Estimated cost for osmosis preventative treatment

[MattS]

Hi there, I'm about to purchase a yacht (between 28 - 31ft depending on what I settle on!) and have been trying to find something online to help me understand an order of magnitude cost for preventative osmosis treatment. Some of the vessels I'm looking at don't have an osmosis problem yet, but are over 30 years old and haven't had any kind of preventative treatment.

I know it's hard for someone to answer "How much would it cost?" so I'd also take advice on how what I could do / where I could go to get a rough quote / idea of cost? I'm in Kent so any recommendations for companies that do the treatments would also be good!

Thanks for your help

 

[Slowboat35]

If a boat hasn't had 'preventative' treatment and has managed 30 years without it I'd suggest it clearly doesn't need it, so why bother?
If a boat has osmosis and it isn't serious just ignore it. No boat has ever sunk from osmosis afaik. If one has severe osmosis just walk away.

 

[Carib]

There's a very helpful write up on this and related issues on the Yachtsnet site (also take a look at the Yachtsnet archive pages for boat model info, if you haven't found them yet!).

 

[pvb]

Welcome to the forums!

As Slowboat35 pointed out, this shouldn't be a priority for you. There are lots of other things to spend your money on (as you'll rapidly discover!).

 

[Easticks28]

If a boat hasn't had 'preventative' treatment and has managed 30 years without it I'd suggest it clearly doesn't need it, so why bother?
If a boat has osmosis and it isn't serious just ignore it. No boat has ever sunk from osmosis afaik. If one has severe osmosis just walk away.

But many have sunk with it. I was told this 16 years agowhen I purchased my current boat. It comes out each winter from November until around Easter. The mild osmosis of those days has now largely gone. I can only put this down to the lay up gradually drying out over winter.
Whils there will be plenty who wish to get their sticky fingers in your wallet, don't waste your money. I'm sure there are more exciting things to spend it on .

 

[jwilson]

If by "preventative osmosis treatment" you mean a gelpeel and epoxy job I'd be very, very against it. You are removing a sound bit of your boat and sticking on a replacement. Also gelpeel type osmosis treatments seem to work better on advanced osmosis than on very early stage.

If however you mean just coating the existing gelcoat underbody with epoxy paint, fine as long as the hull is fairly dry. Can't hurt and might do good.

 

[Resolution]

But many have sunk with it

Is that really so? Can you quote any verified cases? Just curious.

 

[Easticks28]

Is that really so? Can you quote any verified cases? Just curious.

With, not because of osmosis.
I doubt that such would be reported .

 

[sailorman]

With, not because of osmosis.
I doubt that such would be reported .

much like cv19

 

[Spirit (of Glenans)]

If an old boat has no osmosis, it's unlikely to do so now, but if it does develop a few blisters just grind them out on end of season liftout, and fill, fair and epoxy them before antifouling in spring.
Do't overthink it, there is a lot more to occupy you when you buy a boat.

 

[vyv_cox]

I treated my 35 ft boat with Gelshield 200 myself. Hard work but got five coats on. Cost was the epoxy and some abrasives. Pic of me doing so here Installing Yacht Legs

 

[JumbleDuck]

Echoing a bit what has been said ... if you buy a boat and she's out the water and all the antifould has been removed back to the gel coat - by you or by the previous owner - then for piece of mind it could be worth slapping on some anti-osmosis barrier paint. It's not cheap, though. You are supposed to put on five boats, and a good price for one coat over 8 square metres is £90. So, roughly speaking, paint alone will cost you £60 per square meter. You're looking a ~9m boats which are probably 30 square metres or so underwater, so there's £1800 right there.

I put 9 coats on the bottom of a wee Hunter 490 (16' LOA) because my local chandler sold me some out-of-date Gelshield for a tenner a tin. and because each tin did one and a half coats, so six tines led to nine coats. It's easy enough to do. and even at £1800 I think it might be worth while if the bottom is already stripped.

Otherwise, as people have said, just deal with any blisters as and when they pop up (sic) and don't worry about it too much.

 

[peter gibbs]

If there are blisters you might want to look elsewhere. You could be facing quite a lot of cost and loss of use whilst it's being dealt with.

If there are no blisters after several seasons, you are highly unlikely to be troubled. It's a game of chance but previous history assists your decision. And the major builds put a lot of effort into getting their layups secure against the risk.

Osmosis was the rage when I started sailing. Stories of hands going through the weakened hull etc. There were severe cases requiring drying out and recoating. But this is so rare these days as to consider a minor risk.

PWG

 

[Quandary]

I think that is a substantial over estimate JD if you are talking only of the material cost.
Jotun Penguard HB (with low temp additive for application in Scotland) gave me the approved 5 coats from 25l when I last did it in 2012. 33ft. boat with lead fin keel. It cost less than £300. I used to do it about every seven years when the AF gor rough and flaky but not so keen these days. An encapsulated keel would of course need more.
It was probably unnecessary but I had scraped all the AF off, so took the opportunity.

 

[JumbleDuck]

I think that is a substantial over estimate JD if you are talking only of the material cost.

Good point. I was going from the Marinescene website, which said 8.1m from 2.5 litres, but I got 1.5 coats (about 6 square metres) out of every 500 ml can. Perhaps their estimate is coverage for five coats.

 

[MattS]

Thanks all - really appreciate the advice.

 

[Stemar]

If there are big blisters you might want to look elsewhere. You could be facing quite a lot of cost and loss of use whilst it's being dealt with.

Agreed, with one small change.
A few small ones can be treated while the boat's out of the water for other things or, quite simply, ignored.

 

[guardian]

Unless you have problems like this then don't bother:

 

[E39mad]

Gelcoat is purely a finisher to make the hull look smooth/shiny and is not a structural part of the yacht. All gelcoats are permeable unless a barrier is put on them (preferably when as dry as possible) or the gelcoat is epoxy based.

Osmosis occurs when strands from the lay up matt (usually Chopped Strand Matt CSM) punctures the gelcoat during initial layup in the mould, and water is drawn up the strand when the boat is the water and the gelcoat becomes permeable. Many builders in the 1990's in particular started to put a shield between the gelcoat and layup to stop strands puncturing the gelcoat. Mild osmosis is not usually an issue if it has not entered the layup matt and has purely blistered the gelcoat. It is then just a cosmetic issue but should be checked on a regular basis to ensure it doesn't go any further.

 

[James_Calvert]

We did our Sadler 32 with International Gelshield about 30 years ago when she was just a few years old. It's lasted well, except for some overenthusiastic rubbing down over the years, and has done the job.

Regarding quantities and cost, we used the smaller 750ml tins, one per coat. This wasn't enough to include the rudder which we left uncoated, and whilst we didn't do the cast iron keel either, we did extend the coating above the waterline to the top edge of the boot top.