adding bouyancy ?

[gramos]

can the forum tell me if its feasible to add bouyancy to a cats hulls ? hull type is a fine entry to D section with fixed keels i have several reasons for trying to achieve this : more bridgedeck clearance , better load capacity , and ,if at the bows, less pitching . the hulls are originally a lerouge jeffcat 32 ft design stretched to 38 ft .

[Meanz Beanz]

Adding buoyancy in the bows can cause problems, you need good reserve buoyancy in the right form, nothing that will slow the boat when she noses into a wave or else it becomes counter productive and may help to produce one of the problems you are trying to avoid. I think it would be very difficult to substantially alter a boats behavior without doing extensive/prohibitive modifications & it sounds like the boat has already been changed significantly. Personally I would be looking to trade to the boat you need.

[gramos]

Adding buoyancy in the bows can cause problems, you need good reserve buoyancy in the right form, nothing that will slow the boat when she noses into a wave or else it becomes counter productive and may help to produce one of the problems you are trying to avoid. I think it would be very difficult to substantially alter a boats behavior without doing extensive/prohibitive modifications & it sounds like the boat has already been changed significantly. Personally I would be looking to trade to the boat you need.

the boat has gone through some evolution and its been a continual course of improvement , if i had the money ,of course i would trade up to a bigger/faster boat , but i dont ! thats why i use this ,and other forums to sound out ideas with , i presumed , similar minded enthusiasts . improving the boat is a continual source of amusement, interest and learning . i am always appreciative of constructive input. i would not reverse any of the mods i have made they have all worked , i am happy to say ! my current thinking is adding "torpedo " shapes to below the waterline at the bows as the catana cats do to reduce pitching some more and increase forward buoyancy . has anyone experience of this ?

[TeddyDiver]

my current thinking is adding "torpedo " shapes to below the waterline at the bows as the catana cats do to reduce pitching some more and increase forward buoyancy . has anyone experience of this ?
Something like bulbs:confused:

[gramos]

teddy , yes like bulbs but inline with the bows not forward .i saw a solaris recently with bulbs fitted from new , with "winglets " on each side looked like doodlebugs ! the owner said they forced the bows DOWN the faster he went ! i swam around them and the wings were inclined upwards but maybe not enough .

[Meanz Beanz]

the owner said they forced the bows DOWN the faster he went !

That sounds lethal!

[Bruce Woods]

Before you start attaching bow bulbs, sit down and calculate how much actual buoyancy you will gain. Some of the bow bulbs I see out there seem like a total WAFTAM. Very little buoyancy gained for the weight of materials used.

Maybe could have got the same result by moving the spare anchor further aft.

[gramos]

Bruce , WAFTAM ? , i do follow all the usual cat edicts, keeping weight off the boat and centrering whats left ! anchor at mastfoot , spare fwd in cockpit etc etc, . the idea is to build 1200 x 150mm long tubes and fair them in under the bows , like torpedoes ,keeping the construction light and strong ,without entering the existing hulls .i would think the added buoyancy would be 75/ 100 /kilos per side ,giving the extra i want at the right end of the boat . i am also thinking about wings attached (by welding ) onto the bottoms of my s/s rudders -again to reduce pitching ....

[Bruce Woods]

Bruce , WAFTAM ? , i do follow all the usual cat edicts, keeping weight off the boat and centrering whats left ! anchor at mastfoot , spare fwd in cockpit etc etc, . the idea is to build 1200 x 150mm long tubes and fair them in under the bows , like torpedoes ,keeping the construction light and strong ,without entering the existing hulls .i would think the added buoyancy would be 75/ 100 /kilos per side ,giving the extra i want at the right end of the boat . i am also thinking about wings attached (by welding ) onto the bottoms of my s/s rudders -again to reduce pitching ....


So you will be attaching them UNDER the bow? Have you thought about the CLR changes and what the new rocker profile will do too handling. S/S rudders don't sound like a high performance addition. Is there anything else you are not telling us?

[gramos]

like what bruce ?? s/s rudders are fabricated from 2mm plate with 40mm stocks and VERY fair , hollow and really well made .yes, you got it ,under the bows not projecting, as in the catana bow profile- have a look at them

[Bruce Woods]

Bruce , WAFTAM ? , i do follow all the usual cat edicts, keeping weight off the boat and centrering whats left ! anchor at mastfoot , spare fwd in cockpit etc etc, . the idea is to build 1200 x 150mm long tubes and fair them in under the bows , like torpedoes ,keeping the construction light and strong ,without entering the existing hulls .i would think the added buoyancy would be 75/ 100 /kilos per side ,giving the extra i want at the right end of the boat . i am also thinking about wings attached (by welding ) onto the bottoms of my s/s rudders -again to reduce pitching ....


Ok Gramos lets back up abit.
1200x150 mm od tubes have a volume of around 21 liters. Say roughly 21 kg's of buoyancy. So lets say you build them out of very light materials and graft them on the bottom of the bows . Hopefully you don't use cheap polystyrene foam that absorbs water over time.So you end up with around 35
kilos of buoyancy after a lot of work. To stop them acting as weed traps you set them back a little from the bows so now that 35 kilos is centered aft a little.

MMMMMMMM try sitting aft a little in the cockpit before you go to all this trouble and see what difference it really makes. Remember Crowthers hulls had extremely fine ends in the era when he started adding bulbs that made a noticeable difference. It was an attempt to rectify a design fault. His latter designs had better buoyancy distribution along with his trademark tulip shaped bows.