Help needed with fiberglass for a custom hull

[NUBoatguy]

I am a student building a hull that my group designed for a competition we are entering. Approximate dimensions are 16'L x 40"W x 24"D. We had planned to make a plug cover it with a first wall of fiberglass then put in thin balsa ribs filled in with expanding foam then a final level of fiberglass. Like every project we want to keep weight low and cost low.

I am trying to figure out how many layers of glass we need for the first and second layers along with which types cloth and resins will work best. I am leaning towards epoxy for good adhesion to the ribs along with flexible crack resistance.

I talked to a supplier about how much we might need to get the job done but I couldn't tell him how thick we wanted each of the two layers to be. Help and advice on any part of the project is welcome and appreciated.

[messabout]

Boatguy; describe the boat a little more thoroughly. In particular, tell us the intended purpose. Is it to be a row boat, sailboat, powerboat ? If power boat, how much power do you intend to apply, etc, etc. Will it be a pond boat or will it be an open water boat......? All that application stuff plays into the scantling decisions.

[Joe Petrich]

When you said "plug" (something you build a mold around) did you mean "a female mold" (something you build the boat in), or are you building the boat over some forms, a male mold? The female mold would be used for a production run and the male mold would be better for a single "one off" hull.

[NUBoatguy]

The boat will compete in a sprint and endurance race using electric power gathered by solar panels. Her is a link to the event http://www.solarsplash.com/index.php power will max out at about 20hp hopefully. There will be two motors on the sprint configuration and one on the endurance. Our design will look something like this



That is a boat designed by another school that resembles our plan.


I meant it will be a male mold since we are only making one.

I had liked the fiberglass sandwich method because it seemed like an easier method, but I have heard that it is one of the heavier and expensive way to go. Considering the boat will be carrying 100lbs of batteries, 300lbs of solar panels, around 175lbs of pilot, around 125lbs of motors and maybe 60lbs of miscellaneous other items the method we choose will have to be pretty robust.

We are a student group so we don't have much money so a method that doesn't require much special tooling is preferred.

Thanks for the help.

[FAST FRED]

The usual system for a GRP one of is fairly expensive and time consuming.

Look at cold molding with plywood , some complex shapes can easily be done , and strong and light boats result.

There would be no need for the weight of a GRP coating if the boast is not expected to last for years.

Wood is "green" is a good BS point for a competition .

The skill level is not too high and changes can be made fairly easily.

FF

[DrCraze]

How long of a service life do you need from this venture?

[NUBoatguy]

I was thinking 3-4 years, by then the group will get around to a redesign

[DrCraze]

I would think a ply hull would be the way to go, if you don't mind checking you wouldn't need to epoxy seal or glass the hull and you could spend the money saved on other things. You can get some great shapes out of ply by using a double diagonal strip ply method too, and the epoxy necessary is minimal compared to a full fiberglass composite hull.
Since you are doing a solar competition this is the best choice. You don't want to waste weight on anything not mission critical. Sheathing the exterior of the hull in epoxy would would add a considerable amount of weight.

[tunnels]

3/4 of the boat is not nessasary so why have it ? all that extra weight is just along for the ride and slowing the boat down .
It needs to ride on a cushion of air ,the use of an efficent aerodynamic shape will give the strength needed , Stream lining and reduced water friction and put the driver on DIET to reduce weight !

[BertKu]

Originally Posted by NUBoatguy

I was thinking 3-4 years, by then the group will get around to a redesign

Hi, you don't have much time. Only 31 days before your start signal sounds.
Why are the electric motors so heavy. ?? Can't you use Brushless motors?

Also what about LiPO4 batterypack for that short period of time. Short of money?, Yes you need a sponsor for those costs. Have one of you students spending his time, day and night getting sponsorship for such a battery. The rest makes the boat.
Bert

[NUBoatguy]

Most of the hull design comes from the endurance event where most of the boat will be in the water and running as a displacement hull. That pic is of the sprint running allot faster and planing.

Any good books about ply hull building that you recommend?

I wish we were going to be ready for this year, our plan is to compete next year.
The motors are not that heave that includes all the drive train stuff too (chopped out old Evinrude outboards). We have to go lead acid per the rules of the competition. but we are still always on the hunt for sponsors.

[tunnels]

Combinations of ply malamine and glass . Ply sheets are not always the same weight for the same size and same timber ! do some research on air craft building and constuction methods wood frame with material stretched over a ply or wooden frames flys so its got to be light weight . Cedar ply if you can find any I have used Gaboon plwood and that was very light weight !

[dsharp]

Search for "carolina hulls". They are built on plywood jigs with battens that run fore and aft. Plywood strips are glued diagonally.