Cracked Royalex stern repair

Thank you for all the help.

The cracks more towards the center guttered out fine, although it’s not easy to see the crack once you’re in the foam core with all it’s lines, bubbles and shadows.

However, a portion of the single crack that extends from the extreme bow “sits up” on the right, then on the left, for about 5 inches total. After dremeling a spot all the way down to my skid plate (but not through it) I see a hairline crack where the Royalex has lifted from the skid plate, and probably for the entire 5 inches. The skid plate itself is not cracked there.

How do I proceed?

Yes, it is a bit tricky to follow the cracks through the foam core. Sometimes, forcibly flexing the hull helps temporarily open them up.

I assume the hairline crack in the Royalex you are seeing is from the inside of the hull? If it appears the skid plate has de-laminated from the Royalex, I would open up the area enough to ensure that you can get epoxy down into the void between the two without leaving significant air gaps. You might want to use unthickened epoxy for that purpose and warm the area judiciously with a heat gun after application to ensure that the epoxy gets to where it needs to go.

I don’t know whether I would do that “opening up” from the inside or through the skid plate. Probably the former but I would have to actually see it to decide. In general, I would try to disrupt structures that are still intact to the least extent possible.

@pblanc said:
I assume the hairline crack in the Royalex you are seeing is from the inside of the hull?

Yes

I don’t know whether I would do that “opening up” from the inside or through the skid plate. Probably the former but I would have to actually see it to decide. In general, I would try to disrupt structures that are still intact to the least extent possible.

I was wondering about that. The horizontal delamination crack is at the extreme end and it’s way too narrow to open it up at that horizontal angle from the inside with the Dremel, or any other tool I can think of. My first thought was to remove the portion of the skid plate where it has delaminated from the outside, fill with thickened G/flex from the outside, and put cloth over it. However, I was reluctant precisely because I did not want to destroy the mostly intact skid plate. I currently don’t see any other way, though.

Here’s a photo. You can see the delamination crack between the black (skid plate) and sliver of green below the purple. I believe this crack extends for 5 inches but I have not guttered it out to that extent yet.

I would probably continue to gutter out the crack lengthwise until you reach a point at which the skid plate seems to remain strongly attached to the ABS. You might be able to judge the width of the area from which the skid plate has delaminated by inserting something thin under the ABS and using it like a feeler gauge. If the delamination does not extend to far laterally you may be able to get epoxy in there by using a dental syringe with a thin, drawn-out tip.

The inside repair turned out pretty nicely and with only minor hiccups: Despite the fact that I carefully measured out my aramid patches, after cutting them they grew by 2 inches and became somewhat narrow. I tried again with the same result and was out of aramid at that point.

I also could not get rid of all air bubbles between the peel ply and resin in the extreme end of the canoe, as trying to push the air up the vertical walls from the horizontal center line with a squeegee always resulted in the peel ply getting lifted up again at the center line.

Here are some pictures. I still need to paint.

Guttered out cracks filled with resin, with plastic patch template placed:

Area taped and ready to go:

Aramid patches cut at different biases:

Concentric patches epoxied in place:

Looks good.

That looks like a good repair.

,Plain open weave fabrics, in which the fibers of the weft and warp are not fixed to each other in any way, will act like those Chinese finger traps that some might have played with as a kid. The cut patches will tend to distort by elongating and narrowing, or vice verse. I use whatever template I am using to cut out the patches to mark an outline on the hull and then try to work the fibers of the patch out to the correct width as I wet out the cloth in order to minimize distortion.

Applying patches in a concavity is a bit tricky. I usually use two implements such as two squeeges, or a sgueege and a stir stick, holding the patch down on the hull in the concavity while using the other to wet out the cloth. If you are using peel ply, it is more important to avoid air voids between the patch and hull than it is to get out all the air bubbles from under the peel ply.

How does the outside of the damaged hull look?

@pblanc said:
How does the outside of the damaged hull look?

I’m in the process of guttering out the cracks but am once again having trouble detecting the maximum depth of the cracks. From time to time, I push both sides of the hull inward a little to find the hairline again, but of course squeezing too much could propagate the crack!

I dremeled the outside cracks down to what I believe is the foam core (white) and can still see a crack. I took a photo. Note that this boat’s outside ABS layer is half green and half red (!), with the green on the outside, touching the vinyl and the red on the inside, touching the foam core. As you can see, there’s still a hairline crack visible in the middle of the white foam core.

Should I continue to dig deeper (I must be at 50% of wall thickness)? Or should I just leave it alone at this point, fill with G/flex and cover with cloth?

I did one a few months ago and never went that deep. I filled it with several coats of G-flex and then used glass tape over that with a few more coats of G-flex.
I painted it with Krylon Fusion. It passed sea trials and you would never know it had been cracked. One of them was four feet long with another three footer joining it.

@JackL, were you able to completely gutter out your crack? Or did you gutter out some with the crack still visible when you filled it with G/flex?

The honey consistency of G/flex means it can’t really penetrate tiny hairline cracks, but if some deeper portion of the crack is left unguttered, wouldn’t the crack propagate next time you hit a rock? Maybe it doesn’t matter…

I would open up just the center of the cracked core enough to make sure that your epoxy gets down into the crack and has a good bonding surface. You might be able to best do that using a small, angled pick. Have you already repaired the hull on the other side opposite that crack?

@pblanc said:
Have you already repaired the hull on the other side opposite that crack?

I repaired the inside cracks with two concentric aramid patches (photos a few posts above). The larger patch overlaps maybe 35% of the area opposite the outside cracks. In hindsight, I should have just increased the width of my inner patch to completely cover the areas opposite the outside cracks.

No, I did very little guttering. On the long cracks I used a can opener just to open them a tad, ( a 1/8 " V" groove.). On the bow part which was a deep wide in then f opening, I first stuffed wetted out shredded fiberglass, then used wetted out tape, followed by a few coats of straight G-flex

@pblanc said:
I would open up just the center of the cracked core enough to make sure that your epoxy gets down into the crack and has a good bonding surface. You might be able to best do that using a small, angled pick.

That was a good tip. I was able to use a nail cleaner/file from a toe nail clipper to rip through the remaining crack in the foam core. I decided to fill the cracks with unthickened and slightly warmed epoxy to increase the chance that it fills the cracks completely. Still need to sand the epoxy flush:



@pblanc said:
I usually try to make patches overlap the undamaged portion of the hull by 2 inches, but if the cracks extend to the existing abrasion plate or into it, I would probably simply butt the end of the external patches up to the side of the abrasion plate, then thicken the existing abrasion plate with another layer of cloth. I would probably use S fiberglass for that purpose as it is a bit stronger than Dynel. But that plan would be subject to modification based on what I saw when I removed the vinyl over and around the cracks.

Rather than several individual patches, I was going to put on a single large patch covering both cracks as well as the existing skid plate. I marked the outline of that patch on the hull.

One big patch will be a bit heavier, of course, but probably better from an overall strength standpoint. And it would avoid introducing a bunch of new stress risers at the edges of several individual patches. You could also extend the patch with a forward “tongue” running the length of the existing skid plate, if you wish, to keep the thickness of that skid plate uniform, then paint the skid plate itself black.

I’ve been meaning to post these pictures of the last steps involved in this repair.

Inside Kevlar patch painted:

Outside sanded and taped:

Resin, cloth and peel ply (mostly) applied.

After peeling the peel ply, there were areas full of many tiny and some larger air bubbles. Good enough, I think (hope), but not great compared to some of my earlier repairs. I first suspected that there were too many air bubbles in the epoxy due to vigorous mixing, but I now think that maybe I did not use enough resin for such a large area, only 4oz below and 4oz on top of the cloth. Or maybe I peeled the peel ply to early, after about 2+ hours. But would that cause mini bubbles?

Painted flat black:

First trip:

Thank you very much for your help.

Boat looks good and so does little Frankie. Hope you can bring both back up to the Ozark Rendezvous one of these days.

@pblanc said:
Boat looks good and so does little Frankie. Hope you can bring both back up to the Ozark Rendezvous one of these days.

Unfortunately we won’t be able to make the Rendezvous this fall but would like to attend in the spring.

Mu guess is that the Spring Rendezvous will be back at the North Fork of the White River, but that is yet to be determined. Attendance at this spring’s event on the Buffalo was not too good, in part because of a poor weather forecast. Hopefully, we will have a few more people at the Current River in October.