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Re: Lets have a chat about multis.
Deck clearance depends on the size and design of the boat. More is usually better but if you have full standing headroom on the bridgedeck cabin on a 32' cat plus 3' of bridgedeck clearance you would have really tall windage. This would raise your center of gravity and center of effort and probably make the boat unstable. If you take the same boat but make it open bridgedeck, no bridgedeck cabin, then your CG and CE would remain lower. The Gemini for example has a low bridgedeck because it has a narrow beam and needs to keep the CG and CE low to maintain stability.
Some cats go as low as a 7to1 ratio and other 16to1. If you have the length to be able to handle all the weight then the 16 to 1 would be a much quicker boat. If the cat is smaller and needs to support a good sized cruising load they would lean towards a fatter hull.