How to reinforce a wood/fibreglass trimaran's bottom?

[joceline]

Hi I'm very new to boat design. I'm studying to build a trimaran out of plywood and fibreglass. The boat will only travel on a river.

The problem is that there's many obstacles in this river (dead wood, rocks, sandbanks, etc...).

So I'm wondering how I can best reinforce the bottom and bow of the hulls?

Can I use a steel plate inside/outside the hulls for strength? How should I attach it to the wood, so that I can still easily put the layers of fibreglass/epoxy onto them?

Thanks for any help.

Joceline.

[PAR]

It's best to approach the problem a little differently then you seem to be. What will the speed of the boat be? How is the boat currently constructed? Why do you think it's unable to tolerate the impacts of debris and other floating or fixed indignities? I mention this because these are fairly common issues, addressed in the design process or considered during repairs or upgrades, suggesting your current experience level, hasn't exposed you to the usual solutions employed.

It might be easier to give us the year, make and model of trimaran you'd like to modify. Where you'll sail this boat (specifically) and a little more detail as to why you think this boat isn't sufficiently equipped to cope with your boating area.

[Landlubber]

...and also why a tri, why not a cat, or flat bottom boat and how big is this boat...and main purpose of use.

[PAR]

I don't think hull configuration is particularly import, though size, speed, weight and intended use are.

[BATAAN]

Originally Posted by PAR

I don't think hull configuration is particularly import, though size, speed, weight and intended use are.

Lighter is better maybe when you hit rocks, but then, heavier is stronger. Intended use designs the boat for you if you look at it properly.
Steel reinforcement in a trimaran is not the usual approach, but extra layers of cloth and epoxy are.
Why a tri? They have very little interior space for the expense (3 hulls etc), tack slowly and are hard to berth. Cats are better, but monohulls are the usual approach to a boat design conundrum.

[PAR]

but then, heavier is stronger

Much experience with Kevlar and other "too light" materials Bataan?

[BATAAN]

No, I do not have that experience, but I worked as the wood lamination repair tech in a yard that used the materials and observed as much as I could. Yes, they are very much stronger when properly engineered and built, long-lasting, non-corroding and really a wonderful boatbuilding tool. I especially like carbon spars for modern lug rigs like ROXANNE.
The only problem I saw with high-tech was owners breaking the boats and complaining because the repair costs were so high. Sensible sailors would make a very light, highly stressed boat last a very long time and go anywhere on the planet they wished, idiots will screw anything up. The last ten years of around-the-world sleds is a great example of working high-tech, but at a cost.
I favor heavy traditional stuff because it's so accessible, cheap and easy to fix. No bias against modern things, they just are fussy and costly for seemingly marginal return sometimes, not always of course.
In major motion picture visual special effects where I have worked for years we have a saying that "90% of perfect is easy and cheap, it's the last 10% that will triple the budget". Same in boats maybe? Movie miniature in pic cost $300k to build plus $200k filming, but in the film you can't tell the difference between her and the 4 times larger LADY WASHINGTON. That's the last 10%, like a kevlar/carbon engineered fast sailing boat over a light wooden boat or f/g of similar design.
Some customers want the best, are willing to pay for it, and will get it from a craft shop that knows its stuff.

[rwatson]

Originally Posted by joceline

Hi I'm very new to boat design. I'm studying to build a trimaran out of plywood and fibreglass. The boat will only travel on a river.

The problem is that there's many obstacles in this river (dead wood, rocks, sandbanks, etc...).

So I'm wondering how I can best reinforce the bottom and bow of the hulls?

Can I use a steel plate inside/outside the hulls for strength? How should I attach it to the wood, so that I can still easily put the layers of fibreglass/epoxy onto them?

Thanks for any help.

Joceline.

Pound for pound, fibreglass is a lot stronger than steel. You are probably best to get a very heavy fibreglass bottom built, the boat will be lighter for the same strength as steel, so will have less impact with obstacles.

large commercial fishing boats, minesweepers and other large commercial boats are built using very thick fibreglass.

Also. combining fibreglass and steel can be problematic due to expansion differences, moisture entrapment etc tec