: If I want lightness wouldn't just taping the outer hull seams rather than
: glassing the whole hull make sense? Would enough primer to hide the tape
: edges negate any weight savings? I am assuming a painted hull.

: Vic

The more glass and epoxy you leave off the lighter the finished kayak will be. In addition the thinner you make the plywood or strips the lighter it will be. Unfortunately it will also be weaker flexurally, less puncture resistant and less abrasion resistant.

The primary strength of a sandwich structure is developed in the two surface layers of epoxy glass. The thicker the glass and the further apart the two glass layers are the stronger the system. Unfortunately the glass/epoxy is the heaviest part of the system. The core is needed to make the two glass layers and the core act as one structure. The primary function of the core is to resist shear forces between the glass layers. The glass layers act as tension and compression members. I can't go into a strength of materials engineering course here but you can look at
http://oneoceankayaks.com/Sandcore.htm
for a more in depth discussion.

So to develop strength in a sandwich system and lighten the system the efforts seem to be using stronger and stiffer materials to replace the glass (kevlar, carbon), using tighter weave glass, using multiple layers of lighter glass and using multiple layers of glass with different orientations. Using a thicker core with lighter glass would maintain flexural strength but sacrifice puncture resistance.

The bottom line really becomes what is your planned use of the kayak and what risks are you willing to take and share with your paddling buddies.

If I were really serious about paddling efficiency, I would stick with a tried and proven design, use good construction techniques, revarnish the bottom to keep it smooth to avoid drag, pack light on stowed gear and most of all lose 10 pounds off my gut. The water doesn't care if the weight is the boat, the paddler or the cargo. Displacement is displacement. And really, what is 10 pounds when the boat, paddler and cargo together weigh 300 pounds? I don't like swimming long distances in cold water I'll keep the structure. If I were racing I'd feel differently.