What is osmosis? can your boat sink if it has this?

Question

descriptions of boats for sale often say there is no osmosis. How serious is this problem on fibreglass boats? Does it occur naturally and get worse to the point that the boat would sink? What can be done to prevent or reverse it?

Answer 1

For 80's Kid...

Osmosis..."the passage of water or other solvents through a semipermeable membrane"

In this case the membrane is the boat's gelcoat and descriptive term is correct.

---ya putz.

Blisters in the gelcoat below the waterline. A saltwater  and freshwater (with weak gelcoat)environment issue. The salt molecules migrate into the gelcoat and draw water into the gelcoat. The water pops the gelcoat. Freezing cycles worsen the condition. You get bigger bubbles and blisters.

I agree with Micheal H below about ratios of gelcoat mixes in the past...and acetic acid bubbles.  And yes...a path can form to the inside of the boat...and yes, in the strictest sense...if your batteries are dead and your pumps don't work and you're a MORON....your boat CAN sink!!!

The boat gains weight...the underlying laminate can also get infected in very bad cases...leads to leaks and weak spots.

You gotta grind them out....or strip/peel the hull....thoroughly wash/flush with fresh water....thoroughly dry out...then coat with Epoxy or Vinylester to waterproof the hull.

Note also: that Vacuum bagging does not happen on hull exteriors much or at all...that's a fresh build/ molding and lay-up technique. Nor would vacuum bagging with poly give a perfectly smooth finish....not a chance.

The epoxy/vinylester treatment is highly recommended from factory new before launching.

Answer 2

Michael H has is dead right. It's a layup problem when the hull was first built, but you don't see the problem until years later.

One thing nobody has really mentioned is that osmosis is a COSMETIC problem. A boat with osmosis will not sink, nor does osmosis make it structurally unsound. The problem is that it looks unsightly, it will only get worse and it's pretty expensive to put right (unless you do it yourself). A boat with osmosis will be hard to sell because of the above, but it's not unseaworthy and it won't sink.

Osmosis can happen in almost any GRP hull and just because there's no evidence now doesn't mean you'll never see any. Having said that, if the hull is at least 10-years old and has never shown any evidence of osmosis then it's unlikely to do so now (though not impossible).

When you buy a GRP boat one of the things the surveyor will do for you is give you a feel for the moisture content of the hull. This gives you a rough idea of whether you might suffer from osmosis in the future. (A wet hull generates more osmotic pressure than a dry one).

Don't buy a boat that shows osmosis - it'll cost you a LOT of money to correct. But don't loose any sleep over osmosis after you've bought your boat!

Answer 3

Have to say i disagree with some of the answers above.

Osmosis is not a salt water issue. ( fibreglass narrow boats suffer from it too )

Its not caused by water getting through pinholes in the gel coat - that is a symptom

Osmosis is caused by the incorrect mixing of the resins used to make fibreglass. It results in a reaction  that produces acetic acid. This forms pockets that expand, creating bubbles with a very weak film that is easliy pierced.

If you poke a hole in an osmosis bubble, it smells like vinegar - acetic acid - try it.

You need to root out all the weak bits, thoroughly dry them,  and repair them to gain full strength again.

Eventually, osmosis can cause a boat to take on water as the bubbles join up and create a "channel" from the outside to the inside. This will first be seen by "damp" patches on the inside of the hull.

The first signs are small marks on the outer hull, little more than "stipples". A bad case will show large bubbles that are easy to push in and out by hand, probably breakign them - they go very brittle. Even these are not the end of the world, they can be repaired but its a dry-dock job.

Answer 4

I know what osmosis is, and I've never heard of people using this term when referring to boats.  Many people who don't know what they're talking about use useless terms and over-use nautical terms to make it sound like they have a clue.  My advice is don't even deal with people that are talking about the osmosis of a boat, because something is not right, either with them or their boat.  DOES THE BOAT LEAK?  This is a normal way to discuss the seaworthyness of a vessel.  Osmosis occurs in living cell membranes of plants and animals, WTF are they talking about?!

Answer 5

Any thing that sits in water absorbs it, this is osmosis. Its not the end of the world when the GRP absorbs water depends on the extent. We had a princess 40 with slight osmosis the boat yard qouted £5k to sort it. When the chap came to buy it the surveyor said there was not alot of point in doing it as it was only slight and would come back over time any way.

Basically water gets behind the gel coat and it looks like the bottom of the boat has blisters (which it has) water blisters. Wooden boats dont get this they are supposed to absorb the water to remain water tight, its just GRP ones, and eventually they nearly all do. Just some take a lot longer than other.

Answer 6

have a read here.............

http://www.nautica.it/info/maint/osmosi_...

Answer 7

Osmosis is a breakdown of the outer skin of the fibre glass,i know it is below the water line,but not sure if it breaks down above the water line aswell.it can be treated by specialists

Answer 8

When we first made fibreglass boats we thought that the gelcoat (the outer layer) was waterproof. Turned out it was not neccessarily the case. If the gelcoat layer had a few pinholes then water could get in under the gelcoat. As water cools it expands so after a few winters (even if the boat was taken out of the water over winter) the water behind the pinholes expanded to make the gelcoat bubble.

Please note here that this problem does'nt effect the waterproof integrity of the hull, so the boat would not sink - but it looks really bad.

The cure is to use a special grinder (must keep the bits out of the atmosphere and especially out of your lungs) to grind off the old gelcoat and replace it with modern (waterproof) gelcoat. The liquid gelcoat is spead on the stripped hull and 'bagged' with polythene to make a super smooth new finish to your hull. As you can imagine, this is quite an expensive operation - but time is money and the end results are fantastic and permanent, so if you find a boat with osmosis get a quote for the stripping and replacement and knock this of the asking price of the boat ('cos the owner will end up paying for it sooner or later).

Hope this helps Bigpathome.

Answer 9

Osmosis is the leakage of a liquid through a membrane..No osmosis means it is water tight.