Appendix [2] â Comments upon MGN 327 â Design ... AWS
Appendix [2] – Comments upon MGN 327 – Design Guidance W e no te wit h a ppro va l t he ve ry brev it y o f MGN 3 2 7 . Co ns i de r t he his t o ry : Se ve ra l hu ndre d pa ge s o f re s e a rc h were co mple t e d, lea di ng to a 9 5-pa ge F i na l Re po rt, of whic h li tt le mo re t ha n one pa ge o f Desi gn Guida nce co uld be f i rmly gi ve n. Thi s is no t a c riti cis m— i t is a means of highli ghting t hat t he MCA Pro je ct Tea m t he ms e lves rea li ze d t he di ff ic ulty i n e xt ract i ng broa dlyapplica ble gui dance fro m t he s ma ll a nd f o c use d s t udy unde rta ke n. The pe e r re v ie w te a m ha s e xpre ss e d t his s a me f ac t v i a o ur ma ny c o mme nt s o n t he MCA F i na l Re po rt : The s t udy is go o d as fa r as i t go es , but i t s ho uld no t be bro a dly a ppli e d u nt i l i t s t ec hni c a l ba si s is si mi la rly bro a de ne d.
Para gra ph 1.2 sta tes t hat t he purpose o f t he Pro jec t was t o gai n a n i mprove d unde rst a ndi ng. W e be liev e t ha t t he Pro jec t has i ndee d a dde d s ubsta nti a lly to t he unde rs t a ndi ng o f t hese phe no me na . This understandi ng is however based o n a v e ry li mi t e d s e t o f t es t da t a, a nd s ho uld be a pplie d o nly t o c ra ft si mi lar t o t hose te ste d. Ane nt Pa ra gra ph 2 . 1 : Co nt ro l i s no t a lway s los t duri ng s urfi ng. Thi s s ho uld bette r rea d “a nd directio na l co ntro l MAY t e mpo ra ri ly be los t. ” Re ga rdi n g Pa ra gra p h 3 . 1 : The re i s i ns u f f i c i e nt e x pe ri me nt a l da t a t o dete rmi ne whet her t his is a lways t he case, no t wha t t he li mi t s o f “f i ne ” a nd “bro a d” mi ght be . Re ga rdi ng Pa ra gra ph 3 . 2 : No t a ll hi gh s peed / li ght ly loa de d craft a re of s ha llo w dra f t . As no te d i n t he f ull c o mme nt s , SW ATH a nd SW ATH-li ke forms (i nc ludi ng so me tri mara ns) c learly di ffer i n t his area. Additio na lly, we be lieve t he re is a n i mpo rta nt ro le playe d by ine rtia l feat ures , i nc ludi ng mass mo me nts o f i ne rtia, whic h have no t yet bee n st udie d. I ne rtia l pro perties are very i mporta nt i n latera l ca psi zi ng, a nd it is reaso na ble to e xpect the m to be i mpo rta nt i n pitc h- a nd ya w-a xis eve nts as we ll (i.e., bow divi ng a nd broac hi ng).
Re ga rdi n g Pa ra g ra p h 5 . 4 : No t e t ha t t he mo de ls ha d di f f e re nt s ui te s of unde rwate r a ppe nda ges – e. g. s hafts, s truts, & rudde rs . The Gui da nce give n is lo gica l, t ha t addi ng e quiva le nt a ppe nda ge s wo uld li ke ly res ult i n equivalent be havior, but it is i n fact an e xt ra po lati o n f ro m, a nd not t he di rect res ult o f, t he t est pro gra m. The revi e w tea m wa s qui te s ke pt ica l of t he i mpli c a t io n t hat di re ct io na l stability, i n t he classical sense, is re leva nt t o t he bro ach a nd bo w-dive phe no me na. It is qui te possi ble t ha t o t he r dy na mi c s a re pres e nt whi c h q ui t e o v e rri de c o nv e nt i o na l di rec tio na l st a bi lity so luti o ns. I n c o nc lusio n, t he revie w tea m co ns ist e nt ly co nc urs t ha t t he MCA gui da nce is ge ne ra lly correc t fo r t he hull f o rms t es te d, but ca uti o ns t ha t t he re ma y be o t he r fa ct ors o f gre at er i mpo rt a nc e (e . g., i ne rt ia ) a nd t ha t t he gui da nce s ho uld no t be re lie d upo n f o r hull f o rms di f fe ri ng f ro m t hos e te ste d.
Para gra ph 1.2 sta tes t hat t he purpose o f t he Pro jec t was t o gai n a n i mprove d unde rst a ndi ng. W e be liev e t ha t t he Pro jec t has i ndee d a dde d s ubsta nti a lly to t he unde rs t a ndi ng o f t hese phe no me na . This understandi ng is however based o n a v e ry li mi t e d s e t o f t es t da t a, a nd s ho uld be a pplie d o nly t o c ra ft si mi lar t o t hose te ste d. Ane nt Pa ra gra ph 2 . 1 : Co nt ro l i s no t a lway s los t duri ng s urfi ng. Thi s s ho uld bette r rea d “a nd directio na l co ntro l MAY t e mpo ra ri ly be los t. ” Re ga rdi n g Pa ra gra p h 3 . 1 : The re i s i ns u f f i c i e nt e x pe ri me nt a l da t a t o dete rmi ne whet her t his is a lways t he case, no t wha t t he li mi t s o f “f i ne ” a nd “bro a d” mi ght be . Re ga rdi ng Pa ra gra ph 3 . 2 : No t a ll hi gh s peed / li ght ly loa de d craft a re of s ha llo w dra f t . As no te d i n t he f ull c o mme nt s , SW ATH a nd SW ATH-li ke forms (i nc ludi ng so me tri mara ns) c learly di ffer i n t his area. Additio na lly, we be lieve t he re is a n i mpo rta nt ro le playe d by ine rtia l feat ures , i nc ludi ng mass mo me nts o f i ne rtia, whic h have no t yet bee n st udie d. I ne rtia l pro perties are very i mporta nt i n latera l ca psi zi ng, a nd it is reaso na ble to e xpect the m to be i mpo rta nt i n pitc h- a nd ya w-a xis eve nts as we ll (i.e., bow divi ng a nd broac hi ng).
Re ga rdi n g Pa ra g ra p h 5 . 4 : No t e t ha t t he mo de ls ha d di f f e re nt s ui te s of unde rwate r a ppe nda ges – e. g. s hafts, s truts, & rudde rs . The Gui da nce give n is lo gica l, t ha t addi ng e quiva le nt a ppe nda ge s wo uld li ke ly res ult i n equivalent be havior, but it is i n fact an e xt ra po lati o n f ro m, a nd not t he di rect res ult o f, t he t est pro gra m. The revi e w tea m wa s qui te s ke pt ica l of t he i mpli c a t io n t hat di re ct io na l stability, i n t he classical sense, is re leva nt t o t he bro ach a nd bo w-dive phe no me na. It is qui te possi ble t ha t o t he r dy na mi c s a re pres e nt whi c h q ui t e o v e rri de c o nv e nt i o na l di rec tio na l st a bi lity so luti o ns. I n c o nc lusio n, t he revie w tea m co ns ist e nt ly co nc urs t ha t t he MCA gui da nce is ge ne ra lly correc t fo r t he hull f o rms t es te d, but ca uti o ns t ha t t he re ma y be o t he r fa ct ors o f gre at er i mpo rt a nc e (e . g., i ne rt ia ) a nd t ha t t he gui da nce s ho uld no t be re lie d upo n f o r hull f o rms di f fe ri ng f ro m t hos e te ste d.
