S-Glass skid plates (?)

[Fleetwalker]

I put a nice dent in the stem of my Royalex Old Town Penobscot when I hit a rock a couple of weekends ago. Luckily, there does not appear to any hole.

I've been using heat to push the dent out, and I'm planning on fairing out the dent with G/flex. However, I think the area probably ought to have some added reinforcement on it. I do downriver racing with the boat, so I'm reluctant to put a full kevlar skidplate on it. I was thinking of making an S-glass quivalent using 6 oz fabric. I'm wondering how many layers are typically used (maybe the answer is just 1). If there are multiple layers, are they usually different sizes? If they are different sizes, do the smaller layers get put on top of the larger ones? Be gentle, I've never glassed anything before.

[pblanc]

I have put about 16 skid plates on 7 Royalex and 1 polyethylene canoe. I have used Dynel cloth and been very pleased with the results thus far. Dynel cloth soaks up a good bit more epoxy than does E or S 'glass, so I just use one layer. On Royalex boats that have worn into the core, however, I will fill and fair with G-flex epoxy and cover the repaired area with a layer of E 'glass (6oz/yd) before applying the Dynel. I have generally used G-flex to bond and fill the Dynel as well, although sometimes I wet the cloth out with G-flex then fill the weave with one or two additional applications of WEST 105/206 epoxy since it is cheaper and less viscous. It is fine to mix G-flex and WEST 105 resin in any ratio you like. I mix graphite powder in with the epoxy on the Dynel which makes it opaque for UV protection and is said to make it a bit more slippery for abrasion resistance. Since the graphite powder is mixed through the epoxy, scratches will also be black and less noticeable, unlike if you paint the skid plate with Krylon Fusion spray paint. The result is a nice, glossy black color. If you want a flat black color instead, just wet sand it with some fine sandpaper.

On a Royalex boat you could use West 105/205 or 105/206 if you wanted. It is cheaper and less viscous. I don't really find wetting out cloth with G-flex to be more difficult but it is more time-consuming because of its greater viscosity. I like the G-flex for filling and fairing dents and voids, however. I usually thicken it with colloidal silica powder for this purpose. It usually takes multiple applications followed by sanding away the excess to really get the void nicely faired. As you fill in the dent you might need to mix up only small batches of epoxy. With the G-flex you can mix very small batches by eye in a 1:1 ratio by volume. You can be off by up to 20% on the mix volume. With WEST 105/205 the mix ratio is more critical and usually requires metering pumps and there is often wastage if only a small amount is required.

It takes more cloth but your repair will be more durable it you cut out your cloth on the bias so that the fibers are aligned at a 45 degree angle to the stem of the boat rather then aligned with the stem and crossing it at right angles. If you use multiple layers of cloth, cut them at different angles so that the fibers are not all crossing the same way.

If you want to use S 'glass I would probably plan on using about 3 layers. The S 'glass repair probably would be a bit stronger than the Dynel if you want to provide additional strength to the stem. The classic advice ala Charlie Walbridge is to apply the largest patch first and make the following patches concentric in shape and progressively smaller. I have done a fair number of multilayer patch repairs using fiberglass and in some the layers were progressively smaller, in some progressively larger and in others the second layer was smaller than the first but the third layer larger than the others. I have seen absolutely no difference in durability. If you like to use peel-ply and wet out all three layers of cloth at the same time, however, then having them become successively smaller will allow you to feather the edges after the epoxy cures. In that case, you would put the smallest patch on your peel-ply, wet it out, put the next larger patch over it, wet it out, then put on the biggest patch, wet it out, then turn the whole thing over and apply it to your boat. I apply one layer at a time and feather the edge before applying the next layer, however.

[KNeal]

I like what pblanc posted and have done pretty much the same thing he is recommending, but only using s-glass. Basically, kevlar is not a preferred material for bow/stern skid plates.

[ezwater]

I use S-glass, and at least three concentric layers would be needed. Largest goes on first, and the largest should be bias cut. For skid plates, West 105 and any suitable West hardener are fine. G-flex is ok, though for a skid plate the 105 is a better match to the impact demands.

[philcanoe]

As you often suggest this course, would you care to elaborate on your reasoning?

....G-flex is ok, though for a skid plate the 105 is a better match to the impact demands.

I know you have good reasoning and past experience experience experience, however wondering why considering the following from West Bro's:
(abrasion? - cost? - weight?)

Taken from: http://www.westsystem.com/ss/west-syste ... lex-epoxy/" onclick="window.open(this.href);return false;

BENEFITS OF G/FLEX EPOXY
Toughness and flexibility
G/flex has been toughened. This gives G/flex the ability to make structural bonds that can absorb the stresses of expansion, contraction, shock, and vibration. G/flex is resilient and impact resistant. With a modulus of elasticity of 150,000 psi (WEST SYSTEM 105 Resin/205 Hardener has a modulus of elasticity of 450,000 psi), G/flex is more flexible and can deflect further before breaking than WEST SYSTEM 105/205, while being much stiffer than typical adhesive sealants

and

http://www.westsystem.com/ss/repairing- ... lex-epoxy/" onclick="window.open(this.href);return false;

and these

http://westsystem.com/ss/search-results ... a=%C2%A0Go" onclick="window.open(this.href);return false;

[Mike W.]

If you're racing the boat, you might as well make it faster while you're fixing it. Slowly heat the bow & clamp it for a narrower entry at & below the water line. Put some s-glass inside to help hold it. Then mix some West System 105 w/ silica powder. Apply this to the outside of the bow & extend the bow at & below the waterline. You can get a slightly longer water line length & a much sharper entry line. Get the shape as close as you can before it goes off, as this stuff gets very hard & sand paper won't do much to it, you'll need a grinder to shape it.

Threadjack:
Who's going to OC Downriver Nats this year? June 19-22 on the Nanty. I hear they're actually going to let folks race 'race' boats.

[Fleetwalker]

Thanks everyone, this is really great info.

As a followup, let's say my concerns are low profile, weight, and impact resistence (in that order). Do you think a single layer of dynel would be my best option in those circumstances?

I realize the weights we're talking about are small on a 55 pound boat, but I'm wondering about the relative amounts of epoxy that are used in 1 layer of dynel versus 3-layers of S-glass.

[ezwater]

PHILCANOE---- I had not seen those comments from West. I don't consider them the same as data, though I would take them seriously.

My personal belief is that there should be a rough match between the resin hardness and the hardness of what the resin bonds to. That's one of the reasons I chisel off the vinyl layer so that I can glass to the ABS. (The other reason is that if the vinyl skims off so easily with a chisel, is the vinyl to ABS bond that good?)

But as to G-flex versus 105, the only way to an answer is to lay up some panels and subject them to impact and bending tests. Maybe West has done that.

A practical consideration is that I'm using that special unwashed, uncoated satin weave S-glass that was temporarily available from Sweet Composites. S-glass has very fine fibers and doesn't wet out easily, and satin weave is even harder to wet out. 105 wet it out nicely. Would it wet out with the thicker G-flex? I don't know, but I'll wait until summer sun is available before I try it out.

I would recommend at least trying G-flex for anyone patching with Kevlar, because I have seen reports that resin bonding to Kevlar fibers is maybe 10 to 15% lower than resin bonding to glass and other fibers. So if G-flex bonds better, it would be a real advantage for Kevlar repairs to the interior of boats.

Anyway, three years ago when the vinyl wore off the underside of the hull below my pedestal seat, I skimmed off the vinyl and laid down a 2 layer wear patch of S-glass with 105 resin. The wear patch has stood up very well, showing little abrasion loss and no cracking.

[pblanc]

The information regarding the modulus of elasticity of G-flex is from WEST. I have used G-flex to wet out E 'glass cloth and tape and Dynel cloth without problems. I haven't used it on S 'glass but I can see that there might be an issue since it is considerably more viscous and it might be harder to get all the air out of the 'glass.

I suspect three layers of S-glass would soak up as much resin as one layer of Dynel if not a bit more. A Dynel abrasion plate is much less thick than the old Kevlar felt plates. I can't say which is better (S 'glass or Dynel). The S 'glass would probably add more strength. The Dynel is advertised as being more abrasion resistant and a number of paddle manufacturers use Dynel to tip their wooden paddles. The Dynel plates that I have put on appear to be holding up extremely well thus far. The Dynel frays less than fiberglass during wet out.

What I do is apply the plate using G-flex mixed with graphite powder. After it cures I thoroughly feather the edge of the plate with sandpaper. I then apply masking tape in a smooth contour around the plate leaving about 1/2" gap all around the plate. I usually apply 2 more coats of epoxy mixed with graphite powder to completely saturate the weave of the Dynel. You can also wet sand the Dynel after the second application of epoxy to get a very smooth surface. G-flex sands very well. The graphite will cover the vinyl color layer of the Royalex. If you remove the masking tape after the last application of epoxy before it is fully cured by dry enough not to sag or run, you will have a nice, sharp outline around the skid plate.

[Todhunter]

I am by no means a glass expert, but I have had success with S-glass and Gflex. I wet out the cloth between two pieces of plastic and squeegeed the resin into the cloth. Heat up the resin and hardener prior to mixing to get a less viscous resin.