Btw, ive read that fresh water is harder on hulls because the 'osmotic pressure is higher' than salt water.
Being a chemist, I think this is a statement coming from basic understanding of osmotic pressure between a salt water and fresh water interface.
An interface between a water, gelcoat, and fiberglass structure is a lot more complex and not one that can be understood in a simple way.
Dave posted above that salt water is more prone to blisters, in counterpoint.
It might be as simple as more freshwater sailors pull their boats to avoid freezing, so they blister less!!
Tiny Blisters
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Jimnkathy
- Deckhand
- Posts: 31
- Joined: Mon Aug 06, 2007 1:57 pm
- Location: Troy Missouri / St Louis - 26X
Yes I totally agree with you. My boat is a prime example. I bought off a guy that kept it slipped for 4 years at lake carlyle and it is full of blisters. I have much work ahead of me.Catigale wrote:Btw, ive read that fresh water is harder on hulls because the 'osmotic pressure is higher' than salt water.
Being a chemist, I think this is a statement coming from basic understanding of osmotic pressure between a salt water and fresh water interface.
An interface between a water, gelcoat, and fiberglass structure is a lot more complex and not one that can be understood in a simple way.
Dave posted above that salt water is more prone to blisters, in counterpoint.
It might be as simple as more freshwater sailors pull their boats to avoid freezing, so they blister less!!
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DaveB
- Admiral
- Posts: 2543
- Joined: Mon Jan 07, 2008 2:34 pm
- Sailboat: MacGregor 26X
- Location: Cape Coral, Florida,1997 Mac. X, 2013 Merc.50hp Big Foot, sold 9/10/15
Osmosis repair
There are may reasons why boats have blistering and one can find many subjects on the Web that are both ill fed and correct assumption to a degree.
Lets stick with the Mac. X for example, the gelcoat is suppose to be between 15-20 mils thick (to less will cause water to penitrate at faster rate to much will cause the gellcoat to get cracks).
The Mac. varies greatly and usually to little Gelcoat and the first cloth layup has air voids because it wasn't rolled out enough. This will cause faster penetration of water and once water gets in between Gelcoat and cloth it causes a acid that eventually penetrates the layup thru time and causeing more damage and much harder to dryout.
I mention Salt water will cause blistering faster because when it does penetrate the gelcoat the reaction is much faster and the further you go in Souther latitude (warmer water) the faster it excelarates.
A Macgregor if left in the water for the season should have a min. 20 mil thick epoxy barrier coat to prevent osmosis.
Blisters can also be caused from the inside of the hull like this Compac I owned.
http://s182.photobucket.com/albums/x25/ ... el%20redo/
Osmosis is a very much problem with boats keeped and water and it's a case by case for correction,sometimes it's so bad it takes 6 mo. to dry out the hull.
Dave
PS:One could buy a Hinkley that layes up it's hull with epoxy $$$$$
Lets stick with the Mac. X for example, the gelcoat is suppose to be between 15-20 mils thick (to less will cause water to penitrate at faster rate to much will cause the gellcoat to get cracks).
The Mac. varies greatly and usually to little Gelcoat and the first cloth layup has air voids because it wasn't rolled out enough. This will cause faster penetration of water and once water gets in between Gelcoat and cloth it causes a acid that eventually penetrates the layup thru time and causeing more damage and much harder to dryout.
I mention Salt water will cause blistering faster because when it does penetrate the gelcoat the reaction is much faster and the further you go in Souther latitude (warmer water) the faster it excelarates.
A Macgregor if left in the water for the season should have a min. 20 mil thick epoxy barrier coat to prevent osmosis.
Blisters can also be caused from the inside of the hull like this Compac I owned.
http://s182.photobucket.com/albums/x25/ ... el%20redo/
Osmosis is a very much problem with boats keeped and water and it's a case by case for correction,sometimes it's so bad it takes 6 mo. to dry out the hull.
Dave
PS:One could buy a Hinkley that layes up it's hull with epoxy $$$$$
Catigale wrote:Btw, ive read that fresh water is harder on hulls because the 'osmotic pressure is higher' than salt water.
Being a chemist, I think this is a statement coming from basic understanding of osmotic pressure between a salt water and fresh water interface.
An interface between a water, gelcoat, and fiberglass structure is a lot more complex and not one that can be understood in a simple way.
Dave posted above that salt water is more prone to blisters, in counterpoint.
It might be as simple as more freshwater sailors pull their boats to avoid freezing, so they blister less!!
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DaveB
- Admiral
- Posts: 2543
- Joined: Mon Jan 07, 2008 2:34 pm
- Sailboat: MacGregor 26X
- Location: Cape Coral, Florida,1997 Mac. X, 2013 Merc.50hp Big Foot, sold 9/10/15
Thats right. I have a detail description in my now outdated computer that describes the chemical reaction. I just have to copy it on a disk and put it in this Puter, like a bunch of other good info. I was going to wait for a rainy day but here in SW Florida it shines.
I am getting close to retirement and will get all the stuff out of the past 20 yrs out of the 4 computers I put to rest, hopefully I can fire them up.
I am doing a lot of fixin on the Mac. 1997 I purchased and includes a lot of those air pockets I described. I bought this with no bottom job so I could see if any repairs were done and so far it looks like below the waterline it's ok except minor scratches and centedboard I can glass easy.
Rudders are comeing off and will regelcoat them.
About 30-40 small (less than a dime) dent's were there were air pockets mainly in cockpit and stern, 3 on Port side but there easy to repair.
Dave
I am getting close to retirement and will get all the stuff out of the past 20 yrs out of the 4 computers I put to rest, hopefully I can fire them up.
I am doing a lot of fixin on the Mac. 1997 I purchased and includes a lot of those air pockets I described. I bought this with no bottom job so I could see if any repairs were done and so far it looks like below the waterline it's ok except minor scratches and centedboard I can glass easy.
Rudders are comeing off and will regelcoat them.
About 30-40 small (less than a dime) dent's were there were air pockets mainly in cockpit and stern, 3 on Port side but there easy to repair.
Dave
Catigale wrote:If there is any electrochemistry going on the salt water will exacerbate this greatly of course, being conductive. The acid formation is probably an oxidation of organics in the FRG and will be electrochemical in nature.