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A n A s s e s s m e n t o f S e a ke e pin g P e rf o rm a n ce

c o n s i de ri n g t h e Op e r ab il it y In di c e s

i n v ari o u s S e a C on di t io n s

K i m , B e o m S e o g

A b s t r a c t

T he seakeeping performance of a ship in various sea conditions has been

assessed only from the amplitudes of ship motions. Nowadays , in addition

t o s hip mot ion char act er is tics , s ynt het ic appr oach cons ider ing all t he

 par am et er s, which ar e thought to affect the over all ab ility t o fulfill their 

mission s, are being dev eloped actively .

In this paper, based on following definitions on the operability and the

seakeeping performance, a reasonable Seakeeping Performance Index (SPI)

is suggested.

¡ ÜOperability

: an ability to execute a given mission at a given position successfully

in a specific environment.

¡ ÜSeakeeping Performance

: an overall ability considering operabilities in various plausible sea

conditions.

T h e m ot ion s of a sh ip ar e pr edict ed by th e S hip M ot ion P rogr am

developed by Seoul National University. Operability Index (OI) for a given

m is sion on ea ch s ea c on dition i s calculat ed a s a w eig ht ed su m of  

 position al oper ability indice s which ar e calculat ed con sid ering th e

seakeeping criteria and the predicted ship motion at a specific place where

t he mis s ion i s execut ed. Th e s eakeeping cr it er ia are det er mined by t he

ship motion amplitude under which no performance degradation occurs,

therefore, should be set carefully from both empirical data and theoretical

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 pr edictions . SP I is a pr obabilistic com bin at ion of oper ability indices

c on s id er in g t h e im por t an ce of t h e g iv en m is sion , t h e du ra tion of t h e

mission, and the environment in which the mission is executed.

T h e S P Is of t w o sh ip s ar e com p ar ed , w h er e ea ch sh ip p erf orm s t h e

same missions but hull form, g eneral arrangement and outboard profile are

different. Futhermore they are compared with the Bales ' seakeeping ranks.

Unlike the seakeeping rank which uses merely the principal dimensions,

SPI uses not only the geometrical informations but also the scenarios of a

given mis sion .

By supplement of seakeeping performance record, SPI will give more

 pr actical gu ideline for the imp rovem ent of seak eeping perf orm an ce in the

design stage.

Key Words : ship motion program, seakeeping criteria, operability index,

seakeeping performance index

Stu dent Number : 96414- 505

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