Osmosis - is it a function of time in water

[trophy160]

I guess the obvious answer to my question is yes, but let me be more specific in my question. I currently have a mud berth, so for 12+ hours a day my boat sits in mud and the rest of the time afloat. I also tend to take it out of the water for probably 4 months per year. It it was to be afloat for 12 months per year, would this significantly increase the time to the onset of osmosis? (its a 10 year old Bavaria).

 

[Tranona]

Two issues really. The first is that based on past experience some boats that are in water all year round get osmosis - but many don't. Second thing is that it is highly unlikely that your Bavaria will be affected at all. The incidence of osmosis has declined rapidly in newer boats because of improved materials and processes. I have the same age Bavaria as you and osmosis is just about the last thing I would worry about. (famous last words!)

 

[Bosun Higgs]

yes. like any chemical process, osmosis is time and temperature dependant.

I dont know if modern Bavs are osmosis proof but I very much doubt it. I read somewhere a tech paper that said the polyester molecule was inherently vulnerable to the processes of degradation that lead to osmosis though its very clear that there are lots of other things that make a hull more or less liable. So unless you go to an epoxy hull you are at risk.

So I would still expect a Bav to be vulnerable to osmosis but much less so that ( say) a Westerly made 15 years earlier. The Bav will have had much better control of the manufacturing process and using better resins etc.

 

[pvb]

I wouldn't worry about osmosis at all. If it gets it, it gets it. And osmosis is a cosmetic condition primarily, not a major structural defect.

However, I might worry about my Bavaria's keel digging itself into the mud repeatedly...

 

[Elessar]

I guess the obvious answer to my question is yes, but let me be more specific in my question. I currently have a mud berth, so for 12+ hours a day my boat sits in mud and the rest of the time afloat. I also tend to take it out of the water for probably 4 months per year. It it was to be afloat for 12 months per year, would this significantly increase the time to the onset of osmosis? (its a 10 year old Bavaria).

i presume you mean reduce and if so yes is the answer.

Epoxies are many times more waterproof than gelcoat and thus epoxy coatings reduce water ingress to levels that are almost insignificant. So this is a better way of preventing early onset than keeping the boat out of the water.

A brand new GRP hull will absorb water from the day it is launched, and without an epoxy coating most GRP laminates will eventually suffer damage from long term immersion in water. With modern isophthalic resins however, "eventually" can be a very long time.

 

[saltwater_gypsy]

A good option is to borrow a Tramex moisture meter and check on the water content of the hull when the boat comes out of the water.You can get a base reading from the hull above the waterline and then get a comparative reading from the the underwater surfaces.

 

[greenalien]

I'd rate a few coats of epoxy paint as the best available insurance against osmosis - but you need to make sure the hull's dried out before you apply it - earlier advice about using a moisture meter is the way to go.

 

[oldgit]

I guess the obvious answer to my question is yes, but let me be more specific in my question. I currently have a mud berth, so for 12+ hours a day my boat sits in mud and the rest of the time afloat. I also tend to take it out of the water for probably 4 months per year. It it was to be afloat for 12 months per year, would this significantly increase the time to the onset of osmosis? (its a 10 year old Bavaria).

My boat was built in 1980.It has spent its entire life floating in assorted marinas, on swinging moorings and has now been on a drying mud berth during my ownership ,it has never ever been hauled ashore to "dry out" at any point in its life except for a couple of days worth of yearly scrape and a further layer of A/F and that can be up to 18 months between lifts.
It had no osmosis when I bought it 8 years ago,it had no sign of osmosis when survey was done last year,specificaly asked about it.
Its a 30year old Princess and no doubt built with all the wrong type ancient resins and stone age methods of layup,so am I lucky or is this osmosis thing just going to merely wait till the boat is sixty years old and then strike.

 

[greenalien]

The 'first great osmosis scare' was in the 1970's. Since then, most builders of GRP graft switched to using clear isophthalic resin below the waterline, which seems to have considerably reduced the problem.

 

[Ubergeekian]

I guess the obvious answer to my question is yes, but let me be more specific in my question. I currently have a mud berth, so for 12+ hours a day my boat sits in mud and the rest of the time afloat. I also tend to take it out of the water for probably 4 months per year. It it was to be afloat for 12 months per year, would this significantly increase the time to the onset of osmosis? (its a 10 year old Bavaria).

In so far as it is likely to have any problems, I don't think there will be any significant difference between sitting in mud and sitting in water: both keep the hull wet.

 

[Clarky]

In so far as it is likely to have any problems, I don't think there will be any significant difference between sitting in mud and sitting in water: both keep the hull wet.

In mud most of the boat will be out the water,in fact only the keels may be in the mud,so there will be a significant difference.

 

[Poignard]

My boat's hull was moulded by Tylers in 1967.

A few years ago I was at a class association rally and rafted up on a similar boat built the same year. She had had osmosis and twice been epoxy coated.

My boat has no epoxy coating and has never had osmosis.

I wouldn't worry unduly if osmosis did appear on mine. I'm sure the hull isn't suddenly going to fall apart. I would just pick out any blisters that appeared and fill them with epoxy putty.

Got to go now - a builder is coming round to quote for installing a damp course in our 1920s house. He says it will fall down if we don't get one.

 

[Deleted member 36384]

...1967 ..... similar boat built the same year. She had had osmosis and twice been epoxy coated .... boat has no epoxy coating and has never had osmosis.....

parsifal your observation has been described in some literature that I have read in "The Hydrolisis Handbook", Edition 4, January 2000. Quote: -

Long time tests proved: Contradicting earlier
theories most “osmosis” hulls, conventionally dried
and epoxy coated without effective acid removal,
become deep damages faster than similar hulls not
treated at all!
Excess water in the laminate does no harm!
Instead, due to temperature differences in the
surroundings, the water moves in and out and thus
washes out a lot of the harmful residues.
Further a free moisture movement in the
laminate has a cooling effect which considerably
slows down the hydrolysis.

Trophy160 if the claims in the book are correct then keeping your boat in a mud berth will have no impact on the ability of the hull to display symptoms of Osmosis. It is already in the water and has absorbed enough water to kick start an hydrolysis process that leads to Osmosis symptoms.