Help! I think I have osmosis

[[70521]]

Boats not sinking due to osmosis is often glibly stated, but impossible to back up. I suspect that, at worst, it's exceedingly rare."*
The commonest form of osmosis arises between outer lay-up and gel-coat (typically in the tissue layer, if there is one). It's superficial (or cosmetic, as pvb puts it) and suggests no structural impairment. If the OP's case is osmosis, it very much looks like that type.

** Contrary to popular belief you can prove a negative, but it's often best not to try. The most celebrated example took many of the world's best minds the better part of four centuries.

My day job involves some forensic engineering into safety critical systems; I would find it very hard to prove that osmosis had ever sunk any vessel. Perhaps something for my retirement, investigating the impact of osmosis on the structural integrity of a hull following the sinking of a vessel, on the other hand I think I'll just go sailing

 

[macd]

The resin is really only there to protect the glass, which provides almost all the structural strength.

In tension, maybe. I've got some jeans made of fibres stronger than glass. They're a little on the floppy side (thankfully).

 

[Akestor]

Iam not an expert but i had osmosis on my boat so here is my thought: These are tine blisters and nothing to worry about. I would just open them with a sharp tool let them dry 1-2 days and then handsand them with 60 grit paper until lamintate is dry. ( that souldnt be more than 1-2 mm deep). On some very large blisters of mine i didnt have to dig more than 3 mms to find the healthy laminate. If you apply some thickended epoxy at the sanded dry area it should stay there for a lifetime dry!

Ps : i have an old 4 meter fiberglass dingy to go to my mooring.. It is in the water for about 20 years or more , the bottom is fool of oysters!! ( a crab also lives there!) No sings of water getting in and i guess its full of osmosis..

 

[Tranona]

All the usual old myths about osmosis coming out without actually seeing whether they are relevant to the OP's question. he does not have a 30 year old MAB but a 6 year old boat that was supposedly built of the very best materials and claimed to have beaten the osmosis problem. I too would be concerned about blisters appearing in the gel coat, as would any buyer looking to spend £250k+ on buying such a boat (that is roughly what they go for).

I don't have any answer, but , despite the fact that Northshore went bust as a builder, the people who built the boat are still operating out of the yard and well worth contacting them for advice.

 

[Concerto]

For the OP I would like to ask if the gel coat was brushed. If it was brushed. then it is most likely that the bubbles are from air trapped in the gel coat from not brushing it out to remove the small bubbles. The thin amount of gel coat over the bubble has a little moisture asborbed and expanded the air in the bubbles. I have had this on my old Westerly Fulmar and it is not a serious problem. It is a tedious job to fix and most likely there will be other areas that will be affected in the future.

 

[Graham376]

All the usual old myths about osmosis coming out without actually seeing whether they are relevant to the OP's question. he does not have a 30 year old MAB but a 6 year old boat that was supposedly built of the very best materials and claimed to have beaten the osmosis problem. I too would be concerned about blisters appearing in the gel coat, as would any buyer looking to spend £250k+ on buying such a boat (that is roughly what they go for).

I don't have any answer, but , despite the fact that Northshore went bust as a builder, the people who built the boat are still operating out of the yard and well worth contacting them for advice.

Although Northshore went bust, what was the warranty and more importantly, was it underwritten so maybe still valid?

 

[pvb]

Although Northshore went bust, what was the warranty and more importantly, was it underwritten so maybe still valid?

It was only a 5 year warranty, and the OP's boat is 6 years old.

 

[pvb]

For the OP I would like to ask if the gel coat was brushed. If it was brushed. then it is most likely that the bubbles are from air trapped in the gel coat from not brushing it out to remove the small bubbles.

It was brushed; Northshore built so few boats that it was very much a "man with brush and bucket of resin" operation.

There are a couple of photos of Northshore's lay-up process in this blog - https://distantshores.ca/boatblog_files/moulding-the-hull-s49.php Note the rather precarious use of planks as a working platform. Note the buckets of resin. Note the open door on the building, so climate control wasn't deemed important. And this was less than 10 years ago.

 

[lw395]

My day job involves some forensic engineering into safety critical systems; I would find it very hard to prove that osmosis had ever sunk any vessel. Perhaps something for my retirement, investigating the impact of osmosis on the structural integrity of a hull following the sinking of a vessel, on the other hand I think I'll just go sailing

Yachts sinking at all is very rare.
Yachts sinking due to structural inadequacy rather than say collision rarer still.
A lot of yachts have some level of osmosis and resin hydrolysis, not many of them sink.

Some yachts do have structural problems.
Having the resin weakened by hydrolysis can only make any potential problems worse.

It would be pretty hard to prove that none of the boats where the keel has fallen off might have lasted longer if the resin had not suffered some degree of hydrolysis.

 

[fisherman]

I had extensive osmosis in my boat, over 26 years, the surveyors, 2001 and 2018 both said, OK, so what. Hull scantlings are enough to cope, the blisters were 10-12mm dia, but in general terms 90% or more of the gelcoat was still attached. It could legitimately have been spot repaired. However, I turned down a boat that has very small blisters as in the pic because they were absolutely everywhere and below w/l, the gel was largely detached, no cure other than a strip and recoat. The insurance company said they would rather a spot repair than strip, which could cause more trouble.
However, Hardman Jones in Gweek told me they had seen a boat scrapped because the blisters were big and the hull thin, depth of damage is related to diameter.

 

[JumbleDuck]

I too would be concerned about blisters appearing in the gel coat, as would any buyer looking to spend £250k+ on buying such a boat (that is roughly what they go for).

It was brushed; Northshore built so few boats that it was very much a "man with brush and bucket of resin" operation.

There are a couple of photos of Northshore's lay-up process in this blog - https://distantshores.ca/boatblog_files/moulding-the-hull-s49.php Note the rather precarious use of planks as a working platform. Note the buckets of resin. Note the open door on the building, so climate control wasn't deemed important. And this was less than 10 years ago.

Whistles thoughtfully. A quarter of a million secondhand, eh? Still, it looks a lot better than the Norfolk shed where Oyster had their hulls built.

 

[JumbleDuck]

Had the boat hauled yesterday and while cleaning her this morning, found a line of hundreds of little blisters along the waterline. The area is normally immersed in water.

Popped one of the blisters and a vinegary fluid came out. So im fairly sure it's osmosis.

I had something very similar on my aged Hunter, which I think was mostly a reaction between the original gel coat and a two-pack layer applied by a later owner. Vinegar smells and all.

 

[jwilson]

I had something very similar on my aged Hunter, which I think was mostly a reaction between the original gel coat and a two-pack layer applied by a later owner. Vinegar smells and all.

Looking at Ocarpop's older posts make it clear this is a 6 year old Southerly - and probably not in UK - neither were obvious from the original post. My original question remains though - are you QUITE SURE this is hull gelcoat, not a painted or sprayed stripe?

 

[pvb]

Looking at Ocarpop's older posts make it clear this is a 6 year old Southerly - and probably not in UK - neither were obvious from the original post. My original question remains though - are you QUITE SURE this is hull gelcoat, not a painted or sprayed stripe?

See post 8.

 

[johnlilley]

There is one more circumstance that does not seem to have been seen as a possibility. It has been known by a few very well known builders that the whole hull above the waterline was resprayed when new. to overcome problems with the cosmetic look of the gel coat such as lack of opacity due to lack of pigment mix, variance in gel coat colour etc.. This respray is usually some form of acrylic or polyurethane two pot and is often subject to blistering at the waterline some years later. If the blisters are just as prolific below the waterline then it could be a laminate problem but if the blistering is above the waterline only the consider the possibility of a previous total respray. When done well it can be almost impossible to detect a respray as against original gel coat. The vinegar smell is also present when this type of paint subsequently fails.

 

[JumbleDuck]

Looking at Ocarpop's older posts make it clear this is a 6 year old Southerly - and probably not in UK - neither were obvious from the original post. My original question remains though - are you QUITE SURE this is hull gelcoat, not a painted or sprayed stripe?

Exactly my thought

See post 8.

I'm not sure how that helps.

 

[lw395]

There is one more circumstance that does not seem to have been seen as a possibility. It has been known by a few very well known builders that the whole hull above the waterline was resprayed when new. to overcome problems with the cosmetic look of the gel coat such as lack of opacity due to lack of pigment mix, variance in gel coat colour etc.. This respray is usually some form of acrylic or polyurethane two pot and is often subject to blistering at the waterline some years later. If the blisters are just as prolific below the waterline then it could be a laminate problem but if the blistering is above the waterline only the consider the possibility of a previous total respray. When done well it can be almost impossible to detect a respray as against original gel coat. The vinegar smell is also present when this type of paint subsequently fails.

Yes, I've seen blistering of painted hulls just above the waterline.
If you pop a few blisters, it's normally pretty obvious whether the liquid is between the paint and the gelcoat, or under the gelcoat.
Is the hull below the waterline epoxied? If so a lack of blisters here doesn't tell us much.

 

[doug748]

......... If the blisters are just as prolific below the waterline then it could be a laminate problem but if the blistering is above the waterline only the consider the possibility of a previous total respray. When done well it can be almost impossible to detect a respray as against original gel coat. The vinegar smell is also present when this type of paint subsequently fails.

Interesting point, have you seen many boats affected like this? Would it be unusual to see it at only 6 years in? Thanks

 

[Concerto]

There is one more circumstance that does not seem to have been seen as a possibility. It has been known by a few very well known builders that the whole hull above the waterline was resprayed when new. to overcome problems with the cosmetic look of the gel coat such as lack of opacity due to lack of pigment mix, variance in gel coat colour etc.. This respray is usually some form of acrylic or polyurethane two pot and is often subject to blistering at the waterline some years later. If the blisters are just as prolific below the waterline then it could be a laminate problem but if the blistering is above the waterline only the consider the possibility of a previous total respray. When done well it can be almost impossible to detect a respray as against original gel coat. The vinegar smell is also present when this type of paint subsequently fails.

My brother has a Contest and I can confirm that the hull is painted and all Contests are painted. So this is a strong possibility. In my earlier post I had forgotten this information.

 

[pvb]

My brother has a Contest and I can confirm that the hull is painted and all Contests are painted. So this is a strong possibility. In my earlier post I had forgotten this information.

Does he have a white hull? Contests were moulded in white gelcoat, but many were painted a different colour.