Wind and CurrentWind and Current

Junior NavigationJunior Navigation

Chapter 12Chapter 12

22

Learning ObjectivesLearning Objectives Distinguish between leeway and currentDistinguish between leeway and current Know the meaning of: Know the meaning of:

DR track; Intended track; Speed of DR track; Intended track; Speed of advance; Course & speed over ground; advance; Course & speed over ground; Course & speed made good; Drift angleCourse & speed made good; Drift angle

Determine course to steer, allowing for Determine course to steer, allowing for current/leewaycurrent/leeway

Determine set and drift of currentDetermine set and drift of current Determine leewayDetermine leeway Understand elements of estimated reckoning Understand elements of estimated reckoning

33

Current vs. LeewayCurrent vs. Leeway Horizontal motion of Horizontal motion of

water water Current vector: Current vector:

both direction (set) both direction (set) and speed (drift)and speed (drift)

Sideways movement Sideways movement caused by wind caused by wind

Magnitude of leeway Magnitude of leeway - varies with:- varies with: Speed & relative Speed & relative

direction of wind direction of wind Type of vessel Type of vessel Speed of vessel Speed of vessel

““Current” - Current” - net offset (DR-to-fix)net offset (DR-to-fix) caused by caused by current, leeway, wave action, and/or steering errorcurrent, leeway, wave action, and/or steering error

44

Vessel Motion Through Vessel Motion Through WaterWater

IntendedIntended Course (C) Course (C)

Direction boat Direction boat isis or or is to is to bebe steered through the steered through the water water

Speed (S)Speed (S) Rate of motion of boat Rate of motion of boat

through water in the through water in the direction it is or is direction it is or is intended to be steered, intended to be steered, assuming no current or assuming no current or leeway effectsleeway effects

DR TrackDR Track Path of boat through Path of boat through

water projected from a water projected from a known position (fix), known position (fix), based solely on course & based solely on course & speedspeed

AccomplishedAccomplished Course (C)Course (C)

Direction a vessel Direction a vessel waswas steered through the steered through the water water

Speed (S)Speed (S) Rate of motion of boat Rate of motion of boat

through water in the through water in the direction it was steered, direction it was steered, assuming no current or assuming no current or leeway effectsleeway effects

DR TrackDR Track Path of boat through Path of boat through

water projected from last water projected from last known position (fix), known position (fix), based solely on course & based solely on course & speedspeed

55

AccomplishedAccomplished Course Over Ground Course Over Ground

(COG)(COG) Actual path over bottomActual path over bottom

Course Made Good (CMG)Course Made Good (CMG) Net direction over bottomNet direction over bottom

Speed Over Ground (SOG)Speed Over Ground (SOG) Actual speed over bottomActual speed over bottom

Speed Made Good (SMG)Speed Made Good (SMG) Average speed over bottomAverage speed over bottom

IntendedIntended Intended Track (TR)Intended Track (TR)

Expected path over Expected path over bottom, bottom, taking current & taking current & leeway into accountleeway into account

Speed of Advance (SOA)Speed of Advance (SOA) Expected speed along Expected speed along

intended track, intended track, taking taking current & leeway into current & leeway into accountaccount

Vessel Motion Over Vessel Motion Over BottomBottom

66

Accomplished MotionAccomplished Motion

1800

GPS1900

Wind and/orCurrent

CS

2030 GPS

SET

DFT

CMGSMG

2000

2030

(Net o

ffse

t)

TR

SOA

COGSOG

COGSOG

COGSOGCO

GSO

G

CO

GSO

G

Allowing for CurrentAllowing for Current

TR= 075°S = 8.0 knSet = 100°Drift = 3.8 knots

DR Course

0

1

3

2

4

5

6

7

8

9

10

11

12

SET 100DFT 3.8 8.0nm

S 8.0C 063SOA 11.3TR 075S 8.0C 063

(Expected path over bottom)

(Expected speed over bottom)(Directio

n boat is ste

ered)

(Speed of boat)

Allowing for Current & Allowing for Current & LeewayLeeway

TR= 075°S = 8.0 knSet = 100°Drift = 3.8 knots

20kn from 315º 5º leeway

0

1

3

2

4

5

6

7

8

9

10

Course to steer

11

12

SET 100DFT 3.8

S 8.0C 063SOA 11.3

S 8.0C 063

1000

GPS

TR 075

1100

C 058

5º drift angle

On which line would you plot your 1100DR position?

20 kts

1100

GPS

Where should your 1100GPS position be?

drift angle co

rrecti

on

99

Puerto Rico to Cristobal, PanamaPuerto Rico to Cristobal, Panama Start:Start: L 18º 00´N, Lo 67º 51´W L 18º 00´N, Lo 67º 51´W Leave:Leave: 0800 1 July 0800 1 July Boat: Boat: 38-foot cutter, should average 6.0 kn on 38-foot cutter, should average 6.0 kn on

this generally downwind coursethis generally downwind course

The captain wants to know:The captain wants to know: What conditions to expect?What conditions to expect? How long the trip will take?How long the trip will take? ETA? ETA? What course to steer from the departure point? What course to steer from the departure point?

Allowing for Current & Allowing for Current & LeewayLeeway

1010

What Conditions to Expect?What Conditions to Expect?

12ft seas 10%Force 4 or 5 Winds out of NE or ECurrent set 270º at 0.8-1.0kn

1111

How long with it take?How long with it take?

T = D / S T = 875 / 6 T = 145.8hrs T = 6days 1.8hrs

1212

What is the ETA?What is the ETA?

ZT 1 Jul 0800 ZD +4 UT 1 Jul 1200 Travel +6 2 UT 7 Jul 1400 ZD (rev) –5 ZT 7 Jul 0900

1313

Course to Steer?Course to Steer?

THE OUTER SCALE IS

READ FROM A

MERIDIA

N OF LONGITUDE. T

HE

INNER SCALE FROM A

PARALLEL

OF LATITUDE.

090

270

180

000

080070 060 050 040

030020

010

000

260250 240 230 220

210209

190

180

100

110

120

130

140

150

160

170

180

280

290

300

310

320

330

340

350

360

170160 150 140 130

350 340 330 320 310

190

200

210

220

230

010

020

030

040

050

1414

C 229

S 6.0

Set 270Dft 0.9

TR 234

SOA 6.7

Course to Steer?

S 6.0

(expected path over bottom)

(boat speed/course through water)

(boat speed over bottom)

(course to steer)

(current affect)

T = D / S T = 875 / 6.7 T = 130.6hrs T = 5days 10.6hrs ETA 6 Jul 1800

T = 6days 1.8hrs ETA 7 Jul 0900

Cristobal

Puerto Rico

C 229

1515

UnderwayUnderway Navigator’s tasks include:Navigator’s tasks include:

log boat’s progress (chart & deck log)log boat’s progress (chart & deck log) Assess current, leeway, and other factors Assess current, leeway, and other factors

affecting boat’s courseaffecting boat’s course Periodically adjust steering course to stay Periodically adjust steering course to stay

on desired trackon desired track

1616

When Fixes & DRs DifferWhen Fixes & DRs Differ Navigator needs to know origin of differenceNavigator needs to know origin of difference Consider what the reason might beConsider what the reason might be Review all data and ask questions:Review all data and ask questions:

Have you plotted correctly?Have you plotted correctly? Does pilot chart show a change in current?Does pilot chart show a change in current? Does observed current match expected current?Does observed current match expected current? Has the wind speed/direction changed?Has the wind speed/direction changed? Have sea conditions/boat performance Have sea conditions/boat performance

changed?changed? Is there an error in calculating DR?Is there an error in calculating DR?

1717

Estimated ReckoningEstimated Reckoning In absence of fixes, rely on DR & knowledge In absence of fixes, rely on DR & knowledge

of boat to determine positionof boat to determine position Consult charts and pubs for average Consult charts and pubs for average

currentscurrents Consider weatherConsider weather

Considering all factors, arrive at an Considering all factors, arrive at an estimated position (EP)estimated position (EP)

Process – called Process – called Estimated ReckoningEstimated Reckoning Takes experience to do correctlyTakes experience to do correctly

The longer without a fix, the more important The longer without a fix, the more important to know the factors that affect your positionto know the factors that affect your position

Navigator’s Job: constant process

of observation, analysis, and

cross-checking position!

1818

Wind and CurrentWind and Current

End ofEnd of

Junior NavigationJunior Navigation

Chapter 12Chapter 12

Turn in your Sight FoldersTurn in your Sight Folders

17ºW

14ºW

15ºW

16ºW

Plot initial and destination coordinates on Plot initial and destination coordinates on the July Pilot Chartthe July Pilot Chart

WP1

WP2

17ºW

14ºW

17ºW

14ºW

15ºW

16ºW

1a. What is the true course for the rhumb 1a. What is the true course for the rhumb line between your initial and destination line between your initial and destination coordinates?coordinates?

WP2

WP1

THE

OU

TER

SC

ALE

IS R

EA

D FR

OM

A

ME

RID

IAN

OF LO

NG

ITUD

E. TH

E

INN

ER

SC

ALE

FRO

M A

PA

RA

LLEL

OF LA

TITUD

E.

090270180000

080070

060

050040

030020

010000

260250

240

230220

210209

190180

100

110

120

130140150160

170

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280

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310320330340

350

360

170160

150

140130

350340

330

320310

190

200

210

220230

010

020

030

040050

C 151

17ºW

14ºW

15ºW

16ºW

1b. What is the expected magnetic 1b. What is the expected magnetic variation along this course?variation along this course?

WP2

C 151

WP1

17ºW

14ºW

15ºW

16ºW

1c. What would be the planned magnetic 1c. What would be the planned magnetic course along this rhumb line course?course along this rhumb line course?

WP2

C 151

T = 151º V = +15ºW M = 166º

WP1

17ºW

14ºW

15ºW

16ºW

1d. What is the distance of this course?1d. What is the distance of this course?

WP2

C 151

9º 10’ 9 x 60 = 540 540 + 10 = 550nm

D 550

WP1

17ºW

14ºW

15ºW

16ºW

1e. Assume an average SMG of 6.0kt, what 1e. Assume an average SMG of 6.0kt, what will be your elapsed time to complete this will be your elapsed time to complete this voyage?voyage?

WP2

C 151

D 550

T = D / S T = 550 / 6.0 T = 91.7 hrs

WP1

17ºW

14ºW

15ºW

16ºW

1f. (Optional) Using GPS determine true 1f. (Optional) Using GPS determine true course, distance and elapsed time for this course, distance and elapsed time for this voyage.voyage.

WP2

C 151

D 550

WP1

Bearing WP1 to WP2 = 151º Distance 548nm Elapsed time 91.3 hrs

17ºW

14ºW

15ºW

16ºW

1g. At 180nm from WP1, what will be: wind 1g. At 180nm from WP1, what will be: wind direction; wind force; current set/drift?direction; wind force; current set/drift?

WP2

C 151

D 550

Direction = SW Force 4 Set 058º-062º Drift 1.5/1.0kn

WP1

X

17ºW

14ºW

15ºW

16ºW

1h. What are the names of major shipping 1h. What are the names of major shipping lanes that cross your course and distance lanes that cross your course and distance from WP1?from WP1?

WP2

C 151

D 550

Cape Hatteras to Virgin Rock – 200nm Cape Hatteras to Gibraltar – 300nm Bimini Island to Bishop Rock – 460nm

WP1

17ºW

14ºW

15ºW

16ºW

1h. What are the coordinates of where your 1h. What are the coordinates of where your route intersects Cape Hatteras to Virgin route intersects Cape Hatteras to Virgin Rocks?Rocks?

WP2

C 151

D 550

L 37º 50’ N, Lo 68º 20’ W

WP1

17ºW

14ºW

15ºW

16ºW

WP1

1h. What is the rhumb line course at this 1h. What is the rhumb line course at this intersection?intersection?

WP2

C 151

D 550

THE OUTER SCALE IS

READ FROM A

MERIDIAN O

F LONGITUDE. THE

INNER SCALE FROM A

PARALLEL

OF LATITUDE.

090

270

180

000

080070 060 050 040

030020

010

000

260250 240 230 220

210209

190180

100

110

120

130

140

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160

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180

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290

300

310

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340

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360

170160 150 140 130

350 340 330 320 310

190

200

210

220

230

010

020

030

040

050

058º

17ºW

14ºW

15ºW

16ºW

WP2

C 151

D 550

1h. What are the coordinates of where 1h. What are the coordinates of where your route intersects Cape Hatteras to your route intersects Cape Hatteras to Gibraltar?Gibraltar?

L 36º 40’ N, Lo 67º 20’ W

WP1

17ºW

14ºW

15ºW

16ºW

1h. What is the rhumb line course at this 1h. What is the rhumb line course at this intersection?intersection?

WP2

C 151

D 550

THE OUTER SCALE IS READ FROM A

MERIDIAN OF LONGITUDE. THE

INNER SCALE FROM A PARALLEL

OF LATITUDE.

090

270

180

000

080 070 060050

040

030

020010

000

260 250 240 230220

210

209190

180

100

110

120

130

140

150

160

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180

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300

310

320

330

340

350

360

170 160 150 140130350 340 330 320 310

190

200

210

220

230

010

020

030

040

050

071º

WP1

3. Sailing Directions - Planning Guide3. Sailing Directions - Planning Guide

Public Holiday Act, 1947

All Government Offices, including Post Offices, are closed on every public holiday.

The following Monday will be observed as a public holiday when a public holiday with a fixed date falls on a Saturday or Sunday.

Store, shops, & businesses, except those with a holiday trading license - able and willing to pay their staff double overtime, will be closed.

All Restaurants are closed, except restaurants owned by hotels which may remain open.

Buses and ferries are on a much-reduced schedule and many taxis do not operate.

3. Sailing Directions – Enroute (Pub 147)3. Sailing Directions – Enroute (Pub 147)

Currents become matters of Currents become matters of concern only within confined concern only within confined

channels leading through channels leading through reefs… flood currents set reefs… flood currents set

directly onto reefs.directly onto reefs.

Saint George’s Saint George’s Harbor has been Harbor has been

reported to be reported to be radar conspicuous.radar conspicuous.

An inbound vessel has An inbound vessel has right-of-way, and should fly right-of-way, and should fly

her national colors while her national colors while navigating channels to navigating channels to

claim priority.claim priority.

3. Sailing Directions – Enroute (Pub 147)3. Sailing Directions – Enroute (Pub 147)

Sea approaches are generally Sea approaches are generally free of dangers, except for two free of dangers, except for two off-lying seamounts to the SW off-lying seamounts to the SW

and the sunken dangers of and the sunken dangers of Bermuda Great Reef.Bermuda Great Reef.

The attention of all mariners is drawn to the dangers The attention of all mariners is drawn to the dangers and hazard of close approach to the reefs which and hazard of close approach to the reefs which

surround Bermuda, especially to the N and NE of the surround Bermuda, especially to the N and NE of the islands. They extend in places to a distance of 12 islands. They extend in places to a distance of 12

miles from the visible land and are virtually unmarked miles from the visible land and are virtually unmarked by navigational aids at their extremities.by navigational aids at their extremities.

Reef informationReef information

3. Sailing Directions – Enroute (Pub 147)3. Sailing Directions – Enroute (Pub 147)

World Port Index 9940World Port Index 9940

World Port Index 9950World Port Index 9950

3. Sailing Directions – Enroute (Pub 147)3. Sailing Directions – Enroute (Pub 147)

Hamilton Harbor is not Hamilton Harbor is not considered to be a good considered to be a good

hurricane anchorage. The hurricane anchorage. The holding ground is good, but holding ground is good, but

space is limited in such space is limited in such circumstances. Great Sound circumstances. Great Sound

is considered preferable. is considered preferable.

World Port Index 9960World Port Index 9960

3. Sailing Directions – Enroute (Pub 147)3. Sailing Directions – Enroute (Pub 147)

Caution – Numerous small Caution – Numerous small craft, which may not be craft, which may not be

carrying anchor lights, may carrying anchor lights, may be found in Hamilton Harbor, be found in Hamilton Harbor,

clear of the main fairway.clear of the main fairway.

8. Entry requirements - Customs8. Entry requirements - CustomsWhat do you do upon arrival?What do you do upon arrival?

What can you bring into Bermuda?What can you bring into Bermuda?8. Entry requirements - Customs8. Entry requirements - Customs

What are the duties?What are the duties?8. Entry requirements - Customs8. Entry requirements - Customs

How much cash can you have onboard?How much cash can you have onboard?8. Entry requirements - Customs8. Entry requirements - Customs

What about food?What about food?8. Entry requirements - Customs8. Entry requirements - Customs

What about food?What about food?8. Entry requirements - Customs8. Entry requirements - Customs

What about pets?What about pets?8. Entry requirements - Customs8. Entry requirements - Customs

How about your medication?How about your medication?8. Entry requirements - Customs8. Entry requirements - Customs

Other items?Other items?8. Entry requirements - Customs8. Entry requirements - Customs