Skeletons in my foam??

[bilgeboy]

The hardtop plan proceeds...

I bought the polyurethane foam this AM. I will pour about a 7x8 ft mold by 1" deep. I'm trying to build this thing as light as possible, so I'm trying to limit the glass laid up on the outside of the foam.

I had the idea of pouring the foam around a skeleton of some sort. Composite tubes I think would be the ideal material for this, but wonder if anyone had other ideas, wood, metal, don't need to add skeleton, etc.

So...do folks pour foam around a skeleton, or reinforce externally? I’m trying to get away with a single layer of glass (with some big overlap) on the outside of this non-structural flybridge cover.

Thanks,

Mike

[zerogara]

Is this a cover to protect the flybridge while the boat is stationary or one that will be on top of the bridge while you're cruising?
I don't know what you consider structural, but somehow this thing must be attached to something and be able to sustain the forces exerted by wind.
7x8' is 56 sq.feet, that's alot of force that will go from the pannel and concentrated by its mounts.
Also, you're saying you have a mold already. Have you laid any material in it already?
Can you find any pictures and links of something similar to help us out!

[bilgeboy]

Thanks for your interest in my first composite project. I've been reading as much as I can at this site. I read the entire Fiber Glast teaching pages that you posted, thanks again for that. I also downloaded the spsystems manual that someone posted. That is an excellent read as well.

The boat is a 32' Bayliner, twin diesel. I have taught myself basic diesel engine maintenance. Last winter I designed some home-made stainless risers. Many hours later I had decent pair, got the engines running cleanly. The risers work well, and I learned a great deal in the process. Gives me some confidence in tackling the composite world.

The next big project is the flybridge canvas. Absolutely dead. $5,000 to re-canvas, and I don't care for the look, waterproofing, and lifespan of canvas. So I want to build a "hardtop". It would be a permanent addition to the boat and cover an 8x7' area.

My main concern was weight. When I consider the inertial forces when getting pitched around in the waves, I figured it has got to be real light. CF is prohibitively expensive, especially if I screw up my first attempt. I thought I could pour some foam in a mold, vacuum bag a single layer of cloth around that with about a 1 foot overlap down the center (both sides-making a sandwich), and then weld up some aluminum or stainless pipe to support as needed after the top was completed. I'm thinking of pipe/tubing around the perimeter, and then two cross-members, bolting the thing to the frame every couple of feet. The supports to the upper deck will be according to looks and strength as needed. Instead of bolts, I had also considered glass and epoxy around the frame, allowing some exposure for welding.

Trying to keep the weight down, I purchased flotation foam, 2lb density. I figured I could reinforce this with a skeleton inside the pour. But purchasing this foam may have been a mistake, as I think more about it. Well, thats how we learn.

You raise a real good point about the wind. I am working with the idea that there is no such thing as a failed experiment, but I am seeking advice to minimize the risk of an expensive "learning event"!

Your recommendations will be much appreciated (as will anyone elses).

Thanks,

Mike

[basstardo]

You could build an aluminum skeleton for it. If you have the capacity to weld aluminum on the t-top, why not make a lattice out of aluminum and build the mount points for the t-top into the lattice, that way when you pour your foam, the mount points are exposed and you could bolt it up or weld it, whichever you prefer. Not sure how much the aluminum materials would cost though, so it could be cost prohibitive.

[bilgeboy]

You bastard...

I don't know your name, but I like your idea! The looks would be alot better, too. No bolts through the top (ie better weatherproofing), and cross bracing would be invisible. I think I'm gonna do this. Aluminum is pretty cheap, and I can MIG the hidden part of the frame together.

Thanks for your thoughts.

All well intentioned ideas always welcome.

Mike

[basstardo]

Let's see some pics when you get it done. Sounds like it'll turn out really well.

Name's Terry by the way...

Good luck.

[arjan]

If you want to keep this light you should use a decent structural foam like coe-cell divinycell or something like this. That way you don't need as much glass on it to stop it from breaking. pourable foam may work but it has no shearstrength and if you end up walking on your dodger it may well break and collapse. The unsupported roof of my catamaran is probably about 8x12 feet, it is made out of 1" core-cell with 36 oz triax on either side. It is solid as a rock.