How much weight would an extra layer of Kevlar add to the bottom of a 18’ vacuum bagged canoe?
Ask the manufacturer. The extra layer
should go on the inside.
Sometimes it makes more sense to add an extra layer of S-glass to the outside of the hull.
What type of Kevlar material? What weight? How wide is the canoe? How far up the sides will it go? Etc.
OK, as a rough estimate lets assume a continuous layer of 5 ounce/square yard plain weave Kevlar fabric, which is a common material and weight used in canoe construction.
Estimate the number of square yards that the partial will require. Multiply the result by 5 ounces.
Assume a roughly 50/50 cloth/resin mix which is fairly typical for hand layup and vacuum bagging.
So take your estimated fabric weight and double it.
Lets assume the maximum width of the bottom partial is 36" (1 yard) and the partial extends the full length of the 6 yard canoe. Obviously the bottom of the canoe does not have the shape of a rectangle. If we guess that the area of the canoe bottom at each end is roughly 1/2 of a 1 x 3 yard rectangle (probably an underestimate since most canoes don't have the shape of 2 triangles joined at the base) you would require a total of 3 square yards of cloth which would weigh 15 ounces. So the total weight would be somewhere around 2 lbs. But if the canoe has very full ends or the partial extends up the chines much it will probably be greater. I think a reasonable guesstimate is around 3 lbs.
But I’d say not much
2x on the glass
When I was refinishing my Crozier Kevlar boat, I was overjoyed to find out that he laid it up with a thin layer of glass for the exterior layer. This allowed me to sand without fear of fuzzing.
My canoe club ordered ‘outfitter’ UL boats from wenonah which have 1 or 2 extra layers of kevlar. Just based on feel, if a true UL layup was ~45lbs, our boats were probably 50.
Call the builder. they can probably tell you quite accurately, but in general, probably 2-4 lbs I’d guess.
Extra Layer in Wenonohas
In the 2015 Catalog , Wenonah lists a "Livery Layup in Ultra Light Canoes" for $200. As per Wenonahs customer service rep , this is the Internal skid pads, with an extra layer of Tuff Weave sandwiched in between the bottom 2 layers of kevlar. I estimate the bottom area Of a MNII (34" width at 4 " wl X 18.5')at roughly 2.85 yds . Multiply that by 6 oz aprox equals 17 oz , x 2 for resin equals aprox 34 oz, does that sound right?
Although tuff weave is a glass/polyester co weave and not Kevlar it is a good material.
It would make more sense to be me if Wenonah put the Extra Layer of Tuf Weave on the outside being its more abrasion and compression resistant than Kevlar. If they are going to put an extra layer in the middle, why not make it Kevlar and save some weight.
Putting Tuf Weave between helps with
some Kevlar delamination issues. Also, Wenonah may want to preserve that Kevlar “look” by keeping one layer outside.
Wenonah’s use of Kevlar for outside layers is a bit puzzling to me, but I’ll admit that their results are satisfactory.