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Osmosis


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Congratulations, Graham. 

Don't worry about the osmosis. The surveyor has to tell you about it and shouldn't offer much on opinion as you might use it against him should something go wrong. You would be HIGHLY unlikely to find an Elysian or Freeman, Seamaster, Bates and the like without some. 

Enjoy boat ownership. 

 

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Morning all - first of congrats on your new boat!, hope you have loads of happy days aboard.

I did find the osmosis thing interesting and something I'd never considered, though have seen the blisters on other items used in water based conditions using grp, which piqued my interest when I was eating a sausage sandwich breakfast just now, which led to a Google search and found this..

http://www.smithandcompany.org/GRP/GRP.html

Quite a long read, but I found it interesting in a "oh I see" moment, not that it changes anything but did seem to lift a veil (for me at least!) of how does it happen, seems a lot more complex than just letting water in!

Happy Sunday all - off to Sandford Mill Museum of power today as it's nice and sunny

Cheers

Ray

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I was very careful of the sun and my lack of natural sun protection on top. However, what a fantastic place, highly recommended for the weather, views, food, and pace of life. Lovely people very pro English as was expected, and of course the deep blue med to swim in.

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I was very careful of the sun and my lack of natural sun protection on top. However, what a fantastic place, highly recommended for the weather, views, food, and pace of life. Lovely people very pro English as was expected, and of course the deep blue med to swim in.

All good Stuart, delighted you had a good holiday there. Now get back and enjoy your day job:naughty:. Will look out for you in less than a fortnight.:wave

cheersIain

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  • 5 months later...

This is a very interesting thread and I am sorry I have come late!

I agree with everything on here, but there are a few tips I have picked up which may be helpful :

Osmosis means semi-permeable membrane, in other words water being absorbed and retained.

There are said to be around 7 different types, depending on how it happened - from the outside through the gel-coat, from inside in the bilges, or from moisture in the laying-up process. It also depends on the quality of the resin and how well the mat was soaked by the laminator. I was always told "you can never use enough resin".

Antifouling is not a protection against osmosis and nor is paint, although 2-packs such as International Perfection 709 are "said" to be, as they are effectively a gel-coat. (These are expensive and should be professionally sprayed.)

Basic rule of thumb - leave it alone! Like mummy always said; "It will never get better if you pick it". 

And now the most important thing - If you have osmosis bubbles, don't leave the boat on the hard in winter. If the bubbles freeze they will all burst, and then you are really in trouble! Leave her in the water over winter.

You will almost certainly never buy a secondhand hire boat that doesn't have osmosis, so ignore it.

When we were selling older boats in France we were sometimes asked "what about osmosis?" and the answer was always "There is no extra charge. It comes in the price".

 

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My view........

In June 2009 we looked at a 1984 Aquafibre 35 for sale by a

large boatyard which had the layout that we wanted.

Unfortunately the survey showed she was riddled with so

much Osmosis that he estimated she probably weighed

around  3/4 ton  extra because of it. He said it would likely

cost around £2000 to put right. The skeg was also rotten

and it turned out that she had been 'on-the-bottom' twice!

His advice was to walk away, which we did.

It proves the worth of having a good survey done.

 

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You have to take great care that the blisters are not caused by the dreaded "Polyestermiite" that are a kind of worm that attack GRP but leave wood alone. They can render the GRP unservicable in a very short time, and can quickly spread to adjacent boats.

There was a big thing made about this by one of the Yachting magazines in the 70's.

Quite a few will remember the issue it was in, and what month.

If you Google " Polyestermite" it will go into great detail. 

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The subject of the thread is osmosis, so that is what I was discussing, but of course, you should never buy a second-hand boat without a survey. 

If you are looking for a big problem with a GRP boat, then make sure the sandwich has not gone rotten in the decks or cabin top. Have a good stomp around the deck and see if it is solid, or squishy. If it has gone squishy in places, around the deck fillers or cleats, then don't buy the boat.

And of course NEVER screw into a GRP moulding without first covering the screws in waterproof mastic. If not you will pay for it a year or two later.

By the way, it is said that if a GRP boat is going to get osmosis, then it will happen in the first 3 years of its life, but will not get any worse after that. In my experience with hire fleets, I think that is probably true.

Remember the old adage :

If God had wanted us to build fibreglass boats, he would have made fibreglass trees.

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2 hours ago, Vaughan said:

If God had wanted us to build fibreglass boats, he would have made fibreglass trees.

Or one particular April many years ago, spaghetti on trees! :naughty: Seriously, back on thread, very good advice, Vaughan.

cheersIain

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2 hours ago, Vaughan said:

If you are looking for a big problem with a GRP boat, then make sure the sandwich has not gone rotten in the decks or cabin top. Have a good stomp around the deck and see if it is solid, or squishy. If it has gone squishy in places, around the deck fillers or cleats, then don't buy the boat.

Yes, very good advice to prospective purchasers and boat owners.

I've found that many secondhand outboard and outdrive powered craft have significant rot in the wooden core of their transoms. The lower mounting bolts of large outboard motors are particularly vulnerable, being permanently underwater. If not tight and sealed correctly, the seep and turn the inner core to mush, just where you want maximum strength.

Noah's ark would still exist somewhere (as a ghastly abandoned plastic hulk) if God had dreamed up glass fibre before trees. :)

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1 hour ago, Strowager said:

Noah's ark would still exist somewhere (as a ghastly abandoned plastic hulk) if God had dreamed up glass fibre before trees. :)

That is a poignant remark if ever I heard one! How right you are!

GRP boats can only go to landfill - they just don't degrade, even if they don't float any more.

Nowadays the sandwich is made of special honeycomb plastic sheeting which is rot proof and I believe the more expensive boats were done in Balsa, which is said to be better, but your average run-of-the-mill deck mould is done in any old shuttering ply and it only needs an open screw hole or a loose deck filler cap, to let in water and air, the ply rots away and you are left with big problems to repair it. In fact you can never repair it perfectly.

 

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True enough Vaughan, GRP sandwich can be almost impossible to repair if it gets waterlogged.

As an owner though, I still prefer GRP, the basic material doesn't biodegrade like wood keeps trying to.

I've owned a number of secondhand sailing dinghies over the years, and the plywood ones were very susceptible to rotting in the hog and chines, whereas the (solid) fibreglass ones could stand decades of neglect and still be as sound as a drum. The annual "refit" was a quick pressure wash.

I've also owned a 40 year old ex-hire cruiser, where the (again solid)  GRP layup was half an inch thick, and only ever needed painting for cosmetic purposes, and showed no signs of structural decay whatsoever, (topsides or hull).

The contrast with friends' planked wooden craft was considerable, with them almost annually needing new planks and sometimes ribs, plus a rigid painting regime.

I'd much rather look in admiration at a well maintained wooden craft than most GRP boats, but my days of trying to maintain a Woodie are well gone......

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Interestingly (and I may have said this before) any remedial work on a fibreglass boat will be a repair. No matter how far you go or how good you are in making the repair it will still be just that. A repair.

With a wooden boat you get to replace the damaged part completely by going from original join to original join meaning it's back to its original state. There is no repair, just replacement of a component.

 

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10 hours ago, JanetAnne said:

Interestingly (and I may have said this before) any remedial work on a fibreglass boat will be a repair. No matter how far you go or how good you are in making the repair it will still be just that. A repair.

With a wooden boat you get to replace the damaged part completely by going from original join to original join meaning it's back to its original state. There is no repair, just replacement of a component.

Without wishing to turn this into a Wood versus GRP contest, and with all due respect, I think you may be splitting hairs there.

In 99% of cases, the only "repairs" needed to GRP boats are from impact damage, causing a hole, or a split, because GRP doesn't biodegrade, like wood, a living material.

GRP holes are "replaced" by fresh "new" GRP layup, moulded in-situ.

When wooden boats need a new plank, ( a much more frequent occurrence, unfortunately), often only the rotting section is cut out and replaced, to the nearest rib or a new scarf joint.

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