Date: 12/7/2002, 12:41 pm
: Since fiberglass is strong in tension, is it structurally necessary to glass
: the inside of the hull, since this side of the "sandwich" should
: be in compression when the boat is floating? Apart from waterproofing the
: wood and using a glass layer for abrasion resistance in the cockpit area,
: I'm wondering if taping the seams (we're talking S&G here) isn't enough
: treatment for the remainder of the inside of the hull. I would think the
: deck should probably be glassed both sides, but maybe not. Am I missing
: something? I'm sure the group has already figured this out.
: Still in the planning stages and (truthfully) trying to get up the nerve to
: order plans (probably Cirrus).
I built a Yare kayak and only glassed the outside and epoxy, seal coated and varnished the inside. I went to a lot of effort to get a nice finish on the deck. I have discovered that the epoxy varnish does not maintain, over time, a watertight barrier. I have a wood stain that has shown up in the deck near the front bulkhead and it seems to follow a small void in the luaun plywood. I have concluded that flexing of the deck will crack the epoxy seal coat and let some moisture in. So both sides should have glass, even if you use a lightweight layer on one side, to avoid getting internal moisture in the wood.
Epoxy-glass is much stronger and stiffer than plywood in both tension and compression. When a material is stiffer it develops stress with less deflection. Epoxy-glass is much stiffer than wood so with layered construction the epoxy-glass carries higher stresses, which is good because it is stronger. When a material is bent the highest stresses are at the two surfaces with compression one side and tension on the other. That is why the stiff stronger material needs to be on both sides of sandwich construction for the most effective and strongest use of the material.
The tendency with to lighten a S&G kayak is to beef up the seams and omit glass on the inside which makes a lighter boat with weaker panels. I would consider using less tape and full glass covering on both sides. How many S&G kayaks have actually failed by breaking seams or breaking in half? The failures seem to be more local i.e. punched holes and abrasions through the exterior glass. The best design to avoid punched holes is full sandwich construction, glass on both sides. And the best design against abrasion is extra layers on the outside wear areas. Where there is full weight glass on the inside, I would consider omitting the tape. And on the outside I would consider making the double layer “football” large enough to cover the chines and using 2 inch wide tape only on the keel.
When something punches against the hull, the local deflection is in, putting the inside surface in tension. Also look at a SOF, how the skin deflects in between the stringers. On a S&G, the angle at the seams makes the seam act like a stiff stringer and the panels in between the seams do bend in. You just can't see it like you can on a SOF.
Just my opinion. We place our bets and take our chances.
Dave
Messages In This Thread
- Other: Interior Glass Needed?
Paul J -- 12/6/2002, 12:18 pm- Re: Other: Interior Glass Needed?
Jason -- 12/7/2002, 8:48 pm- Re: Less Tape & More Glass *LINK*
Dave Houser -- 12/7/2002, 12:41 pm- Re: Less Tape & More Glass
LeeG -- 12/7/2002, 5:33 pm
- Re: Other: Interior or sandwhiched Glass Needed?
Andre Janecki -- 12/7/2002, 7:10 am- Re: Other: Interior Glass Needed?
Nick Schade - Guillemot Kayaks -- 12/6/2002, 6:25 pm- glass first?
Randy Knauff -- 12/7/2002, 1:51 am- Re: glass first?
Bruce S -- 12/7/2002, 7:20 pm- Re: Bend, glass then install radiused decks
Dave Houser -- 12/8/2002, 4:18 pm
- Re: glass first?
Mark Kopp -- 12/7/2002, 3:51 pm- Re: glass first?
Paul G. Jacobson -- 12/7/2002, 4:06 pm- glad I asked
Randy Knauff -- 12/7/2002, 5:00 pm- Re: glad I asked
LeeG -- 12/9/2002, 9:58 am- Re: glad I asked
Ken Sutherland -- 12/7/2002, 9:26 pm - Re: glad I asked
- Re: glad I asked
- glad I asked
- Re: glass first?
Nick Schade - Guillemot Kayaks -- 12/7/2002, 2:39 pm - Re: Bend, glass then install radiused decks
- Re: glass first?
- All Things Considered
Paul J -- 12/6/2002, 4:49 pm- Re: All Things Considered
LeeG -- 12/6/2002, 6:13 pm
- Which side is under tension and compression?
Rick Allnutt -- 12/6/2002, 3:27 pm- Re: Other: Interior Glass Needed?
Rob P -- 12/6/2002, 3:06 pm- Re: Other: Interior Glass Needed?
LeeG -- 12/6/2002, 2:16 pm- Re: Other: Interior Glass Needed?
Jay Babina -- 12/6/2002, 1:47 pm- Re: Other: Interior Glass Needed?
Mike Hanks -- 12/6/2002, 1:19 pm - Re: Less Tape & More Glass *LINK*
- Re: Other: Interior Glass Needed?