Volume Advantage

What would be the advantages of more volume being in the center, front, or rear of the hulls, if that's possible? I'm asking because of some posts I've seen mentioning the Viper's volume being forward. And also that I finally got a good look at the Capricorn at the Tradewinds, and was amazed at size of the hulls.

Thanks in advance for any responses.

I think it would be difficult to discuss volume independently from the shape of the hulls, and other factors. Designing a hull has to consider floatation, weight, shape, center of gravity, mast placement,sail size, sail types, etc.

You must also realize that each particular setup (class rules) may favour a different build of hull.

A-cat currently tend to go towards small freeboards with (very) fine bows in combination with moving the mainbeam waay back.

F18's go a totally different route, mostly because of significantly different way this boat is to be handled.

Same with the F16's; these are (relatively) lightweight boats with an (relatively) oversized engine compared to the hull length. They favour more volume up front even if that results in more drag. Afterall, going slightly slower over the course is still better then being upside down. Luckily the higher drag hit is too small too notice as the (oversized) engine still has enough margin left to compensate for this hit.

Similar (individual) balancing acts are to be found in each class and they tend to favour (slightly) different solutions.

For racing boats with a spinnakerlike the F18's and F16's there is simply no substitute for high freeboard and sufficient volume up front. Ease of handling and recovery margin win the day almost every single time.

Personally, I don't really see any advantage of lots of volume in the centre. Only lots of freeboard (prevent beam slapping)

Wouter

This is a complicated question and admittedly I know just enough about it to be dangerous...but here's my take...volume up front prevents pitch polling and helps keeps the bow up increasing the speed potential and decreasing the sensitivity to wave height. Volume in the center will help with tacking ease allowing the boat a fat middle point to pivot on. Volume in the rear helps the boat plane downwind. Rocker and daggerboard position affect tacking and upwind efficiency. More volume / flatter sections affect drag. Hull shape is a balance of all of these variables.

On a displacement hull, the speed potential is linked to the fineness ratio. For a given length the narrower the hull the faster it can go. Cat hulls are not fully dispacement though so this is only partialy true. Increased volume in general allows the boat handle larger crew weights, which in turn can ballance the horse power from the sail plan and provide better performance. This only works up to a certain point and too much volume will begin to slow you down eventually.

Jake pointed out the advantages of volume. Contra to that: too much volume up front provides bad pressure distribution along the hull and is slow. Too much in the middle and the boat wants to teeter fore and aft and is very difficult to keep in trim fore and aft. Too much volume in the rear and the transom sticks in waves and wants to trip forward.

Good luck in inerpreting any of these in a real world situation.

so, in THEORY, you'd want it long and skinny when sailing flat. As the sails work to push the bows down, you want increasing volume up front to counter this force.

To turn, you want enough volume in the middle to make for a quick pivot.

And to carry weight in the stern effectively, you need volume back there, but not too much as to make drag a problem.

No problem, right?

Make a long skinny bottom section, add two foils in the middle to lift the boat up when you want to turn, and put some huge wings at deck level (like one of those Piewacket boat designs) to keep the sterns up

too bad something like that wouldn't float in real life....

Volume? Just turn it up to eleven and leave it there mate!

Thanks guys! Very informative. The volume in the front to prevent pitch-polling baffles me though, but there's a lot I need to know.

One more question now that we've got the semantics of volume out of the way. If it's not too personal. Where do you consider the volume to be on the Capricorn, Wild Cat and Infusion? OK, I actually have another question, but I'll wait for the responses on this one first.

Once again, thanks for your help.

I don't know if this is what you mean but it might help to think of volume in this context as bouancy. It just makes it harder to submerge the bows.

OK. that makes sense now. I guess when I see the size of the hulls, I'm automatically thinking of additional weight. That definitely clears that up. Thanks!

Try to pitchpole with some inflatable markers attached to your bows... let us know what you learn

Brainstorming from that, race bows with inflatable attachments upwards could make sense for a cruiser/racer: deflate for racing, inflate for cruising. Or deflate upwind and inflate downwind in the AC... I'd be surprised if nobody thought of this before.

There used to be some little foils you could attach to a hobie 16 at the bows to prevent pitch-poling. They weren't race legal, they may still make them I used to see them in the murray's catalog.



Update: I just checked the catalog, apparently they still have them. $116.00

Those sorts of devices always have the same result... once they go under the water they actually cause the pitch pole.

I always thought an inflatable anti-capsize device on the mast would be a good safety feature to prevent larger multis from going full turtle.

You could have an auto-inflater switch at the deck tied to a scuba tank that would inflate an airbag type setup at the masthead. A 15# lift bag would be all it takes for something up to 30 feet.

Once the boat's back up, you could probably even devise a small vacuum pump (manual or battery) to deflate the bag. Or, to keep it simple, have it attached to a halyard or something so you can lower it once you're done.

lots have people have had similar thoughts

usually with something smaller than a scuba bottle though

wow, 600 lbs bouyancy. wonder why you need that much? But I guess a Trimaran has a lot of force pushing the mast down once it gets heeled that far over...