View Full Version : Fiberglass, Dynel, Xynole or Vectra
07-17-2001, 11:31 AM
I need some help on a non-wooden boat topic. Beside my Bolger Gull dory – which I built myself using stitch and glue technology - I have a 17’9” Sawyer Cruiser canoe. It is the super lightweight version - 38 lbs. – made of foam cored Kevlar and clear gel coat. The canoe is almost 20 years old, and the Kevlar has suffered sun damage and has lost most of its strength. In the past several years I have patched holes in the hull with epoxy and fiberglass.
It now needs some major restoration if it is to survive. After sanding off the gel coat, I plan to apply a layer of laminating fabric with epoxy. My problem is what kind of fabric to use. I am considering glass (?weight), Dynel. Vectra or Xynole. My goal is to increase the strength of the hull while retaining flexibility and reduce the chance of puncture while going over beaver dams. Secondarily, I hope to avoid adding any more weight than necessary. I will work for an eventual smooth finish.
Appreciate any replies.
07-17-2001, 11:49 AM
I would be prone to cover the craft with a good quality epoxy and kevlar. Kevlar is flexible, as are Vectra and Xynole (polypropylene fabrics) of which xynole would be the first choice.
07-17-2001, 11:49 AM
First thing you want to do is go to the "Resources/Product Search" Forum and read the thread on "Abrasion Resistance". Too much good stuff there to put in here.
07-17-2001, 11:53 AM
And, after rereading your post, I'm inclined to believe that what you're proposing will about double the weight of the boat. You may want to consider laying up a completely new canoe using this one as a plug.
07-17-2001, 12:46 PM
While the fabric (and also, or more-so the resin and foam) may be suffering from age and ultra violet, it would seem to me that the gist of the problem may be that foam-cored Kevlar, ultralight constructions aren't designed for hitting or running over anything. They never were. They are essentially marathon racing layups which yield the lightest, stiffest boat possible at the expense of durability and impact resistance.
People hear the "bulletproof Kevlar hype" and assume that it applies to any Kevlar hull, which isn't true. A Sawyer Cruiser in the standard glass layup probably weighs about 55 lbs. If you want similar durability in Kevlar, the hull would generally only be 6-8 lbs. lighter. The foam core, ultralight version can produce the same or even better stiffness, for speed, but can't match the durability of the other constructions.
Adding a skin of something in the 6 oz. fabric range and filling it until it's smooth is going to add 15-20 lbs to the hull if it's done carefully. It may add some abrasion resistance but will have very little effect on flexibility or hull strength and will absolutely kill whatever resale value the canoe has as a Kevlar boat. I think I'd patch it up, get what I could for it and start looking for a boat that's built to do what you need a boat to do.
If you use it as a plug to build a new one, I'm sure you'll want to pay the designer for his time. His name is Lynn Tuttle and last I heard he lives in Batavia Illinois....
07-18-2001, 12:39 AM
I agree that just adding glass to the outside will add a lot of weight. White water racing kayaks used to use only 3 or 4 layers of glass and polypropylene or nylon and they were really fragile. So, if your existing hull really has little strength left you would probably have to add more than one layer. i.e. lots of weight.
If you really plan to save the existing hull, consider adding some foam and glass stringers and frames on the inside. This would not add so much weight. Since strength varies as the span squared, reducing the span by installing stringers and frames will greatly increase the strength of the boat.
There is a drawback to this solution though. Turns out that impact resistance is related to the amount of area deflected by the impact. In other words spreading a given load over a larger area is better. The stringers and frames I suggested tend to reduce deflection and distribute a given impact load over a smaller area. Your boat would be much stronger but may be somewhat more likely to be punctured from impact.
Probably two hat stringers per side and a frame every 3 feet or so would triple the strength of your boat. 1/2" thick foam stringers about an inch wide on top tapering to 2" wide against the hull would be about right. Glass with 2 layers of crowfoot weave 6 oz glass fabric on the bias (i.e. orient fibers plus or minus 45 deg to the stringer). Additionally add 2 or 3 layers of 6 oz unidirectional glass fibers to the top (1" wide) of the stringer. Such a stringer will weigh about .08 pounds per linear foot if you are careful with resin usage.
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