Small trimarans under 20'

It bothers me you are drawing a boat based on "looks".
How about a little engineering - pick a displacement you want for the ama, choose the length to keep it fast, position it fore and aft to take care of pitchpoling.

Your "look" upside down won't do you much good.

 

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Consider the sketch below carefully-it's just a suggestion of another way to think about and design an ama for an under 20' tri. The idea is to use a smaller ama but to combine it with a shape used to connect the ama to the crossarms in such a way that when the boat is at 90 degrees the center of buoyancy of the ama + connecting shape is more toward the mast tip than the same old same old making it much more difficult to capsize. The "connecting shape" is designed to have considerable buoyancy.
See the rough sketch:

click

 

I am a very visual person, and it helps tremendously to actually draw out the ideas I have, and see where the problems arise, but that alone should not be relied on, I agree.

What do you mean by "upside down look"? You mean the reverse bow? The vaka is already built, so the bow on it won't be changing. As for the amas, I literally copied the shape of the AC72 boats, made the amas a bit less tall, and changed the profile on the upper rear behind the crossbars.

Here is the boat as it is right now, pre-modifications. Note the bow. Ps: The main hull performs perfectly in choppy conditions, it pierces just fine and it just keeps driving straight through.


Doug, I'm sorry, I'm really not a fan of planing amas. I would prefer wave-piercing very narrow displacement. Too much bouncing around if they plane. Planing amas only work if the water is relatively flat. In my experience, at least where I sail, its either dead calm and flat, or its windy and you have 1+ foot waves, spaced maybe 15 feet apart. Sometimes if its been blowing really strong for a while, they go up to about 2 feet.

 

I think upchurchmr is referring to capsizing when he say upside down

the big problem with your rig as drawn is you cannot let the mainsail out past, what 45deg?, before it hits the shrouds.

Richard Woods

 

Rcnesneg,

I knew you were thinking of your SOF main hull when I said the H14 mast was heavy.

Using these together is real close to mixing the "add amas and a light rig to a canoe" technology with full power beach cat stuff.

You goals seem to include
- wide beam
- flying the main hull
- Inclined ama daggers for "foil assist"
- Sufficient ama buoyancy to support one crew at rest

Flying the main hull for a wide beam tri requires a strong but light platform and a rig that provides sufficient power.

An all aluminum H14 mast with an extension up top (above the hounds is less loaded) and full sized H16 sails might be an ok way to get adequate power at a low cost.

You need to have some idea of the structural loads at key locations. Can your main hull take the down force from the mast and the up forces from the forestay and mainsheet?

As an example, consider 500 lbs for the main sheet based on a 5 to 1 advantage and 100 lbs of line load in a gust. If the distance from the mast to forestay attachment is the same as the distance for the mast to mainsheet attachment, it would provide 500 lbs of up force at the nose to stay in balance with the main sheet. This put 1000 lbs of down force at the mast.

 

I'd be very leery of a square or over square beam on a small boat that doesn't use a lifting foil on the daggerboard and doesn't use a rudder t-foil. Using the dimensions provided, the boat will have enough RM that it will require around 2lb/sq.ft. pressure-and thats with the crew in the center-to fly the main hull. That's 33% more pressure than the wind required to sail an F18 with the crew on twin trapezes. All kinds of issues are raised by this so you need to look at it carefully. Not to belabor a point but this is the exact same situation I faced with the Fire Arrow-and solved.

 

It always amuses me when someone sees a plate of food and says "that looks nice". So what!

Remember the shape of cars from the 30-40's, drawn for low resistance and streamlined, by people working on the "that looks nice" principle. As soon as they put cars in windtunnels the shapes changed to what we have today

Richard Woods

 

a Home design

A home design I found

www.youtube.com/watch?v=wkLEjtgvdcg

www.youtube.com/watch?v=hSBFxtQnF8s


https://www.youtube.com/watch?v=wkLEjtgvdcg
https://www.youtube.com/watch?v=hSBFxtQnF8s

 

20 and under

Thanks, Warwick! Very interesting. I want to compliment you for posting on the youtube video site that you had posted the video here-damn decent thing to do!

 

I am only to happy to support our forum as well.

 

Thanks everyone for your input! It's obvious there's a lot to consider here. Basically I want to convert it to something capable of keeping up with a Hobie 16 in higher wind, and an F18 or F20 in very light wind, but without the cost, which is a bit of a conflict. Perhaps I should start a separate thread so as to avoid hijacking this one.

 

is it just me or does the drawing look like the very basics of any foil design.

doug, look, honestly brother ive thought about building YOUR boat because I thought it would shut you up. But, I have learned that you have always "thought of some design previous to anyone in the multihull world", which in my book, should make you world famous by now (coming from a previous security software designer lol).

I have a huge obsession with foilers especially because i can build sensor guided foiler with the stuff i do for work.

but doug, i have to say, you ruin foiling for me. just in general. ruined. when i want to consult you , and that day may come, i will.... but for now you continue to interject your ideas into everything we discuss here.

and trust me, i know you wont, but this comes from a "foiling is the future.... and i think doug might have hit a home run if he would get off his ***" type of person.

 

First, you castigate me because I said I wasn't sure that the Fire Arrow would be suitable for the Everglades Challenge, then when I show a foil that might make it possible for the boat to do the challenge you castigate me again. Can't win with you-not that I care. If you're the type of person that would allow somebody else to "ruin" something you're interested in, you are beyond help.
I didn't say I invented a new type of foil, I said that I just remembered a T-foil application for shallow water use on a trimaran ama and that I talked over with a friend. Too bad that "ruins" the use of foils for you!!

 

Doug your enthusiasm for foiling is "enthusiasm on steroids " and I have to applaud you on just how thick skinned you are but can you remember the boy at school who totally interjected into every conversation and tried to be part of every conversation. Can you remember how many mates he had. Well that's you at the moment.

Do everybody a favour and restrict yourself to just one really really well thought out post on one thread per day and you would be amazed at just how everyone will contribute new and better ideas to this foiling revolution, at the moment your enthusiasm is restricting people from participating in these discussions which can only hinder foil and small trimaran development.

Now I'm willing to make a bet to myself that on past form, we'll now get even more Doug posts for the next couple of days. Ah well life is predictible I guess.

 

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If you and 2f2D would contribute something other than knocking me, maybe you'd be hailed as a great Saviours. As it is, something like three out of your last four posts have been about me instead of your own sketches or trimaran ideas. Criticize my ideas if you can , but of course you know I'll likely respond. But that should be the way it works. Others have participated in this long thread despite me being around-it's too bad you don't have what it takes to get in a adult conversation with no personal attacks. Oh, well so be it.....
SA is just around the corner.........
edited 7:36pm tonight-to remove the words "horse manure"