Multihull cruiser - comments requested

[Pericles]

Ally may be lightweight compared with steel, but not compared with composites. I gave you the figures on 7th December. It is the Proa boat form that is nostalgic, not the rest of the kit. Yes, it is the Boat Design forum and the corollary is that some boat designs are unsatisfactory if built with inappropriate materials, i.e. too heavy for the performance required and to a design that is intrinsically less safe for the purposes desired, a comfortable cruising vessel.

Your design isn't sea kindly and the ama must always be to the lee of the sails otherwise the vessel will founder, hence coming about is not possible. It will not tack or gybe safely and tending the sails will be more dangerous given the placing of the mast. Add a second ama and build a trimaran.

Redou,

You write like someone who won't be told! You can persist with what you want to do, because ultimately, you ARE FREE to do whatever you want to. True freedom is the willingness to accept the consequences of one's actions, to the point of being drowned, I suppose. However, you really do not have the right to endanger the lives of others such as the USCG who will put to sea in the worst conditions to save lives. Everyone's actions do have consequences and eventually Karma catches up. No man is an island. Be advised!

Pericles

[masalai]

Like minds again Pericles, This southerner has to be the dumbest inbread idjit that could be around. He operates two identical threads on the same subject and must have the hide of a rino, or been belted by bricks not to be able to understand a simple "Don't do it!"

[Kay9]

I started life as a boarding officer in the USCG and under title 10 We could terminate a "manifestly unsafe voyage" I feel that if the CG see this boat built anything like your drawing you will find yourself and your vessel terminated. And remember there are no FEDERAL missdermeanors, only felonys. Wich is what you will likely be charged with if you try to take this design to sea.

At least you would if I was the boarding officer.

[masalai]

Kay9, regardless of your name, and origin, I have to now consider you as an ally in deed. Thanks. Brownie points added, sorry forgot to sign, but then anonymus praise is OK?

[BWD]

kay9 you're funny, and from the tone of your post I do believe you were a boarding officer.
Reminds me of last Labor Day,
we were boarded on our 16 foot skiff by the CG, as
1) they like being stationed on the Chesapeake better than the Euphrates
2) It was Labor Day
3) We had a lady aboard
4) Could not quite get in shallows before they lit that cursed blue lantern.

As usual with young coasties, they misunderestimated both their draft and drift, so drifted down on us repeatedly, (uhm, do y'all have any fenders?) until their twin 225 outboards began to drag in the mud.
Then THEY had to ask US for a line.
It took some good humor on our part not to fire our engine and claim salvage on their vessel.
Naturally, all was right with our ship (more or less)
and I have yet to receive a summons or citation.
I may frame that boarding certificate, though.
Good times.

The relevant point is that the skiff is more or less a piece of junk, and poorly designed, though it has a good motor. We knew what we were doing though, although it may not have looked like it to a 20 yr old coastie.

So maybe lighten up a bit.
And yeah, I mean lighten up that catamaran/proa too, probably by using wood. Or foam if you are wealthy.

[Guest625101138]

Originally Posted by redou

Hello. First post. Here is a jpeg of a design I've been working on. .............
My interest is in sailing characteristics of such a vessel. Would anyone care to comment on the following questions?
a) Hard to turn or manouvre in limited space? Compared to a 36 ft. monohull heavy cruiser?
b) upwind ability in degrees? with boards down? Suggestions on the shape and location of boards?
c) ability of vessel to 'heave to' or ride out a storm? modifications to make this possible?
d) suitability of one or two junk (jonque) sails? if masts not on centerline?
e) speed of boat - 34 ft waterline - compared to monohull cruiser
f) could one person dock and undock such a craft?

The inspiration is the Ndrua, although smaller hull is not shorter. I think shorter small hull will slow boat down with shortened waterline. Boat is not shunted like the Ndrua, but tacked like a catamaran. My logic is one larger hull to carry people, equipment and stores. Smaller hull provides righting moment for sails, deck space and buoyancy in case larger hull is holed. I calculated wetted surface of both hulls combined comparable to heavy monohull cruiser.
I am not sure about location of masts relative to different sized hulls but
think 1/4 distance from large hull centerline to small hull centerline is justified
by smaller hull carrying 1/4 weight. Any and all comments would be most appreciated as I do not know much about sailboats. Thank you for your time.
Redou@i-55.com

Redou
The concept is interesting and thought provoking. I regard it as "twitchy" though.

To explain; I think you may have dismissed the comparitive merits of a trimaran too quickly. It is possible to operate a trimaran on the main hull in light air and on one of the amas in heavy air. The boat characteristics are balanced for roll irrespective of tack.

By contrast, with the single ama you rely on its buoyancy on one tack and its weight on the other - hence the characteristics are unbalanced. Once the ama achieves lift off it is not going to stop - crew get dunked.

I have an outrigger canoe that I pedal (see attached). I have the very small weight of the ama to provide righting moment and no paddle to help prevent capsize. Any initial roll to starboard and I get dunked. So I have learnt to lean into a turn to port and am very wary of beam seas.

More recently I added twin amas (other photo - I took this photo and both boats are set up for my weight so trims are not correct; yellow too deep, black too high). The amas normally just sit above the water level so offer no drag. The extra ama adds a tiny bit of extra weight to the main hull but its contribution to drag is much less than the single ama with its own weight.

Although not quite the same as you propose I have found advantage in twin amas over a single.

Rick W.

[masalai]

Redou you are a waste of breath. good luck

[Petros]

Hey Redou,

I have great idea for you. I would never want to stop someone from experimenting with unconventional designs, but this is quite major project without anything similar to compare it with. So why don't you build a 50 percent scale "model" out of plywood or some other inexpensive materials and take it out and try it as a sailing canoe kind of thing. I build 16 foot skin-on-frame kayaks and canoes for about $50 each with salvaged lumber and about 100 hours of work. You could do it in even less time by using plywood frames instead of steam bent ribs.

18 foot should be more than big enough to get it on the water and try it out to see how it handles. It will also give you an inexpensive "mule" to experiment with, make changes, add ballast, refine the design, try different mast locations, sail rigs, etc.

Then you can take pictures of it and post it here for us to see. And you can see if all these "experts" know what they are talking about.

Better test out the concept on something small, manageable and inexpensive rather than make a big and expensive mistake. You will also quickly prove these naysayers wrong, or eat humble pie and save yourself a lot trouble (better than eating 16,000 lb of alum!).

I would be happy to assist you in designing a simple scaled wood version of it if you are unfamiliar with small boat wood construction. It might keep you out of trouble too.

[Kay9]

BWD. Yep that was me. Except I was 19 and a boarding officer and I was CERTAIN that the mear fact that I was wearing CG blue meant I know WAY more then anyone else about boating, navigation, and drinking. Im 45 now and after 6 years in the CG went on to SIU went up the Hawse managed to get a 3Mates Unlimited and 1600 Ton Master, now Im pretty sure I dont know cra@ about seamanship and boating and will allways be learning

That said, I still feel the guy is heading for real trouble with the CG if his boat looks anything like his picture.

[Kay9]

Amas were originally designed by south sea islanders. Where the trade wind blows allmost exclusively in one direction all the time. With this knowledge the islanders could count on being on the same tack during an intire voyage. On the return trip the would move the ama to the other side. These conditions are not true for Louisianna. Not even by a long shot. Wind is often out of the SE but in a seconds notice can change to the SW or even N. Also with the 200+ days a year of sailing on the Gulf coast of the US thunderstorms are an allmost daily occurance, with the wind blowing off of them in ALL direction often in excess of 30 Knts. There is simply no way you can expect your vessel, as designed to do anything but got to sea and then turn turtle. If this is your intent in owning the boat, might I suggest you take the money you plan on spending on you boat and setting afire.

A lot of folks here are being extreemly generous and are offering you a lot of FREE help in building a craft with your desires in mind for cruising and construction. You should really LISTEN.

[bobg3723]

Hello Redou,

I read your post and I myself was thinking along similar lines of a polynesian ndrua type cargo vessel ...only women and wine are granted passage in my vaca, hehe.

Surfing the web awhile back, I actually came across this type of multihull form (asymetric hull crossection) on a multi-tonnage research vessel!!! But I'm almost sure it wasn't a cruise ship, because it would have scared off all the hicks down the gangplank.

You've pretty much stated your objectives in this design. And they are reasonable goals.

Bob

[bobg3723]

Originally Posted by redou

I checked out the harryproa site. It seems the harryproa is a very light twin hulled, wide beamed craft made to go fast. It has a conventional sloop or aerorig in the lee hull and uses the weight of the upwind hull as a righting moment against the force of wind on the sails. Quite an interesting and unconventional design.
My concept is much more conventional. A metal multihull cruiser, 16,000 lbs. with full load. The safety of metal construction. Outperforms monohulls under most circumstances. Faster in both light air and heavy. Carries a true cruising load, the safety of two hulls. Can be singlehanded. I am not sure this is possible.

Your ndrua is essentially a double hull and would undoubtably have all the catamaran's ideosychracies. Not a bad thing, but you might consider incorporating in your design the directionablity of one of those prop driving sea- weed wackers common among those asian countries who ply thier sampans among the mangroves and estuaries if you dont have a yulo handy.

[bobg3723]

Originally Posted by masalai

a) Having a straight keel-line will inhibit turning moment (have a look at the shape of a "hobicat" lots of what used to be called "banana" on those hulls.
.

On the other hand, a straight keel will hold a course with less attention paid to the rudder. One might find that usefull in minimizing leeway on long voyages.

[bobg3723]

Originally Posted by redou

I checked out the harryproa site. It seems the harryproa is a very light twin hulled, wide beamed craft made to go fast. It has a conventional sloop or aerorig in the lee hull and uses the weight of the upwind hull as a righting moment against the force of wind on the sails. Quite an interesting and unconventional design.
My concept is much more conventional. A metal multihull cruiser, 16,000 lbs. with full load. The safety of metal construction. Outperforms monohulls under most circumstances. Faster in both light air and heavy. Carries a true cruising load, the safety of two hulls. Can be singlehanded. I am not sure this is possible.

It seems there are those here that confuse your ndrua with an ama flying shunting proa. I came across this interesting bit of background about your ndrua, here: www.multihull.de/down/ndrua-gb.pdf

[Tad]

First off Boatdesign.net is "For Sure" here to encourage, advise, and learn from alternate viewpoints. This also requires those that seek such advice accept it in the spirit which it was offered, i.e., if you don't like it ignore it! If you submit an unconventional vessel, there will be questions and you must be prepared to defend your concept and theories. You submitted the idea hoping for peer review; don’t be surprised that there are naysayers in the crowd. Unfortunately every forum, by its open nature, includes a certain amount of chaff with the nuggets of wheat. Thus you get what you pay for…..

Also, nothing (or at least very little) in boat design has never been done before. In looking over the initial post I was reminded of the drawing below, published about 17 years ago in Multihulls for Cruising and Racing by Derek Harvey. An interesting boat IMO.