From pools to waterfalls

The chal­len­ge of wa­ter aboard

Superyacht - - Tecnica -

is what it ta­kes to fill a clas­sic round Ja­cuz­zi. What are the main pro­blems cau­sed by a pool on board, ob­viou­sly when it’s full? The main is­sue is the free sur­fa­ce ef­fect. This in ef­fect is lin­ked to the mass of wa­ter held in the pool and its iner­tia, that can be ex­ci­ted, for exam­ple, by lon­gi­tu­di­nal ac­ce­le­ra­tion cau­sed by a ya­cht’s pit­ching mo­tion. When the na­tu­ral fre­quen­cy of iner­tia of the wa­ter ap­proa­ches the va­lue of the fre­quen­cy of the pit­ching mo­tion, the wa­ter starts to re­so­na­te ge­ne­ra­ting si­za­ble wa­ves. The ta­sk of the de­si­gner is to en­su­re that the­se two va­lues stay well apart by wor­king prin­ci­pal­ly on the vo­lu­mes and sha­pe of the pool. As you your­self said, an on board pool de­ter­mi­nes po­ten­tial pro­blems lin­ked to the mo­ve­ment of the wa­ter in­si­de the pool. In technical terms the pre­sen­ce of a full pool, and in par- ti­cu­lar its sur­fa­ce that is free to mo­ve, de­ter­mi­nes re­du­ced ves­sel sta­bi­li­ty (see box wi­th de­tails) and hen­ce im­pin­ges upon its sa­fe­ty. How do ya­cht re­gi­stries that eva­lua­te sa­fe­ty aboard ad­dress the pre­sen­ce of pools aboard? From a technical point of view a pool is an open tank and, as su­ch, mu­st not com­pro­mi­se a ves­sel’s sta­bi­li­ty. Thus, if I want the ves­sel to be ope­ra­ti­ve al­so wi­th a fil­led pool I need to show that the ves­sels’ re­qui­red le­vel of sta­bi­li­ty is ne­ver­the­less main­tai­ned, in other words that sta­bi­li­ty is in no way com­pro­mi­sed in any of the ca­ses fo­re­seen. Whe­re it’s im­pos­si­ble to meet the re­qui­red stan­dards in terms of sta­bi­li­ty be­cau­se the pool is par­ti­cu­lar­ly lar­ge, or may­be ve­ry hi­gh up, the re­gi­stries

re­qui­re for the pool to be com­ple­te­ly drai­na­ble in 3 mi­nu­tes. This is an MCA (Ma­ri­ti­me and Coast­guard Agen­cy) LY3 (Lar­ge Ya­cht), re­qui­re­ment, in other words the mo­st re­cent ver­sion of the re­gu­la­tions used for lar­ge yachts. From what si­ze up can we start tal­king about a pool? Can a Ja­cuz­zi 1 me­tre across be con­si­de­red a pool? From the point of view of re­gu­la­tions the­re’s no dif­fe­ren­ce bet­ween a Ja­cuz­zi and a lar­ge pool, bo­th ha­ve to meet re­qui­re­men­ts in terms of sta­bi­li­ty, wha­te­ver the si­ze. For su­re, a Ja­cuz­zi is qui­te a dif­fe­rent thing to a lar­ge pool. Small Ja­cuz­zis ha­ve al­ways been on big yachts but we­re not con­si­de­red pools be­cau­se, wi­th tho­se si­zes, a per­son in one can’t mo­ve around that mu­ch. In­stead, sin­ce 10 years ago we’ve star­ted tal­king about true and pro­per pools, of amoun­ts of wa­ter that al­low a per­son to swim, even if wi­th a de­vi­ce that crea­tes a cur­rent to swim again­st. Thus pools need to be deep enou­gh to ma­ke it pos­si­ble to swim and need lar­ge quan­ti­ties of wa­ter: no lon­ger the 1,800 li­tres of a lar­ge Ja­cuz­zi, but 8,000, 10,000 li­tres of wa­ter. The­se lar­ge quan­ti­ties fur­ther de­ter­mi­ne the need to stock this wa­ter that can­not be wa­st

ed, sim­ply th­ro­wing it away, it

The sce­nic wa­ter­fall de­si­gned by Fran­ce­sco Pasz­ko­w­ski for the sun deck of the new CRN 80 me­tre.

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