Multi-hull boat design

[NorthWoods]

It came up on the other forum- bateau2, that there aren't enough good quality power cat designs in stitch and glue for amateur builders. I was wondering why this is. We came up with some questions about what makes a power cat better than a monohull, and what makes them worse.

I think they get a bad rap because they may be more expensive to build and they're kind of ugly when compared to monohulls until you get over about 30' in length. I think because of the bad spin surrounding them, they tend to get overlooked by designers, who have to balance marketability against their own desires or likes.

But my contention is that they are poorly promoted. Their benefits are seldom discussed and their looks don't seem to be making any headway. What do others think? I raised the point about them being rejected by traditionalists, but that was met with, well they're traditionalists, enough said. But I think that's the wrong way to confront the problem, and one that will only lead to a continuation of the status quo. I think if you look at this problem as a problem of pursuation and ask, how do we get the traditionalist to take a second look at the catamaran, then you've just gone a long way toward solving the problem.

It's easy to simply say, well they're different and you either love them or hate them. If you marketed anything new that way, you'd quickly be out of business. What is it about the catamaran that I should love? What should I look at again? What obstacles must be overcome to get folks to want a catamaran?

Who wants to play? Anybody?

[NorthWoods]

Well, I guess you weren't that serious a proponent.

[JEM]

might want to give people more than 1.5 hours to reply. :lol:

[NorthWoods]

Yeah, that was to someone specific. I hope folks do reply because I'm serious. I'd like to know why a few old Glen-l designs and one Bruce Robert design seem to be the only power cats around.

And who says they can't look better than they do?

[kiwi]

[quote=NorthWoods]I'd like to know why a few old Glen-l designs and one Bruce Robert design seem to be the only power cats around.

And who says they can't look better than they do?[/quote]

My take on power cats: As you all know I am a multihull nut but small live-abord power cats are as ugly as sin, that is why I will build a TW28... The TW28 will also go through narrow canal locks and under low bridges.

I really love the looks of the Glen-l Aqua Cat and the line drawings are in my "boats to redraw for S&G" folder. The boat would be a river/canal boat and have a couple of 10/15 HP 4-strookes to push it at the 15 km/h legal limit here. I would not go out in the estuary with it, there is not enough hull clearance.

In last months "Neptune Moteur" there is a sea test of the Fountaine Pajot 35' cat. They have put a full fly bridge on the thing and well... it does have lots of space inside
:twisted:

I would go further than you Dave and say that good looks start at over 40'.

On the bateau forum the request is for a 21' boat for fishing. I can't see why a 21'-24' power cat could not be designed for S&G composite. I think it would have a little more building time and material required. Commercial fishermen are moving to catamarans in the over 60' categorie. There is also some potential in the wave piercer type at this size maybe? A real designer will tell us.

Tony

[kiwi]

[url]http://www.tennantdesign.co.nz/articles/66/diplacementpowercats.html[/url]

One of the more respected designers of multihulls. No displacement power cat less than 30' is the executive summary.

Tony

[Toni_V]

Yeah, I agree that cats should be quite big to be practical. Cat's efficiency comes from narrow hulls and in smaller boat the narrow hulls are quite un-usable for accomodation etc.

Actually my freeship boat started out as a catamaran. It turned out ok looking (I think, for that lenght);
INSERT INTO phpbb_posts (old_post_id, topic_id, forum_id, poster_id, post_time, poster_ip, post_username, post_subject, post_text, enable_bbcode, enable_smilies, enable_sig) VALUES but the hulls are quite narrow to be pratical and too wide that there would be any efficiency advantage over monohull. Also, it's really clear that cat will have much more work than monohull.

But the good sides show up too, Freeship calculates metacentric height (stability thingy);
INSERT INTO phpbb_posts (old_post_id, topic_id, forum_id, poster_id, post_time, poster_ip, post_username, post_subject, post_text, enable_bbcode, enable_smilies, enable_sig) VALUES and for the monohull (The thread I started) it's 1.5 metres, for this cat it's over 3 metres.

Well, i'll spam few pics from the cat too. The numbers are:

lenght 8m
good standing headroom inside hulls, 2m
displacement about 2.5 tons
each hull is 0.9m wide at and widest part of bottom, width is 1.1m at 1.2m height.

[img]http://personal.inet.fi/koti/piia.ruokonen/paatit/cat_Image1.jpg[/img]
[img]http://personal.inet.fi/koti/piia.ruokonen/paatit/cat_Image4.jpg[/img]
[img]http://personal.inet.fi/koti/piia.ruokonen/paatit/cat_Image9.jpg[/img]
[img]http://personal.inet.fi/koti/piia.ruokonen/paatit/cat_Image11.jpg[/img]

[JEM]

Could it be that no one wants to take the first step?

I'd think draft would be an issue on a displacement style cat. But what about a planing power cat? Keeping the pontoons flatish and full should offer comparable draft.

Also, since it's a smaller boat it would have less height to the tunnel to keep COG lower. Would "sneezing" become more of an issue then?

[NorthWoods]

Hmmm... what's sneezing? That's the first thing I noticed about them is the draft requirements, and the beam. There's no chance of launching anything with a draft greater than a couple of feet in some of the lakes around me. They seem extremely potentialicious, since you could make them much wider than a monohull, but is it that you can't realize that potential in a trailerable boat design, which is what most people will be looking for in an amateur build?

I think I understand what your saying Tony, about the hull on the aqua cat not having enough clearence, but what happens if you nose dive it, will it not cut through the waves, or will it act as a foil and pull the boat under, while under power? Is it dangerous?

Also, Toni, nice work again on the hull designing. That is a good looking open cat.

See, the thing is, I was reading my Seidman's Complete Sailor and my Edmund's Designing for Power and Sail, and they both say, above the water line, the hull styling is basically an open book, so why do so many smaller cats look like thier top sides were an afterthought (probably with the exception of a couple of glen-l designs which I would characterize as old-fashioned, but not necessarily ugly).

Couldn't a good designer come up with a contemporary top side for one of these things with a decent "floor plan" that doesn't freak people out. Like maybe no beam sleeping for one. Hmmm...maybe I'm being too hasty, is it more comfortable to sleep across the ship?

[JEM]

Sneezing (a term I had to learn) is when the water reaches the top of the tunnel, gets backed up, and sprays out forward and thus back into your face.

I believe it's only an issue if your under way at a decent speed. I've never ridden a power cat and had that happen.

I had a guy ask me to help him design a plug mold for a 32' power cat. His design was strickly a fishing/work boat. Completely open and except for misc benches, consol, etc.