Dream Boat Has Osmosis, What to Do?

[PeterV]

I was in exactly your position, I couldn’t afford the boat I wanted, until I saw one for sale for £5000. Not sold because it had loose stanchions, crazed windows and a crack in the hull. The rigging was original and all the sheaves in the mast were seized solid.
But, 3 weeks on the hard had the mast and rigging sorted, the hull repaired and strengthened, the deck repaired and stanchions sound and we enjoyed the rest of the year sailing a boat we never thought we could afford.

enjoy yourself.

 

[Refueler]

IMHO the sander won't be suitable for the job. The Dremel might, with a suitable tool attached. A sander will take the top off the blister, but you need to go slightly deeper, to dig out the delaminated layup
The weapon of choice is an angle grinder. Lidl or Aldi are sure to offer DIY-quality cordless models soon at a comparatively cheap price. Besides osmosis, you will find all sorts of uses for it.

The guy has the ideal tool at hand .. Dremel.

I wince when I see people approach a hull with angle grinder ... it doesn't take much of a slip to gouge too deep. Watched one guy slip when he had AG in hand ... the gouge he caused was serious.

Sander - I agree ... not worth it.

OP's comment about sanding of the whole underhulls AF etc ..... personally I would not. Its difficult to keep the hull surface straight and smooth without causing 'sanding waves' .....

 

[Refueler]

I found severe osmosis on my first boat and power-planed the bottom (at a time when they were still grit blasting, if only I'd patented the method!) jet washed it, tented and waited a whole season for it to dry before putting on two layers of epoxy. What a waste of time, sailing and effort! What I should have done was to ignore it or at most use a mini router to cut out the boils.

I would suggest a cutting tool is better than a grinding tool in terms of finish, but you will get through them and they aren't cheap.

Do wear a good quality mask and NBC overalls. Ideally have vacuum extraction of the dust. SWMBO holding a hoover nozzle would suffice for a few blisters.

Power Planer is a method - but have seen planers blunt very quickly ...

Its what I would use if I was to strip AF and layers of old paint etc.

But as I said earlier - he has a Dremel .... perfect tool for odd blisters.

 

[Rappey]

My friend sat in a deck chair under his boat and used a 20mm grinding ball in a die grinder. Worked perfectly.

 

[dankilb]

I completed a full osmosis ‘treatment’ (grind, fill, fair and epoxy barrier) on a 41’ with hundreds of apparent blisters (I always think twice about reiterating this online, but the model is well known for the problem). The job was done outdoors in N Wales over a late summer/winter last year, largely single handed. I’m no boat builder, but the end result was a fair hull, with a 9 coat epoxy barrier, and zero blisters. If it comes to it (and with two blisters - you’re likely fussin about nothin!) it can be remedied DIY.

(p.s. we were also lucky that our boat had passively dried for 7 years and was therefore a suitable candidate for ‘treating’ any osmosis without artificial heat, vacuum, gel peel, or anything like that…)

 

[ghostlymoron]

You have got a good bargaining chip. Why not use it to maximum advantage?

If the boat is already at a low price, it sounds as though he's already priced in the osmosis.
"Seller doesn't want to drop price much more because the boat is already cheap for it's make and model and I can't really argue. He's right."
No harm in trying a few more quid I suppose.

 

[neilf39]

Finger sander with 80 grit is a good way to work around blisters. Very controllable.

 

[Chiara’s slave]

Finger sander with 80 grit is a good way to work around blisters. Very controllable.

This, or that grinding ball idea above would be my weapon of choice. If I were minded to do anything.
‘My boat has osmosis, what shall I do?’
‘Go sailing’. is the best answer, do the grinding at your convenience.

 

[dankilb]

Couldn’t have done ours without the die grinder (cordless Milwaukee). The finger sander is also a good suggestion - and I’ve used it a lot during our refit - but I’d hazard it’d take at least twice as long (assuming ‘proper’ osmosis and hundreds of blisters). Great thing about the die grinder is speed of the ‘touch and go’ method.

 

[harvey38]

Use a battery powered drill and fit a rotary burr bit https://www.amazon.co.uk/gp/product/B07JB87HX2/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

Quite therapeutic and satisfying

 

[Chiara’s slave]

Use a battery powered drill and fit a rotary burr bit https://www.amazon.co.uk/gp/product/B07JB87HX2/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

Quite therapeutic and satisfying

Like squeezing spots……

 

[Poignard]

Or scraping off wallpaper...

 

[fisherman]

I bought my FV in 1992, and found osmosis pretty much all over, blisters 10mm-20mm. I sold it in 2018 with the same osmosis, after a survey. Also had an insurance survey in 2001.
If you really want to deal with it I suggest do a marked out section each winter lift out, it will seem less daunting.
As far as I can find out, if you have a really thin hull and really big blisters it might be a problem. I saw a FV with blisters 80mm dia, still going.

 

[Jim@sea]

In 1982 I had a car bodyshop so was using body filler and two pack paint every day, this was before International Paint started selling Two Pack Pain , (which is identical to car paint)
I had bought a 1973 Nauticat 33 which had been treated for Osmosis in 1979 (at 6 years) and it had been re-painted with single pack paint, and some blisters were coming back.
I gouged them out, filled the holes with car body filler and hand painted the hull with Two Pack paint, Three years later the blisters had not returned.
Leaping forward to 2012, I bought a 1986 Boat which had Osmosis blisters and I did the same again.
But 6 months later two of the blisters had returned in an area of the deep keel where the GRP would have been quite thick.
My method of stopping the blisters coming through again was to open up a half inch wide hole and just over a quarter of an inch deep, drill a small hole in the centre, screwing a stainless steel screw into the small hole with the head of the screw below the level of the gel coat. And using the filler which is recommended for under the waterline, filled the hole. The idea being that the filler would grab the s/s screw and resist any movement which would result in a new blister. I then painted the area with 8 coats of 2 pack paint.
Never did find out if it worked, as I sold the boat.

 

[fisherman]

+1 on angle grinder: it tends to polish the substrate when a ragged surface would be better.

 

[KREW2]

Use a Forstener bit to drill the gelcoat off a few of the blisters. If the underlying matt coat is firm just let it dry out and fill and fair. If the matt coat is spongy and wet I would seek further advice.

 

[steveeasy]

Just deal with spots.plenty of time to revisit the osmosis in the years to come.
steveeasy

 

[fisherman]

GRP is very forgiving. I hit a buoy (don't ask), 14 ton boat hits 6 ton buoy, it was laid over with the topmark in the water. I assumed I was sinking but had a quick look. Impact 5ft back from the bow above WL, the deckbeams had punched the other side of the boat out, the deck was up in the air, the gel coat was crazed....but the hull had sprung back and was intact, so carried on for the day. Next day did a patch up job, refit the deck and forehatch. Next liftout, ground off the impact area, about 2-3 sq ft of gel coat, and the first layer of substrate, which was replaced, then remade the gel coat and painted with Perfection which was the existing finish. Repaired cracked top hat frames inside. Good as new, passed survey.
A similar boat went ashore in Mylor, 10ft of the side was replaced at the builders yard, moulded a new section and stuck it in.
When the Plymouth Pilot, 18ft workboat, was introduced in the 70s, the builder invited people who questioned the strength to attack a square foot panel with a sledge hammer.

 

[The Real Flipper]

Well this has been a great read. Thanks for all of the suggestions!
A lot of knowledge in this thread...
Sorry I can't respond to everybody. I get 'typed out' at a certain point

Once you have mastered fixing the first ones, it will become part of your regular maintenance.
.
https://wiki.westerly-owners.co.uk/images/3/3f/Concerto.pdf

This short video is 18 months later than the above link to show even more work completed.

If you want to know what I am currently doing, then click on the link in my signature and then read this thread and the further links.
Round Britian day 1

Just in the 'shortlist' of other items the boat needs, I've found boat maintenance to be much more work than expected.
Your video and PDF show that in great detail!
BTW really nice job fixing up that Westerly. Looks great. I really enjoyed the video and the read. Very educational.
And its gratifying to see the before and afters.

How old is the boat? If it has a couple of small blisters after say 20 years then you might get a couple more in the next 10 years. If under the waterline it is not even cosmetic as it will not show.
I don't think an epoxy coating is recommended any more unless you completely strip the gelcoat. It seals in any problems which will later cause the coating to fail. Just look on it as a small extra winter maintenance job to clean out and fill blisters as they appear.
Some reading here from West Epoxy if you download the PDF instruction manual for blister repair. West
Also go to the Monty Mariner download page and you will find more information at the bottom of the list.
Hopefully this will reassure you that you have a relatively minor problem that will not stop you sailing and enjoying the new boat.

It's a 40 something year old boat.
So stripping the gelcoat will be required to do a full 'correct' job. Hmm interesting. Well that explains why paying someone for the job is so costly. I've seen estimates of 5,000 Euros just for sanding! And 10 grand for the full job. Shocking really.

Of course the benefit is that you can take that off of your list of recurring annual maintenance.
So although I have to say that while I am not going to worry about more than patching up the 'verification' holes that confirmed the osmosis this year, if I can get a good settlement from the seller I'll see if I can find someone to do the Full Monty job next winter so I can forget about it.

Truth is I was already kind of overwhelmed with what the boat needs done already.

One thing's for sure. This boat's going to get me in better shape! Haha!
Seriously...

Do wear a good quality mask and NBC overalls. Ideally have vacuum extraction of the dust. SWMBO holding a hoover nozzle would suffice for a few blisters.

What kind of mask is recommended? I sanded a day with my hand sander before applying antifouling and was pretty sick for several days after. I had a charcoal/cotton cheap mask (3 for 5 Euros) and apparently it did little.

Also learned that I am not nearly in good enough shape to do a full sand down. I was sore for a week and learned this work really is heavy!

If the boat is already at a low price, it sounds as though he's already priced in the osmosis.
"Seller doesn't want to drop price much more because the boat is already cheap for it's make and model and I can't really argue. He's right."
No harm in trying a few more quid I suppose.

Well I'm going to take the advices and not sweat the osmosis too much.
And I'm now negotiating for a *little* better deal.

I'd love to do a full refit like Concerto, but I'm just not up to it physically as I've had some health issues.

Unfortunately the list of 'stuff' the boat needs attention to is a bit longer than I elaborated in my first post. And I think the price of the boat reflects those. Surveyor found a full page of 'maintenance items' good news is they are more labor than parts price heavy so I already had plenty of work ahead.

That I'm more than happy to do for the opportunity to own this 'dream' boat!

The osmosis just adds to the workload.

So basically if I can negotiate enough to pay for all or most of just a professional sand/grind down, I'll do that next winter and be done with it. Then I can get on with everything else it needs.
Of course that would require me to do all of the painting to build it back up. But I should be in better shape by then and of course I can't ask him to pay for the full job for the price I'm getting.

The best news from this thread is that I can patch those open spots and get sailing this year!
And I don't have to sweat that I'm ruining the boat.

I'll try to work something fair and a good deal for both the seller and me. The boat sat a few years. And I don't think he realized how fast a boat deteriorates when sitting, until the survey came in!

I'm sure he's not happy at all to hear about this osmosis now.
So given whats said by everyone here I'm not going to rake him over the coals about it.

In the end its great news that I'll be sailing this year

 

[The Real Flipper]

GRP is very forgiving. I hit a buoy (don't ask), 14 ton boat hits 6 ton buoy, it was laid over with the topmark in the water. I assumed I was sinking but had a quick look. Impact 5ft back from the bow above WL, the deckbeams had punched the other side of the boat out, the deck was up in the air, the gel coat was crazed....but the hull had sprung back and was intact, so carried on for the day. Next day did a patch up job, refit the deck and forehatch. Next liftout, ground off the impact area, about 2-3 sq ft of gel coat, and the first layer of substrate, which was replaced, then remade the gel coat and painted with Perfection which was the existing finish. Repaired cracked top hat frames inside. Good as new, passed survey.
A similar boat went ashore in Mylor, 10ft of the side was replaced at the builders yard, moulded a new section and stuck it in.
When the Plymouth Pilot, 18ft workboat, was introduced in the 70s, the builder invited people who questioned the strength to attack a square foot panel with a sledge hammer.

Well when you put it that way, a few little bumps don't sound so bad!
LOL