when people talk about ozmosis on a boat what are they talking about?

Answer 1

Well its simple osmosis is the net movement of water through a selective permeable membrane from a region of low solute potential to a region of high solute potential (or equivalently, from a region of high solvent potential to a region of low solvent potential). The partially permeable membrane must be permeable to the solvent, but not to the solute, resulting in a pressure gradient across the membrane. Osmosis is a natural phenomenon. Many plant cells perform osmosis. This is because the osmotic entry of water is opposed and eventually equaled by the pressure exerted by the cell wall, creating a steady state. In fact, osmotic pressure is the main cause of support in plant leaves.

In aboat it causes blisters - osmosis, or the appearance of blisters on fiberglass hulls. Many believe that osmosis is a problem generated from outside a hull, it in fact appears to be a problem that exists within the laminates, long before the boat ever sees the water! And, it is a problem that affects polyester resins most severely.

Where industry experts appear to originally felt that osmosis had to follow voids or paths in the hull laminates (lay-up), and that these voids were the result of poor quality control by the builder. While a poorly constructed hull could influence osmosis, it is not the primary cause.

Polyester resins need to be post cured at 80º - 90º C (176° - 194° F) in order to fully cure. As the hulls have no high temperature post curing, there exists in quite a high number of hulls, some degree of styrene (as moisture), alkali, and other random, uncured components, usually sitting in “pockets”, sometimes deep in the laminate schedule, sometimes nearer the surface. In some hulls, as soon as these pockets are exposed to any moisture, a reaction called hydrolysis takes place. And hydrolysis is a nasty customer indeed!

In severe cases it can reduce the bonding quality of resin, allowing the unsaturated fiberglass to become wet mush! Further complicating this mess, is the formation of pthalic acid by the hydrolysis reaction. Pthalic acid attacks the “dangling-ends”, or the portion of the cross-linked molecules that did not form a full link, due to the incomplete cure of the laminates.

Repair techniques involved peeling, (good!), drying, either by normal temperature exposure, or with heat lamp accelerating. Following this by closely monitoring with a moisture meter, until an acceptable level of “drying” had occurred, and then repairing any blister craters, we would then apply a barrier coating, usually an epoxy.

Three to five years later, more blisters appear! Why? The drying of the hull in itself cannot remove the styrene pockets, pthalic acids, glycols and other residues. It stays in the hull, and as soon as the boat is re-launched and water molecules enter the hull and mix with the residues, the hydrolysis begins again. Unfortunately, many boats are re-sold before the blisters re-appear, and the new owner believes he has purchased a hull that has had a “complete” blister job, properly done, and that he or she can look forward to many trouble-free years without osmosis problems.

The proper treatment of osmosis blistering, or hydrolysis as it should be more properly referred to, is high temperature heat, under vacuum, at between 85º - 95º C (185° - 203° F), applied to a peeled hull, normally from 7-10 days. Now, rather than just drying the laminates, the hot vacuum vaporizes the styrene and glycol residues, at the same time the hull is drying out. And, the process normally takes 7-10 days, rather than months of trying to get the hull to dry by conventional methods.

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Answer 2

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Answer 3

easy, and i'm suprised many of the other answers are wrong.

its the breakdown of the grp resin into acetic acid. is causes pockets of acid creating blisters. the blisters burst and draw water in.

you can confirm osmosis by peicing a suspect bubble. it will be an oily liquid that smells of vinegar.

you can fix it by digging out the efffected areas and building back up wth fibre and resin.

small bubbles, less that 5 mm, are ok. when it gets to 15-25mm you need to adress it.

if you leave it, it will spread and rot the fibre.

the initial cause is incorrect mixing in the resin mix.

Answer 4

It something that happens to grp or fibre glass boats.
you should check for blisters as the boat gets older thigh you can usually rub down and paint with a thin later of resin ,then paint.
good site about osmosis on boats here
http://www.passionforpaint.co.uk/osmosis.htm

Answer 5

This has a more common name "Boat Pox ".
Its a condition where water seeps through the gel coat ,A real lot of trouble if your boat has this ,If you have tiny blisters on the gel coat and the hull is heavier when you take it out of the water in the autumn then your boat has a good chance of having the dreaded pox.

Answer 6

osmosis is the process of water moving from an area of high concentration to an area of low concentration. It is used on ships in realtion to water purification to produce drinking water.

Answer 7

its when the gel coat gets chiped off usually below the water line,the water then get absorbed into the lamitations of the fibre glass,in time the boat gets soft patches and water loged,the best cure is radiation process,there are other methods.

Answer 8

osmosis is where mineral salts of low concentration go to an area of high concentration , ie. a plants roots taking minerals from the soil , reverse osmosis is where the opposite occurs ie. making drinking water from seawater.

Answer 9

Porosity in the hull allowing water to seep through.

Answer 10

Osmosis, I think it's how they get fresh drinking water on ships in the ocean (removes the salt)