A Photo & Discussion Forum for Wharram Design Enthusiasts
Thanks to all who commented. I've decided on a couple layers of Kevlar cloth tape topped off with a layer of glass. A couple layers of Kevlar; 1 layer 2" wide plus a layer 6", so to protect against the abrasion up the sides of the keel when the boat dries out and settles into the gritty mud daily, or I beach in the gravel. That will cost about $60 US for the Kevlar and less than $10 for the glass, plus epoxy. I might add an epoxy glued (no screws) sacrificial strip of wood to the keel before the Kevlar. Still pondering that.
Since the anti-fouling paint erodes off the bottem 3" off the keel, because of the daily drying, I'm going to try a couple layers of epoxy mixed with copper powder just on the bottom 3 o 4". Even as that abrades away it should stay anti-fouled. Hopefully it'll last longer than the bottom paint that only lasts a couple months at the keel.
I'm many months away from re-launch but after a year or so in the water I'll post on how well it works or doesn't.
Sorry I don't have much advice yet, I have finished the keel repair but have not re-launched. I have been also widening with new cross beams and cockpit. What I can tell you is that I did use 2 layers of kevlar and overlapped a layer of 6 oz glass. Working upside down is a pain so I coated with epoxy first and let it get sticky enough to lay in the kevlar without it falling off, this usually took a couple hours to get tacky enough to hold it up. Then I let it firm up a little before wetting out, if too early the added weight of the wetting out wanted to pull it away. That method worked good except I had to work around the support blocks holding the boat up high enough to work comfortably. This meant splices in the kevlar which is next to impossible to grind or sand without a fuzzy mess. Cutting the kevlar is tough enough, I found that laying the tape on a steel block and cutting it with a wide cold chisel and a heavy sledge hammer blow. That left a nice sharp edge that I was able to carefully splice after moving the supports. My first layer of kevlar was 2" the second was 4" and the glass layer was 6" which left a nice gradual edge that was easy to fair out. I then coated with two coats of epoxy mixed with copper powder to give a sacrificial anti-foul because of my daily tide dry out at moorage.
I chose kevlar over any extra wood or metal strips because of my paranoia with mechanical fastenings. Every option I could think of would still be sacrificial and I felt the kevlar is so tough and I could easily repair glass epoxy damage on a low tide without a haul out. I also plan to be more vigilant about avoiding rocks and reefs, unlike my last encounter which was "I'm sure we're far enough away from that reef" without checking the chart more carefully. I now have gps chart plotter onboard which probably would have helped avoided that contact.
I had many careful beachings with just the original glass taped keel with no damage at all so I'm confident with this kevlar and glass combination as far as beaching. I'm committed to re-launch spring of 2011 if my health and money holds up. I don't plan on any hard contact except for normal beaching which I'm already confident in, so probably not much more to report in the future unless I have another bout of stupidity.
For my Tiki 21' Polinesio I use the bretrand's method, glueing an extra laminated keel and glassed it. Then screw and glued on a brass strip 1/8 x 3/4. So the keel skin is not affected by screws. This system perform very well since 2000, every time on the water and very many, many beaching. And sometimes grounding.
For paint the botton we beach the boat (very charged - we living aboard) and lift the hulls from the tide line using wood handspike... Nine years with no problems.
Bravo! it function pretty well.
I'm skeptical that you would get a good bond between stainless steel and epoxy. At very least, I would think you'd want to rough up the bonding surface of the metal for some "tooth". You could experiment with a small piece (seems to be the usual advice from the epoxy makers) and see how it bonds. If it doesn't, you've got your answer. If it does bond under controlled conditions, you still have a leap of faith to get to actual working conditions at sea.
I didn't get around to adding the UHMW poly to my keels before our recent trip, but the biaxial tape held up well. It's only test came in one location where we had to tie up in some shallows, and she grounded on some scattered oysters/mud at low tide. It just left a few scratches in the bottom paint. I'll report back to this topic after I've added the UHMW poly this summer.