Strip hulls and epoxy/fibreglass sheathing

[Bill Baillie]

I've read in the Forum and other places that in order to produce the stiffest hull with strip planking you should sheathe both the inside and out side with fibreglass and epoxy. However, other sources have said that if the wooden core gets wet through a break in the outside sheath then the wood may never dry and rot will set in.
Is it better to sheathe both sides or only the outside? If you sheathe only the outside, do you need to provide additional framing on the inside?
I would welcome any opinions that the Forumites may have.

[On Vacation]

Lots of depends, there. The design, plans if purchased, and materials can change requirements of construction. A few threads have been on here, at great lengths, discussing strip planking. It is really no different that a plywood boat hull, that can vary with factors determined by the individual hull specs. Give us some more details. Water worries should not be the determining factor, to whether you do encapsulate or not.

[Keith Wilson]

Like oyster says, lots of "depends" Small boats where weight and strength-to-weight ratio is critical (canoes, kayaks, that sort of thing) are almost always fiberglassed on both sides. Larger boats aren't. It used to be common to build edge-nailed strip-planked boats with no fiberglass at all and lots of steam-bent frames. What are you thinking of building?

[Norm Bernstein]

From what I've read, strip-epoxy construction is essentially 'core' construction; the coring material (the strips) don't add all that much strength, but the 'sandwich' (i.e., coring material between two epoxy glass layers) is very strong.

I suspect that designs that don't call for an inner glass layer derive their strength from framing, longitudinals, etc.

I'm doing a 15' catboat which will have glass on both sides... 1/4" eastern white cedar strip planking. Check out the website:
The Ellipticat website

[On Vacation]

Originally posted by Norm Bernstein:

WRONG
From what I've read, strip-epoxy construction is essentially 'core' construction; the coring material (the strips) don't add all that much strength, but the 'sandwich' (i.e., coring material between two epoxy glass layers) is very strong.
WRONG
I suspect that designs that don't call for an inner glass layer derive their strength from framing, longitudinals, etc.

I'm doing a 15' catboat which will have glass on both sides... 1/4" eastern white cedar strip planking. Check out the website:
The Ellipticat website

DEPENDS Many designs, scantlings, and methods, different deminsions.
This forum is full of inquires and many never return for a follow up comment. They just drift of into the sunset. Why take time to respond? Comment is not even there for archieves to make it even a decent discusion.

[ 11-26-2003, 12:18 PM: Message edited by: Oyster ]

[JimD]

I have also not heard a convincing argument that sheathing both sides amounts to coring. Many stripped hulls, even quite big ones do not insist on glassing the inside. I vote for the 'Depends' concensus

[TimothyB]

I agree with 'Depends'. Let me toss in my view as well.

There are basically 2 kinds of strip planking. The first we'll call 'Traditional Strip Plank' and the second we'll call 'Core Strip Plank'

The seminal, basic design difference between Trad. and Core type is in the Traditional type the wood is considered structural, in the core type it is not.

Yes, you can have some designs which rely more on the core AS structural components, but that is not the basic design intent. You either design it as core or you don't.

The issue is simple. You can't decide both are primarily structural and have your thesis be valid, design wise. Think about a panel with wood sheathed in FG. The FG will take all of the strain before the wood ever gets any, and FG or certainly carbon fiber etc needs to completely break before the core material will take any strain.

So even if we made the core as strong as necessary to withstand a load, if that load causes the FG matrix to fail it will then be being applied as a shock load on the core, and shock loads have a LOT more instantanous force than static loads. The core could easily fail, even though it was designed to withstand a static load of the same amount!

Thats a case where you would have been better NOT to glass a boat. Or to glass it a hell of a lot more.

This is why it is important to know if the design DEPENDS on FG sheathing for strength or not. If it does NOT depend on it, it is Traditional, and you should not sheath it in anything too stiff, if you sheath it at all.

[ 11-26-2003, 03:10 PM: Message edited by: TimothyB ]