: It depends on how strong you need them/want them. At a minimum you'll
: encapsulate the wood parts in two coats of epoxy resin. That doesn't add
: any strength to speak of, but it keeps the plywood from rotting. If you
: want any additional strength you add glass cloth. At a minimum, seal the
: wood with a scant quantity of resin, apply a layer of glass and squeegee
: on one layer of resin. You don't need to fill the weave unless you are
: doing this on the side of the hatch lip that makes contact with the rubber
: seal. Then you want to avoid the waffle pattern of the weave.

: You are using 3mm plywood -- thinnest and weakest stuff around -- for your
: bulkheads. WHY?

: I'd use the 4mm for the bulkheads, too, if I had enough. Or, if stuck with
: 3mm, I'd cover both sides with at least one layer of glass cloth and
: resin. No need to fill the weave. For economy, and a slight weight saving
: (fraction of an ounce) you can cut the cloth so it comes to within an inch
: of the edge of the bulkhead. Then, when you install the bulkhead, with a
: fillet and at least 2 inch wide bias-cut cloth strips or glass tape,
: covered by a second layer of wider tape ( 3 or 4 inches wide) the
: overlapping glass will provide additional strength.

: There is a school of thought that preaches against tightly fitted bulkheads,
: saying they might promote stiff areas of the hull, where stresses can
: concentrate (these areas they call "stress risers") and that
: damage to the hull would occur at these points. If you follow that line of
: reasoning, then forget the fillets and attach the bulkhead with just the
: glass cloth or tape and resin, allowing the bulkhead to be at least 1/8th
: inch away from the sides ( up to maybe 3/8ths) of the boat on all sides.
: This way the bulkhead's joint with the hull can flex, wliminating the
: stress risers. Along the same line, your 3mm ply is going to flex plenty,
: and a single layer of glass will just stiffen it a little bit, while
: adding some strength.

: The bulkheads take stress and abuse from all directions: impacts to the hull,
: weight on the deck, expasion of air in the sealed areas, resistance to
: water pressure from shipped water or totally flooded cockpits, and gear
: sliding back and forth as the boat rocks. (I dearly love cooking in my
: cast iron frying pan, and despite the weight, I take it camping -- but it
: is an effective sldege hammer when it rolls around.) Anyhow, you want
: strong bulkheads. If you put 2, 3 or 4 layers of glass on both sides of
: your bulkheads no one would blame you for your extravagance.

: Hope this helps.

: PGJ
You are foolish to believe that you will need to reinforce the bulk heads to such an extent. The 3mm ply will be just fine and you only need a fillet of glass fiber thickened epoxy on both sides. The strenght in the verticle forces is extreamly high. You don't need to worry about stresses from the hull or sitting on the deck. It will handle it with no worries. The strength in the horizontal forces is limited. This can be an advantage to allow a slight flexing of the hull in case of an impact. And ask youself if your gear will be slamming against the bulkheads. I always pack so tightly that it isn't remotely a possibillity. If it is a sealed area, then you may have problems due to pressure build up. Water pressure in the cockpit should not be a problem, but air pressure most certainly will be...Solution; don't store your Yak with the hatch covers sealed. One last thought on strength: the bulk heads act as a huge I beam, just look at the supperior strength of manufactured wooden I beams in the manufacturing of new homes...Food for thought.