12 foot trimaran, can someone tell me if this center hull looks about right?

[jtrosclair]

I am designing a 12 foot trimaran to be carried in my truck. For that reason, it can't really be longer than 12 feet. I have already built 10 foot amas from the Drifter 12L plans from Mark Gumbercht.

My design goal is something that is fast with one person, but can be sailed with two people. This would be a crew weight of about 330 pounds. I am basically trying to build a Bazooka 12 trimaran. There is little info on these trimarans because they only made 26 of them, and stopped making them some years ago. I have created my own center hull design in freeship and would like some criticism before I finalize and build.

The boat will be sailed in lake Ponchartrain which can be pretty choppy. I'd like to deck the first 4 feet of hull and then put a self draining cockpit for the remaining 8 feet. The foot of the sail is about 8 feet long, so I anticipate mounting the mast 2 feet from the bow.

The rig will be a 65 square foot unstayed cat rig from a Sea Eagle inflatable catamaran. It is a boomed square head rig which furls on the mast like a Hobie Bravo or Adventure island.

1.) How important is it that the transom never be in the water? To achieve this my design would end up with a portion of the stern not in the water when just sailing with one person. This shortens the already short waterline. Do you think there is too much rocker in the rear? What about the front?

2.) Do you think it's too wide? Would I be better off with a narrower hull with more draft? At the designed waterline in the linesplan, it's displacing about 450 pounds. I assume the complete boat will come in around 120-140 pounds. This leaves about 320 pounds for the crew.


Any help is appreciated. Let me know if I should post some other files from freeship.

 

[oldmulti]

Jtrosclair. If your weight estimates are OK then the shape is OK. You need to understand where the centre of buoyancy is and where your weight will be placed on the tri, as this dictates if the stern will drag occurs. In most designs the centre of buoyancy is 52 to 55 % aft from the bow. The thinner the hull the better BUT if it cannot carry the weight you want it will gain to much wetted surface slowing you down in light weather. The Drifter main hull works well and I suspect your main hull will work well. The greatest test is building and sailing it. Good luck.

 

[jtrosclair]

Jtrosclair. If your weight estimates are OK then the shape is OK. You need to understand where the centre of buoyancy is and where your weight will be placed on the tri, as this dictates if the stern will drag occurs. In most designs the centre of buoyancy is 52 to 55 % aft from the bow. The thinner the hull the better BUT if it cannot carry the weight you want it will gain to much wetted surface slowing you down in light weather. The Drifter main hull works well and I suspect your main hull will work well. The greatest test is building and sailing it. Good luck.

I actually cut the frames for the main drifter hull, but it is really more of a boat for protected waters. I also did not want a boat where I sat in the hull like a kayak. I've tried to add as much volume aft as possible because I anticipate the center of the crew weight should skew aft. But the design did end up with a waterline beam of 1.887 feet. That puts the length to beam ratio at 1: 6.35; this seems high. Should I be aiming for a wide flat aft section for planing? Or a thinner canoe section for low drag? I'm not sure if the rig would really have the horsepower to plane it with two people in most scenarios.

 

[upchurchmr]

The shape looks good assuming you have done your bouyancy and CG correctly.
A small multihull is extremely sensitive to where the sailor weight is located.
Not unusual to have to move 2 feet for the difference between tacking and reaching.
If you can't move your cg due to the restricted length, you will have to accept that some times you will not have the "propper" trim, meaning the lowest drag.

I hope you make a thread to let us follow your design and build.

 

[guzzis3]

If you want to design your own great but if you are just wanting to get a boat on the water you might like to look at Ray Kendricks Scarab 3.5

Plans for Scarab 350 trimaran http://www.teamscarab.com.au/Scarab350Des.html

There is also a round version built in foam sandwich.

Plans for Scarab 12 trimaran trimaran http://www.teamscarab.com.au/Scarab%2012Des.html

Just offering options. Whatever you do have fun and I hope it turns out well

 

[redreuben]

And at A$150.00 how can you go wrong ?

 

[upchurchmr]

Hughes has a similar design.
Marples has a similar design.
There are a couple others I think.

OP have you seen them?

A round bilged version in strip plank / ply should be easy and quick. And cheap (my favorite).

 

[jtrosclair]

If you want to design your own great but if you are just wanting to get a boat on the water you might like to look at Ray Kendricks Scarab 3.5

Plans for Scarab 350 trimaran http://www.teamscarab.com.au/Scarab350Des.html

There is also a round version built in foam sandwich.

Plans for Scarab 12 trimaran trimaran http://www.teamscarab.com.au/Scarab%2012Des.html

Just offering options. Whatever you do have fun and I hope it turns out well

I had actually purchased his plans for the Scarab 10. But it doesn't fulfill my design needs. I need this boat to be able to be broken down into the major components (hulls, crossbeams) for storage. The Scarab designs are all folding. Also, overall the Scarab designs are a little more complicated. They have a lot of chines and pieces. This is my first boat and I wanted to build it relatively quickly and cheaply. If I build something like a Scarab, I'll want to invest in real marine plywood, etc. That rapidly increases the price. Long term, I am intrigued by the Scarab 16.

 

[jtrosclair]

Hughes has a similar design.
Marples has a similar design.
There are a couple others I think.

OP have you seen them?

A round bilged version in strip plank / ply should be easy and quick. And cheap (my favorite).

I've looked at them all, but none are quite what I'm looking for. The seaclipper 13 is close, but the flared out cockpit at the top of the hull would interfere with my intended storage solution.

 

[guzzis3]

The 3.5 is demountable not folding. Even if it were it would be trivial to change the beams to fixed 1 piece.

Have you seen the free trimaran plans here:

Plans & Kits - Free Plans - Duckworks Boat Builders Supply https://duckworks.com/free-plans/

Might be worth downloading and having a look.

As I said it's all up to you, whatever you decide is good. Just pointing to things that might help.