osmosis from the inside?

voicilesrosbifs

voicilesrosbifs

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Much said and written about osmosis from the outside of GRP hull in salt water, but anybody had instances of osmosis from inside where, for instance, water is up against GRP layup for extended period. Example that prompts this is a foam-filled Sadler that's got some moisture behind the foam, trapped betwixt foam and hull. Your thoughts, please, ladies and gentlemen!
 
Not uncommon, many catamarans that had fresh water tanks built into the mimi keels had this problem till the builders decided to line them with epoxy.

This is also the reason to remove water from bilges, particularly fresh water.

Avagoodweekend......
 
Not unknown for water to get in and then foam to break down. And, yes potential osmosis from the inside. I understand it is possible to make good these failures and it is worth taking professional advice. I would be less concerned about osmosis than losing the panel stiffness because of deterioration of the foam.
 
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Much said and written about osmosis from the outside of GRP hull in salt water, but anybody had instances of osmosis from inside where, for instance, water is up against GRP layup for extended period. Example that prompts this is a foam-filled Sadler that's got some moisture behind the foam, trapped betwixt foam and hull. Your thoughts, please, ladies and gentlemen!

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Is the foam showing any sign of holding moisture or is it breaking down, or just delaminating between foam and glass?

Any of the above will require urgent work to prevent a possible failure. Not the end of the world but depending on the type of failure it be costly and time consuming, if not dangerous.

Avagoodweekend......
 
I don't think the foam is breaking up - at this stage it appears there's moisture between foam and hull. Sadlers don't rely on the foam for structural integrity AFAIK, but it certainly would not help general stiffness to have delamination.

Thanks for comments - confirms my gloomy premonitions /forums/images/graemlins/frown.gif
 
My observation was based on 2 29s that friends had, both of which had delamination in the forward bow panel which lead to cracking from flex on the outer skins. Both were repaired and as far as I know are still OK.
 
Yes - got some osmosis in the inner lining on a Sadler where the water tank (dont you just love bag tanks) had long had a small leak. Dope of a previous owner hadnt noticed.

Not worried - whats half a dozen small blisters in an inner lining - and out of sight at that.

All sandwich laminates are dodgy really, which is why HR were very reluctant to start using them and also Hunter boats. Much easier to repair something solid.
 
Spoken to Mike Lucas, the Sadler expert in the past on this foam core construction. He seems to be unaware of any problems, or at least not admitting it. Conflicting advise abounds. Some say never drill any holes low down in inner moulding for fittings. Others drill holes low down to dry out !
Have heard of epoxy treatments carried out on Sadler 29's costing £16,000 because the floor had to be cut out and foam removed to dry out. Conversely, another less expensive method is to drill holes in the bottom to drain then use Hotvac at low temperature to draw moisture out of foam.
Some say that the outer hull has strength enough - indeed one Sadler 29 I believe was built without inner foam and moulding.

It would be nice to get to the definitive answer 'cos I am also considering a Sadler 29 !!!!!!!
 
Not sure you are right about HRs Think they have had cored topsides for many years. One of their weaknesses is that the substantial looking rubbing strake is in fact a foam cored part of the main hull moulding and a bit of a B if it gets damaged. I know of at least one HR (second hand source but reliable) that has had serious delamination problems. However rather like failures in Mercedes they don't happen so you don't hear about them!
 
We too have been investigating Sadler 29's and soggy foam seems to be a common problem with foam core boats in general!?
I guess that there are two issues -
1) The foam core dissolving and affecting rigidity.
2) Osmosis
Later Sadlers were injected with a different foam but not sure what difference it makes to this issue if any?

Ultimately does anyone know whether it can be repaired and what is the cost - if we find a boat with this problem, should we walk away as potential first timers?

Agree with theoldplucker - a definitive answer would be good!

Have you had a professional opinion or a survey done to know which areas are affected?
 
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I guess that there are two issues -
1) The foam core dissolving and affecting rigidity.
2) Osmosis
Later Sadlers were injected with a different foam but not sure what difference it makes to this issue if any?

Ultimately does anyone know whether it can be repaired and what is the cost - if we find a boat with this problem, should we walk away as potential first timers? - a definitive answer would be good!

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Core foam dissolving is a result of 'open cell' foam in most cases, the more expensive closed cell foam is used in most modern constructions.

In general terms any boat that has foam below the water line or in the rubbing strake should be avoided.

Repair is possible but very expensive, all the old foam must be removed, the remaining skin cleaned and the foam replaced with closed cell material and a new lay-up over it, some just remove the inner liner and glass over the original out skin.

By the way, blisters developing at the point of contact between gag tank and hull are more likely to be wicking or just in the ssurface rather than osmotic, they can be avoided altogether by placing a liner between the tank bladder and the hull.

Hope this helps.

Avagoodweekend......
 
You folks must be psychic - I never said it was a 29 but indeed it is! Boat very promising otherwise, proper survey done, just waiting for the results. Fingernails already well bitten, starting on the knuckles soon. I'll post again when I know the worst.... /forums/images/graemlins/confused.gif
 
A definitive answer is needed. The trade owes it to the buying public and owners. Without it, there could be a drastic fall in values of foam core constructed boats.
I see the salient points are :-

(A) Does it really matter if the foam core becomes unstuck from outer hull in a Sadler - I believe it occurs in bow sections from beating into heavy seas - panting. Is not the outer hull strong enough ?

(B) Does foam, open cell or closed cell disintegrate ?

(C) Accepted open cell will absorb water, does closed cell absorb any water at all ?

(D) What was the year that Sadler and other manufacturers moved to closed cell ?

(E) Worth cutting a hole in inner core at lowest point creating a sump that can be pumped dry ? Some say definitely not.

(F) Drying out for epoxy treatment methods - Cutting out floor and removing foam, dry, epoxy and then replace floor - expensive.
Or, drilling holes in bottom externally to drain, then Hotvac at low temp. to dry - less expensive.

(G) Are some yards taking the more expensive route to generate income ?

(H) Surveyors - are they just over cautious to cover their backs ( which is understandable).


(I) Another unwise construction method like balsa cored decks or nothing to worry about ?

Many will steer clear of Sadlers and other foam cores until we have some truth which would be a pity because of the Sadler's practical layout and sailing capabilities.

Osmosis seems not a concern in the fishing industry. Fishing boats affected are treated by breaking out blisters, washing, left to dry, then filled, sanded, antifouled. Why not the same approach in private boats which are used a lot less ?

Come on surveyors and boat repairers out there, lets have some candid responses.
 
I'm not convinced that a Sadler is 'foam core' construction, that implies that the foam is one of the layers in the glass/resin layup. Surely a Sadler is 'foam filled' which is a very different proposition. Or am I totally wrong?
 
Had a survey done on a 29. Surveyor phoned up and said "Just don't"

Phew. Boat was for sale for ages after that.

I understand the 26 & 29s (foam filled) can be lovely to use, but just make sure you get a tip top one.
 
You are absolutely right. Foam cored means the hull is laid up with gel coat, then glass then foam (or it could be balsa) then more glass. Almost universal now - reduced weight, greater panel stiffness - and pretty reliable, particularly with modern techniques of manufacture including material control, resin infusion, vacuum bagging etc.

The Sadler method of construction uses two hull mouldings, an inner and outer. The inner is placed into the outer while the latter is still in the mould and the gap between the two filled with closed cell foam. Etap use essentially the same process. I had direct experience in using the technique in the 1970/80s at Tremlett on small sportboats. Great idea in theory but difficult to get right.

Biggest long term problems are caused by water getting into the void between the mouldings, and perhaps also flexing of the necessarily thinner outer hull cause a breakdown of the bond with the foam.

On the two that I know about it was very easy to spot - ripples on the outer bow panels and hollow sounds when tapped. Repair was straight forward by removing the inner skin taking out the decayed foam. The inner skin was then bonded back and the void refoamed. Care must also be taken to ensure there are no leaks though things like chain plates.

The 26s 29s and 34s built using this method are still very attractive boats and I don't think this sort of problem would be a no -no provided the price reflected the repair costs.
 
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(I) Another unwise construction method like balsa cored decks or nothing to worry about ?



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If you are going to worry about balsa decks then you are going to worry about almost all boats. Yet its more of an issue than foam filled hulls because you have many more fittings penetrating the skin and vulnerable to leaks in a deck than you have in a hull. Plus the deck is far more visible and requires a better cosmetic finish so repair is way more difficult.
 
The surveyor's report came through - extremely thorough and (from these forums) well respected chap, commented on the localised incidences of moisture under the foam as 'undesirable'... but did not see this as a major fault and the rest of the hull/topsides got a clean bill of health so we've taken the plunge (with a bit off the price).

No point paying for an expert opinion if you don't believe the results..... interesting that a survey from a couple of years earlier didn't pick any of it up.

When we've had time to draw breath we'll address the water that's there already, meantime we're concentrating on not adding to it by sealing a few small but significant bits of indifferent maintenance that probably were the cause in the first place.
 
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