Hull Cracks- Repair or Paint Over?

[bigd14]

I am prepping the topsides for paint and I came across a very fine network of cracks in the gelcoat. I figured they would sand out but it appears that they extend into the fiberglass. You can see the fine cracks still in the white gelcoat in the photo. There is no cracking that I can see on the interior portion of the hull. This area is in the starboard stern quarter. The cracks extend a bit into the bottom paint area but i didn't want to sand that all off yet. Does this look like its from an impact or from oilcanning? Should I try to repair this somehow, or reinforce the hull from the inside, or not worry about it? The area feels and sounds solid when tapped.

Thanks

Doug

[Rachel]

To me that looks like it came from some kind of impact, or maybe gradual over-pressure like from a boat stand or piling. I can see it's near the waterline, but where is it on the boat in general - can you "zoom out" a bit?

I'll be interested to read what others think about it, since I'm not real fiberglass expert.

[Quetzalsailor]

I'm no expert, either. However, if mine, I'd grind a bit more, into the 'glass mat reinforcement (just to get rid of the shattered neat polyester), scrub with my favorite solvent, and coat out in epoxy. I'd add a smidge of 'glass if I'd gone too deep to fill with glazing putties. No need to go through the mat, it's just there to keep the cloth reinforcement from telegraphing through the gelcoat.

Those look like a pretty minor impact but the damage will extend an unknown depth into the hull thickness. It looks like a small area, so I'd have no real concern for the strength of the hull. The repair above is intended to keep the cracks from telegraphing back into the new paint.

Our old '72 Morgan 27's starboard quarter below the waterline was damaged by an ill-placed cradle prop when shipped new from FL to delivery in NJ. Similar looking cracks in the gelcoat extended around the 2' x 2.5' area. Clearly, the area had been bent in. So, tension cracks on the outside in the gelcoat, and tension cracks in the middle of the area on the inside (which could not be seen). There was no further deterioration and no cracking in the bottom paint in the years we had the boat, sold in 2005. Had I done a bottom job, which she sorely needed due to the many coats of bottom paint, I'd have added a bit of glass to the inside and repaired the cracks on the outside as described above.

[Tim]

I see no particular fear of real structural issues from what you've shown, but since you're halfway there already, take the steps necessary to help prevent the cracks from showing through your new paint. Go ahead and grind out the remaining cracks through the gelcoat and into the top layer of laminate (often a chopped mat layer, as indicated above). I am guessing you'll have removed the cracks by this point, after which you can fill and fair as required.

Since you're likely to remove only the gelcoat (and perhaps some of the skin layer) and nothing structural, you probably won't need new fiberglass--just filler--but leave that determination till you've ground out the offending area.

That said, they barely show, and are near the waterline; ergo, you could easily get away with doing nothing, if you could live with the prospect of the cracks faintly showing through your new boottop paint.

[avd155]

I had very similar cracks emanating from the two aft stands I have holding up my boat. These cracks were below the waterline and were hidden by bottom paint until I sanded it off.

I wasn't sure to do with them either, but I ended up grinding out the cracks and found that they weren't very deep. After a very basic grind, I ended up wetting out the whole area, then filling with a 407/Barrier Coat mix. I'm not 100% sure if I'll keep that repair or if I'll go back and put in a piece of glass. At this point, I think I'll probably end up leaving it, since the depth of the repair area is quite low. However, if I do decide to add glass, I'll have to grind the area deeper in order to make room for the glass-work to not protrude.

[bigd14]

Thanks for the replies. I will do a little more sanding and see how deep these things are, then decide what to do. Regardless of what I do, looks like I won't be getting the paint done this weekend. Its always something!

Doug

[Hirilondë]

Its always something!

Roseanne Roseannadanna would agree with you.

[bigd14]

Here are a couple shots of todays effort. I ground away all the gelcoat then began grinding out the cracks on the topsides. The cracks appeared a little deeper below the waterline, so I decided not to grind them out all the way for fear of removing too much material. Instead I covered the entire area with light fiberglass cloth. It should prevent any further cracking. Now more fairing and sanding. Darnit, I thought I was done with that part!

Here is where it is located on the boat, shot from the stern.



Here is a closeup showing how much deeper the cracks are below the waterline. I imagine some water worked its way in there. Also, note the two vertical lines that almost appear to be areas of drier fiberglass. A manufacturing relic, or damage from stands/impact? We'll never know. Oh, does anyone know what the red layer might be? It was put on two years ago when the boatyard stripped the bottom paint off with a pressure washer, filled a bunch of resulting dings and chips in the gelcoat with some kind of putty, then put the red layer on followed by the bottom paint. The red layer comes off easily when wiped with acetone. I'l try to stop by the yard sometime to find out. I am hoping that it is some kind of barrier layer, but the fact that it wipes of with acetone doesn't give me much faith in that idea.


And the layer of fiberglass installed...

[Tim]

If the red comes off with acetone, it's likely just a bottom paint. Perhaps the yard applied it as a "signal coat" beneath the blue?

[Rachel]

I'm just guessing, but could the vertical lines be where different pieces of cloth overlapped? (That may be completely obviously wrong when you are looking at the boat in person, I realize.)

[daydreamer92]

To me, the cracks or slashes look a lot like what I was finding on the waterline of my 2nd Fixit boat. I assumed the scratches came from scraping against some sharpish object while bobbing. If I remember my scratches well enough , they are on the widest part of the boat too, the part that would "stick out" most; kinda looks like a boat would if large cats used it as a scratching post. I filled some of 'em with Marine-tex and sanded down.

[bigd14]

Rachel, overlapping layers is probably the most logical explanation for the vertical lines. Daydreamer the cracks were very fine in the gelcoat, defintely not scratches. I'm not convinced it was from a sudden impact either, there were no scuffs in the gelcoat. My bet is on a poorly placed support sometime in the boats past. Either that or some kind of flexing (oilcanning maybe). Anyway, thanks for the thoughts and advice. I'll provide updates on the finishing of this part on my project thread.

Doug