osmosis prevalence in mk2s v mk3s

[gypsyrider]

Greetings all, another pesky question. I recently looked at a mk3 that even in the photos had quite a degree of blistering which was confirmed by a marine engineer as definately osmosis. My question therefore is : are the mk3s more prevalent than the mk2s to the dreaded osmosis due to the differing building technique of their construction. I am soon going to have a look at a mk2 and before spending about a grand on slipping and survey (only to find osmosis) I am going to employ one of the marine divers available in sydney to clean the hull and tell me if it is worth spending time and money going any further. I am also arranging a swing mooring at Brooklyn to home the yacht when I find the right one. Thanking you all for your indulgence on this matter I understand that there is no exact answer to my question but previous experience of members can help with what they have found over a long period of time. Thanks again. Your friend in Top Hatting to be. Gypsyrider.

[Dolphin]

Don't worry too much about blisters. These were on Felicite. At her last slipping last month there were none.
Top Hat hulls are quite thick.
The photo is in the gallery section, Felicite.

gallery/image.php?album_id=10&image_id=123

[Troppo]

Gypsyrider, I am not exactly answering your question here, but just giving you some idea of my experience with trying to get a boat free of osmosis and what happened next. I certainly think you should be wary of osmosis but it doesn't necessarily mean a boat is no good.

My old Mk 2 Windchaser had a survey done a year before I purchased saying no osmosis. When I had her up on a slip, I noticed some old and large osmosis blister repairs. A year later when up on the slip again I paid more attention as I saw tiny blisters up to 20 cent size on port side of hull, practically nothing on starboard side. Probably there the year before but now a bit bigger and I was looking harder. To confirm osmosis, I punctured blisters with small sharp screwdriver. Dark smelly fluid leaked out.

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Photos show port side as only a couple on starboard side.

Ground out shallow depressions to remove affected materials, flushed with fresh water several times over a few days then let it dry out for a few more days while doing (lots) of other repair work. Then did the standard repair with brushing on epoxy, then a layer of fairing epoxy stuff that can go under the waterline, sanded back, primed and painted. The next year there was no problems. Year after that I had sold her so don't know if any more osmosis started.

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From my experience, the small osmosis blisters were mostly cosmetic. A couple of the bubbles did go a bit deeper than I was happy with but mostly they were shallow and the fibreglass is thick. The evidence of some repaired old big osmosis spots was a concern as I wondered if the small osmosis blisters would just keep growing. The osmosis repair I did was simple enough BUT, time on the slip to hopefully allow the hull fibreglass to dry out a bit costs money.

troppo