Boat with osmosis - buy or not?

[Rivers & creeks]

I wish I could buy a flipping boat with my head for once, so please just tell me to walk away. We have fallen for it though.

We wanted a nice big floating home for our obscenely long teachers' holidays o) and we found a beauty of a Colvic Watson 31.6 but on close inspection the hull has a number of blisters about the size of a 5p / 20p piece. They are just raised or swollen by no more than 3mm, when you crack one it smells of vinegar. I suppose if I had to guess I'd say there were about 50 or 60 on each side. The seller has been quoted £7000 to peel the gelcoat and reapply and epoxy coat, the yard is a large and reputable one. The issue is that I'm sure I've seen these things in the mags and people talk about grinding them out filling and all being well. Should I offer another £7000 off the price, and do a DIY job?

Or should I just leave it and find a boat that's not got "it"?

 

[sarabande]

try a PM to Caer Urfa of this forum. He is the archivist for the CW group, and what he doesn't know about CWs is not worth knowing.

FWIW, I had a CW 34 for 6 years. It's difficult to imagine the construction of th ehull being affected by osmosis, bcs it is so thick.


The 32 is fineboat, indeed, and masses of space. Which one are you looking at ? (I promise not to rush out an beat you to it !)

 

[deep denial]

The problem of osmosis is only in the sale, not in the ownership. So if you plan to keep the boat for a long while, don't worry about the osmosis, offer the 7k less, and use the reduction to get the boat fixed up buy someone like Hayling yacht co, who do a proper job, and you will have no problems

 

[Lakesailor]

I've had a couple of older boats with cosmetic osmosis (isn't it all?).
As has been suggested, the Colvics are so massively built that it's just a matter of you being happy enough knowing it has it. It won't sink or degrade.
Not sure the Watson would be my choice, but if it was, and cheap enough, I would go for it.
I usually would say run away, there are plenty of boats available, but on this occasion I would probably be wrong.
The only thing to consider is that the treatment could last a fair while and you will have paid for a boat you can't use.
Still, 20p size blisters are not the end of the world. Maybe use it for a year or two and monitor the development whilst trousering the reduction in price.

 

[curlysue]

If the boat is everything you want then reduce whatever your offer was by £7000 and if it is accepted ( which I would be surprised if it wasn't ) get the hull sorted by a reputable yard. You will have a boat with a better hull than you originally thought you were looking at. You could also consider have it coppered while its out the water as this would save on anti fouling for a few years. If they don't accept walk away.

 

[Deleted member 36384]

Have It Fixed At A Reputable Yard

I would not grind them out and DIY it as the blisters may just be a surface indication of a more serious problem. Although many folks state that Osmosis is "just cosmetic" it can be quite serious. If the boat is a proverbial Friday boat then the GRP cloth may not have been wet out properly at layup and their could be deeper, more serious defects with the laminate. Further, you may find that more develop after you have spent all this time fixing what you now see.

If you wish to buy obtain the services of a reputable surveyor who understands Osmosis. Get an independent check on the hull condition and a price to rectify it from your surveyor. There is no point on taking on a known problem that is expensive to fix based on the sellers Opinion.

If it was me I would have the job done by a reputable yard for these reasons: it fixes the problem once and for all, DIY will be a much bigger and longer job than you think, its likely to be the fastest way onto the water, you can enjoy the boat not worrying about future blisters. The last reason is the most important, after all I assume you are buying it for leisure purposes.

 

[Monique]

My 2p's worth.....

Osmosis will happen to every GRP boat in the world. Including Swans, HR's and Island Packets. This is because GRP is not water proof as most people think and water infiltrates the layers accumulating in the air bubbles present in the medium.

No boat has ever sank because of it. It is an annoyance which once treated properly will be a thing of the past.

A mate had his 45 ' Swan treated twice. (The initial repair was poor). He was quoted as much as EUR 18000 and eventually gave the second contract out for EUR 4500 to a local firm with more cost sense. This was done 4 years ago and no problem since. Nor, in my opinion, likely to happen again.

I followed the process as I live near the yard where it was done.

The repair is done by drying out the boat for an extended period, checking moisture levels all over the hull periodically. A special hygrometer is used. Then the offending areas are marked and either ground or blasted down to the sound substrate. The rest of the hull is sanded down and epoxy is laid over the entire hull below the water line.

This is sanded again to give a smooth finish and your anti foul is applied. The epoxy if done slowly at the correct temperature, is far more "waterproof" than fibreglass. You may note that your boat will float considerably higher when you get her back in the water...... to emphasise the amount of water present in the hull before drying out. This was the case here and it was very noticeable. (He won many subsequent regattas and claims the long dry out has given him an edge)

Get the discount, get the job done in the future and enjoy your CW. Fair winds

 

[Deleted member 36384]

Water Saturation and Significant Weight Loss After Drying Is A Fallacy

.... You may note that your boat will float considerably higher when you get her back in the water...... to emphasise the amount of water present in the hull before drying out.

This is a fallacy which is common. The permeability of the polyester matrix is so small that that the relative absorbed water weight is tiny compared to the GRP laminate. Further the majority of the weight of boat is contained in the ballast, hull above the water line, fittings and rigging. The hull below the water line is but a fraction of the total weight. Proportionately it can only ever add add a small increase in weight.

Think about this example. Do you really believe that you could squeeze the equivalent volume of say 2 tins of antifouling, for example, into the GRP laminate without some major voids in the laminate. What weight is in 2 tins of antifouling? Not enough to make a Gnats fart of a difference. The actual volume of water molecules is tiny.

The scenario that you claim happened would have to have a permeability equal to that of a sponge. Its not physically possible to have a noticeable weight difference due to drying out only.

There is quite a bit of explanation behind the science of this fact if you want to look for it.

One explanation for his speed increase is that the underwater surface was faired smoother than the pre treatment hull.

 

[Rivers & creeks]

I'm a bit confused by the replies, assuming the little blisters are not deep, why not grind, dry and fill? Am I missing something that makes that a pointless exercise? Preliminary info suggests she has been continuously in the water for at least 6 years with no winter lift and dry outs. Having said that, she was only launched in 1991. She was built in 1980 so before the days of isophthalic resins.

 

[ghostlymoron]

Why buy a boat with a problem. There are plenty of boats for sale out there. What's special about this one. Walk away is my advice. You'll find another and not have lengthy and expensive repairs.

 

[Poignard]

Should I offer another £7000 off the price, and do a DIY job?

Offer £10,000 less and go sailing.

 

[Phideaux]

I'm a bit confused by the replies, assuming the little blisters are not deep, why not grind, dry and fill? Am I missing something that makes that a pointless exercise? Preliminary info suggests she has been continuously in the water for at least 6 years with no winter lift and dry outs. Having said that, she was only launched in 1991. She was built in 1980 so before the days of isophthalic resins.

As I'm intending to buy a boat that, unfortunately, has some osmosis blisters that require treatment, I'll quote a statement that appears to sum up the various articles that I've read on the subject. Obviously, there are various vested interests at work in both camps, but I don't think the problem will necessarily be cured just by treating the existing blisters; you may find that they start appearing elsewhere. At the very least, you need a good surveyor to check the moisture levels throughout the hull.

"Contradicting earlier theories, the damage from “osmosis” is not caused by excessive water permeation. There are absolutely no osmotic forces involved as the gelcoat is an absorbing material which can never act as an osmotic membrane! Instead it is the process of hydrolysis, which creates the water soluble corrosive products which in turn create the familiar cavities. (Hydrolysis is the general term given to the reaction of any material with water, for example organic compounds like polyester resin, itself the main constituent of GRP laminates.)

Once the cavities have formed, then excess water will enter giving rise to high moisture readings. This process may normally be slow, but the presence of free acids or alkalis will greatly accelerate it.

The first point to note is that it is the phthallic acid, formed in the process of hydrolysis of polyester resin, which causes the chain reaction and subsequent laminate damage, not the water! The acid forms as water insoluble crystals and cannot be washed out of the laminate as claimed by some. Even after years of hard-standing and weekly washes, the acid will remain in the capillaries and cavities, fixed in styrene and glycol. However, water will react with PVA binders in the laminate, reducing them to acetic acid. It is this that gives the strong smell of vinegar when blisters are burst. Even so, it must be noted that the laminate can become severely damaged before any warning blisters appear.

Osmosis blisters are not only a cosmetic problem. They are the visible sign that the hydrolysis of the polyester has affected at least one laminate layer.By the time the first blister shows, hydrolysed alkali products will have reduced the bond between fibre-glass and polyester deep in the laminate below the water line! This in turn, will have caused a 20-30% loss of structural strength which no “dry and shield” treatment can restore. Without a proper treatment large parts of the laminate layers will sooner or later have larger areas of polyester hydrolysed with only soft wet fibreglass left."

I'd be delighted to find out this was all b*****ks as it would save me about £7k too.

 

[fastjedi]

A less expensive route to fixing the hull is to find a dry grit blaster with the right touch. This will remove all affected areas of gel coat..... leave to dry over an extended period + damp readings to monitor progress ..... then epoxy fill and epoxy coat the hull

 

[Mark-1]

As I'm intending to buy a boat that, unfortunately, has some osmosis blisters that require treatment, I'll quote a statement that appears to sum up the various articles that I've read on the subject. Obviously, there are various vested interests at work in both camps, but I don't think the problem will necessarily be cured just by treating the existing blisters; you may find that they start appearing elsewhere. At the very least, you need a good surveyor to check the moisture levels throughout the hull.

"Contradicting earlier theories, the damage from “osmosis” is not caused by excessive water permeation. There are absolutely no osmotic forces involved as the gelcoat is an absorbing material which can never act as an osmotic membrane! Instead it is the process of hydrolysis, which creates the water soluble corrosive products which in turn create the familiar cavities. (Hydrolysis is the general term given to the reaction of any material with water, for example organic compounds like polyester resin, itself the main constituent of GRP laminates.)

Once the cavities have formed, then excess water will enter giving rise to high moisture readings. This process may normally be slow, but the presence of free acids or alkalis will greatly accelerate it.

The first point to note is that it is the phthallic acid, formed in the process of hydrolysis of polyester resin, which causes the chain reaction and subsequent laminate damage, not the water! The acid forms as water insoluble crystals and cannot be washed out of the laminate as claimed by some. Even after years of hard-standing and weekly washes, the acid will remain in the capillaries and cavities, fixed in styrene and glycol. However, water will react with PVA binders in the laminate, reducing them to acetic acid. It is this that gives the strong smell of vinegar when blisters are burst. Even so, it must be noted that the laminate can become severely damaged before any warning blisters appear.

Osmosis blisters are not only a cosmetic problem. They are the visible sign that the hydrolysis of the polyester has affected at least one laminate layer.By the time the first blister shows, hydrolysed alkali products will have reduced the bond between fibre-glass and polyester deep in the laminate below the water line! This in turn, will have caused a 20-30% loss of structural strength which no “dry and shield” treatment can restore. Without a proper treatment large parts of the laminate layers will sooner or later have larger areas of polyester hydrolysed with only soft wet fibreglass left."

I'd be delighted to find out this was all b*****ks as it would save me about £7k too.

I think Fibreglass Boats by Hugo Du Plessis is essential reading on this topic.

From memory he would agree with "There are absolutely no osmotic forces involved".

 

[Phideaux]

A less expensive route to fixing the hull is to find a dry grit blaster with the right touch. This will remove all affected areas of gel coat..... leave to dry over an extended period + damp readings to monitor progress ..... then epoxy fill and epoxy coat the hull

The advice from one of the main researchers in the areas of cause, effect and treatment recommends the following (he's Swedish so sometime the English is a bit odd):

"When such a treatment is too expensive in relation to the value of the boat, our experience is: Do not watershield, just sand eventually blisters open once a year and apply antifouling only. This will retain de-laminations and the softening of the hull for much longer than an epoxy coating!"

Have a look at http://www.osmosisinfo.com/

The reference to "watershield" is I think means an epoxy coating. It might be utter bunkum, but I've not read anything that doesn't sound plausible (and my knowledge of science is reasonably good).

 

[Phideaux]

I think Fibreglass Boats by Hugo Du Plessis is essential reading on this topic.

From memory he would agree with "There are absolutely no osmotic forces involved".

As a biological scientist I'd agree. For osmosis you need a semi-permeable membrane and an osmotic potential across it.

What we have is water being slowly absorbed by the gel-coat, contacting the underlying fibreglass and resin which contains un-reacted styrene. Fibreglass laminate can contain 10-15% uncured and not totally cured polyester resin. Such uncured resin can be transformed into its original acid-alkali-glycol substances by adding of a few water molecules and forms pthtallic and acetic acids. Where this happens at the surface of the laminate, directly below the gel-coat, the acetic acid has a greater volume/pressure than the surrounding gelcoat and so pushes up blisters. As well as pushing blisters up, it probably also pushes down further into the laminate. This also forms a route for further water to penetrate, react with styrene deeper in the laminate, build up pressure within the laminate etc etc etc...

 

[doug748]

I'm a bit confused by the replies, assuming the little blisters are not deep, why not grind, dry and fill? Am I missing something that makes that a pointless exercise?

This is exactly what a pal of mine did and he has a super boat which he bought very cheaply.

If, after several seasons, you are still: digging them out and filling them in, then you might consider stripping the hull. On the other hand things might stabilize and you can Gelshield over the lot and forget about it.
Either way, as Parsival has said, the key is buying at the right price. Oh, and keeping the boat a good while, if you need to resell quickly prospective buyers will have the same doubts as you.

 

[Lakesailor]

So according these various theories the substrate is damaged by Osmosis (for want of a better description).
Does this mean that contary to common belief boats have sunk as a result of Osmosis?

I like the advice of just digging out and filling blisters instead of spending the value of a small car on a repair.
No doubt the vested interests of boatyards and osmosis treatment specialists will disagree.

 

[Boo2]

Hi Phideaux,

"Contradicting earlier theories, the damage from “osmosis” is not caused by excessive water permeation. There are absolutely no osmotic forces involved as the gelcoat is an absorbing material which can never act as an osmotic membrane!..."

I think this must be c0ck. Whether or not the gelcoat is absorbing or not, the reason the water forms blisters is because the pressure in the blister is high enough to burst the gelcoat and laminate layer(s) beneath it. This pressure can only be osmotic, and the following statements about the concentration of acidic compounds only serve to confirm that.

"...Instead it is the process of hydrolysis, which creates the water soluble corrosive products which in turn create the familiar cavities. (Hydrolysis is the general term given to the reaction of any material with water, for example organic compounds like polyester resin, itself the main constituent of GRP laminates.)

Once the cavities have formed, then excess water will enter giving rise to high moisture readings. This process may normally be slow, but the presence of free acids or alkalis will greatly accelerate it...."

Water will only accumulate within the cavities if there is room for it. Osmotic pressure will cause it to make room for itself if there are compounds it can disolve so causing an osmotic imbalance.

To recap : blisters can only form if the water pressure in the cavities in the moulding is higher than the strength of the gelcoat / laminate.

I don't think Mark-1 has the quote "There are absolutely no osmotic forces involved" correctly attributed. Whether it is or not the statement is plainly wrong, otherwise how could blisters form ? To see that blisters are caused by osmosis you only need to consider a boat which is moulded but never launched.

I second the recommendation for Hugo du Plessis's book, he is an acknowledged expert and runs a yacht surveying / fibreglass specialist company. There's a copy of the previous edition in the Brighton Library if you'd like a gander. Don't read the chapter "replacing a gel coat" until you've read the chapter "Can the gel coat be saved".

HdP is one of many people around (eg on the web), who recommend individual grinding back of blisters (up the the several hundreds mark) in preference to replacing the gel coat. This is something that can be done by the owner. His remarks about cowboys removing glassfibre up to an inch deep by the enthusiastic application of sand blasters makes that seem preferable even if you have to do some every year.

..."I'd be delighted to find out this was all b*****ks as it would save me about £7k too.

I'd get it surveyed and decide after that. HdP is in Lymington so he might even survey it for you, assuming he's still in the business.

Hth,

Boo2

 

[Boo2]

As a biological scientist I'd agree. For osmosis you need a semi-permeable membrane and an osmotic potential across it.

What we have is water being slowly absorbed by the gel-coat, contacting the underlying fibreglass and resin which contains un-reacted styrene. Fibreglass laminate can contain 10-15% uncured and not totally cured polyester resin. Such uncured resin can be transformed into its original acid-alkali-glycol substances by adding of a few water molecules and forms pthtallic and acetic acids. Where this happens at the surface of the laminate, directly below the gel-coat, the acetic acid has a greater volume/pressure than the surrounding gelcoat and so pushes up blisters. As well as pushing blisters up, it probably also pushes down further into the laminate. This also forms a route for further water to penetrate, react with styrene deeper in the laminate, build up pressure within the laminate etc etc etc...

Well, istm you have described osmosis.

The gel coat allows water molecules through without permitting the solute back out so it is acting as a semi permeable membrane despite appearances to the contrary.

Boo2