SSC-208
SLAMMING OF SHIPS:A CRITICAL REVIEW OF THE
CURRENT STATE OF KNOWLEDGE
This document has been approved
for public release and sale; its
distribution is unlimited.
SHIP STRUCTURE COMMITTEE
1970
SHIP STRUCTURE COMMITTEE
MEMBER AGENCIES:
UNITED STATES cOAST GUARD
NAVAL SHIP SYSTEMS COMMANDMILITARY SEA TRANSPORTATION SERVICE
MARITIME ADMINISTRATION
AMERICAN BUREAU OF SHIPPING
1970
ADDRESS CORRESPONDENCE TO:
SECRETARYSHIP STRUCTURE COMMITTEE
U.S. COAST GUARD HEADQUARTERS
WASHINGTON, D.C. 20591
Dear Sir:..
To assure the utility of data accumulated in a project that willmeasure strain caused by a ships bow leaving and reentering the water,called slamming, a critical review of existing knowledge and, hence,development areas required, was undertaken.
Herewith, is a report containing the review.
Sincerely,
h
/ ~.,.,, ~.,
N/&.. 1---
W.F. ea, IIIRADM, U. S. Coast GuardChairman, Ship Structure Committee
SSC-208
Technical Report
to the
Ship Structure Committee
on
project SR-172, Slamming Studies
SLAMMING OF SHIPS:A CRITICAL REVIEW OF THE CURRENT STATE OF KNOWLEDGE
by
J. R. Henry and F. C, Bailey
Teledyne Materials ResearchWaltham, Massachusetts
under
Department of the NavyContracts: NObs 94252
NOO024-67-C-5312NOO024-69-C-5231
ThLs document has been app~oved fop pubhk rehase and sale;its distribution is un~imited.
U.S. Coast Guard HeadquartersWashington, D.C.
1970
ABSTRACT
This critical review of the current status of the knowledge ofbottom slamming phenomena was undertaken to assure that maximum value willbe gleaned from recorded data obtained on the SS WoZvwine Stat~. The re-view covers experimental laboratory and ship data and their correlationwith available theory; statistical considerations in slamming and in theocean environment; and structural implications and possible design im-provements. Although there are certain areas in the theory which requireexpansion, the most pressing need is for additional full-scale experimen-tal data to provide confirmation of existing analytical techniques.
ii
CONTENTS
PAGE
INTRODUCTION . . . . . . . .
EXPERIMENTAL DATA. m . . . .
THEORIES. . . . . . . . . .
THEORETICAL AND EXPERIMENTAL
. . . . . . .
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. . . . . . .
CORRELATION .
STATISTICAL APPROACH TO SLAMMING . . . . .
.
STATISTICAL APPROACH TO WAVE CHARACTERISTICS
STRUCTURAL IMPLICATIONS. . . . . . . . . . .
DESIGN IMPROVEMENTS. . . . . . . . . . . . .
SUMMARY AND RECOMMENDATIONS . . . . . . . .
REFERENCES. . . . . . . . . . . . . . . . .
LISTOFSYMBOLS. . . . . . . . . . . . . . .
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iii
SHIP STRUCTURE COMMITTEE
The SHIP STRUCTURE COMMITTEE is constituted to prosecute a researchprogram to improve the hull structures of ships by an extension of knowledgepertaining to design, materials and methods of fabrication.
RADMChief,
u.
Capt. W. R. Riblett, USNHead. Ship Enqineerinq Divis
W. F, Rea, III, USCG, ChairmanOffice of Merchant Marine SafetyS. Coast Guard Headquarters
Mr. E. S. Dillonon Dewtv Chief
Naval Ship En~ineerin~ Center Offic; of Ship ConstructionMaritime Administration
Capt. T. J, Banvard, USNMaintenance and Repair Officer Mr. C. J, L. Schoefer, Vice PresidentMilitary Sealift Command American Bureau of Shipping
SHIP STRUCTURE SUBCOMMITTEE
The SHIP STRUCTURE SUBCOMMITTEE acts for the Ship Structure Committeeon technical matters by providing technical coordination for the determinationof goals and objectives of the program, and by evaluating and interpreting theresults in tqrms of ship structural design, construction and operation.
NAVAL SHIP ENGINEERING CENTER
Mr. J. B. OBrien - Acting ChairmanMr. J, B. OBrien - Contract AdministratorMr. G. Sorkin - MemberMr. H. S. Sayre - AlternateMr. I. Fioriti - Alternate
MARITIME ADMINISTRATION
Mr. F. Dashnaw - MemberMr. A. Flaillar - MemberMr. R. Falls - AlternateMr. W. G. Frederick - Alternate
AMERICAN BUREAU OF SHIPPING
Mr. S. G. Stiansen - MemberMr. F. J. Crum - Member
OFFICE OF NAVAL RESEARCH
Mr. J. M. Crowley - MemberDr. W. G. Rauch - Alternate
NAVAL SHIP RESEARCH & DEVELOPMENT CENTER
Mr. A. B. Stavovy - Alternate
MILITARY SEALIFT COMMAND
Mr. R. R. Askren - MemberLt. J. G. T. E. Koster, USN - Member
U. S. COAST GUARD
LCDR C. S. Loosmore, USCG - SecretaryCDR C. R. Thompson, USCG - MemberLCDR J, W. Kime, USCG - AlternateCapt. L, A, Colucciello, USCG - Alternate
NATIONAL ACADEMY OF SCIENCES
Mr. A. R. Lytle, LiaisonMr. R. W. Rumke, LiaisonProf. R. A. Yagle, Liaison
SOCIETY OF NAVAL ARCHITECTS & MARINEENGINEERS
?Ir.T, M. Buermann. Liai~nnAMERICAN IRON AND STEEL INSTITUTE
Dr. J. R. LeCron, Liaison
BRITISH NAVY STAFF
Dr. V. Flint, Liaison
WELDING RESEARCH COUNCIL
Mr. K. H. Koopmen, LiaisonMr. C. Larson, Liaison
I. INTRODUCTION
Bottom slamming has been recognized for many years as a source of damage to ships.The phenomenon results when the ships bow emerges from the water and subsequently
submerges at an attitude such that the angle between the bottom plates and water issmall. This action produces large forces for short-time durations. The impulses sogenerated can cause vibratory motion of the entire ship to the extent that shipsmasters intuitively reduce the forward speed and/or change the ships heading re-sulting in an undesirable change in schedule. Minor or occasionally moderate slamminghas been known to cause local buckling and plastic deformations in bottom plates inthe forefoot region of the ship. These deformations increase the maintenance costsbecause of additional drydocking charges necessary to make repairs following the moresevere cases of slamming. Hard slamming produces large impulses that set the entireship into vibratory motions which persist for up to one minute. In summary, slammingcan generate large bending stresses in the hull girders, deformations in bottomplates and bulkheads, damage to cargo, and 10SS or damage to shipboard equipment.
Much information has been collected on slamming effects on ships and the statisti-cal motion of irregular seas. These data have had little or no impact on the designof future ships to withstand heavy, Irregular seas with moderate to severe slamming.In the early stages of design, only rigid body motion Is Investigated and verified bymodel tests for regular sea conditions, The flexlb~lity of the hull must be takeninto account when it is subjected to irregular seas resulting in slamming. It is notsufficient to use the statistical maximum slamming load as a static force in the de-sign of the hull.
Under Ship Structure Committee project SR-172, Slamming Studies, TeledyneMaterials Research has installed instrumentation aboard the SS WOLVERINE STATE tOmeasure the following: (~) slamming pressures on the forward bottom, (2) verticalaccelerations, and (3) midship stresses. The purpose of this ins~allation is tocollect data which will assist in predicting the incidence of sla~ing and the re-sulting gross response of the vessel. In order to assure that maximum value willbe gleaned from the recorded data, this crit$cal review of the current status ofthe knowledge of bottom slamming phenomena was undertaken. This report summarizesthe review and presents recommendations for future studies.
It is recognized that slamming can be induced by sudden bow flare immersion aswell as bottom impact. Even though some of the theoretical and experimental workto be cited is applicable to both mechanisms, the report will be directed princi-pally at bottom impact slamming, which is the mechanism most commonly encounteredin merchant ships.
II. EXPERIMENTAL DATA
Because of the several random variables involved in both wave motion and wave-induced motion of ships, it is necessary to acquire actual data from shipboardmeasurements. From these data, one can establish the extent to which the responsescan be described by theories of probability. If the data indicate that normal lawsof probability hold true, then many parameters can be calculated which would havedesign implications.
. .
2
This sectfon contains a review of typical shipboard measurements (Section A) andlaboratory model tests (Section B) that establish the significant parameters affect- ing slamming.
A. Ship Data
Several attempts to measure slamming effects on ships are described in the
literature. Various pressure gages, accelerometers, and strain gages were placedthroughout the ship to record external pressures on the hull, accelerations relatedto bow pitching and heaving forces, and bending strains of sections of the forefootand mid-section. A typical example of these types of measurements is shown inFigure 11-1.
