only skin deep?

[lumphammer]

I have been investigating a 'star' shaped crack that the surveyor found on the bottom of my boat. When scraping away the antifouling I have found what appears to be a epoxy coat over a plain grp hull.
See photo

There doesn't appear to be any damage to the underlying grp, which seems to have a smooth finish.

Any help on what to do to make repairs?

 

[Krusty]

I expect others will advise on repair, but I suggest you inspect the INSIDE of the hull immediately behind the cracking. I have found many of these on various boats, including my own, and invariably they have been at the pressure-point of a hard fixed object. In a seaway the hull flexes sharply over this point, and the gelcoat cracks.
Repair to the gelcoat is easy enough, but unless you remove the hard spot it will keep recurring.
The owner of one boat was mystified, as there was nothing against the hull on the inside. But when the sliding chart-table over the quarterberth was pulled out it came hard against the hull! Shaving 10mm off the corner did the trick. Good hunting!

 

[boatmike]

Not quite sure what I am looking at here. It may be that you are one of the fortunate minority who have unpigmented gel coat below the waterline. If you have removed what you believe to be the Epoxy coating and there is no evidence of cracking beneath and the surface as you say is smooth and not glass rich you are OK to just repair the patch with more epoxy. If there are cracks underneath the epoxy then follow the advice given by the previous poster.

 

[boatmike]

Second thought. Perhaps you have only removed antifoul and there is no epoxy coat just unpigmented gel coat. Usually epoxy is pigmented. Either way, no crack equals no problem. Old antifoul often becomes brittle and cracks and does not mean a problem beneath.

 

[oldsaltoz]

G'day Lumphammer,

This looks like a simple case of bad preparation prior to adding antifoul; normal practice after epoxy coating is wash with fresh water from a running hose and a rub with a scotchbrite plastic scourer till the water stops forming beads, this removes the residue left by the curing process. Then a light sanding, just enough to remove the high gloss then apply an epoxy primer coat prior to antifoul.

If this is the case you can expect more flaking, The lazy fix is to treat the exposed area as above and wait for the next bit to flake off then treat that area and so on.

The alternative is remove all antifouling and treat as above.

Tip: When applying epoxy primer, let the first cure then when ready to apply the antifoul add a thin coat of primer and antifoul when still tacky, this will give the first layer of antifoul a good key and prevent flaking later.

Avagoodweekend......