size from"small pleasure ccaft to the fishing fleet size, Including heavy trawlers,purse siners, oceangoing cr'stse ships, ferries, and freighters.
c. Brea.-a ter Description.
(1) Desin. The structure is of the Alaska-catama' n or ladder type,23 feet wide and 6 feet deep, made of posttensioned, foam-filled modules oflightweight reinforced concrete (Fig. 3). The main breakwater is 963 feetlong, parallel to the shore (and Tongass Narrows). A separas 120-foot sec-tion was positioned off the end of a rock breakwater forming Bar Harbor No. 2to attenuate waves from the south. Ihe layout is shown in F,.are 4. A 165-foot section planned at the northern end was omitted to avoid :,Znflict with aloading pier. Anchor chains at 60-foot Intervals connect th.. breakwater toconcrete anchor blocks weighing 18 tons on the inside and 60 t-ns on tle out-side; 100-ton anchors hold the 120-foot section.
(2) ln:-alt.ation. Itntallation began in Octo-Pr 1979. Storm damage"occurred during construction to unassembled units mo..- ad at the site. Thecost (1980) of the breakwater was $1,400 per foot. Iho~e responsible for the
* breakwater design, construction, and operation are ato fallowb:
Owmnr-Operator: City and Borough of NatCchikan, Alaska
Designers: U.S. Army Engineer District, AlaskaAnchorage, Alaska
Tryck, Nymaa and RayesAnchorage, Ataska
4uilder: Concrete TechnologyTacoma, iashingtou
luotallers: Dawoao Conastruction
Smart Crane CoapanyKotchikan. Alaoka
Ttw, following ameonta on installation woro ia tractod fe 4a tactervt* ~with out of the intallera of Smart crmxfe copany (A. SmAr):
Tte wAjor difficulty pertneced was strtaitaog, flushiag, dreas-tag, and Oealeta the Poattnotwio Cables itn the ros-t-and tuets.Wttoika between 4jaertt a4ultc rarely ltrod up. Th* geriral am• s"blytechaique Was a dtiffcult prueoedure to carry out I a eid euiot-t rons. Lar4ge diaaetor, 1eor .tfieod ddlvatlvixed . tu ld h4v"been raster to une. 11w 1-inah c•ble uth threaded t*ud* u*A- kojoin 240-foot seetans t&s difftcalt to tightien, Aittoe OWe eiblerotated aA ithe nuts wood totwd~~. Towtiig of the (240.-I not t nsw3iery difticult O~eeeti at a fery lo li ped. A swkit "is 41,alit
* anoore o A tug. Vi te was doftilt -ite of he *torC
11 ia iO uhrWO4co
- I.- -0
sit
flol~ ~'Srr
0 v0
4~ý I I t~i
K' it
A'" AV - i
- - - V'12-
-. .n-i
-l , -. * -:, *]
S ' .,. '•~* •1
:'" , 'I !'' ~ // / -•/t I -. l
.!.....iV..
--- 1- (4. .- -t /*
.;iI
II*~
A. c. . .I " -- . .
,,V " '-' ' .' A1
:"// .• / ,,••/: , , ,- . l . ,•.
,",.' H!.'
'-I,: ( , •.
0a ",
• 44'-, , , . ,, , i.-~ - . ... ,
"':,H. , • , . a. •
I . 1..3
: - t
i. /
"
I7-7
4 bottom slope and bottom conditions; 6- to 8-ton steel anchors would havebeen much better, Special receptacles for navigation lights should bedesigned into the breakwater units.
The following comments on the design and installation of the floatingbreakwater were provided by the U.S. Army Engineer District, Alaska:
Use epoxy coatings over steel reinforcement to reduce cor:o-slon. Provide positive locking devices at the ends of connectingcables. Obtain sufficient bottom data to allow workable anchoragedesigns. Some problems with anchor placement were experienced owingto a lack of good topography and know'edge of what materials theanchors would be set on. Consideration should be given to providi~iga method of regreasing tendons and cables. This design was made withthe premise that vessels would not be allowed to tie up to the bieak-water. The design must provide heavy wales and recessed bolts toallow for protection of the breakwater from vessels that tie up tem-porarily. Provide for connections on end units for possible futurechanges In configuration. These can be temporarily seated withknockouts. Adequate lighting should be provided for foul weathervisibility of the breakwater to supplement U.S. Coast Guaid furnishedltghts. Radar visibility should also be provided. Better qualitycontrol should be achieved to eliminate careless slopping of greaseon concrete surfaces adjacent to the prestressed cable anchors. Pre-paration of construction specifications should consider the require-ment for a specific assembly method, such as on a sinkable barge, orin the water, or in a dredged area which can be flooded. Materialsand procedures used should be compatible with the assembly method.Constcuction problems were experienced during the process of cappingthe prestress cable heads in the water. Further consideration mightbe given to a cofferdam design which would allow this to be accom-plished in the dry. Consideration should be given to monitoringanchor chains to determine actual mooring forces to compare withdesign forces.
(3) Performance. The boat slips had not been installed as of Sep-tember 1980, so there are no data on breakwater effectiveness. The harbormas-ter expressed the opinion that the breakwater does peiform as expected. Pre-vailing wind waves attacking the breakwater are at a high incident angle, andthe alinement seems good, with lower transmission than fur normally incidentwaves,
The instaler (B. Sart) was on a barge tied to the breakwater during astorm with gusts up to 70 knots. He reported wave periods of 3.5 to 4 secondsand wave heights to 4 feet. based on the height of the barge rail above meanwater level: ". . . the breakwater really knocked the waves down." Threewavelengths were observed in the 100-foot barge length, which would correspondto about a 2.7-second period, ratter than the 3 to 4 seconds reported.
Logs up to 2 feet in diameter have worked their way into the interiorspaces of the breakwater, but have conveniently worked their way out. Therehas been rapid marine growth on the subtaerged surfaces.
14
- -- .'- - . . . .
Although Coast Guard regulations require lights only at the ends of thebreakwater, intermediate lights and radar targets would be helpful to naviga-tors because the breakwater profile is low, long, and difficult to see in thedark, stormy weather that is so frequent at the site. The breakwater has onlya 12-inch freeboard, instead of the 18 inches called for in the design. Afabrication error is believed to have caused the overdraft.
Wakes from vessels moving down Tongass Narrows from north to south movedirectly through the opening between the end of the rock breakwater formingBar Harbor No. 2 and the southern end of the floating breakwater, causingmotion of the slips and boats in Bar Harbor. The breakwater reduces the reg-
- ular boat wake quite well, but the potential exists for the large fishing ves-sel, tug, or freighter to set a wake that will be very evident behind thebreakwater.
d. Discussion. The water depths at the site indicate the floating break-water is the logical type to meet the local need for additional mooragespace. In the design of future breakwaters of this type, attention should begiven to the difficulties encotntered in the field in carrying out the post-tensioning operation, the connection of modules, and the placement of theheavy anchors. The omission of the breakwater section at the north end of theharbor (Fig. 5) means that some of the mooring area will receive undamped waveenergy. Possibly, the placement of slips in this section should be delayeduntil alternative protection is provided.
South-traveling wind waves and boat wake readily pass into Bar HarborNo. 2 between the south end of the floating breakwater and the north end ofthe rock breakwater. Some corrective alternatives are as follows:
(a) Aid a stub section about normal to the south end of the pres-ent floaLing breakwarer. Alinement would have to give due regard towavus from the south being reflected in adverse directions.
(h) Reinstall the log breakwater (or similar) that previouslyshielded Bar Harbor No. 2.
(c) MAust the anchor system of the main breakwater to allow itto he rotated about 5e, and add an extension to narrow the harborentran.ae from its present 400-toot width.
A pragmatic view is to adapt the floating breakwater to accommodate tran-sient moorings. As it is uow. transient boaters remove covers from the anchorchaitn wells, fasten lites to hawse pipe or chains, then leave without replac-tag thie covers. Tiedown cleats. Lhicker walers, camels, or other fenderingsystems would be required, along with a walkway to make a connection with themain floats. Thi" connection could oe removed during the off-season.
, 2. .i.ka, Alaska.
a. locatic,.. 11tomsen Harbor is on the east side of the waterway betweenJaponski Island and hzaranof Island, where Sitka .s located (Figs. 6 and 7).T1he waterway is about 1,•00 feet wide and 40 teet deep. The breakwater isused for transient Moorage and has a *tsh-c0eaniig facility (see Fig. 8) for"the counvetaence tit the harbor uiers.
Is
. .~ .. ........
a. North end of harbor.
b. South edof hairbor.
Figure S. Phot~os of apA a t both niorth anidsouth of harbor. IKOtchikafl Alaska.
16
3 -3
~ t4.,tcaI Mile
* Ii
4 t s 0
Al
6. \/ SITKA HARBOR=s 6; Scale 1:5,000
SOUNDINGS IN FATHOMSAT MEAN LOWER LOW WATIR
T' 3,
4: jl' 3.
3, 3. 3i
.5 7
2bi..- • u:'." -•,, '' "
414y i . 41 J1
-,.•,. , - " ..•,. .• tA ab * . ' 3l%
N S
\\ - -,A le.i ...
-%
6 .~'~
Fi~ur• 6. Sithka br~akwvst~r (from d10S ehar• 17327).
17
. . 0
-~~ 0.1t
00 8-
" " .,p
#4
.pI D,,ckC
UlU
0(0
14~ 0
'4 a--I4
SS
7777
a. Floating breakwater.
b.Fish-clteaning facility.
F~igure 8. Photos of facilities at Thomnseni Harbor,Sitka, Alaska.
19
b. Site Conditions. The principal wave window lies in a 450 sector cen-tered about the northwesterly direction, and has a fetch cluttered by smallislands out to about 3.5 nautical miles, then opens into Sitka Sound. The siteis effectively shielded from other directions. The winter low-presci~re sys-tems off the Alaskan coast generate high winds. Local lore reports thatspeeds of 60 knots are common. However, the annual summary of winds at Japon-
* liski Airport (see Table) indicates that 40-knot winds are rare (Amerman,1980)1. The many islands in the path of the winds must create highly non-uniform wind fields.
Table. Winds at Japonski Airport, Sitka, Alaska (Amerman, 1980)2
Windspeed (kn)Direction 0-3 4-10 11-21 22-27 28-40 40+ Pct. Avg.
N. 1.6 0.5 0.1 0.0 0.0 0.0 2.1 3.0NNE. 0.2 0.1 0.0 0.0 0.0 0.0 0.2 4.1NE. 1.7 1.7 0.4 0.0 0.0 0.0 3.8 5.3ENE. 0.3 0.6 0.3 0.0 0.0 0.0 1.3 6.6E. 3.4 6.3 1.6 0.1 0.0 0.0 11.3 6.5ESE. 1.0 4.7 4.0 0.3 0.1 0.0 10.1 10.7SE. 3.7 10.0 4.1 0.2 0.1 0.0 18.1 7.9SSE. 0.3 0.9 0.3 0.1 0.0 10.1 8.1S. 3.3 4.7 1.4 0.1 0.0 9.5 6.4SSW. 0.5 1.6 0.3 0.0 0.0 2.5 6.6SW 2.2 4.6 0.6 0.0 7.3 5.6WSW. 0.2 0.7 0.1 0.0 0.0 0.0 1.0 5.4W. 2.1 2.1 0.1 0.0 0.0 0.0 4.3 4.2WNW. 0.6 1.6 0.4 0.0 0.0 0.0 2.6 6.8NW. 3.1 5.5 1.2 0.0 9.9 6.0NNW. 0.3 0.4 0.1 0.0 0.0 0.0 0.8 6.0Calm 13.4
Total 24.5 46.2 14.8 0.8 0.2 0.0 86.6 6.0
The harbor serves a fishing fleet and pleasure craft with moorage fees at$6 per foot per year, with a 2-year waiting list. The mix of boats is shift-ing toward larger sizes.
Tide data are as follows:
High: 12.0 feet MLLW
Diurnal range: 9.4 feet
Mean range: 7.7 feet
Low: 5.0 feet MLLW
IA4ERMAN, R., "Sitka Small Boat Harbor Rite Study," State of Alaska, Depart-ment of Transportation atnd Public Facilities, Division of Harbor Design andConstruction, Apr. 1980.
S2ANERMAN, R'# op. cit2
20
Tidal currents are 1 knot maximum on both flood and ebb. Bottom elevationsare -35 feet MLLW under the long leg of the breakwater and -6 feet MLLW at theshoreward end of the short leg.
Waves estimated at 4 feet in height have been reported coming in from thenorthwest. These strike the breakwater at an appre,ýiable angle and are atten-uated quite effectively. Ocean swell penetrates the offshore islands andpasses through the breakwater. Boat wake is a common loading from the pleas-ure craft, fishing vessels, and the occasional tug which ply the channel.
c. Breakwater Description.
(1) Desin. The structure was the second one built of the Alaska-" catamaran or ladder type, and consists of 3- by 5- by 18-foot reinforced,
lightweight concrete pontoons cast over solid polystyrene foam blocks. Threepontoons were posttensioned on site to form 60-foot modules, which were then
4. linked with a chain-rubber back fender connector as illustrated in Figure 9.The main leg of the breakwater is 685 feet long; the shorter one is 275 feetlong, with a 3.5-foot draft.
Anchoring was accomplished with 1-1/4- and 1-3/8-inch galvanized stud-linkchain at each module fastened to stake piles. Where the stake piles could not"be driven to adequate penetration, as determined by jetting tests beforeinstallation, concrete blocks were added to increase lateral resistance; 29-ton units were used on the windward leg of the north-facing (short) leg of thebreakwater, and 12-ton units were used on the west-facing (long) leg. A space"of about 6 feet is maintained between the two breakwaters at the junction ofthe "L" base. This design feature was used to avoid stress problems likelywith a positive connection.
(2) Installation. The breakwater was installed in 1973 at a cost of$480 per foot. Those responsible for the breakwater design, *.... " on, and
* operation are as follows:
Owner-Operator: Owned by State of Alaska, but operatedby City of Sitka
Designer: State of Alaska, JuneauDivision of Harbar Design and
Construction
Design Enginee': D.S. Miller
Fabricator:. Xellingham Marine ItdustriesBelliugham$ Washington
Installation: Units were fabricated in Bellingham andbarged to the site. basic dimensiongof the breakwater were chosen to facil-itate shipping and onsite erection withequipment readily available in thearea. T.O. Paddock Company, Juneau,was the erection contractor.
21
a. Module connection.
b- KOdul@e cOguction vith feader misig
Ftgurqe 9. fttl Of mudulceOm eo cttou", Uumoau 16rbor.
(3) Performance. The users are satisfied with protection affordedby the breakwater. Mooring lines and dispositions are adapted to accept theswell and boat wake that enter the harbor.
No underwater components of the breakwater have been checked. The onlyuaintenance provlem has been repairing and replacing worn chain links con-necting the modules; several rubber bumpers, part of the connecting systemsbetween modules, have disappeared (Fig. 9). There is some correlation betweenmissing bumpers and worn chain links. Although the breakwater is not consid-ered the responsibiity of the harbormaster, he has been welding worn connect-ing links and checking for other stress points.
"Lightweight concrete was used in forming the breakwater modules. Thereare several spall areas that have been attributed to banging of corners, etc.,during transport and construction. Some of these were successfully patchedwith epoxy shortly after construction. Some of the reinforcement is exposedand rusty, but spalling is slow, if at all.
Because of the shortage of mooring spaces, large trawlers tie up to bothsides of the breakwater, and may be the cause of the nonlinear breakwateralinement observed. The mass per foot of the trawlers may exceed that of thebreakwater. A differential draft has developed on some sections, with 14"inches of freeboard on one side of a pontoon and only 12 inches on the otherside. No explanation is offered. Marine growth at Sitka is not as active asat Ketchikan.
d. Discussion. The breakwater has performw4 satisfactorily during its7-year life. Although the swell transmitted into the harbor has been a nui-sance, the users have adapted. Maintenance problems have been minor, mostlyinvolving replacing worn chain links. Underwater components should be inspec-ted. The present 3-link chain-rubber bumper module connections should bereplaced with & never, Improved design such as that employed in the revisionsat the Tenakee Springs breakwater, discussed in the following section. Tran-sitnt boats usually tie up at a floating breakwater, whether or not such useis authorized. Designs should recognize this pattern or operatious personnelshould be given time and authority to restrict tie-ups.
3. Tenokee Springs,. Moaa.
a. Location. Tenakee Springs, Alaska (Fig. lO), is a small village about60 miles southwest of Juneau, Alaska, with about 80 permanent residents whoare income-dependent upon fishing, crahbing (cann ry recently closed), .log-ging, retirement incomes, and limited tourim.
b. Site Wnditions. A owUl natural habtw is unprotected from thewest withate a bmut 5 miles out of Crab My around to the southe4otw hý.e the fetch ts about 3 miles from (brer 84y. Stores frco these diruc-tions are cowon tinter occurrences. There are no wind recordo for the stte,but according to local residents, speeds rauging fro& 60 to 70 miles per hourhave oCufred.
Tide data include a maximum range froo -ý to 420 feet NLW. Tidal cur-rents are less than I kAot at the breakwater site. bottom olevation arefollows:
It tavn 1. SN~IllM 1,04
C 'IV
CrabJ
Vn0301t ~ 'f. L. lk
*,~qP ~ ~eieisj 2 "I& 4~* grM)I'y.1
*4600
K Ii-%m'~-ONA :r
is 61 ai 2mp-
f, am set L) m"G
it T~ I
It1i ItC
tots
It tiafl
4~~' It V.1,40 ,
>6 ~Scale. 1:217.N028 S *~ l
Ii
Ii0SA
Along inner row of anchors: -15 feet NLLW
2 Along breakwater: -30 feet
Along outer row of anchors: -45 to -55 feet
* A wave monitoring program was in operation durtng the winter season of1973-74. However, maximum windspeeds recorded were only about 30 knots, which"is not representative of the usual winter season when, according to local res-idents, waves 4 feet and higher occur. Boat wake is not a problem.
The harbor is without power or other amenities. There is no harbormaste;nor deaignated official on the site. The operation is best described as "Alas-ken informai." Long-time local residents are a good source of information onthe harbor.
c. Breakwater Description.
(1) Desi.n. This structure was the first of the Alaska-catanaran orladder type, consisting of 3- by 5- by 15-foot reinforced, lightweight con-
Screte pontoons with solid polystyrene foam core. Units of 15 feet were post-tensioned with 1-1/2-inch galvanized bars to form the ladder module, 5 feetdeep, 21 feet wide, and 60 feet long, with a draft of about 3.5 feet. Fivemodules were coupled with chain linkt av- compression bumpers to form a 4hal-low V-shaped breaký.•iter 308 feet long, as shown in Figure 11. The V-Joint wasa weak link in the system, and was removed in 1977. The alinement was thenstraightened (see Fig. 12.a) with module connectors of a modified design shownin Figure 13, and an additional 60-foot icdtiou of breakwater added to helpclose off a wave window froa the southeast.
Anchor chains of 1-318-inch stud links at each of the tive 60-foot moduLesare attached oa the harborside to 26-ton concrete anchors and to two 26-tonanchors on the seaward side. A shallow soil layer over rock ruled out the useof stake piles at the site.
(2) tnstallation. The breakwater was installed in the fall oa 1972at a cast of $4-2-sp -irToot. It had been designed for field assembly wheirefacilities and equtpmcnt s*a WVre imited. The poutooas 4ad octher Cowpoueutswere barged to the site.
Assembly probhlms were cauted primarily by aoosquare facee en surfacesii ~that wore to be watched. Soae apalling of concrete oeectared dtavtn OhW d'ývet-opsent of the specified pos'teasioaed forees and was attribotetd to iswroperloeatiat of reinforcitg satal durtig fabricattioo. bitwaloa tuo tri couwce*.ttag modulesk aut be acural.e to avoid assitdly delays. %hose responsible torthe breakvator deotga, couastuctton* and opeoratiou ace as follows.
tietgur-Ottu-Opratr: state of MlaskAWtftlioot tof rota VW Mtgbo aDviswoa of Rerbor Wa dta 44d
Jutwau
-, •-` :e.•• •` ``-r•-• -•- • -- L• - r`-`.``r-*r•• •r*••• - .--- '- .-- -.-.. -, , .
,.5
00
" Ilr~toli New lroaaltt!
)i '; 5 . 0CC ( S , Sht 4 ) " " .
-20.. ..
-. N
N, '-- -N -•"' "'.""35- ,, 0
-4 0 N , , - ' , ' , - -5
Existing Breakwater N,
"N"- Existing P/silIflc of 1 -3
0' O" ' " iv"to0
" "'.,,0
S• ~~.. ,, , ' ,,4 5 f* '.~ N N ,/' Install Now CosoIIOtIiol 8 TOOe For Job)
N. \• - 30'i \ \ N0 50 100
SftNN N~ N -40
N \\\4 5
'S -50NN
55
Figure 11. Floating breakwater layout) Tenakee Springs) Alaska*
A',
! .4
26
.4r
a. Floating breakwater alinement.
.IN
Springs, Alaska.
27
~- --- -. - - - - - - -
I AC,0OO*AvAf 41 WIM*
ALA
4-4
Figurte 13. Repwacef n ACMul 4pcue .0t-m AMP& £toatin
breakwater, ~~~tnaeSpig,
---- ...
28 ýV'
Builder: Bellingham Marine IndustriesBellingham, Washington
Installer: Hartinsen BuildersPetersburg, Alaska
(3) Performance. The users are satisfied with the protectionafforded by the breakwater. Prior to Its installation, winter moorage was
'; risky and the boats often had to be moved to more sheltered waters duringstorms. The outer chain on the base of the V-section in the initialbreakwater layout broke during a storm (D. Miller, personal communication).This connection has been eliminated by the new alinement and new connectorshave been installed (see Fig. 12,b).
Some wire and rod reinforcement is exposed and rusted where the concretehas spalled off, as illustrated in Figure 14, but no progressive deteriorationis apparent. The spalling seems to have been the result of construction hand-ling and installation, rather than from use-oriented causes.
d. Discussion. Thie breakwater design is well matched to the site condi-tions for construction as well as to exposure and use. In 8 years, the onlymaintenance has been the straightening of the dog-leg alinement, a well-recog-nized weakness in the initial design layout. The new module connectors alsopromise to eliminate another weakness--the slack codition that develops asthe rubber fender unit loses its resiliency.
4. Auke Bay, Alaska.
a. Location. Auke Bay (Fig. 15), located about 20 miles north of Juneau,Alaska, is a popular moorage for pleasure fishing craft of area residents andtransient boats during the summer season.
b. Site Condition. The upper end of the bay, the breakwater site, is
well-sheltered except toward the southeast, where (bghlan Island limits thefetch to about 2.5 miles, except for a very narrow window of about 6 miles.There are no data avai!.tble on either tides or currents. Currents at thebreakwater are not likely to be a concern. No record'.ngs of wake couditions
.- are available.
c. Breakwater Description.
(I) Design and Installation. one 60-foot and two 120-foot lengths of4-inch-diameter oilp surplussed from the .Aayeska project were designedas a replacement for a decayed log breakwater shielding a small, privatelyowned marina at the head of Auke Bay. The breakwater sections were fabricatedin Seattle and barged to Juneau where they were off-loaded, as shown in Figure16, for to,ýing to Auke Bay. A wooden walkway on the pipes provides access to24-inch pipes, also with walkways, which serve as boat slips. The pipes wereballasted with seawater to a I-foot freeboard.
The breakwater was installed in July 1980 at a cost of $400 per foot.Anchor chain connection holds the breakwater in place. Those responsible forthe breakwater design, construction, and operation are as follows:
29
* S-
a. Exposed reinforcement~.
b. Epoy Pateh.
Teiuakot Sprtings. Alaska.
30)
4
IFloating BreaAsks ter
A4 I NOTE CPA.' Num;otus uncfl~e* Moo.W4 buoys
0e amcaamd in ow noelMUI COefW of
X ldl._".,'%l* ".... 1AKA ... " -.BAYm4 Nro~o
•24b
S°' I •S,/I
"I. *0.2 ", ';.. = .. *,moP l l.31 % W,),• 4 • ;~
b•in ,.| 4 ''• , •
of , ,' 4 30', ' , " .''
W. .1,
1031
*~2 w 3- r,',_ ...j. \'" 4• . • ; I". ,,.: "*i% ( |• \,,1. \•( .
, __ ,",1* S'4AD,,' ,) , I, ..1 ' 4. ,, .. l \ I ! - 1 .ta
" 4o)* " ,• , , i''"• f Sce].e: 1 :40,000 i
3931
I
.
04
U20
4,vJ
'AL 1-4
-7 T
Owner: Robert Weems
Designer: David S. Miller
(2) Performance. There are no data available.
d. Discussion. The breakwater is an innovative use of surplus mate-"rial. The pipe and anchor chain, available at scrap metal prices, should pro-vide better protection than the old log breakwater it replaces. The designallowed the owner to do the towing and much of the installation which mini-mized costs.
5. Friday Harbor, Washington (Port of Friday. Harbor).
"a. Location. Port of Friday Harbor, Washington (Fig. 17), is a major
stopping point for pleasure craft enroute to Canadian waters as well as tocruises in the San Juan Islands. It is also a stop for the Washington State"Ferry System, which serves the islands, and is a connection to VancouverIsland (Canada). Fishing vessels also use the harbor.
b. Site Conditions. As shown in Figure 17, there are two windwave expo-sures--to the southeast with a fetch of about 1 nautical mile and to thenortheast with a fetch of about 2 nautical miles. Windspeeds associated withthe northeaster that affects the region every few years reach the 50-knotrange with gusts to 70 miles per hour and impose the critical design conditionfor the breakwater because of the longer fetch in that direction. A set ofspoed-duration curves is shown in Figure 18.
Tide data are as follows:
Highest (30 December 1952): 11.00 feet MLLW
NNIlW: 7.70 feet
Mean: 4.75 feet
MLLW: 0.00 foot
Lowest (15 January 1949): -3.80 feet
Tidal currents are less than I knot. Bottom elevations are as follows:
Along inner row of anchors: -52 feet MLLW
Along main breakwater: -42 feet
Along inner row of anchors: -30 feet
Wave heights and periods of 2.9 feet, 2.8 seconds from the northeast and2.9 feet, 2.4 seconds from the southeast were weasured by the U.S. Army Engi-neer District, Seattle, during an observation period 1969-71. Similar waveweasurements were recorded from December 1974 to March 1975 by a University ofWashington project. However, neither of these monitoring periods was opera-tional when the critical northeaster occurred. Wakes from boats are a common
33
i I4 P 63 71 13
35 8a 53916, 6a 83 72 573
. 74 7
78 7e/ 64
/77 9 4 2
22 14 82 6 11$614792421
27 1
(74 68 576 45 1 't, 3 1?
30 its
80 62 Read Rock 4616 "* 26 37 61
"IlVeflity Of WaSftlngton2*Oftanqrshic Laboea 29 28 23
-- 6 24 6 st 6365 4S 2546 4
33 32 4
-' 7Dreakwat~er a 24
73 6f S 7 3
&.4
71 1..-, ?1.
74 14. a\Port ofFriday 1A A
HabrFloating,!~ ~
fit t
dS
Figure 17. Friday H~arbor, Washingtoni (from NO)S eIjart 18425).
34
70NOTE: Curves are 9stirnabes of probable maximum,
65 baled on USWI summary of strong winds atBeli~ngham, Wash., from 1930 to 1959,Whldby Island hourly wind record from 1949
so to 1951, anid detailed wind record forFriday Herb i from Now. 1969 to May 1971.
55
45
SSE 45
20
355
Ouratean tlhe)Figure IS. Wtndspeed-durActio curves, Friday Harbor, Washingtot.
oeccurreace. Large ferries eitcher approaching or leaving the landing, pasaclose to the breakwater, white moving at A eotwiderable sopeed.
c. Breakwariýr )Jescriprtton.
(1) Destgn and Installation. The floatingj breakwater 4t the Portof Friday Harbor and the oft at Toaakee Springs vsre the firsat thaj surh struc-tures of major dimension designed4 tor the h'acifte Notthwost Ln4 Wereý insteilLedat about the same time in October 1972. The Friday Utarbor sitructure, a dif-
feruc ypethn te Aasan addr tyLe, uses four rows 4t pollyale-fia pon-toonts about S by S by 10 feet in overall difflnsion, Linked by a cimbotr WAtrtxto formf a 24-fooc-t~tde stectL,-u drafting about 18 incetsp. A aitmptifted erf~gssection is aghqw i t. Figure. 19. The breakwater is laid out ic an t-shape toface into OWiw rIticdl Wind Wave directions. The anrctteasc-iactng teg isd 647
- -feet lone, (ace Vigfs. ZO and 21); t4he swautwast leg to 22) feot Long.4
The 4anchor siyoted consrists of liS pairs. of autethor Lifwa spacekd 4abut SUfeet apart. Thie lines have three suections, a 32'fooat lengtdh af 7/b-inchWelded alloy ethAin attacetd Wd 06t bV0akwateV, Liken 4 lotngthi of braided ftylontitnae, Uith another leng'th oft ehain eotnaectngte to stakeý ptitet. The sitakLe ptiesystemd was chosea toecauge of thW deep, 4o1t makeriAl at 0 athe- Vic e scopeofthOW seaiward side Ns about I o" :. tho WtAt4wrd sidel Vsi aibout I Wt 4.
Tito insitailevd corst of ctte ftoa~ttg briakwAcer wasi $126 por t soat(97)Those responsiblo for thd bcedAkwacor desiign, coas~ti~ttetk.t And OpCatiott. 404asfollaos:
CC
10 v
4po
4p c 0
OD
4 0A
I0. J
' ~\I \ \\ \
.-4,--
c_ _ ..-- - -0-- 1-- s • •
Am..t.
4 Oel
\ \l b - *OP
""7 7#7
a. Dock to floating breakvaccar.
44i-
h.Lac%& WO oft tt'.4tttt& bcttaksaC r.
Vi~uri 21. toeo ot parofl F rcAy ItwrtN4 tbattiag
Ownur-Operscor., Putt oi Friday HarborFriday RHarbor, Washington(Jack fairweathur, htarboriausccr)
Desigser: Reid, Mliddleston and AssoriatesEdmo~dS4, Washington
Fabricator: PolysLicering, Inc.(mawttafactnrsed pontoons)
Monroe, Washington
Intwtller: American Pile Driving Co., Inc.(assembled breakwater)
Everett, W~ashirrticoa
The breakwater was assembled in EvurtWsigoadtwdt the
()Performnance. Boat wauke seems to caose as wtat cotlceCit As. witidwave transmlsttton. This responsze is not surpsrising, minc, the bonting activ-ity' occursq wore often In the milder --easious. Wind wave transmis~sion ont theorder uf 1 foot is considered tolerable.
itaineunace costs have been high. The structure was damaged extensivelyin a storm on 7 Decembetr L972, barely 2 months after the- installation; 34 ofthe wvintoons cracked aQd camev loose- frcna tite structure (21 on the outer row,12 zr the second row, 4td I. on 04htt third row), euuwstng it to lose buoyancy.The faittr,rs werv duo to muttrtat fatigue; where. the pontoons werv: supported bythe timber structisre. Other pontoons htave failed from simialr c-auses. Recentruptacemeiatm.s ha-ve t een wtth v~casting of Marley plastic whtich h~ave nlot shown,iny &igti of distress. Fifteent pontootns wtro replaced4 in thAe lapring t'4 19t0 AtA twmit cost of $$I,U0O.
Plants are artderwmzy for An enlarged harbor and replacriwnt brvakwa:'4r ofthe couor,et~e e4155(iFQ type. Tho tww breakutrer is being deosIgne4d by ýhe lieS.Army Engineer District, Seattle, and, it auttuwircd, will boe construrtred byt he Cuips of Kaginteors nuader Soction 107 of the 1%i River aad Harbor Act.Utdversity of Wasiftntna 1'4 reviovwing the desi44.
4. 'IfsOesqsston. The p5ýrnrwau'ter Lint Oiw breakwater hasi beent les. than* hopod fur by the titers. The ma1fn peojbtea&3 were ato~udwith 4 design Con-
figurationt that relied on a mateirial aed, fabcicmttio toQ!tutiqtre which did "otpro4uo the expetewd iie-eitt hrceiis. There! Utak a poh toget thfe broakwater tinto place dadt pr'iduet~~incomaee wflh otrtgiee thea
desgaeoatre~iaZehedutle toe kuwh a novel antd tflntuv4ttve LQLWdpt. it %theproosd Wba epawo7;nf it, 4uthort4eed, ttw exivtitin breakwiteor can hw put to-goodusefortzeiliktoi& within the %arbr.
44 Locationt. The t~aiversiiy Ot ý6tihitintoa Ogt~4A0L&rtJybekw4cer is 4,*b3ot ", Iat tile awrth of th, Port of Friday ttarbt.c (Fitt. 19??. The
constructed to allow the marine-related activities in the research programs tobe operational year round.
b. Site Conditions. Tide data are the same as Port of Friday Harbor.The breakwater was designed for a 1.5-k.iot current.
The design parameters were 46-k1not wind, fetch-limited, significant waveheight of 3.0 feet, period of 3.5 seconds, current of 1.5 knots. Boat wakesare common.
c. Breakwater Description.
(1) Design and Installation. The breakwater is a reinforced con-crete caisson cast over a polystyrene foam core with a cross section 4.5 by 15feet with an 18-inch freeboard and is L-shaped with two 130-foot sections onthe long leg parallel to the shore, and one similar section on the short leg(see Fig. 22). The anchor system is laid out to maintain about a 6-foot spacebetween the sections to avoid linkage problems. Short gangways provide accessbetween units. The breakwaters are used as staging areas to handle nets andother gear, and also to provide a protected mooring area. The surface of theunits was left rough for good footing.
The anchor system consists of two anchor lines of I-inch stud-link chainat each end of each section, with one line to the outside at 450 to the break-
water, and the secund at the same angle to the inside.
The bottom conditions at the site, a shallow covering of rock, led torestraint supplied by attaching clump weights to the anchor lines. These wereconcrete blocks 4.5 by 4.5 by 3 feet. The main anchors were concrete blocks .
by 8 by 6 feet.
The breakwater was installed in 1979 at a cost of $790 per foot. Thoseresponsible for the breakwater design and operation are as follows:
Owner-Operator: University of WashingtonOceanographiz LaboratoryFriday Harbor, Washington
Designer: ABAM Engineers1127 Port of Tacoma RoadTacoma, Washington
(2) Performance. The users are satisfied with the breakwater per-formance which has made possible the desired year-round operation of the labo-ratory activities. The roughened surface provides good footing, but is hardto clean. An unforeseen benefit from the view of the marine biologist is thatthe breakwater has attracted marine growths and animals distinctly differentfrom those around the Port of Friday Harbor breakwater, only a few hundredyards distant.
Some adjustments in the breakwater were necessary after installation.The gangways between the sections had to be redesigned to provide greaterfreedom of movement to avoid being overstressed. One of the sections did not
40
C ':}C C',
I O
a. Access ramp to floating breakwater.
b. Gangway between sections.
i-A-
- .-. -.-- I .
c. Bull rail detail.
Figure 22. Photos of University of Washington Oceano-graphic Laboratory, Friday Harbor.
41
_• .. ... . . -.. • .- . .. - ...... ,..... . ,
float with the required uniform freeboard ana had to be ballasted with Styro-foam billets. Presumably, a form slipped during casting, resulting in a heav-ier and nonuniform unit.
The 2- by 4-inch tie piece on the bull rail is too light for its purposeand has broken in a few places. This member should be at least 4 by 4 inch-es. The installation of the anchors required extra, expensive site prepara-tion which might have been avoided with more informative foundation surveysand better matching of anchor type to bottom conditions. No special mainten-ance problems have developed.
d. Discussion. The breakwater type is very appropriate for the site andhas met the users' expectations.
7. Blaine, Washington.
a. Location. Semiahmoo Spit Marina is located in Drayton harbor (seeFig. 23) at Blaine, Washington.
b. Site Conditions. Drayton Harbor (Fig. 23) is quite shallow; themarina site had to be dredged to -1.0 feet MLLW. The site is exposed only tothe southerly quadrant, with a high tide fetch of 1.5 nautical miles to thesouth and 2 nautical miles to the southeast.
Tide data include a mean range of 5.9 feet and a diurnal range of 9.5feet. Ib data are available on tidal currents.
Data on wind waves used for design are not available. The exposure to thesouth and southeast is likely zo experience winds in the more than 40-knotrange every winter, with 50-knot speeds on occasiou.
c. Breakwater Description.
(I) Design and Installati.on. The breakwater is of the concrete cais-son type cast in 4.5- by 15- by 25-foot units using polystyrene foam blocks asinterior formwork and for positive flotation, with a 3-foot draft. The total.length of the breakwater, arranged in a U-shape (Fig. 24), will be 3,500feet. The marina will have 840 slips for pleasure craft and fishing boats.
The units are truck-hauled to the site where four of the units are post-tensioned together to form 60-foot modules, which are then coupled by a chain-rubber fender connector as illustrated in Figure 24.
Tha. anchor system makes use of clump weights on anchor lines consisting ofsuccessive length of nylon rope and chain to stake piles, as shown in Figure25, with a set of lines at each module connection. Figure 26 illustrates theunits and connections. Those responsible for the breakwater design, construc-tion, and operation are as foilows:
Owner-,Operator: Port of BellinghamP.O. Box 728Iellingham, Washington
42
'A H210 0 DAY y 73241 A.2
5 4
........ .. o ... ..
Ste for Floatin 2
/Brea~kwater
51*~~~~ Ai. O .:
A,0
14%2 1 X;DRAYTONMerc'T24 0ro ctof
Scl :3,0 aCe. 28542
Fiur 2. emahooSptMain: lae:Wahigtn(towNO Car 142)
Ik43
DRYO O
RUBBER 12"X 120X3.On LONG W On 0 BORE On 1. 0. STEEL PIPE/X 9 0X 9 0 1W 4m
H LE AT CENTER AND- 1.1, CROSSY.LAUGHLIki "MISSING LINK* REPLACEMENTWELDD TOIt.I I X1On CROSBY -LAUGHLIN FORCED EYE BOLT W " LONG
ANH I *t " THREAD AND SQUARED ENDANCH110fft 1-28X I.fX 10"X10" W 1-d%3 0 HOLE AT CENTER (4) '72%6"
(GRADE 2)-\ X4 X 4" W I - '71;O HOLE AT CENTER
'.4D
ELEVATION SI0E VICW
Figure 24. Mo~dUic Coonieetton, Semiatmoo Spit ftbaL'rig brodkW4t~f-
44
"* • 5s wa _ _ CONNECT ROPE TO CIWN
"27 0LW SHCKL AT EACH END
00MLLW050
.4' "0 •dlo0 ELE VATINES" ' ' _ _ j, EITHEll-1O000 O 1200• iREOGIO ELEVATIONdS
SEAWARO SIDE OAR Stua •4
Figure . Sotatao Spit Ha&'toa aatwhor duotail.
Scataho br,4kla~tor.
46
Designer: URS4th and Vine BuildingSeattle, Washington
Designer-Fabricator: Bellingham Marine IndustriesBellingham, Washington
(3) Performance. No information is available. The breakwater was"under construction in February 1981.
d. Discussion. Module connections have been a source of concern for manyfloating breakwaters. The design for the Semiahmoo connectors provides for"restraint, flexibility, adjustments for maintaining a no-slack connection, andalso appears to be easily assembled in the field.
The Semiahmoo site could be a good site for a field measurement program tocollect data on breakwater structural, kinematic, and hydraulic responses.The input data would be limited naturally by the shallow-water conditions andprobability of storm and high tide coexistence.
8. Langley, Washington.
a. Location. Langley, Washington (Fig. 27), is a small community on thesoutheast side of Whidbey Island and faces Saratoga Passage.
b. Site Conditions. The fetch is long, 8 to 12 nautical miles to thenorthwest and about 4 nautical miles to the east-northeast. Wind data spe-cific to the site are not available, buc the speed-duration curves for PugetSound (Fig. 28) should be representative for design purposes.
Tide data, gathered at Tulalip, Washington, include a mean range of 7.6feet and a diurnal range of 11.2 feet.
c. Breakwater Description.
(1) Design and Installation. The breakwater is the Goodyear modulefloating tire type, composed of tire groups banded together with belting andnylon bolts, with Styrofoam added to the tire crowns for extra buoyancy. Thenorthwest-facing section has a planform of 52 by 230 feet; the east-facingsection is 65 by 216 feet. Figure 29 is an east-facing view of the installa-tion. The breakwater is anchored by cables fastened to piling.
Those responsible for the breakwater design and operation are as follows:
Owner-Operator: Port of Whidbey Island
Designer: Parametrix, Inc.Everett, Washington
(2) Performance. The breakwater reduces the short-crested waves sat-isfactorily, but transmits too much energy in the lower frequencies. Connec-tions in the boat slips were overstressed, and boats have not been permittedto use them. The slips were removed for the .980-81 winter season. The northend of the east bre-kwatee has been sinking, possibly due to the combination
47
7. 7-
6529
414
4~^ 7259. '5
39 25
663g.M Q 6 Q AI/64 1 A
644
17 'W 9615
67S 63
2i18,0-12 WA4 afta
45 24 64
57 14
60 7 2 ýp 5 M 5 -CJ
57 M 2766 6
\20ur 27. 64~iin 40t ~ekat~ age, ahn$ (tom NS chrt 14437
54 Al46
* 80
Note: These Curves Representotiveof Puget Sound Coostof Regions
70 Where no Significonl Shelteringis Provided.
60
E~50
0S
CL
30iStCU-RitSV fCO k6 ...
Z4-YEAR RECORD AT 5A.TAC ME-...AIRPORT AkO 5ELECTED 5"!11MRE[CORDS AT WFSTrPOINr 39WIERAU'CCAOTMENT S PLANT. ]
0 I 2 3 4 5 6Durotion (hr)
F-4U 28. Q di-4U4ti00 VUVV4* P &et
Figure 29. Photo Of floating tire breakwater,Langley, washinston.
of current drag and loss of buoyancy. Reports on other Styrofoam-fitted tirebreakwaters state that the, foam breaks downi under the continuous tioxure expe-rienced in the wind wave exposure.
'The owner-operAtor is not satisfied with the pertorusa-ae of the- break-
d. Disvtussion. The site, with it* l~ong fetcht tip Saratoga Passage andthe frequency of windsi fromf that direction, exporiences more oeve:re cotditionstitan are appropriate for thte type of brea4kwater Winstalld.
9. Everett, Muttiogton.
Z. Loatuion. The breakwater ia at 4 large. Stall-cratt h4rbor 0tW liesalong a waterway in the Port of Everott (Fig. 30). Theo waterway is wikly aboat000t feet wide; thus, tho br ''warter servos priwArtty to protect the b~arboritro' boat wAke-.
6.Site, Voaditiottn. 'Tide dazi ta Iclde a meiau r-attg of 7.4 feet anid adiurnal raftge of 11.1 toot. tidal kcurrents aNi 00ttied t to 2kttots.
(I) Witin ARjnatt4n The# bro'Akwdtor Id ot the eaatecatoeeitlwutr-flpt east avor a styrotoaxm 00or sadng '*VrltOMiCi~ 1 ~I$ tu iot404d 4rat af I.$ fect. the ftorth kwettion (*4e Figt4 VS and 1) is1 VWNot04a; tho iiutth kceCioUi bL4 4W Nt toang.
11
44 .A9 , ,..'. dP'Floa ,tin Brawae
14:
: IX
~ 'F' Poo.1 /If / I
jM,4 : ~ ______Is
V~' ~ _______
1*1 IOWN
~face%t
/ L f I ~ bla ~
Fi~gro i.ý 4*hftet", ~o~ttt-brozkw~tcr itt
a.Pile bent floating breakwater.
Yt"Lurc )1. Phtotm of d tto.utlg brVaI04Le~r at OW Pr
ofEeot Iuit-ot
The breakwater was installed in 1979 at a coet of $273 per foot. Vhebreakwater is anchored by pile bents, as itll:strated in Figure 31. Thooe"responsible for the breakwater design, construction, rand operation dre as
follows:
Omer-Operator: Port of EvervLt"Everett, WasitngtLon
Designer; Retd, Hiddleton and Asvoci;AtesEdmonds, uashington
Breakwater Desigiur-Fabrtcator;: elllingham Niri.ne tndostrievHellinghama, Lhingtuon
(2) Performance. The breakwater has perform~ed favorably. T'e boatchanneI is easy to keep uwder survwillance, so boat sp,,ds are ld, tin c4eck.
10. Port Orchard, Washixton.
a. iocatton. Port Orchard (Fig. 32) lieu across SticlAir Inlet fromBremerton, WaUhington.
b. Site - Conditions. lhe prevailing wttds in. the ar,.,A are from the sootth.so the harb site is well shielded from that direct:or. Tte naI opoiwure5are to the southwest and the northeast with fetches 1.5 and 4 'iuuttc•al Mtites,respectively. Tht wiadspeed-duration curves in Figure 28 are the beat a-.-il-able dati.
Tide data are as follows:
Highaest (estimated); 14.7 fetutKL
,: MawI: IL.7 i~et.
6.8 toeet
MLLW:. 0.0 toot-La et: (otW.d: 4S toot
T1it c :treronts axe less thaa t kwt..
c. . ireakter teNrtptton.
(1) lstga k utAllattoit. Tho bkte L41 14i Uut i two
as t ~nr~ ~ ad 11. TheW L-iihiped tit0fi -E I'sw~ tootlong And cawpoe4 of rtt,•b t et e oreed eofteto eoAt uver golid
Styrooia cve utt5 I 4ky 12 toot and 21 oclaug, vith 4 1e~tit oi 1.d toet.Thre* O Lh5~ p one ~h r to forif 04-too't Lsidtdei
.ghteh te w the u ifti ith the o stt wetitally n •iitae 1;tour 1IoACteCtor5 W U4011.t •4(0 joftt. The t OWCtit-W ti oC aidttatctiortsreqetla tut tto wvait4 e i by 8 by 42 toec 4"4 ut o4 1 ,,l ti""ra.ogt 412)l•
4 1ir'.e3, 42 39
42, 43943440 0 412 43
•,41 34 . 42 46S"42 41 0 4 44
'40 * MARKER• '*.2 39 4 1 4 4
. 43 3 44.4! 40 43 3
0.1 393 2 37 At384 43 A 44;37 38 39 39
-- ------------------------ -----------
,a, ,43 -436 __3, 32 3 3583
•°• MIAý11ht l NAIIII(*Al Mill. 1 39•,•(:01116-f-[ - °090 loo, mJl 40
S36 Al
27 3
A\34 Flooling 20_34 ,Breowter 0S..3. i e I0 d S"3 2 �2834 30 39 $s
34 •3 31 7 "
_C "*. O" .
W 34A.3• L"34 .4
-. • ,.,3 2 31 3 S
S31 24
,. ' .. UAW
S. ....... .. 3.." ..•.• .. ..
•:"~ ~ ......•d •
77--• ,,.,:: :':''..... '.: ... C.. . '-...-
"Fgue3. o|;Ortir rotti br'kvaer_ Y (rd oNSdar Se)
:C > - .. . . ,-- - r--..--- -- . .. , .. , .. .. .. . . ---.....- -
'. "
_'q ff" IN. 4•IE
Figure 33. Floating breakwater and marina, Port Orchard, Washington.
Bolt Connector
* 7-- -- BREAKWATER
" ///~MODULE/
Rubber Donut
Figure 34. Schematic drawing of module connection, PortOrchard floating breakwater.
55
The L-shaped section is anchored by a composite 24-inch anchor line of3/8-inch welded alloy chain, braided nylon line and a lower length of chainfastened to stake piles. The chains cross beneath the breakwater to provideas much clearance as possible close to the breakwater. The west section isrestrained by pile bents. A deep, soft muck is the typical foundation mate-rial at the site.
Those responsible for the breakwater design, construction, and operationare as follows:
Owner/Operator: Port of BremnertonBremerton, Washington
Designer: Reid, Middleton and AssociatesEdmonds, Washington
Fabricator: Bellingham Marine IndustriesBellingham, Washington
(2) Performance. The management and boat owners expressed satisfac-tion with the breakwater. Storm damage has been handled well since installa-tion, with the exception of the western seL ion which has been hit by twostorms with reported significant wave heights of 4 feet--well in excess ofdesign values. When the waves incident to the west breakwater exceed heightsof about 2 feet, there is a greater transmission than desired, but this is nota severe problem.
The north breakwater has performed very well. One connection failure wasprobably due to a faulty fabrication detail; it waa successfully repaired.All the anchor chains have corroded badly and are being replaced. The orig-inal ones were made of 3/8-inch chain, with no cathodic protection; thereplacements are of 1/2-inch chain, with zinc anode sacrificial bLocks 2 by 2by 30 inches with two placed on each anchor line. The cost of the anchor linerepair is estimated at $30,000. Figure 35 illustrates the piling and chainconnections.
Some of the anchor piles have been attacked by marine borers. Replace-"ments will be cut off below the mudline, to be out of reach of these borers.There is only a small area of concrete spalling in the center of two pontoons.
d. Discussion. The west breakwater was apparently underdesigned forthe wave climate that develops from the west. Other design aspects haveworked out well, except for the anchor chains. The new design with both aheavier chain and cathodic protection should ensure a much longer life thanthe 6 yaars for the initial system. Boat wake from the larger vessels passesthrough the breakwater, but users appear to have adapted to this inconven-ience.
11. Camas-Washougal,•Waihington.
a. Location. The breakwater at Port of Camas-Washougal, about 20 mileseast of Vancouver, Washington (Figs. 36 and 37), parallels the. north shore ofthe Chlumbia River, and serves to protect a marina catering ItArgely to pleas-ure craft.
56
a. Weakened anchor pile.
of,,
b. Corroded anchor chaini with nylon anchor 1itie.
~tgu~ 3~. PhIpolace-l an' t'o elainet I Pr
Oretad floatW6 bretkwuiter.
57
It I!
,\4,
II,
4- ul.
Ou Z
01..444
Ce-.4
/ 4,
01 ')- 404 I, 7' 6Uj4U J -, 0'
4 4,1404 .7,
e~ QD C14
C3 N
itC
a. Floating breaskwater section.
b. Debris twrrier 4adwI nt~u tloutttg buew4kuacr.
Vigatr 31. Mtotors ot the Port utCs4ihos1
59
b. Site Conditions. The important winds come downriver from the eastwhere tie fetch is about 1.9 miles. No tidal current measurements have beenmsade at the site, but speeds of 3 to 4 knots have been estimated, with higherspeeds possible during periods of peak flood flows.
Winds blowing down the Columbia River develop wavetn that break and passover the top of the breakwater, but have not caused problems with mooredboats.
c. Breakwater Design.
(1) Design and Installation. The breakwater is a caisson-type struc-"ture constructed of lightweight, reinforced concrete cast over Styrofoamblocks ini units 3 by 10 feet in the cross section and 12 feet long, draftingabout 18 inches. T1e units are held together with timber walers. The mainsection parallel to the shore (and river) is 1,073 feet long, and is held byguide pile dolphins spac-ed about 84 feet apart (Fig. 38). A 233-focýt sectionof breakwater is set at about a 450 angle to the upstream end of the mainbreakwater to serve as a trash deflector (Fig. 37,b). The breakwater isdesigned to provide transient moorage and public access with special fishingfacilities provided. It was installed in early 1979. Those responsible forthe breakwater design, construction, and installation are as follows:
Owner-Operator: Port of Camas-Washougal,Waviington
Project Designer: Parietrix, Inc.Van.:ouver, Washington
Breakwater Designer-Fabricator: HelLingham Marine IndustriesBel .inghau, Washington
(2) Performance. The wind waves wcve nearly parallel to the break-waterr, so t 7Wr-l i _Ceffctively attenuated. Vhe only problem reported is thatfrom the boat wake generated by vessels pass.t% close to the breakwater athigh speeds. The trash deflector it not effective. togs tend to jam up on itand then work uadernt.atilh tr a.tt move into the marina. The river current keepsthe breakwater s.nugged up against the pile reatraints.
d. Discussito. The overall system meets to be perforwing very well, andthe owner Is satisfied. This site could serve as a field monitoring stationfor force on pile-restrainted breakwaters, although the river crrent would be"an Qevr-prvoent additive to the wave loadtins frod wind or boat.
IMl. SUM.MKY AW tCLUSIO(S
Line of tho more perplextig proble"s facing the designer for a floatinbreakwater is the spactficatino of 4 realistic wave ctitmte. Local data 4rerarely av4ilabl4 atd coatetporry awthods ot developittg a•A appropriate designspectra for Ohe vartable fetch eanditions usually wOuivttorOd at potentialfloating brea•ier •i•tes leave much subjective freedo&m tit scitying princi-pal praneters. Ropefulty, th1 two-diwatsiopA wave "elo beitn developedVill nfrro OWe proiesent no" of utwirt4taty.
'.3I
b. W~ide pile detail.
Ftpure ia. ehoLuM of the win sect ion of the Portot Catas-UAshc~ug4tl tloauiew breakwater.
At some sites, boat wake loadings may be more important than those fromthe wind-generated waves. Better models depicting wake loadings are needed.The floating breakwater transmission characteristics are sensitive to the wakefrom certain hull-speed distance-orientation cases.
The recently developed analytical methods treating the floating breakwateras a dynamic system are an improvement over static methods, but field data arestill needed to refine the values of the various coefficients in the analysesand to verify the general methodology. Possible field installations should bescreened as potential field measurement sites. The system being fabricatedfor Semiahmoo Spit Marina, Blaine, Washington, looks promising because theexposure is such that frequent winds of the 30- to 50-knot range should occurmost of the winter season. The water depth is shallow, which will restrictwave buildup.
The users of the floating breakwaters of the concrete caisson or ladder(Alaskan) type seem to be quite satisfied with their effectiveness and main-tenance costs. Some of this satisfaction is likely attributable to an adjust-ment in expectation of what can be accomplished in reducing wave heightswithin a given budget, developing adequate mooring techniques, and an aware-ness of crowded conditions at all moorage sites. The use of this type ofbreakwater seems to be confined to the western Pacific coast.
Tenakee Springs, installed in 1973, followed by Sitka and Port Orchard(installed in 1974), are the sites with the longest history of performance forthe concrete units. Early problems at Tenakee related to -Alinement and moduleconnections have been corrected; anchor cha-is are being replaced at PortOrchard. Presetit design knowledge would have avoided these tw problems.Otherwise, the units have performed very satisfactorily.
The other early breakwater of major dimension (for the area surveyed) wasthe one at Friday Harbor (installed in 1973), consisting of large plastic flo-tation tanks with a timber deck. A major storm shortly after installationcaused extensive dazna&;e. Plans are underway for replacement with a concretecaisson and an enlarged configuration to accommodate the expanding demand for
moo rages,
The floating tire breakwaters should be restricted to sites where waveconditioas are quite mild. Experiences to date show that, when subject.ed toan active wave climate, there is a rapid deterioration in buoyancy due tobreakdo~i of flot~ttion and fatiguing of the systems used to hold the tirestogether. Karine growLth will aiso diminish scructural buoyancy.
Bottom conditions at a proposed itte should be determined carefully toprovide a sound basis for specification of another type. Extra costs havebeen incurred at Ketchikan and at the Friday Harbor Oceenogruphic L4boratoryPiite due to unforeseen foundation Conditious.
No damage to anchor systems from wave loadings has been reported. Thor-ough anchor inspections are ditticult bocause of marine growths 4od sedimen-
tation. However, there ar- many instances where an Anchor litte could tw dis-connected at the breakwater and be partially exponva tor a wrire detailedlook. Tite one data point on longevity of a•tchor chain is that Lcnw the Port
Orchard installation, wbere a rOpl4cetmnt 4fttr 6 yC4rs It" bWte "Cessary.
62
However, the new design with larger chain and cathodic protection is expectedto last a long time.
"The connections between modules have been the "Acnille's Heel" in floatingbreakwater design. Experience has had to substitute for analysis in evalua-ting the loadings to be transferred between modules. The recent dynamicstr-actural response modules are expected to provide realistic design values,thereby replacing the costly empirical experience approach. Some design pro-gressiuns show tip in the installations covered in this report. The rubber inthe chain-bumper system of the initial Tenakee design took a permanent set andSallowed slack to develop. The replacement deaign eliminated the set problemby connecting the flexible rubber fender rigidly to each module. The connec-tiong of the breakwater deck to the flotation modules in the Friday Harborbreakwater invited stress reversals and concentrations 'iith subsequent fatiguefailures. The layout of the connections for the Srmialunoo Harina looked likea practical way of provltiiig a resilient, flexible connection well suited tofield assembly. Its performance, however, suggests it was unlderdesigned forthe loading imposed by the high winds experienced in the 198L-82 winter. thecurrent design trend for the caisson-type breakwater is to replace the flex-ible connection by postteasioning modules to form a continuous structure.Although more expensive, fabrication and field assembly procedures are more"exacting; therefore, the final product should be cost-effective.
Design data for the pile-restrained breakwater have * rather weak base."Logical assumptions about wave loadings on such piling can lead to forcesthat do not appear to develop in the fialt.. Dynamic i;,talysis will require theresolution of the interaction between the piling and the breakwater; such asynthesis would be aided greatly by some prototype data. The floating break-water at Camas-Washougal would be a possible site for tietd experiments, aswould the unit at Evo-rett Harbor. An etiergy absorbing connection betwe.tn thepile collar and the breakwater would relieve some of the dynftnic load. A sug-gested design would be concentric annular rings, with the annulus taken up tbyrubber fendertig material.
The pros and cons of lightweight versus regular weight cnciete may havebeen resolved by market conditions. Suitable lightweight aggregate has becowdvery expensive.
Some htaadardization of breakwater dimensIont could lead to lower dedignatl fabrication costs.
Those breakwaters where the freeboard is more thati I toot should havesafety ladders provided at intervals of about ISO fNet to allow a persou toclimb onto the breakwater assisted.
Navigation or radar targe-it siuhld We placed at raore frequent intervalsthat those required by U.S. Coast Guard re~ulatiorts. Vw floatit.g breakwaterti difficult to see under dark. otoray conditions.
Some designers strongly pr'efr chain or chtait-aylof line anchnr lttns ovVcable, Which it.s likly to be twre vulnerable to cetion.
Quality control in fabrication isa v"ry it rtoAlt etottin ateqOitt cover-age of retnforcement and strict adherence to dilntsitots so the utritl wiltfloat with Untformt ad sptdecifd freoboard.
63
Neither of tIM installations 3t Sitka or Tenakue Springs ha. experiencedany iring of consequence, TheC Puget Sound sites are ice-free.
Wat-r quality problems that could arise in a small-craft hIrbo•r enclosedby an io•permeahle harrier are avoided by the floating breakwaters. IIn manyrases, tOe floating breakwater an4 anchor lines enhance or provide additionalhabitat.
"Some designs for the concrete raisson breakwater have proposed a hullowstru,:-ure, thus eliminating the rost of the usual Styrofoam rore, and then"relying on Lite integrity of the cotncrete shell ntid inspections to avoid lossof buoyancy throtigh leakage. The koam core provides a good foirm for castingand also allows the box to be formed by a continuosis pour. However, care mustN! exCrCised to assutre that the foam does ttot rompress duringt the p)ouringoperattions, thereby alteritig the design freeboard levels. It is suggested thatfabricators b! allowed the option of which merild is the mW)st economical, orOthit close cost comparisons be mtde before a design is fixed. The foam Core
is good insurance againsL flooding.
i$4i !!, -
-e a
O-.C c~. c
0 w
u 0 2 0.*VCC
c 0 1
V0 1. .3,0 6 C C: . jG. i. j .C 02J IV
-c 0 -I 3 cCGm
-,c m )
2)UCD C. I D J )
0 CL. C W W0)-~~ a. cc,--0~0
.-Z w , w.- Ln t, *0c %co > 0 Z
.0 a ZIP MO -V00 D w C r_ go A t
X c21 w~ %00 *.0.4) U
-~~~~W to to CL*.. 3 l L ) ..
00 CcD
0 -- a D.
2)0 0 00 ).'.) 2 .) 0. 1D. .D ;
S C c 0 d
0 c z)C 1c U w I 00 0c0c
00a u- 30 2) 4) r v4~* aD IOV~ U~ vtA m~ L 0. w 0 c (h *00 l c 0 C D D a
96 > 3)> 0 fa G 0
CO.. U-O go. w~0 D a v 0V o A
0~~4 4))W 0~
E C 1GD1 = 4 0 ** aDG ,1
13< - 4.)~ . 0 -t Go -0~ -A 4..OO1w C ) 911 IV, D 44 c
U ~ GD4) 002)/~. * A..mu
aC a 2 C0 to3)" 0~ 50 WD0 cc0 D.-. 0 C1 I .004 ).. * C I
acJ *o VD J0
m 2 ) .. r). -3 -,C -M vD . :'~ 2D 0 C ) . toU~~C 0l.02 04 40 1"U I D O D
*3- 4 13 > 0 ml, 3GD 1 4)3 I& *o4-3 -A 3 0 00 O ) 4 .>.I4 b. OD
tc w , a ~ cc luW D D G l4.~ . G~~ .20)-~~~~30 4 W 1 0I O -
10 w 0 -)U GU) C6 goC ~ 3). I.4).UI
.o .pe .o ' L . w)~ le4 ) *x*C *.lC 0.0f.0.~ GD GD4).- C*U9
