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Old 17-02-2024, 07:32   #1
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Osmosis not weeping

The surveyor report states that osmosis is present in the underwater surfaces of the hull. Approximately 15 to 20 blisters found with an average size of a tennis ball. No blisters are weeping and all appear to be hard. Tap test shows only a slight difference in noise which confirms only surface penetration.

This is from a surveyor report for a sailing boat I am interested in buying. The boat is in Queensland (Australia) and I am in Western Australia. I am undecided if it's worth it to fly over or not to inspect. Considering I am in the South Pacific and Indian ocean, what are the options? If the blisters are tackled one by one, grinding the gelcoat and expose the glass for fixing, is any way to "accelerate" the drying time before applying new layers of glass, fairing and gelcoat again?

This is my first post, not sure if I am in the right forum, my searches about osmosis didn't clarify anything, my understanding is that if I don't cure it, it will get worse and will attack the core at some point. So, shall I run?
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Old 17-02-2024, 10:17   #2
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Re: Osmosis not weeping

My understanding is you have to repair your hull (e.g. see: https://www.cruisersforum.com/forums...30#post3138730). About six years ago, we had hull blisters ground out. Then, polyester vinyl was applied. Finally, epoxy was put on. We've had no problems since. Our boat had had this repair done previously, about ten years before we did ours.
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Old 17-02-2024, 10:46   #3
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Re: Osmosis not weeping

How do you know they are not weeping ? Were they punctured ?
Hydrolysis fluid in blisters that size will be under tremendous pressure ... they will sound solid. If you do puncture one, wear safety glasses, the pressure is impressive.

If your description is accurate I would be quite surprised if there were no hydrolytic fluid in those blisters. If there is such fluid, drying time before it can be repaired should be measured in months, maybe even a year or more.

There is a process to hurry the drying and to flush the contaminants but it's gonna cost. Hot Vac Hull Cure Osmosis.
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Old 17-02-2024, 14:12   #4
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Re: Osmosis not weeping

Welcome aboard CF Franco_oz.
You are in the right forum.
That is a significant number of good sized blisters and the problem must have been developing for some time. Untreated, it will get worse. How old is the surveyor's report.

Should you run is a complex question as there maybe many other reasons to proceed cautiously forward rather than run the other way. However should you proceed, know that the osmosis needs fixing now, not later. It can also signal there could be other delayed (expensive) maintenance in other difficult to access areas of the boat e.g. engine / shaft / chainplates and so on.
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Old 17-02-2024, 15:00   #5
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Re: Osmosis not weeping

Franco Oz I never peirce an osmosis blister unless the owner gives me permission. If the boats being put straight back in the water after the survey then you don't want to damage the hull coating.
When I used to repair osmosis and was in a hurry I would grind out the blister then cook it with a heat gun. You could definitely see plenty of moisture evaporating. Then fiberglass and fair with epoxy. I have seen one yacht have countless blisters repaired like this and five years later the hull still looked perfect.
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Old 17-02-2024, 17:56   #6
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Re: Osmosis not weeping

Quote:
Originally Posted by Wotname View Post
Welcome aboard CF Franco_oz.
You are in the right forum.
That is a significant number of good sized blisters and the problem must have been developing for some time. Untreated, it will get worse. How old is the surveyor's report.

Should you run is a complex question as there maybe many other reasons to proceed cautiously forward rather than run the other way. However should you proceed, know that the osmosis needs fixing now, not later. It can also signal there could be other delayed (expensive) maintenance in other difficult to access areas of the boat e.g. engine / shaft / chainplates and so on.
Good morning Wotname, survey is from November 2033, I haven't seen the boat yet, all other findings are not a deal breaker for me, only the engine mounts look a tad weird to me.

The report says the blisters are not weeping, so I have to believe that until the boat comes out and I can see it myself.

The problem (or dilemma) is that we are now undecided between flying out to inspect this boat or not. We already flew out from Perth to Melbourne to look at a boat in Geelong which looks ok on the surface but I need to fly back, put an offer (subject to sea trial and haulout) and take it from there. The Geelong boat has a very old Volvo Penta MD17 engine, unfortunately I don't have good experience with Volvo. This boat in Qld has a Nanni engine which I have plenty experience with. Also as I don't know anyone in both places I am mainly relying on my personal experience and knowledge. Both boats have pros and cons, just the decision is harder now. I done a few refitting and engine swaps in vessels when I was much younger, now at 60 I am not as agile as I was...
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Old 17-02-2024, 20:38   #7
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Re: Osmosis not weeping

No1 question,is it a cored hull I/e balsa or foam ,the liquid in the blisters may well be in the core and not leaking externally ,does the vsl have in built tanks ,if so are there blisters in the tanks or bilges ,just some questions for your surveyor,plus how is the keel attached .⛵️⚓️
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Old 19-02-2024, 05:49   #8
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Re: Osmosis not weeping

Ops, just realised my typo about survey date. No I don't live in the future, it was meant to be 2023.
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Old 19-02-2024, 06:05   #9
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Re: Osmosis not weeping

Quote:
Originally Posted by Franco_oz View Post
Ops, just realised my typo about survey date. No I don't live in the future, it was meant to be 2023.
Dang. No stock tips then?

Osmosis and blistering are not necessarily the same thing. Osmosis is absorption of water in the polyester resin, it often causes blisters but you can have absorbed water without blisters or weeping. A good surveyor will be able to tell the difference.
Blisters can be spot repaired pretty easy especially if the water absorbtion is localized.
Osmosis can be fixed by throughly drying out the hull and a new barrier coat, but it's a long and tedious process.
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