C-Forum

I just bought a Descender. I have not paddled white water to speak of in a about 20 years - used to run II-III with my wife in a Mad River Explorer. Really enjoyed it - did a lot of swimming on our last run - wife got scared and chilled and that was it. Only I-II since then. Anyway the kids are grown, I'm newly single, and I have passed the half century mark which I think makes me old enough to paddle a Descender (since I have noticed a few posts talking about "old farts" paddling Whitesells)

I can't find a plaque on the boat only the numbers A184-11-BC hand written inside the bow and stern - I'm guessing that these numbers were not from the manufacture.

There are three things that probably need attention. Two small delaminations and cracked vinyl/PVC on the inside of the stern along the keel line. I think that maybe it hit a rock after running a ledge but the outside of the hull has no sign of a major impact. The crack is pretty jagged and I'm wondering how brittle the hull is.

This is what I am thinking as far as repairs and I was hoping to get some advice especially if I am about to make a big mistake. Hopefully the pictures are good enough. I have tapped over the entire hull and these are the only issues I can hear.

First, the cracking on the inside of the stern. I can't tell yet if the PVC and the vinyl are cracked or if it is just the vinyl. I guess I should sand through the vinyl and see what the extent of the damage is. PIC below. Assuming that the PVC on the inside of the core is cracked would it be sufficient to widen the crack enough to get any sand/dirt out, fill the voids with something like West Systems G-Flex and then cover the whole area with S or E glass? I'm confused about when S glass is needed, etc. I can't really hear that there is a delamination problem in in the middle of the cracked area from the inside or the outside from tapping on the hull.
Second, the blister. This area is really soft and it is thin (thinner than I think the PVC layer is?) and as far as I can tell has not opened up yet. There is a pretty major crease along the hull in this area. Are the PVC layers actually made up of multiple thin PVC sheets? I haven't been able to find anything except for a diagram that shows multiple PVC sheets. Anyway, I guess I will cut the raised area off with a sharp chisel. I got a recommendation from the place that sold me the G-Flex to keep it connected on one side, peel it back, sand it, flash it, and glue it back down. I guess after I cut around the "blister" I would sand around the edges outside of the damaged area so that I could feather it back in when I glue it back down. I guess I have to just get to cutting it and see if it is down to the foam or not. I have read some posts that say leave it alone until it breaks open. This, section is under a knee pad. I think it is the original pad so I am hoping that there isn't an issue with too much adhesive...


Third, the raised area on the keel line right under the pedestal. I don't know exactly what happened in this area but the PVC is thick and not at all soft. I think that from tapping there might be a hollow area here but I'm not sure. It seems to me that this is the major wear area. The vinyl is long gone but PVC seems to not be warn down much. I guess the question is should I cut it off and patch with S or E glass or just reinforce?
Maybe I should just ignore these things since I am not going to be doing anything over class III until I get more paddling practice but I want to be ready for spring...

First there is no PVC (polyvinyl chloride) in Royalex. Royalex is a 5 layer sandwich composite thermoplastic material with an outer layer of colored vinyl on the inside and outside. The structural part of the Royalex consists of three layers of ABS (acrylonitrile butadiene), with solid layers on both sides enclosing an inner core of ABS foam. The foam core provides rigidity and also renders the specific gravity of Royalex less than 1.0 so it doesn't sink. That is why Royalex boats have no flotation tanks.

The inner and outer vinyl layers are relatively thin and don't provide much strength but do provide UV protection since ABS degrades fairly readily with UV exposure. The vinyl also provides a bit of abrasion protection. The whole sandwich is/was bonded together with heat treatment and big rollers.

ABS is not very abrasion resistant and gouges pretty readily. The ABS solid layers are often pigmented as well. I have seen black, gray, yellow, green, tan, and off-white. Any areas of exposed ABS should be readily apparent as they will be a dramatically different color than the rest of the outside or inside. I would examine these exposed areas for softness or sponginess by pressing in with your thumb. If there is significant give I would consider the ABS to be thinned out and would reinforce that area with G Flex epoxy and cloth. I generally use S fiberglass for exterior patches and aramid (Kevlar) for interior ones, but E fiberglass works as well and fiberglass is fine for interior patches. If you have areas of exposed ABS that seem strong and not thinned out I would at least cover them with a spray paint like Krylon Fusion to protect them from UV exposure. The paint will get scratched off over time but it is a simple thing to clean off the hull and respray as needed.

If you have areas of abrasion or cracks that have penetrated to the foam core, you will see an ivory material that looks a bit like baby Swiss cheese. Any such areas should be filled in. I use G Flex with silica powder mixed in. Some have used Gorilla Glue with good results. Cracks should be "guttered out" and the edges beveled before filling which will ensure good penetration of the epoxy down into the foam core and provides a larger bonding surface. I use picks and a Dremel tool with a conical grinding bit to do this. You can sand off any excess G Flex after it cures. If you have only a small crack or cracks you might just fill them and paint over the exposed ABS. I usually apply a cloth patch over larger or multiple cracks.

It is possible for sizable cracks in the solid ABS layers to be lurking beneath vinyl which has only a minimal split, and even under vinyl that appears completely intact. If you have areas that seem soft under any vinyl that has splits I would assume a crack or cracks to be present. To remove the vinyl layer you can sometimes use a wood chisel to scrape it off but you have to be careful not to damage the ABS too much. You can remove the vinyl by sanding but you might be surprised how much sanding it takes to get it off even though it is relatively thin.

On your boat, the "bubble" might simply be nothing more than the outer vinyl layer that has separated from the underlying ABS. I would probably just cut it away at the edges then repair the underlying ABS as needed. The bulged out area under the pedestal might simply be deformity that has developed in the Royalex due to the "stress riser" that the front of the saddle or pedestal creates. The paddlers weight resting on the pedestal makes the section of Royalex beneath it pretty immovable whereas the ends of those long boats flex up and down considerably, especially going over ledges and drops. It is pretty common for cracks to develop in the ABS right along the front edge of the pedestal or slightly in front of it.

I recently worked on an older Royalex canoe which required removing vinyl, guttering and filling cracks, and applying interior and exterior patches. It might be worth your while to look at an album of photos I made of the process. Read the captions on the individual photos for a more complete description of what was being done:

http://www.flickr.com/photos/42020723@N ... 7942924708" onclick="window.open(this.href);return false;

If you have any questions about it, send me a PM.

Great job on the step-by-step, Pblanc. And sweet job on the ME.

Thanks for the detailed response and suggestions, pblanc! I need to learn my plastics - hopefully I will not make that mistake again. Sweet Composites is pretty close to work so I think I will head over there in the next few days and get my repair supplies. The blister I think has at least some ABS in the raised area since there are scratches through the blue vinyl, that's why I as asking if the ABS layer is made up of multiple thin layers. I guess I will peel off the vinyl in the inside of the stern to see how many cracks are under there.

Very impressive restore as well.

Thanks milkman and gnsmith116. No the solid layers of ABS in the Royalex are one uniform layer. I have not seen just a portion of the solid layer of ABS peel away leaving the rest covering the foam core, but I suppose it could. If that is what happened, I don't think I would try bonding it back down unless it was quite thick. I suspect I would just fill in any exposed core and then rebuild the thinned ABS layer using epoxy and cloth, in multiple layers if need be.

You can fill soft spots and delaminated voids in the Royalex with Gorilla glue. This works great because you do not have to try to dry out the layers since G-Glue is water activated, and there is almost always moisture in there you cannot get to. If not, just use a spray bottle to dampen the inside first. You will need to create an opening with a slit or drill a hole into the void to get the G-glue in there, then work it through the void with a putty knife handle or a piece of wood. Then put some plastic wrap and a board over the spot and clamp it down using cam straps. The excess G-Glue will foam out and this will keep you from having a deformed bulge in the repair. Then just scrape and sand away the excess and you have a "relaminated" repair. If you want you can then glue some ABS plastic over the repair but it probably will not be necessary as G-Glue is waterproof. This is the best repair I have found for delaminated Royalex, although it will increase the weight of the boat the more repairs you do.

Glueing a blister.

I drill a small hole in the center of the blister and then inject resin, at an angle, into the void. To inject I use small 10 ml syringes that can be bought from a fibre glass shop. I use the most viscous resin I can find so that it will travel thru the needle; Gflex and Epoxy Glue don't flow thru the needle.
When injecting it is a process of "fracking" the blister, boxing the 360 degrees.

The trick is to not inject too much, so as to not create a solid lens of brittle cured resin, usually 5-7ml is enough and then I squeegee/smear it into the interior edges of the blister using a flat stick, working from the centre to the outside.
The actual voids are usually larger than the visible raised blister, you want to get out into the edges where the material is separated but not yet visibly raised.

I observe the problem as being the "reversing of the curve', a changing of the radius between the interior and exterior vinyls, and this creates the two separated, formerly bonded layers. The repair goal is to glue the outer layer of vinyl and the inner layer of vinyl back together.

Having done the blisters on one chine I then prop/support the hull on it's outside chine on the floor at an angle. On the inside of the chine I weight the blister down with whatever I have that is heavy, compressing the interior and exterior hull vinyl together. A release barrier of saran wrap can be applied to deal with any back flow leakage although just covering the hole with gaffer tape usually prevents resin from escaping.
It works for me, doing one chine in one night, the other chine the next eve. If the blister is under a D ring I just drill thru, leaving the pad in place.
I find that the end result is stiffer than factory. I expect that the repair will fail at some time, for some reason but... I haven not yet come upon the time, or upon the reason. Tough enough so far.

I have done several hulls this way, the last being an Occoee, my go to hull.

I love what others have done on this thread, I admire your professional work and thanks for the image documentation. C1 B1 has lots of very generous people, the best.
Einar