Unusual material - structural fiberglass

[erikgreen]

Just wondering - I recently saw a new hull construction project on another site use structural fiberglass I beams and U channels to create a fly bridge deck, and the stuff looked pretty interesting. They basically supported the deck with it, and some of the U channels were used as chase tubes.

For those not familiar with it, it's basically heavily made fiberglass in standard structural steel type shapes. Check out the website for one manufacturer here: http://www.strongwell.com/products/pultruded_prod/struc_shapes/index.shtml

It has some similarities to boat fiberglass, in that it's made with isopthalic poly resin, linear roving at the core, surrounded by continuous strand mat and surfacing veil. Different types are fire resistant or use VE resin for different properties. The parts are supposed to be 30% lighter than aluminum.

I'm thinking something like the square or rectangular tubes or i-beams might make a good stringer substitute, or just a great way to stiffen a thin deck.

Can you imagine using an I beam shape for a stringer? Coat the bottom with peanut butter to bed it, then a small fillet at the edge and you can glass it in place using horizontal cloth strips instead of a 90 degree transition. The top of the beam makes a very wide deck support surface you can drill and screw into with no problems.

You'd have to pick a size and shape that would more or less match the hull for flex (not too stiff), and bed it and tab it properly, but you wouldn't have to cover the stringers to protect them, or even use a lot of glass for tabs. The large bottom face would provide 10-15x more gluing surface than plywood on edge does.

Has anyone run into these anywhere? Think they'd work in marine use?

Erik

 

[proshadetree]

Re: Unusual material - structural fiberglass

I dont know how you would bend the I-beam to fit a hull but it looks like it would be great if you could.

 

[westexasrepublic]

Re: Unusual material - structural fiberglass

im a steel detailer by trade and can tell you these shapes are strong, problem would be flexing to fit the curve of a boat hull.....I know on steel structures it takes litteraly a ton of power to add camber to a beam wide flange I beam or otherwise....

according to the tolerances that I read, these structures are designed to hold a load without sagging

A U_shape would seem more ideal, but there is only one way to find out Id love to know.

but I can still see areas they can bee used and how you could make it work, Erik you had good point going about tabbing in an I-beam structure if you did use it.

 

[Bondo]

Re: Unusual material - structural fiberglass

I'm thinking something like the square or rectangular tubes or i-beams might make a good stringer substitute, or just a great way to stiffen a thin deck.

Ayuh,... I've been collecting junk Railroad crossing barriers for Years,...
They're a fiberglass box beam...
They start out as 2, 1/2"x 6, then joint down to a 2x4 at the small end...
Haven't built anything out of 'em yet though,...
An early thought was stringers, but the scope of a hull just ain't Straight....

 

[erikgreen]

Re: Unusual material - structural fiberglass

True on the straightness thing. I'm thinking they might work as a single piece for the straight part, then they could either be kerf cut and curved for a shallow hull bottom (weaker), or paired with a more standard foam/glass stringer section in the front of the boat (complicated).

You could get the "tall" version of the I-beam and trim the bottom when needed to match the hull, again assuming a shallow hull curve.

Actually, if you used multiple straight sections of these you could approximate your hull curve and make up the difference with extra bedding or tabs. For the most part the stringers in my 22 footer are straight or nearly so, with just a slope at the front.

If you use an I-beam for this that's less than the height of your deck, you'll be mounting spacers on top of it to make up the difference anyway, or else using separate deck supports. So the usual stringer shape with a straight top and curved bottom edge doesn't apply.

Kinda like this:

(excuse the crude art.. top half of pic is stringer version, bottom is beam.

You'd lay the stuff out on your hull bottom which is a more or less straight slope for most hulls right up to the bow, and glass it in place. Use a couple butt blocks to join the beam sections (blue), or just heavy glass and epoxy putty. Then you'd install your deck supports(red) to get a level deck.

The stuff isn't super cheap, for a 3 inch tall I-beam it's about $5 a foot, but I suspect that small beam would be enough strength for most stringer needs, it'd never rot, and it would save underdecks space. Easy chase tube layout.

They also offer 4x8 panels of the stuff, solid glass. You could cut standard stringers out of it, but that'd be overkill and miss a lot of the advantages of just laying in a fiberglass stringer.

When I get a chance I'm going to pick up some of this stuff to try out. If there's a way to make it work as a replacement for the standard ply/glass stringers, I think it'd be worth the price, especially since you'd get the money back if you sold the boat ("no rot stringers" is almost as good as "carbon fiber composite" for adding $$ to your sale price).

Erik

 

[Greg Mrozinski]

Re: Unusual material - structural fiberglass

Erik,

All good thoughts and ideas. One thing to note, many bows are compound in shape meaning that they not only rise up as you go from the stern forward but they curve inward...not so much in the stern areas but much more right at the bow.

 

[erikgreen]

Re: Unusual material - structural fiberglass

Yeah, I figured that.. but couldn't you just turn the shorter sections at the front inward as well as upward to match, then build the joint up with glass?

You'd have to miter the end of the stringer in two planes to get a reasonably close joint, but it could be done...

Most stringers don't run all the way up to the bow anyway, so you could also substitute other structure there and skip the most forward stringer bits...

 

[Greg Mrozinski]

Re: Unusual material - structural fiberglass

Sure thing no reason you couldn't. And yeah I thought about the "most stringers not going all the wy to the bow" right after I hit the submit reply button. :redface: