Possibly osmosis - from the inside out?

M

markg

New Member
I think our club boat may have osmosis. I've looked at the Wiki on hull repair (http://www.laserforum.org/know/index.php?title=Hull_Repair) and that all seems good info. However, for our boat,
1. I'm not sure if this IS osmosis
2. I'm not sure how to check how bad it is.

The symptoms are that the underside of the hull has quite a few very small, pimply blisters on it. Like the face of what a ping-pong bat used to look like 20 years ago. The pimples are 1 - 2 mm diameter maximum and are raised up a little tiny bit.

The reason i think it's osmosis is because when the boat was brought back from its last sail, it took a number of guys to get it on the dolly. When they undid the bung at the back, a lot of water drained out. I suspect that this boat has been used by club members and stored with the bung still in - thereby trapping salt-water in the hull. The boiling Thai sunshine wont have added anything beneficial to this salty cocktail either i suspect.

Does this sound like osmosis? If it has come from the inside-out, will just sanding off the gel-coat and carrying out a hull repair (as listed in the wiki link above) be enough or will the whole of the inside of the hull be shot? There is no inspection port on this boat by the way.
 
The blisters you describe did not come from inside. The boat was probably stored on a wet carpet.
The blisters are entirely cosmetic but.. On a community boat it will now be the ugly boat and the mistreated boat and when people race it their heads will tell them to sail slower while using the ugly boat and....

You know the rest.

The boat may dry flat and the plastic may just go back to flat and stay looking fine forever.

More likely, some of the blisters will dry and shrink and others will break and chip out.

The fix is to dig out every one of them and fix them individually.
It will consume a weeked but the product will be very nice.

For everybody with any fiberglass reinforced polyester boat. Do not let it stay wet for long periods or it may grow blisters

For fiberglass trailered boats ...WET THICK CARPET IS BAD!!!
If you must carpet your trailer bunks use polypropylene carpet because it can wick moisture away. But don't trust any carpet to dry before it blisters your toy.

The article with directions for the repair is on the page linked below. Click on How to Make Your Bottom Pretty.

http://schrothfiberglass.com/LaserMaint.htm

My real suggestion?? Just sail it.
 
Thanks for your reply and also the link to prettying up your bottom. :confused:
I can however confirm that the boat certainly hasn't been stored on carpet. It's stored on it's dolly under a coconut tree.

Here's some additional info. I used the boat last year quite a bit and noticed that she let water in. I was always careful about leaving her stored on a slight slope with the hull bung out, so all water could drain out. I then bought my own laser and paid little attention to the club boat. In fact, it hardly got used. The occasional times that it does get used, people are obviously leaving the hull bung in when they've finished. :mad:

We drained the water, turned the boat upside down and noticed quite a few cracks where the hull meets the deck. That's where the water has been coming in.

Now, i don't know too much about osmosis, but I'm assuming that a keel boat moored in water gets it's osmosis from the outside-in. My concern is that the club laser has got osmosis from the inside-out. And i'm not sure how to tell how bad that is..........there is no inspection hatch.

She is upside down and under cover now as the cracks in the hull/deck are being repaired. Maybe the pimples will go away as the bung is out and air is flowing all over her. I really hope so. As far as i know she is the only other laser, apart from mine, on the island, and our little club can't afford to replace her just yet.

Thanks again for the useful links you posted - and your advice about just sailing her !!
Markg
 
Osmosis is a process not something a boat "has.".
Blistering is the result of osmotic pressure across semipermeable membranes.
Generally here is how blisters happen in boats:
There is a nice clean lake and a plastic semi permeable membrane. There is something soluble in the laminate whose molecules are too large to pass through the plastic semipermeable membrane. The water passes through the membrane and a soultion is formed inside the membrane. The solution contains molecules not present on the lake side of the membrane.

For some reason, solutions on opposite sides of a semipermeable membrane "try" to equalize their concentrations. (I am not real sure about how or why but I know the various molecules studied at the same school where Thermos containers learned to know when to keep hot things hot versus cold things cold)
Anyway, a phenomenon called osmotic pressure occurs which in the boat's case would be: There are long chain polymers in a water solution on the inside of the laminate. There are virtually no long chain polymer molecules in the lake. As a result lots and lots of water comes rushing into the laminate to make the concentration of polymers the same on each side of the membrane.
Blisters grow. Sometimes trhey pop. Sometimes they delaminate huge areas. Somewtimes trhey just get real hard and quit growing. I suspect that is another thing.
The "another thing.": The osmotic pressure caused by different concentrations on the two sides of the membrane varies from one chemical to another. Maybe the pressure in the blister sometimes reaches the osmotic pressre generated by the particular chemical content differences and the growth slows or even stops..

You are conducting osmosis like this all over your body right now. Your lungs are sending CO2 across membranes to the less concentrated air. The air is sending Oxygen across membranes to the less concentraed you.
Your blood is doing the osmosis thing with cell walls and there are sugars and air and all sorts of stuff being passed back and forth.

Anyway...

my point??

I don't reeally have one. I just felt like typing.

Or.

Maybe the point is, if the boat is delaminated and soft and useless..it is hurt.

I have no idea why a boat would grow what I call "carpet blisters" just because it was filled with water.

I could speculate but this post is already absurdly long and I have work to do.
 
Just an idea but if the hull contains salty water from the Andaman and the boat is parked outside from June to September when it rains every day then the hull will have fresh water on the outside and salty water on the inside. Fresh water may try to migrate through the gelcoat semi-permeable mebrane from outside to inside to equalise the salt concentration and get trapped between gelcoat and glass causing the blisters?
 
I'll buy that.

Sounds like a mighty good hypothesis.

In fact, I service boats on a warm fresh water lake. It is 86 degrees F / 30 C today in lake Travis. The blistering here is worse than almost anywhere as warm clean solvent is the strongest solvent.
The very worst blistering ( assuming otherwise same brands and designs and age) happens in boats moved from salt water to Lake Travis.
 
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