Opinion/help on design I have 3d model pics

Hi. I would appreciate any constructive criticism on my "boat" design. Its supposed to be a tritoon stand up paddleboard type thing. I'm mostly concerned with structural integrity.
Will it hold and can i maintain a watertight seal between the pontoons and deck.
Secondly weight. I want to be able to lift with the help of another person and transport on the roof of my 4runner.
Other points of consideration the center pontoon peice is optional maybe? Anyway the foam will be sanded and coated with epoxy to watertight and strengthen a bit. All wood will be coated in epoxy as Well. What do you guys think. Im a poor boy which is why i decided to make my own but also i have no technical design experience. I dont want to waste a bunch of money and time on something that will fall apart. I want to use this at the beach. Thanks

 

Also any drawback to the asymmetrical shape of the side pontoons vs symmetrical?

 

1) It would be a heck of a lot easier / cheaper / less stressful to just go out and buy a stand up paddleboard, even a brand new one.
2) Any standard type of stand up paddleboard will be MUCH easier to paddle than your trimaran shape.
3) You will have a lot of hull form and skin friction resistance with those hulls, in comparison to a generic type of paddleboard.
4) You could make the bows more pointed, but this is not going to help very much.
5) It would probably be more effective if it is regarded as a rowing boat rather than as a stand up paddler?
6) Asymmetric hulls apparently only offer an advantage (re resistance) when planing or when proceeding at fairly high Froude numbers (re long and skinny displacement vessels) - but you will never get anywhere near these speeds while paddling (or rowing).
7) If you want extra load carrying capacity for 2 crew to eg go fishing (I like the coolers - essential outfit items!) then maybe acquire 2 second hand paddleboards and convert them into a catamaran?

 

A few observations, there seems little point in the complication of three hull elements, cheap foam is not a suitable structure, coated with epoxy won't change that much, you would need some re-inforcement with the epoxy. This could start becoming a bit heavy, and expensive, with all the structure you have drawn. Maybe better to just make a mono paddleboard with a glass skin.

 

Pat, the design that you have drawn will have excessive wetted surface that will cause extra effort to propel it. For a human powered boat, think in terms of the surface friction, caused by the amount of wetted surface, of the hull and what you can contrive to minimize that affect. I suspect that if you are unalterably committed to a multihull configuration, then eliminate the middle pontoon and go for a catamaran plan form. The stability will be better among other things. Make the cat pontoons symmetrical at the front and raise the bottom in an upward curve at the back end so that you have an amount of rocker that will help clear the transom at the aft end.

keep us informed of your progress................

 

I have just been doing some very rough / approximate calculations - and if you just had a catamaran form (ie do away with the centre hull) then you are probably looking at approx. 100 lbs / inch immersion for the two hulls (and this will be fairly constant, as the hulls have no flare).
If say you and your friend weigh 150 lbs each, and the boat optimistically weighs 150 lbs, and you have another 50 lbs in the coolers, then you have a displacement of 500 lbs already, and a draft of perhaps 5".
Even with a hull depth of 10", you will only have about 5" of freeboard - and it could get 'interesting' if both of you venture away from the centerline re your stability.
And your transverse beams connecting the hulls might only be an inch above the water surface - in any slight chop (that is more than a ripple) then the wavelets will be hitting these beams, creating even more resistance.

 

Thanks for the insights. I was looking at paddleboards initially. Even though ive actually never used a single or multi person paddleboard in my head i wanted something a little more robust,roomy and stable. Who knows maybe they would be fine. I realise my design would be a slow and barge like which im fine with. I wasnt really planning on going fast or anything just getting past the breakers and chill and fish. I was mostly wanting to have a nice stable and roomy fishing platform for more than 1 person that could also be a bit ocean worthy as far as small waves and wake and stuff just in case I wanted to cruise around a bit. Plus look cool hehe. But I suppose you guys are right about the weight and hulls too big and heavy and weak. I was inspired by this cool paddleboard called the L4expedition. But its basically 3k and thats a lil too rich for my blood for a glorified paddleboard. Well thanks for the insights guess I'll have to figure something else out.

 

Oh I figured the middle one would of made it more stable. But thats why I asked cause I have no idea hehe. I figured it was unnecessary but i thought it would help give me more floatation and keep me a bit safer from nose diving on a wave...and I though it looked cool lol.

 

Sooo if you guys check out the L4expedition sup that had inspired me. If I scaled down a bit and made it more like that but with my same materials and similar build process. Think that would work? Or is it just too much of an uphill battle (heavy and weak) with these materials.

 

"Breakers" ? They literally will break anything that isn't robust. I'm inclined to think a couple of canoes connected by cross beams might be the go. Seal them up and put a sheet a ply on as your deck. That might get back to the beach OK without going off course too much.

 

Well Idk if breakers was the right word. I just meant the small breaking waves coming in close to the shore. Thanks for the ideas.

 

I am thinking that there must be a lot of second hand SUP's for sale on E-bay by disgruntled owners who buy them on impulse and then quickly tire of them - your best bet might be to try to find a couple of cheap ones, and convert them into a basic catamaran?

 

One inch foam is plenty bendy for what you have, so you don't need to sand anything except possibly the bow contour. You need to coat and paint the foam, and a thin veil of glass will add a lot of surface protection. Four ounce deck weave would be plenty to allow you to handle the boat without denting the foam. You should shoot for about 4 inches of draft with a single crew, and adjust the width of the pontoons accordingly. That suggests about 7-8" draft with 2 and gear, so 14" hull depth would be about the minimum practical. As others have mentioned, your hull has a lot of surface area. It isn't the most efficient to propel, so plan on a beefy trolling motor at least. Or a little gas kicker.

You appear to show double bulkheads. They aren't necessary, nor are the wood headers. Just scab the beams to the face of a single bulkhead, glue them, and tab with two layers of 4 once glass extending abut 6 inches down the bulkhead. glue the bulkheads to the hull, fillet the joint, and tab the bulkheads to the hull with 3 inch 9 ounce tape. An old lightbulb makes a good filleting tool for this.

With the small size of the panels the deck has to span, you can easily get away with 6 mm fir or meranti ply. The fir is cheaper, rougher, and will soak up way more epoxy, so I think the meranti will probably work out better in the end. Consider polyester Dynel fabric as it is nonskid if not totally filled epoxy. Or just seal completely with epoxy and apply boat carpet.

Make sure your center of buoyancy and center of gravity match. You want this puppy floating as level as possible, not down by the stern. This doesn't look to be the case at present.

 

That is some serious "pink (blue?) plywood thinking" (an engineering term for using the wrong design technique for a composite structure).

What you'd drawn is a badly designed jonboat filled with foam. Congrats.

 

Haha well if i had some machinery (like a band saw or welder and metal bender) and budget to use better materials I would like to think i could come up with something better. But I'm trying to build something light with crappy materials i can actually work with. I only have box cutters and a t-square.