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Old 11-05-2019, 01:45   #1
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Cracks on underwater hull

Does someone know what those cracks are? Have no experience ..
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Old 11-05-2019, 02:44   #2
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Re: Cracks on underwater hull

some more fotos here Cruisers & Sailing Forums - baff's Album: Hull of a Marieholm 32E
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Old 11-05-2019, 03:22   #3
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Re: Cracks on underwater hull

It looks like you have a thick coat of old bottom paint that is cracking and peeling. Perhaps you could try chipping off the cracked paint and sanding to the gelcoat underneath. I suspect the gelcoat will be fine.
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Old 11-05-2019, 03:48   #4
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Re: Cracks on underwater hull

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Does someone know what those cracks are? Have no experience ..
Can you tell us the "make"of yacht, age, history etc. Maybe cracked paint - barrier coat? (as has been suggested)
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Old 11-05-2019, 03:59   #5
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Re: Cracks on underwater hull

Marieholm 32E of 1980 (Location northern Sweden)
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Old 11-05-2019, 04:22   #6
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Re: Cracks on underwater hull

I think you'll find they are cracks in the gelcoat. If you scan through these images you'll see a photo of some cracks that look very much like yours. (I tried to access the website but they are not responding)


https://forums.iboats.com/filedata/f...4&d=1400605050

https://www.google.com.au/search?biw...Bfywm96dbuVFM:
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Old 11-05-2019, 06:14   #7
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Re: Cracks on underwater hull

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Originally Posted by Copacabana View Post
It looks like you have a thick coat of old bottom paint that is cracking and peeling. Perhaps you could try chipping off the cracked paint and sanding to the gelcoat underneath. I suspect the gelcoat will be fine.

Agree with the comment above and it looks like old bottom paint coming off and it was put on the hard w/lots of growth on it. Remove bottom paint then make an assessment. Possibly use chemical stripper to remove bottom paint so you don't over sand using heavy grit and remove the gelcoat unnecessarily.



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Old 11-05-2019, 06:20   #8
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Re: Cracks on underwater hull

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Possibly use chemical stripper to remove bottom paint so you don't over sand using heavy grit and remove the gelcoat unnecessarily.

Thank's for that advice
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Old 11-05-2019, 07:03   #9
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Re: Cracks on underwater hull

That's pretty ugly. Hopefully it's just many layers of bottom paint but it appears like more than that to me. Maybe bondo repaired areas from damage on the leading edge of the hull. Brittle old resin or thick gel coat that was sprayed in the mold and accumulated too thick maybe without glass reinforcement.
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Old 11-05-2019, 12:15   #10
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Re: Cracks on underwater hull

Yes, chemical stripper like one of the "orange" strippers, preferably the type that comes with pads you apply over it to keep the stripper moist and then absorb most of the crud. That makes the cleanup much simpler too, prevents hazmat issues with paint dust.
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Old 12-05-2019, 04:50   #11
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Re: Cracks on underwater hull

Older barrier paints were actually a product made out of epoxy coal tar. Interlux VC tar was put on a lot of boats as a barrier coat then antifouling put over that. After 10 to 15 years it starts to shrink and crack very similar to your attached photos.

As stated above you need to remove the antifouling and barrier coats to see if you have more issues underneath.
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Old 12-05-2019, 05:04   #12
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Re: Cracks on underwater hull

If you really want to get to the root of the problem, I would have the bottom blasted with soda or crushed walnut shells. This can be done in a day. Personally I am too lazy and consider it an investment in my body and sanity to hire this out. I am doing this job right now on a 50'er, and the hired out blasting was satisfying to see it done in hours, what would have taken me weeks of doing it part time. Once this is done you will have a much clearer idea of what is going on.

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Old 12-05-2019, 12:19   #13
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Re: Cracks on underwater hull

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That's pretty ugly. Hopefully it's just many layers of bottom paint but it appears like more than that to me. Maybe bondo repaired areas from damage on the leading edge of the hull. Brittle old resin or thick gel coat that was sprayed in the mold and accumulated too thick maybe without glass reinforcement.


Unfortunately Bondi does not work below the waterline. Once the crud is cleaned off the assessment should be easier
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