Osmotic activity on a laid up boat?.

[megan]

When I bought my boat the survey noted "some general slight osmotic activity" on her hull, that was some five years ago. The boat has been out of the water for the last three years, although the hull has been exposed to the weather. So my question is what will have happened to the osmotic activity during the time she was out of the water, will the hull have dried out, or will the osmotic activity start where it left of when I launch her this year. <font color="blue">

 

[pvb]

Most likely outcome...

The most likely outcome is that osmotic activity will restart after launching. Whilst the boat was out of the water, osmosis wouldn't happen (it needs water on the outside of the hull). Any blisters evident 3 years ago may have decreased in size, but this is more than likely to be a result of moisture simply spreading within the laminate. However, remember that lots of boats have minor osmosis, and it's primarily a cosmetic problem - it won't result in sinking!

 

[Stemar]

Such knowledge as I have is purely theoretical, and gained from wandering around the net and talking to people, so don't take it as Gospel.

First the bad news:
The problem is that once blisters form, they will almost always contain styrene. If this isn't got rid of, it will draw water back in, so I would think the answer to both parts of your question is yes.

Now the good news:
Which was the last boat you heard of that sank or became structurally unsound due to osmosis? No-one I know is aware of one. Severe blistering - and the severity depends far more on the size of the blisters than their number - if left untreated can weaken the structure severely. However, this would be delamination, not osmosis and due to seriously defective materials or workmanship. Was it the last series of Swans that suffered from this and virtually had to have their hulls rebuilt under them?

Have a look at http://www.yachtsurvey.com/blisters.htm, then decide if it's worth doing anything about it at a later date, but I certainly wouldn't lose any sleep over anything a surveyor describes as "slight osmotic activity"

 

[Mudplugger]

Sorry, but you have given little info on your bio, to be able to make any firm reccs, but if the boat has been out of the water for the period of time that you say, then would suggest removal of antifouling, 3-5 coats of VC Tar Epoxy and new antifouling before you go back in. The surveyor's comment's sound more like back covering than constructive comment. HTH

 

[jonjo]

[ QUOTE ]
then would suggest removal of antifouling, 3-5 coats of VC Tar Epoxy

[/ QUOTE ]
This was my idea as well but I did not post in fear that the resident boat building pro thought police would arrive. Seems a shame not to take advantage of a dry hull.

 

[boatmike]

Very difficult to judge "slight osmotic activity" and I agree it could be a surveyor covering his posterior. I also don't believe in extreme action to correct minor problems. Can you actually see any blisters? Are they very localised?
One school of thought is that if you have now dried out and can't see any appreciable blistering then antifoul and relaunch and inspect again next year. Another would be to epoxy coat first to take advantage of the fact that you have dried out. If I could really not see any appreciable blistering the latter might be a way of arresting further blistering at this stage but I would certainly get the hull checked for moisture content first to ensure you are not sealing in the problem which can make it worse. Without inspecting it I would usually advise that if it aint broke don't mend it. Antifoul and launch and check next year...

 

[Birdseye]

To be pedantic - you cant have osmotic activity when one side of the osmotic membrane (the gelcoat) isnt in a water based fluid. So the only osmotic activity going on will be the very limited when the gel is wet due to rain etc, and in areas like the pads supporting the hull.

But if you have an osmosis problem, the hull will never dry out completely however long the boat is out of the water. Bit like a dish of salt left in the cabin, the liquid in the laminate / blisters is hygroscopic and will hold onto its water.

Apparently, most boats over 10/15 years old have some limited osmotic activity. But as long as its limited, its not fatal.

 

[BrendanS]

Osmotic activity will reverse, just like a pan of salt water left out to dry, the salt will dry out - that used to be how they manufactured salt. Any hull left out of water long enough will dry out.

However, osmotic 'activity' in hulls, is not true osmotic potential as used in pure scientific sense, as other things going on. Hulls will dry out though if left out of water long enough

Better things to be getting on with though, like sailing.

as has often been mentioned here. Boats don't sink from osmosis, it's purely cosmetic apart from a very, very, very few examples which are usually down to very bad layup where the actual integrity of hull was compromised from day one - not a normal problem