Does leaving on the hard for months promote osmosis?

[Pavalijo]

Whilst antifouling in the boatyard I got talking to a neighbour. He only takes his Bavaria out of the water every 2 years and then for only 3 weeks. He believes that drying the hull out gives a greater likelihood of suffering osmosis.

Now I took mine out in November and am putting her back in this week - in the belief that allowing the hull to dry will reduce the chances of osmosis.

Who is right (BTW I am new to all this and my neighbour has sailed all his life and owned a yacht for several years, so I suspect my logic may be flawed but wanted to check).

I do not believe that my boat (1996 Moody) is particularly prone to osmosis and survey readings 12 months ago were ok (higher than a new hull but normal apparently) but I want to "do the right thing"!

Thanks in anticipation and sorry if this is common knowledge, but after a great deal of reading I have found nothing on this specific issue,

Paul

 

[rotrax]

Whilst antifouling in the boatyard I got talking to a neighbour. He only takes his Bavaria out of the water every 2 years and then for only 3 weeks. He believes that drying the hull out gives a greater likelihood of suffering osmosis.

Now I took mine out in November and am putting her back in this week - in the belief that allowing the hull to dry will reduce the chances of osmosis.

Who is right (BTW I am new to all this and my neighbour has sailed all his life and owned a yacht for several years, so I suspect my logic may be flawed but wanted to check).

I do not believe that my boat (1996 Moody) is particularly prone to osmosis and survey readings 12 months ago were ok (higher than a new hull but normal apparently) but I want to "do the right thing"!

Thanks in anticipation and sorry if this is common knowledge, but after a great deal of reading I have found nothing on this specific issue,

Paul

If you ask about Osmosis, you will get many conflicting answers.

The only ones who sing out of the same hymnbook are the ones who do expensive Osmosis treatments......................................

 

[Deleted member 36384]

Your neighbour may have read a book that explains Osmosis as Hydrolysis. In this book it is claimed that the chemical reaction is slowed down by keeping the boat in the water. The water molecules continue to pass through the GRP and keep the reaction cooler compared to a hull where the reaction is happening anyway but is now out the water. I'll see if I can find a link later to the book.

 

[Just_sayin']

Five seconds.

https://www.google.co.uk/search?q=w...oats&ie=UTF-8&oe=UTF-8&hl=en-gb&client=safari

 

[Deleted member 36384]

The book I am referring to is:-

Osmosis, Myth and Reality About Hydrolyse Blistering and Delamination In FRP boat hulls, by Bengt Blomberg

I am sure that he allows the book to be downloaded free, just search on Google for it.

 

[Pavalijo]

Thanks for the pointers. I briefly scan read this from Just-sayin's link
http://www.passionforpaint.co.uk/pdf/osmosis3.pdf
where wintering on the hard where possible is recommended when moisture readings start rising. Says it will not reverse the process but will slow it down.
I am sure that the scientists around this subject will have a range of views and will google the book later, thanks Old Boots - just off to clean the hull as the rain is clearing.

 

[Javelin]

If you ask about Osmosis, you will get many conflicting answers.

The only ones who sing out of the same hymnbook are the ones who do expensive Osmosis treatments......................................

Hmm, we do expensive Osmosis treatment,
(expensive being a relative term depending largely on yard hourly rates + cost of grit blasting + cost of epoxy resin)

However I've yet to hear of a boat sinking due to Osmosis.
In 99% of cases we see here at the yard its a cosmetic issue only and apart from a really bad rudder I've yet to see an example that MUST be fixed.
So most of the time after inspection we say don't worry about it, just keep an eye on it after each lift.

Often the only time we advise to have the treatment done is when the owner wants to sell.

 

[garvellachs]

Tony Staton-Bevan in his book "Osmosis & Glassfibre Yacht Construction" says: "If at all possible, the vessel should be stored ashore when not in use. The benefits here are ... the hull will not be absorbing water ... and it may even partially dry out. It is no coincidence that those craft left afloat for 12 months every year, develop blisters much earlier." (p108, 2nd edition, 1995)

He also warns that fresh water and warmer water should be avoided if possible. And he says that removing years of layers of anti-foul paint can lead to subsequent blistering if not replaced by epoxy. When writing he was surveying 250 grp boats a year so worth listening to by those who have older boats?

 

[Deleted member 36384]

Tony Staton-Bevan in his book "Osmosis & Glassfibre Yacht Construction" says: "If at all possible, the vessel should be stored ashore when not in use. The benefits here are ... the hull will not be absorbing water ... and it may even partially dry out. It is no coincidence that those craft left afloat for 12 months every year, develop blisters much earlier." (p108, 2nd edition, 1995)

He also warns that fresh water and warmer water should be avoided if possible. And he says that removing years of layers of anti-foul paint can lead to subsequent blistering if not replaced by epoxy. When writing he was surveying 250 grp boats a year so worth listening to by those who have older boats?

I wonder what removal of antifoul has to do with it, it's porous, so is providing no protection I would have thought. Perhaps that is when it's noticed, when layers are taken off.
; intriguing.

 

[garvellachs]

He says: "...such a build up actually provides a water-resistant barrier. I regularly encounter cases where blisters appear within 12 months of anti-fouling paint removal".

 

[Just_sayin']

That's really surprising.

So a heavily anti-fouled boat left in the water all year is less likely to get osmosis than one stored ashore anti-foul free.

?

 

[Spyro]

I don't know the answer but would love to know how much "drying" there would be between November and now on the Clyde? Not much I suspect unless under cover.

 

[jwilson]

That's really surprising.

So a heavily anti-fouled boat left in the water all year is less likely to get osmosis than one stored ashore anti-foul free.

?

No, but a heavy layer of old antifouling does seem to give a small degree of protection: again and again we see boats of maybe 20 years old that "develop blisters" for the first time within a year or so of having lots of old antifouling stripped off. Of course a smooth hull (instead of a crusty-with-old-AF one) makes it easier to spot blisters.

Despite this I don't regards lots of AF thickness as good: it always ends up rough and I prefer to sail faster with a smooth hull.

GRP is not a perfect material for boat hulls, it's just the least bad option for building production hulls at a reasonable cost. Personally I have my current GRP hull in England out of the water 4 months of the year, with dried bilges and a dehumidifier inside. Before that my last and older boat was in the water 364 days a year in the tropics, and had plenty of blisters. But the GRP was very thick compared to my current modern boat.