Dave wrote: >>Matt, on a typical vacuum bagged layup, where are the "fold prone" areas? I recognize this will depend somewhat on the design, but if you could generalize some, it would help. I have reinforced the deck of my main touring yak (Eddyline Wind Dancer) aft of the rear hatch, and am thinking about adding a layer or two of epoxy/glass to the underside of the deck, forward of the cockpit, as well. Any other locations I should consider?<< It doesn't matter if it is vacuum bagged or hand laid the breaks will occur where the stresses concentrate. Most likely the damage will be on the deck as the deck is usually a lighter weight lay-up than the hull. Beyond that it depends on what causes the folding forces and where the particular kayak is most likely to fold. A big breaker buckling the deck from above will likely put stress cracks in the gelcoat (parallel to the length of the kayak) where the gelcoat is put under tension by the "frog croakering" in of the deck (usually above the seam where the deck transitions from sharper curve to flatter). If you stick one end of a kayak in the sand and pole-vault off the bottom as I have done on several occasions in dumping breakers the compression fracture (if it occurs) will most likely be a vertical crack a few inches long going across the curve of the deck just above the seam and it will occur about one half way between the end of the kayak and the next thing that makes the kayak stiff enough that it can't fold in that area (such as the cockpit or a hatch). The light surf reinforcements are mainly in the deck area curve just above the seams and from the reinforcing around the cockpit to within about 3 feet of the stern or bow. Your particular kayak may also have a problem with the curve of the bilges getting compression fractures as the flat hull slams down onto a small wave after getting airborne going out over a cresting wave. This will depend on the huskiness of the lay-up of your particular boat. If it is a lightweight or cored hull I'd stay out of the surf. A compression fracture usually busts up the gelcoat for a quarter inch around the crack. They are easy to patch on the inside but take a little work to make look like new again on the gelcoat side. Dave again: >>Also, is there a reference you can suggest for adapting vacuum bagging to a reinforcement job like this? I don't think my usual technique (wet out the glass with epoxy and squeegee the excess out) gives a very good job, especially when I want more than one layer of glass. (Usually let the resin get to the almost stiff phase before I lay on the second layer of glass, but sometimes I have tacked a second layer on top of a still-wet squeegee layer -- the glass moves around a lot.)<< Sand where you are going to add material and well beyond. use material that is the same or more flexible than the material in the kayak (so the patch doesn't flake off). (Note: sanding is not necessary with hand layed kayak unless it has a surface coat of a resin that fully cures put over the original lay-up--or the lay-up contained "surface agent"--explained below). I'd lay it up wet and with different sizes for each layer so the result is like a beveled edge (always try to avoid a large discontinuity in thickness over a short area that will create a stress riser). Lastly, I would cover the area with wax paper and smooth it and squeeze out the bubbles that you can. The waxed paper lets the resin cure hard on the inside surface and with a smoother surface (much more like the vacuum-bagging you started with). This not only makes a smoother surface but it is much easier to sand off the rough edges too. This is because being fully cured rather than gummy (air inhibited) on the surface, the sandpaper doesn't quickly gum up. If the wax paper trick is too difficult over that large an area get some "surface agent" (a liquid wax you mix with the resin that floats to the top and seals out the air so the surface can fully cure). Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Mon Apr 17 2000 - 04:52:08 PDT
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