Complete a/f removal: WHEN?

[Elessar]

We had her sand blasted 4y ago when she was 23yo, right before we mounted the fin stabs,
Around the stabs, we have added extra layers of grp, so in that zone she had to be sanded to bare grp anyway.

Blue Angel had many layers of old hard antifouling, at least 6 layers with different colors,
Apart from the esthetics, and the smoothness of the hull, another argument was the weight of the paint,
In a rough calculation about 500kg of old paint went off.

After sand blasting, The yard has put a epoxy coating (by hand) , and Micron77 antifouling

And since then, each year, we had her pressure washed, antifouling nearly completely off, coating stay’s intact
and place just one new layer of Micron 77

Now I have one concern,
When we purchased the boat in 2011 she had zero osmosis (confirmed by the surveyer)
One season after the sand blasting we discovered (actually the painter did) a few spots of osmosis in the zone between the props.
I believe they did only “one” layer of epoxy hull coating,
Could the sand blasting / not enough layers of epoxy, be a reason for these spots of osmosis or is it just age of the boat ?

Unfortunately I have no better contribution/ answer to your thread / question

No 23 year old boat that has no epoxy has zero osmosis. It's just hasn't developed into osmotic blistering. Sometimes the epoxy can induce the blistering as it seals the boat.

But are you sure it's osmotic blistering - it could be poor adhesion of the epoxy to the hull. It looks identical.

So first step is burst a bubble and taste the fluid in it. Vinegar = osmosis. Salt = poor adhesion.

If its the latter scrape, sand and re-epoxy the area.

If its the former din't worry it worn't sink. I'd dremel out the holes, wash them out every day for a couple of weeks and fill with epoxy filler. Then epoxy around the area you think is thin. It might get worse, or it might not, depending on how localised it is.

 

[BartW]

No 23 year old boat that has no epoxy has zero osmosis. It's just hasn't developed into osmotic blistering. Sometimes the epoxy can induce the blistering as it seals the boat.

But are you sure it's osmotic blistering - it could be poor adhesion of the epoxy to the hull. It looks identical.

So first step is burst a bubble and taste the fluid in it. Vinegar = osmosis. Salt = poor adhesion.

If its the latter scrape, sand and re-epoxy the area.

If its the former din't worry it worn't sink. I'd dremel out the holes, wash them out every day for a couple of weeks and fill with epoxy filler. Then epoxy around the area you think is thin. It might get worse, or it might not, depending on how localised it is.

thanks for clear and straightforward advice,
boat wil hopefully stay a few months on the dry this winter,
so time available to check and repair as per your advice.
and put one more layer of epoxy paint before new antifouling.

 

[wellf100]

Yep, I'm also making up my mind towards CC rather than Aquamarine or similar, for the reasons discussed.

But if you would get any additional feedbacks on how easily fouling can be cleaned away from a hull coated with a foul release system after the boat has not moved for longish periods, I for one would be interested! :encouragement:

I notice they do a small rib kit for £40. If you wanted to test it where you are you could perhaps apply it to your tender and leave it in the water for a while and see how it does.
https://www.aquamarineuk.com/pages/rib-preparation-maintenance

 

[wellf100]

by the way sorry if i come across like an Aquamarine salesman! I'm definitely not of course but I do seem to be the only one on the forum who has actually tried it!

 

[Eren]

After sand blasting, The yard has put a epoxy coating (by hand) , and Micron77 antifouling

And since then, each year, we had her pressure washed, antifouling nearly completely off, coating stay’s intact
and place just one new layer of Micron 77

Micron77 worked out very well in my boat at Med. I put on 3 layers each time and take the boat to drydock in every two years. Before I go out for long trips, I hire a diver and have the bottom cleaned. Works like this in the last 6 years. I only began to worry a bit now that the hull was always in water for so long time. So I plan to have her on drydock for a couple of months next winter.

 

[MapisM]

No 23 year old boat that has no epoxy has zero osmosis. It's just hasn't developed into osmotic blistering. Sometimes the epoxy can induce the blistering as it seals the boat.

But are you sure it's osmotic blistering - it could be poor adhesion of the epoxy to the hull. It looks identical.

I see what you mean ref no 23 yo boats has zero osmosis unless epoxied, but my money is on the latter (poor adhesion of the epoxy in places - with no actual osmosis underneath.

Reason being that up to the late 80s/early 90s, which is BA vintage, the resins used for hull lamination were strictly performance oriented, without caring a lot about effects on health, through inhalation and contact.
Or without knowing a lot about them, which is just about the same.

As a result, emphysema or worse were not uncommon among workers dealing with these resins.
I knew two of these folks, who sadly died of lung cancer before reaching their pension age...
Otoh, when it comes to serious osmosis, i.e. chemical decomposition with release of liquid with vinegar/solvent smell, that's extremely rare also nowadays, even if compared with more modern hulls, whose chemistry has been improved radically in terms of operators health (and rightly so, of course), but not so much in terms of performace/stability.

Sure, you can still find a 30yo GRP hull badly affected by osmosis, but that's mostly because also back in those days, not all yards used to work equally well.
Otoh, Canados was surely among the best, and in fact bad osmosis is unheard of, on their earlier GRP hulls - pretty much as with Hatteras, and some others.
I'd be curious to hear from BartW about his findings after BA will be on the hard.

 

[MapisM]

I'm not convinced on fouling release systems for hulls and I have trialled some. And if they don't work you need to remove and replace the gelcoat to use paint aver again, so I wouldn't be an early adopter. I think they work on props though now.

I meant to ask before but I forgot, which is the foul release product that you are using for u/w gear?
Btw, I'm assuming that by props you also mean rudders, shafts and brackets - but if not, I'd be curious to hear why.

 

[Elessar]

I meant to ask before but I forgot, which is the foul release product that you are using for u/w gear?
Btw, I'm assuming that by props you also mean rudders, shafts and brackets - but if not, I'd be curious to hear why.

I'm not using it yet on this boat - I helped a friend put it on. He's writing at article for the mag so I'm not being specific. He might jump in and say. Yes it goes on all the bronze bits. I will be using this as I've seen it does definitely improve things.

The one I trialed on the hull of my old boat was a prototype from a well known brand. They didn't put it on the market.

 

[Elessar]

I see what you mean ref no 23 yo boats has zero osmosis unless epoxied, but my money is on the latter (poor adhesion of the epoxy in places - with no actual osmosis underneath.

Reason being that up to the late 80s/early 90s, which is BA vintage, the resins used for hull lamination were strictly performance oriented, without caring a lot about effects on health, through inhalation and contact.
Or without knowing a lot about them, which is just about the same.

As a result, emphysema or worse were not uncommon among workers dealing with these resins.
I knew two of these folks, who sadly died of lung cancer before reaching their pension age...
Otoh, when it comes to serious osmosis, i.e. chemical decomposition with release of liquid with vinegar/solvent smell, that's extremely rare also nowadays, even if compared with more modern hulls, whose chemistry has been improved radically in terms of operators health (and rightly so, of course), but not so much in terms of performace/stability.

Sure, you can still find a 30yo GRP hull badly affected by osmosis, but that's mostly because also back in those days, not all yards used to work equally well.
Otoh, Canados was surely among the best, and in fact bad osmosis is unheard of, on their earlier GRP hulls - pretty much as with Hatteras, and some others.
I'd be curious to hear from BartW about his findings after BA will be on the hard.

My point was I didn't believe the surveyor saying that it has no osmosis - ie NO water has passed through the semi permeable membrane (the gelcoat) into the semi soluble substrate (the GRP). That doesn't mean there is anything wrong with the boat.

We boaters tend only to use the O word when the layup breaks down enough to cause osmotic blistering. I'm not saying it has that.

I agree with you BTW that he's more likely to have poorly adhered epoxy not osmotic blistering, the timeline supports this.

 

[longjohnsilver]

We coppercoated Eos 3 years ago, after using International epoxy and I was very grateful for the great advice provided by Elessar, without which the whole process could have gone massively (&expensively) wrong.

If you go down that route make sure that you, or the yard, know what they're doing.

 

[MapisM]

My point was I didn't believe the surveyor saying that it has no osmosis - ie NO water has passed through the semi permeable membrane (the gelcoat) into the semi soluble substrate (the GRP). That doesn't mean there is anything wrong with the boat.

We boaters tend only to use the O word when the layup breaks down enough to cause osmotic blistering. I'm not saying it has that.

I agree with you BTW that he's more likely to have poorly adhered epoxy not osmotic blistering, the timeline supports this.

We are possibly going into semantics a bit, but in my understanding, when water molecules pass through the gelcoat and find their way inside the GRP (which translates in high humidity readings), it is technically correct to call the process osmosis regardless of the fact that it's affecting a boat hull, but that does not necessarily translate in the chemical decomposition of the resins that is normally known (and feared) as THE osmosis in boat hulls.
In other words, I would guess that the surveyor might have used the term osmosis in the same way as "we boaters" use it...

 

[Elessar]

We are possibly going into semantics a bit, but in my understanding, when water molecules pass through the gelcoat and find their way inside the GRP (which translates in high humidity readings), it is technically correct to call the process osmosis regardless of the fact that it's affecting a boat hull, but that does not necessarily translate in the chemical decomposition of the resins that is normally known (and feared) as THE osmosis in boat hulls.
In other words, I would guess that the surveyor might have used the term osmosis in the same way as "we boaters" use it...

Yep all agreed !!

 

[Rocksteadee]

Saw the trial with different prop treatment. Did you get an outcome? Or too soon yet?