Flat Panel Construction

[Saltifinch]

Could someone please clarify to me how flat panel construction works? A lot of builders mention it, but I'd like to understand better how the process works.

As I understand it, a core material is fiberglassed on both sides, moved into place on the boat, bent to fit as needed, and then once all these pieces are in place, a final fiberglass coat is applied to bind all panels together.

Is my understanding correct?

[NevilleCat]

Usually just fiberglass epoxy taped together
to curve panels a series of cuts or kerfs are made into the panel and bogged up with thickened epoxy as it is bent to form.

https://www.duflex.com.au/services/joining-the-panels/

[Craig Cape Town]

Hi.
Take a gander at kelsall.com . (One of the DIY catamaran build sites.) They describe the method with pics. I looked at this build method before but went with a strip plank plan from Woods cats instead, only because of my skill with woodwork.

[Chotu]

Originally Posted by Saltifinch

Could someone please clarify to me how flat panel construction works? A lot of builders mention it, but I'd like to understand better how the process works.

As I understand it, a core material is fiberglassed on both sides, moved into place on the boat, bent to fit as needed, and then once all these pieces are in place, a final fiberglass coat is applied to bind all panels together.

Is my understanding correct?

You've got it.

The "fiberglass coat" you mention at the end is called taping. You run a layer of 8-12" biax on the seams between the flat panels to join then together.

Depending on the desired hull shape you want to come out with, it's a faster way to get the hull up because it's much easier to make flat panels than curved ones.

[Saltifinch]

So is simply fiberglass taping the seams between panels strong enough? I mean, obviously it is, since its a used method. But I thought the entire point of fiberglassing was to have long fibers providing the real strength.

I suppose its still better than a chopped fiber boat

[Chotu]

Originally Posted by Saltifinch

So is simply fiberglass taping the seams between panels strong enough? I mean, obviously it is, since its a used method. But I thought the entire point of fiberglassing was to have long fibers providing the real strength.

I suppose its still better than a chopped fiber boat

It’s more than strong enough. Significantly better than a chopped fiber boat.

All boats have joints and seams. That’s all these are.

Check out the different types of fiberglass weaves available. Triaxial, biaxial and unidirectional.

Your panels will likely use triaxial to make it easy. You line up the 0 degree or “uni” type fibers of the triaxial along the axis needing the most stiffness. Then in the other directions, the biaxial part of the triaxial creates a criss cross pattern to cover strength In the other directions.

When you “tape” the seam with biaxial fiberglass strips, you are using the same thing that’s holding the panel together to begin with.

Have no doubts whatsoever as to the quality of taping joints on a fiberglass boat. It’s as strong as the panel itself. And a bit stiffer.

That’s how your bulkheads are installed too. Taped in (if it’s a high quality boat). Mass produced boats often tab in bulkheads to save money.

[Tusitala]

you should definitely check out Kelsall.com as posted above. Derek has been evolving this construction method a long time, like the 80's. He doesn't just have flat panels either, he designed several different simple to build molds to use depending on where on the hull or deck ( bulkheads also ) it's to be used. FWIW Derek was the first person to use foam core (Airex) for hull construction in Multihulls. As you can imagine it's a huge advantage to have large fair panels to join together, you end up with a very nice smooth hull quickly. the only system I've seen that competes is Constant Camber, by Jim Brown/Dick Newick/John Marples. Of course then you're building in wood, not foam.

[Saltifinch]

So would the panel have each layer of fiberglass tapered back successively? For example, the first layer is 3 mm away from the edge, the second layer is 6mm. I'm assuming you would need to do this in order for the taping to remain flush with the rest of the panel.