Isn’t an epoxy coating alone hard enough to withstand minor abrasions for a S&G kayak?
Not sure on a yak, but
I used it on my canoe instead of useing kevlar skidplates. A year later the epoxy is still holding up great.
many other ideas, such as Armacoatings, which have been discussed in another thread.
Epoxy + Cloth…
…will certainly do the job.
My S&G kayaks have a strip of 4", 6oz. FG tape along the keel as part of the basic construction; since our shores are rocky, I add another strip of 3" on top of that. My first VK, built in 2001, has yet to show any sign of abrasion along the keel.
If you mix epoxy and sand
until it is thick and apply it, it will last forever.
what do you mean “keel strip”?
A 1/100" of epoxy coating isn't doing much, it's the few hundredths of epoxy coating on X weight glass that provides durability. A 1/100" coating of epoxy on 9oz glass is tougher than on 6oz glass is tougher than 4oz glass is tougher than 2oz glass is tougher than 1/100th on wood.
I'm assuming a regular sized kayak with a regular sized person using 6oz cloth over ply with about three or four fill coats sanded down to two. If you are talking about the strip of the keel between the ends about a foot before the ends turn up then yes, that is tough enough although rolling on two more fill coats in the middle about 2" wide wouldn't be a bad idea. Actually you should do that at all corners as sanding takes down those fill coats much quicker than the flat areas.
Most of the wear won't be along that middle strip though. It'll be at the stern where the two center keel panels come together and at the bow. The wear from sliding impacts is all over the bottom of the hull and not just along the center of the keel.
The wear at the ends from hitting the beach or being dragged a couple dozen feet is easily 10X what happens under the middle of the hull and one layer of 6oz cloth and a bunch of "coats" of epoxy is NOT enough at the very ends.
The problem with s&g construction is that the ends are very fine and a lot of wear gets concentrated into a narrow 3/8"x6" strip. There's a tendency to apply lots of stacked strips of glass to build up a thick area in that little 3/8x6" strip but it ends up requiring a LOT of fairing in. Which should clue one in to the idea of applying a thick material RIGHT AT THAT SPOT and not strips of material that wrap over where it has to be taken back off with fairing.
My suggestion is to apply a material that's 1/8" thick for that 6" strip then tapering down for another 6". That strip could be anywhere from 8"-24" dependin on where it starts/stops. That material could be a range of items but the most convenient is a putty like mix of epoxy with 80%cabosil or high density filler(West Systems) and 20% wood flour(to color). I would suggest shaping the ends BEFORE glassing to make a flat spot at the high wear area to build up the thickness of this mix but it's not critical. This is something you'd apply when the hull is about 90% final sanded with the final sanding removing the mess that occures with the application of the putty.
The way it works is to lay a thick bead down and as it cures use gloved fingers dipped in alcohol to smooth the epoxy putty on. The alcohol dissolves the surface of the epoxy just a little and helps make a very smooth transition. This requires 1/10 the work of fairing hardened epoxy/glass/dynel or whatever.
Other thick materials that can be put on the ends at the keel could be a piece of rope soaked in epoxy, 3/8" half oval brass, dynel cord(JR Sweet). I've used strips of dynel and it's a waste of time for all the effort to fair it in with 3x as much dynel wrapped around the keel and not on the high wear spot.
Some folks like the idea of running a strip of 1 1/2"-3" tape down the entire centerline of the hull and up the ends like you see on some British hulls but it's really not putting material where it's needed. The wear isn't on the sides where the tape is wrapping around. The wear on the bottom of the kayak can be anywhere beyond the very center of the hull bottom as would occur sitting in a kayak in shallow water or bumping to shore.
If you have a light glass layup, 4oz for example, it would be a waste of epoxy and material to run a strip of tape from bow to stern as it really wouldn't protect the area a few inches to either side of the keel. If you have 6oz glass and you want something even tougher than put on a "football" shaped piece of lighter glass like 3.25oz fine weave.
Basically you need a thick material in a very small area at the ends. Putting on a thick material in a small area is more efficient than putting on a lot of material only to have to fair it in on the edges.
go to the bottom of this link of photos to the Arctic Hawk on the right with the bow-on view. That entry on the Hawk is a hand formed bead of thickened epoxy about 1/8" thick from bow to a foot back from the entry where the bottom panel flares out.
All sound good
Thank you guys for good suggestions. Glad I asked.
Agree with LeeG
I added extra cloth and epoxy and wound up going a different route after the bow and stern wore thru to the cloth (everything is contingent on where you launch…wny doesn’t have those smooth pebble or sand launch sites too often)I wnet a different route.
Went to Hobby shop and got several thin sheets of copper. Heated copper cherry red then quenched to make it soft and malleable, and hand formed it to the keel areas taking the hits. cut off excess and laid down a coat of epoxie and the formed copper. Once dry I beveled edges to form a smooth line between keel and copper and applied two more coats of epoxy…That was 2 seasons ago, and I’ve been real impressed with the outcome.
short answer - no
My first S&G (CLC) had just one layer of 6 oz. on the hull - it wore through on the stern after a couple of years, and I am quite careful not to drag or ding it.
The Pygmy I made later called for an additional strip of glass tape all the way along the keel line, and suggests adding another when the first one eventually wears through. I’d highly recommend doing at least that - perhaps two layers at the bow and stern.
Imitators should note that epoxy and
copper may not bond well. Maybe something about your annealing procedure changed that.
Depends on the grade of Epoxy
And the curing mechanism (Catalyst type)
depends on the thickness of said epoxy
and the material the epoxy is providing a bonding matrix.
You could have an epoxy with very high hardness or tensile numbers but at the thin coatings that occur with application by brush it’s irrelevant.
I would bet that if you used a higher tensile epoxy with e-glass and a regular epoxy with s-glass of the same weight the wear would be less with the s-glass.
Pick up a kayak by the bow with the stern sitting on a concrete surface. Drag it back and forth a few feet and it won’t matter how hard the thin coating of epoxy is compared to how thick the material and the nature of the bonded material.
what I’ve used
I’ve gone through the following combos.
Two layers of 9oz 3" tape over 6oz e-glass.
Doesn’t fold well and requires a LOT of fairing.
Five thin strips of 4oz s-glass over 4oz s-glass.
Looks neater and a bit easier to fair over.
Four strips of 6oz e-glass over 6oz eglass. Neater and requires some fairing but less than tape.
Two strips of dynel cloth over two layers 6oz e-glass. A bitch to fair and sticks out like sore thumb unless you paint or highlight it with graphite.
2" wide 9oz unidirectional carbon tape over a few strips of 6oz cloth.
Looks cool, is very hard, the tape doesn’t lay flat without lots of taping over with plastic.
Long loose cord about 3/16" thick made out of loose strands of kevlar.
Looks cool and can be made very smooth but a bitch to fair if any strands stick out after forming.
Long loose cord about 3/16" thick made out of loose strands of s-glass taken from 6oz cloth.
Looks cool and is very easy to fair in.
3/8" half oval brass.
Looks clunky or neat depending on your aesthetics, method of attachment is a bit problematic. I’ve used ring nails and epoxy but think ring nails or screws and 5200 would probably work better.
The putty method using 80/20 cabosil/wood flour.
It’s messy to form but looks very neat when all done.
Dynel cord (looks like a thick loose white shoelace) with 1 1/2" kevlar tape jammed down the middle so it’s about 1/4" thick. Cut and layed on the ends. I had it around. Looks interesting. Is tough.
Experimented with 3/16" polyester cord soaked in thickened epoxy. It’s tough and you could make some interesting accents with all the different kinds of line out there but I wonder if some of the surface treatments on line affect bonding.
That’s about it. As far as most durable for the least effort the half oval is easiest to apply, the thickened putty is the least visible, all the other methods are fun but it pretty much gets down to a thick tough ablative material in a 3/8"x6" strip and not anything else that spreads beyond that point.
A 2" wide strip of dynel, Dyneema or glass, down the entire keel pretty much puts 100X down than what you need on a little strip near the ends.
What I use
I mix up some MAS medium cure epoxy, and load it up with colloidal silica until it’s almost unworkably thick. Then, I paint it onto the prepped and masked surface of my keel, and smooth it.
One application lasts 2-3 years depending on use on my fiberglass kayak. My wooden one, I just sand and re-paint. I’m much less likely to drag that boat up a beach, anyway.
I got some of the epoxy on a piece of the copper I didn’t use (but did anneal) and went out to the garage yesterday to see if it was still there…it was.
I tried a razor blade,and knife and running the piece over concrete and the epoxy, (albeit it wore down with the rubbing on the concrete) stayed put…
Should note the copper looses it’s shine when heated and quenched so maby the surface becomes more porous(?)
All I know for sure is it’s worked over the past season of concrete boat ramps (I use a paddle entry but often comming up to the ramp on takeout or even entering, puts the bow/stern in contact with the ramps)
Do you keep detailed logs of all your builds?
the thing is that I’m inconsistant so there’s some variety to look back on
One person replied to me about using a copper strip buried in epoxy. I thought that was interesting. Keep in mind that I am not dragging my boat over land. The boat is so light that I can carry it out to the deep water. When soft landing, you can’t see where the land is under water is when the abrasion may occur.