what exactly is osmosis and how worried should I be?

[galeus]

I have a fibreglass boat that is currently being repainted at a boatyard.
Early on in the process after antifoul had been removed, moisture readings were taken at various points around the hull and I was advised that readings were high (off the scale) in some places, but Ok in 60/70% of the hull. The hull had many small to medium repairs to it from previous to me work. I have owned the boat for 21 years, which apparently could have seen previous osmosis repairs.
We have always had water in the hull which I have tried halfheartedly to get to the bottom of, but have never agonised over.
The hull has been drying for over a month now after being grit blasted and their is no evidence to my eyes of osmosis as I understand it; ie blisters, or softening, both in the hull or the exterior.
I have opted to not have any osmosis repairs done (about £7,000) and told them to reantifoul it.
The boat is a Colvic Northerner 26'6" and was built in 1984.
I told the chap dealing with me that I have never and still not seen osmosis type blisters or noticed any hull softening, (which drew no comment), so is this still called osmosis and if so do they always require attention?

 

[Scotsailor]

I wouldn’t consider doing anything other than finishing the repainting. Launching. And then going sailing.

 

[Brentwales]

I bought a 1984 boat that wouldn't sell because it was found to have osmosis. I got an absolute bargain and a lovely boat fitted with so much brand new kit. On having the boat lifted out myself for the first time I can see some small blisters about as wide as my thumb. The hull is solid and the bilge has remained nice and dry throughout its time on my drying mooring. The boat is close to 40 years old and has been fantastically looked after.

I'm not bothered at all and you shouldn't be either. There is so much scare talk about osmosis, if the blisters were sizes of dinner plates and parts of the hull felt spongy, I'd understand. I'll be Epoxy priming mine, applying two coats of anti foul and then relaunch, not to have her pulled out for the next 2 maybe 3 seasons.

The only thing to be conscious about is meeting your insurance conditions if you want fully comp, alternatively third party is very accomodating on older boats for liability purposes.

 

[JumbleDuck]

Osmosis is a process whereby an imbalance of fear across a knowledge barrier causes money to flow from the high fear to the low fear side. A barrier coat of information can be used to block the flow and end the problem.

 

[Bobc]

No, you shouldn't be worried. Put it back in the water and forget about it.

 

[lusitano]

Hulls can absorb water from the inside too, so that could account for the high readings in your case. Tracking down and fixing the problem would do no harm
I,d not worry too much about it though, most fibreglass hulls have some level of moisture.
I remember reading a Yachting World article many years by International Paints. They had taken core samples from a yacht"Joshua", one of the earliest fibreglass yachts ever built.
The hull had osmosis and lab tests proved that moisture had been in the hull from the time it was built.
In their opinion, over the years, no degradation or weakening of the structure had taken place as a result of "osmosis"

 

[fisherman]

And a wooden boat will have moisture in the hull, and would probably sink if it dried out.
Blisters are like mushrooms, width a measure of depth. There have been cases where the hull was so lightly built and the blisters so large and prevalent that it was scrapped, according to my local osmosis repair chap, but very rare.

 

[Refueler]

I used to be asked to meter boats ... and "lusitano' coment about water on inside is actually more relevant than many people appreciate.

Various boats - I asked owners if they had ever been flooded ... had standing water in bilge etc. My meters - I have two .... would go off scale when it found damp bulkheads ... standing water even if pumped out ...
One boat in particular - guy had owned for quite a few years and said - no it had never been flooded. I was sure it had as I could tell him where the bulkheads were by my meters ... he was still friendly with previous owner and telephoned him while I was there ....... year before he bought the boat - it had been part filled with rainwater while ashore ...

OK ... back to OP's question ...

The hull has been drying for over a month now after being grit blasted and their is no evidence to my eyes of osmosis as I understand it; ie blisters, or softening, both in the hull or the exterior.

My concern here is that you Grit Blasted the hull ..... depending on the level and intensity of blasting - it may have affected the overall gel coat ... as this is one of the methods used to remove / open up blisters / wicking for drying out - prior to applying a new epoxy shield. If the blasting was light to just remove old Anti-foul - then there really is no reason to carry out Osmosis treatment. I might use an epoxy based two pack preparation coat on the hull before any primer / antifoul if it was mine ...

OK .. the Colvics are heavy and sound boats ... the likelihood of Osmosis causing trouble is extremely limited - to be fair to say - go sail and enjoy the boat. The layup is heavy, its built like a tank ...

My boat built in 70's has high readings ... I have odd very small patches that gel has 'popped off' ... so I got the pressure washer ... gave them a good spray after making sure that I had the whole faulty gel off. Let dry - then filled with Epoxy putty. Sanded back ... When she gets lifted - I have close look at them and rest of hull for further ... nothing ... all fine.

 

[galeus]

Thanks for your positive replies. I have read them out to my wife, who might think I am a bit Gung ho at times

 

[Dan Tribe]

A few years ago, just the mention of osmosis would strike fear into people's hearts.
A prospective buyer of a neighbouring boat asked me for an opinion on a problem. Outside, the bilge showed hairy fibreglass mat and a hole you could stick a finger through. Inside we found a rusted through can of Nitromors which had eaten through the hull. He was reassured because it was OK, it's not osmosis.

 

[europe172]

Osmosis is a process whereby an imbalance of fear across a knowledge barrier causes money to flow from the high fear to the low fear side. A barrier coat of information can be used to block the flow and end the problem.

Best description I have ever read , ?

 

[Stemar]

He was reassured because it was OK, it's not osmosis.

And because it's GRP, as long as you can get to both sides, not hard to repair.

Jumbleduck has the right of it. Yes, it can be a problem on a lightweight hull with a seriously faulty layup, but we're talking about deep, dinner plate sized blisters, not the 10p or less blisters that many boats have and many boatwrights have got rich on.

 

[Dan Tribe]

And because it's GRP, as long as you can get to both sides, not hard to repair.

Jumbleduck has the right of it. Yes, it can be a problem on a lightweight hull with a seriously faulty layup, but we're talking about deep, dinner plate sized blisters, not the 10p or less blisters that many boats have and many boatwrights have got rich on.

Yes I suppose you're right. This was a Hurley 18 so probably a pretty bullet proof lay-up. But I was amused that he was undaunted by having a gallon of paint stripper laying in the bilge, but terrified at the thought of osmosis.

 

[kolyrojer]

I wouldn’t consider doing anything other than finishing the repainting.

 

[V1701]

With all due respect spending 7 grand fixing what may or may not be osmosis on a 40 odd year old 26 footer would be bonkers in anyone's book. The guy you're dealing with knows this, he's trying it on, frankly I would not trust a word he says. Antifoul your boat & go enjoy...

 

[Hoist]

as far as I'm aware a boat has never sank with Osmosis

 

[Mark-1]

Agree with the bulk of the comments - relax.

If you (or your wife!) want it from a more authoritative source:

Fibreglass Boats: Construction, Gel Coat, Stressing, Blistering, Repair, Maintenance: Amazon.co.uk: Hugo Du Plessis: 9781408122747: Books

 

[snowbird30ds]

as far as I'm aware a boat has never sank with Osmosis

Plenty of boats have sunk with osmosis, but not of osmosis.

 

[Caer Urfa]

You say the boat has now been grit blasted? I assume you mean sand blasted,
So you now have a clean hull, I would not just apply antifoul direct now but do a good job and apply some osmosis prevention coatings such as International Gelshield 200 then a primer then 2 x antifoul.

That way you are doing your best to protect your hull

 

[LadyInBed]

If you want to do some reading, you can download http://montymariner.co.uk/wp-content/uploads/2014/02/Osmosis-handbook-9a.pdf from my website.