When is osmosis bad

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boaterbaz

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When do you have to worry about osmosis? Armchairsailors thread on a good buy got me thinking, at what point does osmosis become a problem. I own a 1973 grp yacht, suppose that tomorrow i notice blisters on the hull. How quickly will the hull deteriorate before it becomes a problem and given the value of the boat it could be more economic for the boat to fall to bits rather than treat the hull. I dont know the answers but your thoughts would be appreciated. ps This is a bit tongue in cheek as Drumheller is a part of the family and not an asset like my rapidly devaluing car.
 
I believe that if there is no sign of it now after nearly 40 years in the water, it is probably never going to happen. Having said that I have owned two boats that did have a small amount of blistering. Minor treatment of the blisters and a winter ashore solved it in both cases.

There seems to have been huge over-selling of treatment for osmosis. In many cases it would appear that a more sensible and economic approach is perfectly adequate. As has been said many times 'no boat ever sunk due to osmosis'. Someone will prove me wrong now but I doubt if more than a handful of such severe cases has ever been reported.
 
From what I've gathered, all boats absorb water by osmosis, but this doesn't lead to blistering in all cases. When it does lead to blistering, any blister larger than a saucer is likely to compromise the integrity of the vessel
 
The usual comment to this is "I've never known a boat sink from Osmosis"

An odd blister here & there is a minor irritation to fix & you may end up with a boat that loooks as tho it has chicken pox or having to paint it. Fixing blisters doesn't stop more coming thro elsewhere (if there are problems elsewhere).

Once it starts, it probably isn't going to go away without drastic, complete boat (ie commercial) treatment which will cost around 5-10k, and even then the "guarantees" are very carefull worded to make claims unlikely to succeed.

Weakening of the hull would require de-lamination of fairly large areas - it is still repairable, but the cost escalates.

Time from 1st blister to serious delaminiation will be at least several years, & possibly several decades.
 
Well others have told you how unlikely terminal osmosis will be, you ask the question what if you were to find it on your boat. Repair it would be my answer. Because if you just let it deteriorate and then get another boat, who's to say that wont get osmosis as well?
 
boaterbaz said:
When do you have to worry about osmosis?
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When you sell it.

The blisters that you see are generally small (a few mm) and are present only in the outer layer. How much effect would a hole a few mm in diameter have on the structural integrity of the boat? Answer=None.

So your worry is "how long before a blister becomes a leak?" Well, the blister only affects the first layer of the laminate, and as it has taken several years to become a blister (and probably a bit more to become a hole) it will take several more years to become a hole in the second layer. And then it will take several more years to become a hole in the third layer.... etc. And when it finally does become a hole all the way through -- how difficult will it be to mend a small hole ?
 
timbartlett said:
So your worry is "how long before a blister becomes a leak?" Well, the blister only affects the first layer of the laminate, and as it has taken several years to become a blister (and probably a bit more to become a hole) it will take several more years to become a hole in the second layer. And then it will take several more years to become a hole in the third layer.... etc. And when it finally does become a hole all the way through -- how difficult will it be to mend a small hole ?
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B...b...b...but...hydrolosis! voids!! peeling! drying!! bagging!!! MONEY!!!!!
EVERYBODY PANIC!!!!!!!!!!!!!!!!!!
 
Hmmm...so far very sensible comments. There's usually more bollux talked about osmosis than Bavarias :). Can't add anything more useful than has been said above...so I'll shut up.
 
How serious is osmosis?

Surface or gelcoat blistering is not a structural problem. It is a problem for perceived value though.

Osmosis can cause significant delamination, but in my experience this is rare. The thinner the hull, the more significant the structural deterioration.

If the boat is cored, the laminate is very thin and therefore inter-laminate blistering effects the structural integrity of the hull to a much greater degree. Also moisture can penetrate and degrade the core. Any moisture in the core may be very difficult to remove, and hence could seriously effect the cost of repair.
 
A friend has a Sadler 29 with osmosis and I once ( with his permission) explored one of the blisters with a small screwdriver. What came out was a soft mush and I didnt hit solid GRP until about 5 mm into the laminate. So my guess is that untreated blisters will eventually penetrate the hull depending on thickness and needing a lot of time to get there. But it will happen and indeed I once saw a piccie by Staton-Bevan ( a very good and well established surveyor) showing a bad osmosis blister with a screwdriver going right through the hull.

People will tell you that no boat ever sank from osmosis, but then would you tell your insurance company that osmosis was the likely cause when this would make you uninsured? Of course you wouldn't.

But it does seem to be a pretty slow process in the cold salt waters round the UK so personally I worry rather more about leaky deck fittings, and balsa sandwich decks.
 
I think by the time a boat had sunk through osmosis it would have been uninsurable for many other reasons...:D!

When I look at some of the unused / unloved "hulks" lying around in my area, and indeed anywhere where moorings are relatively cheap, half of them should have sunk years ago, as I suspect they all have osmosis blisters somewhere if not full "bubble-wrap" hulls. I think it's time we all got realistic about this and not perpetuate the urbans myths.
 
I doubt if you will get any Osmosis in Drumheller.

Its very dry there most times of the year, and the Red Deer river is never more that a couple of feet deep at best.
 
Ubergeekian said:
Does your policy exclude sinking from osmosis? Mine doesn't even mention it.
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Doesnt need to. Apart from specific "perils" mentioned in the contract, your insurance policy covers you against accidents. It doesnt cover you against poor maintenance or long term deterioration of the fabric of the boat. If you doubt that, ask your broker.
 
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