Horrible Osmosis Shock

[Frank Holden]

Anybody ever heard of a boat sinking due to osmosis?

Maybe by the time the osmosis gets to the full delamination stage the boat is already in a paddock somewhere.
Whether or not it is worth sorting properly is a question only the owner can answer.
Does he want to keep sailing and keep value in his boat or is he happy giving her away?
I dropped $NZ30,000 on a full strip,HotVac treatment , and vinyl ester job in 2014 because that was a fraction of the value of the boat and I wanted to keep her. She is also a known quantity.
Sell her cheap and buy another which then shows the same issues? Don't think so.
Spend $30,000 on a boat that is then only worth $35,000? Different story.

 

[lustyd]

and addressed it just in time

Just in time for what? Launch? Dinner? Certainly not to save the boat, many are ignored for decades before they're ignored some more.

 

[dankilb]

A fair approach.

But unless planing a sale, not urgent or preventing use of the boat

Aye - agreed.

Just in time for what? Launch? Dinner? Certainly not to save the boat, many are ignored for decades before they're ignored some more.

no to avoid living with blisters ourselves. I’m not against ignoring it either. But we’re now a rare osmosis free example of these boats. Wouldn’t have bothered me particularly to live with blisters - but after years of passive drying we could nip ours in the bud before an effective repair was even more faff (or not worth even contemplating).

 

[fisherman]

I only heard of one boat being scrapped for osmosis. it was a very thin hull with very big blisters. The blister profine is rather like a mushroom, and the surface diameter relates to the depth of the 'stalk'. There was sufficient degradation to affect structural strength, but even so, it didn't sink, but it would not have withstood an impact. I saw a GRP boat for sale that had been overlaminated rather like some folk do to old wood boats, probably for an osmotic reason.

 

[Elessar]

I don't agree with you and I think your understanding is dated and has been superseded by more accurate understanding of the facts. The water does not become denser. if the water contacts uncured chemicals it reacts and forms another compound that is both larger and denser. The process is not osmotic, that has been known for a long time. GRP has pore spaces and permeability, the pressure differential due to hydrostatic head of water and air inside the hull is what drives molecules through the GRP in insignificant volumes as far as mass is concerned. However, the volumes are enough to react with uncured chemicals.

It is fact that my 1974 hull moisture readings decrease over the weeks and months ashore, in winter, in Scotland.

Well we need to agree to differ then. I also disagree with taking a boat out for the winter what a waste! But I can disagree with you and would still buy you a pint.

 

[superheat6k]

Notably the OP does not report actual evidence of actual harm, e.g. delimination or blistering.

I do find it amazing that folk are concerned that a boat that defacto sits immersed in water for most of its life gets some moisture into its structure - so what ?

Take the offending meter and operator and throw both off the nearest quay.

Too many surveyors out there, including, sadly some apparently popular and often recommended on here, that are obsessed with so called 'Osmosis', mostly due to concerns with professional indemnity, rather than actual problems. However, sadly some of these no doubt make a decent side margin from works they recommend.

If the boat ~ 38 years old had a problem it would have manifest long long ago, so the survey 5 or so years ago is the one I would take notice of.

 

[KevinV]

Notably the OP does not report actual evidence of actual harm, e.g. delimination or blistering.

Notably.... he does report blistering

 

[Refueler]

Notably the OP does not report actual evidence of actual harm, e.g. delimination or blistering.

I do find it amazing that folk are concerned that a boat that defacto sits immersed in water for most of its life gets some moisture into its structure - so what ?

Take the offending meter and operator and throw both off the nearest quay.

Too many surveyors out there, including, sadly some apparently popular and often recommended on here, that are obsessed with so called 'Osmosis', mostly due to concerns with professional indemnity, rather than actual problems. However, sadly some of these no doubt make a decent side margin from works they recommend.

If the boat ~ 38 years old had a problem it would have manifest long long ago, so the survey 5 or so years ago is the one I would take notice of.

It is true that some even well known 'Surveyors' have been 'overzealous' in the past and I know some who made money not only on the survey - but by 'pushing' certain companys / methods upon the client. Some being rather questionable.

One of the problems is when surveyor writes his report ... tries to be 'smart' and Insurance company reads - sends out requirements based on that. The results of his wording have a profound effect on clients position. He cannot hide the findings - but needs to report in such reasonable way that client has options.

Most older boats suffer and carry on year after year providing service.

 

[Jim@sea]

A while ago we bought a then 38 year old, 38’ grp boat. Although it had been on the hard for several months we were aware that it had been afloat continuously for five or six years.

We had a pre purchase survey by a well known, well qualified surveyor who stated that, for it’s age it was the driest boat he’d ever seen - he even tested his moisture meter on a couple of nearby boats to check it was actually working.

Fast forward five & a half years & we’ve just had the old, built up layers of antifouling removed & discovered the hull to be not only blistered, but the moisture levels over the entire hull are, quite literally, “off the scale” - even to a point several inches above the waterline.

During our ownership the boat has had two, non consecutive, full years afloat & three winters ashore; twice for about four months & once for seven.

I find it difficult to believe such a rapid deterioration could be possible. Has anyone else had similar experience?

In 1983 I bought a 1973 Nauticat 33 which turned out to have Osmosis. It turned out that it had already been treated in 1980 for the Osmosis but in those days there were not the 2 pack treatments which were available, until later years so when they repaired the hull they may have just used ordinary car filler and I know that when they painted the hull they used single pack paint, which is why 3 years later when I bought it the blisters were pushing through again. Fortunately at that time I had a bodyshop and was using 2 pack iodinate paint on cars and redid the blisters and painted it again.
Leaping forward, 20 years ago I bought a 1986 Colvic Watson which again had been treated with modern paints and again that was starting to blister. That was really difficult to stop blistering as even though I used the proper underwater line filler it came back again. (Had to use a heat gun to dry it out)
(I went to see a Fisher 25 that was for sale and the hull was so covered with hundreds of blisters it put me off)
More recently (2021) I bought a 25 year old American Yacht and there was no sign of Osmosis anywhere.
Perhaps the older boats had a different sort of GRP construction. I once read on this forum about a Quicksilver Power Boat which had been in the water for over 10 years and the Osmosis was that bad that that the hulls was porous.
In 2006 I bought a 1986 French Power Boat (Guy Couch) and there was no sign of any Osmosis. Same age as the Colvic Watson I bought so again it could be that the French boat was built with different GRP.
I believe older boats should not be left in the water for long periods as the older materials used are getting older and start to fail. (could of course be wrong but just my opinion)

 

[Jim@sea]

It is true that some even well known 'Surveyors' have been 'overzealous' in the past and I know some who made money not only on the survey - but by 'pushing' certain companys / methods upon the client. Some being rather questionable.

One of the problems is when surveyor writes his report ... tries to be 'smart' and Insurance company reads - sends out requirements based on that. The results of his wording have a profound effect on clients position. He cannot hide the findings - but needs to report in such reasonable way that client has options.

Most older boats suffer and carry on year after year providing service.

I once bought a boat in the Channel Islands. I asked a boatyard to do a survey. They did not find any Osmosis.
When I later found Osmosis I had another survey by a proper firm of Marine Surveyors. They said that they had previously done a survey on the boat and found Osmosis and said that it had been painted by the very boatyard who did the survey for me. (who never mentioned it)

 

[Stemar]

From what I can gather from taking an interest in "osmosis" over the years, moisture readings in GRP are irrelevant if the layup is sound. Basically, no blisters, no problem. Small blisters up to an inch or so in diameter are also not a problem until the buyer's surveyor spots them and the buyer halves their offer, but if you're the buyer, grab a bargain and deal with them at leisure.

It's only when the blisters get to plate size that they need serious attention, but at that point, I'd want to talk to a proper expert, not just a bloke who offers a strip and epoxy service.

 

[fisherman]

The early Aran class lifeboats started losing speed and it was found they had gained a lot of weight, from 'wicking'. As did my FV, a Cygnus 32, possibly three or more tons extra, but it is 1976 vintage. Plenty of blisters when I got it in 1992, same when I sold it in 2018. The surveys in 2001 and 2018 said "osmosis, so what". Remember though, SFIA standard moulding, clear gel below W/L, any voids injected, and heavy top hat frames fitted in the mould. You can make a moulding to any weight. For instance, the Cygnus DS25 is 13 1/2 oz, the same as a Plymouth Pilot 18ft heavy duty, (3x2oz CSM, 2x woven rovings. The Cygnus is CSM only) but I've seen 18ft mouldings half the weight.

 

[RunAgroundHard]

A find the concept of a 32’ boat having void space in the hull layup equal to 2 to 3 cubic meters that could be filled with water to increase weight very unlikely. That’s like, about 2 or 3 of those builders bags volume. The weight increase must be down to something else.

 

[fisherman]

A find the concept of a 32’ boat having void space in the hull layup equal to 2 to 3 cubic meters that could be filled with water to increase weight very unlikely. That’s like, about 2 or 3 of those builders bags volume. The weight increase must be down to something else.

Yes i often wondered the same thing. Hull 10m long, even saying max 5m a side gunnel to keel, and 1.5cm thick, only 1.5cu m. When launched these boats would typically be 8.5 tons deadweight.
Then there's the junk onboard, ballast, and crucially the top hat frames which were not sealed at the top, and being 10cm x 10cm and 3-4m a side long could hold a lot of water. There were 20 of them a side. Plus beam shelf and other stringers. Certainly full of water, I drilled the hull, above W/L, for a fixing and couldn't figure out where the water came from; had hit a frame.
I was 14.5 tons last lift out. 2 or 3 tons ballast. Maybe 3/4 ton of fuel.
So given all that wet in such an old working boat, plus osmosis, I recommend folk don't worry too much.