Cracked Royalex stern repair

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.