Osmosis

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tim_j_odonnell

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Just had a chat with the surveyor of the boat I currently have an offer on, he wasn't all that enthusiastic, one major point being high moisture readings in the hull

The boat's a 1986 22' Newbridge Venturer, I am wondering how to interpret the survey results - is this to be expected in a boat this age or should I consider walking away from the sale?

And in terms of treating it - my surveyor mentioned it might not be necessaryu to do the whole gel-strip thing, just to epoxy it - does anyone have experience with this?

Thanks
Tim
 
You have either misunderstood your surveyor about epoxy coating a wet boat, or he isnt very good. All you will do with an epoxy coat on a wet boat is seal the water into the laminate, which will continue to deteriorate. Bit like painting wet wood to stop it rotting.

A boat in what I guess is that price bracket probably wont be worth treating at a yard. But its not impossible to do the treatment yourself.

Personally, having been through the aggro and delay (thats the bit that really gets you) of 2 osmosis treatments, I would walk away
 
I had the same thing 3 months ago with a 1984 Voyager. The surveyor was getting highish moisture readings, but he commented that there may be other contributing factors as the boat had been kept in the water for the last 2 years, with only 1 weeks lift last summer, also the temperature on the day was very cold (probably not in your case) and the boat was only lifted for an hour and then refloated so it never had a chance to dry out (especially because of the ambient temperatures). However, my surveyor was positive in discussions about the boat. I had a full discussion with him while he was doing the survey. You've just got to take your surveyors advice, he's the expert and that's why your paying him. You could, of course, use this to get a reduction in the price to cover the potential cost of sorting the problem
 
Depends how much you're paying. This issue has had quite a few threads and the concensus seems to be that if it's cheap and cheerful and you don't want to sell it on too quickly, put up with it. Most boats this age have some osmosis and as others on here have said (including a surveyor) "how many boats have you heard of sinking as a result of osmosis?"
My boat has it, it's on fresh water all the time. I'm not worried.
Given a choice, and you do have a choice, I would look elsewhere. But be wary of lift-out and surveyors' fees building up. You could still end up with a dear boat.
 
It seems clear that osmosis in GRP boats can be a problem.

Can anyone explain why GRP water tanks , sewerage systems etc. which are never away from water are not troubled by the problem ?

Just curious.
 
I think you'll find GRP water tanks are affected quite badly by osmosis. I know of several owners who have had to line/replace GRP tanks when the water started tasting of styrene. Nobody drinks sewage so nobody notices and it's not a terminal illness anyway.
 
I had in mind drinking water tanks and underground systems subject to building control approval and wonder wether its a quality control problem which baths and jacuzzis along with boats may not always be subject to.

I have seen corner cutters add all sorts of filler to extend grp mouldings and cut costs. Should there be some sort of standard for marine equipment as there is in other fields ?
 
Most spas are made from acryalic which like gel coat will absorb water through it most good spas are backed up with a vynil ester epoxy backing to stop the water there and the bulk of the rest of the lay up is a polyester resin, most new boat manufacturers will now use a epoxy first coat or at the very least an isothallic resin after the gel coat.
 
When I bought my 1964 built Invicta and had a survey for insurance purposes, the surveyor reported high moisture readings but there was no sign of blistering below the waterline. I decided not to worry as the hull had been properly epoxied.

As far as I can see any worries would be groundless as the hull appears to be the same as the day I bought it.

As one poster above says: No boat has ever sunk throught osmosis.

In my humble opinion, far too much fuss is made of osmosis as though it was cancer and incurable. If the only problem is a high moisture reading but no blisters, surely this is the best that can be expected for a boat of that age.

Bob
 
Our hot tub (Jacuzzi is such a crass term by commoners /forums/images/graemlins/grin.gif) has now been running for 5 years non stop. Not a jot of damage to the gel coat, nothing.

It is not shiny or glossy like a boat in fact it is pitted to give grip under foot. I wonder if this might be the difference.
 
Here is an exert from http://www.yachtsurvey.com/moreonblisters.html.htm



If you're old enough, you may remember a time in the 1960's when every gas station in town seemed to be digging up their tanks and replacing them with fiberglass. That's because leaking gas tanks mean big trouble. But then there was a period when they were digging them up again, this time to replace leaking tanks caused by blistering of the tanks. Interestingly enough, the first fiberglass tanks that were built did not leak. But then the cost of the plastic resin was high and the tanks expensive. Naturally, to reduce the cost, cheaper resins were developed and sold. So now the trouble begins.

By the mid 1960's tank manufacturers found an agreeable compromise. They would use the high quality resin on the outside of the tank (the part exposed to ground water) and the cheaper resins for the inner layers of the laminate, hence the term "tank coat." A decade later, the plastic pool and spa industry encountered the very same problem and solution. Unfortunately, when applied to boat building, tank coating generally causes more problems than its worth. It makes the process of layup more complicated and prone to error. When only a limited number of boats in a builder's line develop blisters, it is the result of an error, i.e. the lay up crew using the wrong resin.

Follow the link it makes good reading

Dave
 
First class report David.

The most valuable and pertinent part seems to be :-

"If a hull is 5 years old or more and has no blisters whatever, there's about a 95% probability that it never will. If it has even one blister, the chances are very high that it will continue.".

It also sounds as though construction resins should be classified as suitable for contact with water if buyers are to have confidence in the boat building industry. It would be unfortunate if British boat building went the way of the car industry.

Where does the insurance industry stand in this ?
 
I thinkanother important point made in the link is:

Quote

No, the moisture meter isn't going to tell you whether a boat is likely to get blisters or not simply because most boat hulls are saturated with water. The reason why some blister and some don't is basically a matter of quality materials and good techniques. Even when saturated with water, quality hulls are far less prone to blistering.

Unquote
 
not all boats develop osmosis - not all hot tubs or jacuzzis develop osmosis. Depends on manufacture, materials, and conditions. However, jacuzzis were well know for developing osmosis, perhaps things have moved on with better materials
 
[ QUOTE ]
First class report David.

The most valuable and pertinent part seems to be :-

"If a hull is 5 years old or more and has no blisters whatever, there's about a 95% probability that it never will. If it has even one blister, the chances are very high that it will continue.".

It also sounds as though construction resins should be classified as suitable for contact with water if buyers are to have confidence in the boat building industry. It would be unfortunate if British boat building went the way of the car industry.

Where does the insurance industry stand in this ?

[/ QUOTE ]

I'm no expert, but have a science background so I did try and research the problem when I had it. What I learned was that the blisters are the symptom not the problem - just like spots when you have measles. The problem is the development of a soupy solution of nasties that softens the laminate in patches. So if you have an old laminate from the early days where the gel is particularly porous or micro cracked, you can still have little pockets of this soup in the laminate without having blisters.

The nasties arise because some of the constituents of the resin and the coating on the glass fibres are water soluble, not helped by the difficulty of getting a thoroughly catalysed reaction when the catalyst is just a few percent.. In other words its inherent in the use of ortho poly resins but made worse by bad workmanship. Any and every ortho poly boat will get the pox - its a matter of the exposure, the workmanship and time.

And the British boatbuilding industry has gone the way of the car industry already.
 
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