Well, hull beam is an interesting subject... Yes, 12:1 is considered the magic number to begin reaping the benefits of decreased hull resistance, increased speed for a given power, and increased fuel mileage... But there is a whole bunch more than that..For instance the designer has to consider that to support a given tonnage a narrower hull will need more draft than a wider hull... If deeper draft is going to be a problem once the initial hydrostatics is done then the designer has to either lengthen the hulls or fatten the hulls in order to decrease draft... Each choice has it's own problems... For example on length changes, there is a desireable range of length to BOA ratios for a cat... Too narrow for the length decreases stability in certain directions... Too wide also causes stability problems, usually in the other directions... So the designer has to contend with this as he makes changes to the planform... Another issue is how much space is needed in the hulls and why... If this is going to be designed for the charter market, then there has to be fat hulls to hold the opulent heads and staterooms (with more berths shoved under the foreward bridge, etc.).. all of which adds to the tonnage, which adds to the draft, and needs more power for a given speed, and so on... I can only talk about my boat (which is 'supposed' to start building any day now - i hope, i hope)... LEVITATION is a custom designed power cat... Kurt Hughes is doing the design work and I think he has come up with a handsome boat - of course he has been doomed to design it to my specifications with me breathing over his shoulder every inch of the way, so I may be biased.. Some of the tradeoffs in the design stage were <in no particular order> set up for a couple to live aboard (not a weekender with half of your relatives), shallow draft, good stability, fuel efficiency, all living area such as staterooms, galley, dining, settees, on the saloon level (wife has a bad knee), only the heads and showers are down in the hulls <which allows them to use the full hull width and generous length so that they are very nice>, pilot house above the saloon, and on, and on... As a result this ~ 40 foot cat has developed 50 foot hulls with 26 foot beam overall... The hulls remain relatively narrow for length as we played with draft versus hull beam... The additional separation of the hulls is expected to improve fuel efficiency due to lessened wave interference... Anyway, this is a bit about what choices I made in the design of LEVITATION... cheers ... denny --------------------------------- Talk is cheap. Use Yahoo! Messenger to make PC-to-Phone calls. Great rates starting at 1"/min.