Is there such a thing as genuinely closed cell foam? I have just taken a dory apart (Its only 11'6" long and it weighed 500kg on the crane!) and have found a mess of water-soaked foam in between the two skins. It appears that when it was made, foam was injected between the skins, but the foam is sodden and very heavy with water in places.
I am tempted to rivet the thing back together and fit some drains so that if the water gets in again, I can drain it out and guarantee that the inside is dryish.
Any suggestions?
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“When you discover that you are riding a dead horse,
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Try the stuff we use to make racing car fitted seats with .. expands like hell and is very closed cell foam .. should be available from 'Demon Tweeks' who supply all things motor racing.
Some would say you are riding a dead horse - repairing it properly might cost more than the boat is worth.
Anyway, my understanding is that the foam is supposed to be structural. When properly bonded to both skins it makes the hull stiffer, like an I-beam. However, if it is an old dory (and it sounds like it is because newer foam was better at keeping the water out), then it will probably be way over built, so it's not such a concern.
I'm not an expert but I looked into this when I owned a yacht with a soggy core (but I think not 500kg soggy), and it was very solid - I know this because it spent 12 hours bouncing around on some jagged rocks and didn't get holed.
Is there such a thing as genuinely closed cell foam? I have just taken a dory apart (Its only 11'6" long and it weighed 500kg on the crane!) and have found a mess of water-soaked foam in between the two skins. It appears that when it was made, foam was injected between the skins, but the foam is sodden and very heavy with water in places.
It most definitely does exist. I have worked for two companies who manufactured products using MDI based closed cell foam, whose testing confirmed virtually zero water absorption over long periods. A sample of foam I cut from my Sadler 34 has also failed to absorb any water.
However, my own attempts to provide buoyancy for canoes using the two-pack polyurethanes provided by the DIY GRP companies were catastrophic. That foam absorbed water like a sponge and had to be dug out.
Doing the same thing with a dinghy - the foam became totally waterlogged after the outer skin got punctured. I used 'Fireproof expanding foam' from Screwfix. We tested a lump of it by mooring it at the bottom of a water butt for a month. Nil absorption at about 1.2M depth.
However it is 'not very nice' stuff to use. Its bright pink - which caused a number of rude comments at the yard. Thats Ok, but the wretched stuff goes on expanding for nearly 24 hours, and having been over- applied, it distorted the mouldings. We could just chuck it back in the water and get on with it...... And whatever you do, dont get it on your skin - it sticks and does not come off - for days!
Of course if you dont mind walking round with bright pink excrescences on your hands.... it causes people to 'move on up the bus', as it were - quite spectacular really, and probably good for a week or two off work as well
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Is there such a thing as genuinely closed cell foam? I have just taken a dory apart (Its only 11'6" long and it weighed 500kg on the crane!) and have found a mess of water-soaked foam in between the two skins. It appears that when it was made, foam was injected between the skins, but the foam is sodden and very heavy with water in places.
I am tempted to rivet the thing back together and fit some drains so that if the water gets in again, I can drain it out and guarantee that the inside is dryish.
Any suggestions?
Yes closed cell foam does exist and it is supplied in panels direct from the manufacturer. Fundamentally it is used like balsa core, in that the outer skin is moulded, then the foam panel bonded in place, usually with a polyester resin, then the inner skin is laid up over it. It is NOT injected. The two pack syntactic foam you mix and pour or inject is NOT closed cell. It is not entirely pourous but is not designed to resist water penetration for any length of time. It does however "skin" over on exposed surfaces so should not absorb much water. Many rudders are made by pouring such stuff into a cavity between two GRP skins. This is OK only if the outer skins are made entirely waterproof. Otherwise once the water does get in the foam degrades over time and you have a rudder full of water....
Location: 'ang on a mo, I'll just take some bearings
Posts: 17,178
If you don't want the structural benefits, just fillit with polystyrene beads.
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I had access to a RIB with this problem. The solution was to drill a hole at the lowest point on the transom. Ram a copper pipe up the length of the boat, taking out a core of the foam as you go. Leave to let the water drain out. Fit a proper bung type fitting into the hole you drilled. Fit the bug whenever you go out, and when she's laid up, take the bung out.
1. I can rivet the thing back together with no foam and rely on the structural strength of the moldings 'unconnected'. Not too sure about this option...
2. I can try this Screwfix fire-foam stuff - but I wonder whether the skin was part of the water proof property in the bottom of the water-butt?
3. I can obtain some closed cell panels and stick them into the inside of the hull with dabs of Sikaflex, and then apply a small quantity of the expanding foam to the inner surfaces and place the inner skin back on the expanding foam and quickly rivet the inner skin back on. If the small amount of expanding foam does eventually take up water, then its not as a big a deal as having the thing weighing 500 kg which it did before I started this process.
Perhaps I should have drained it out of a bung hole, polished the thing and put it back on e-bay...
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“When you discover that you are riding a dead horse,
the best strategy is to dismount.”
I had access to a RIB with this problem. The solution was to drill a hole at the lowest point on the transom. Ram a copper pipe up the length of the boat, taking out a core of the foam as you go. Leave to let the water drain out. Fit a proper bung type fitting into the hole you drilled. Fit the bug whenever you go out, and when she's laid up, take the bung out.
Not a bad solution, but a bit late when the boat is in two bits!
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“When you discover that you are riding a dead horse,
the best strategy is to dismount.”
Having owned three Dell Quay dories, I spent hours and hours trying to drain out water. I even transported our first one ( 1970s green fibreglass deck) back to Walsall on a lorry, drilled the transom hole and left the dory on a slope for 6 months. No difference whatsoever. I eventually gave up on dories and bought an Orkney Longliner.
If the inner and outer skins are now too floppy without the foam to stiffen up the structure, you could perhaps install some carefully measured frames in the hull (eg foam glassed over to make top hats) and then bed down the inner skin on to these frames.
It would be a good idea to have drain holes in these frames (they could be longitudinal or transverse).
Re buoyancy to replace the foam, an alternative to Ken's suggestion of polystyrene beads would be to fill the void spaces with PET bottles - or perhaps even sturdy milk cartons (we have 2 litre rectangular cartons here with a screw top that stow very nicely).
If the inner and outer skins are now too floppy without the foam to stiffen up the structure, you could perhaps install some carefully measured frames in the hull (eg foam glassed over to make top hats) and then bed down the inner skin on to these frames.
It would be a good idea to have drain holes in these frames (they could be longitudinal or transverse).
The inner and outer skins aren't very floppy at all at the moment - so I suppose that answers the question! However the 'hull' skin has still got quite a bit of expanding foam to dig out of it yet, so I will have a look how it feels when I have dug all of that out in a day or two.
I need to re-glass a hardwood strip into the keel as the old one had broken and the glass was coming away under all the mess of polystyrene bits and expanding foam. This revealed various screws from the aluminium strips which were protecting the 'keels' which had no sealant and I guess were leaking water straight into the boat!
I will try and take some photo's and post them.
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“When you discover that you are riding a dead horse,
the best strategy is to dismount.”
Quote
The inner and outer skins aren't very floppy at all at the moment - so I suppose that answers the question!
End Quote.
To confirm the stiffness of the hull/s; place parallel timbers a couple of feet apart on the ground, place the hull/s across them and stand on the area between the timbers to see how much flex you have. This should give an indication of how far apart any stringers need to be, moving them to the point the flexing is acceptable.
If you decide to add stringers, make up a small profiler to help maintain aneven height, you will be able to glue them to the other hull with a mix of resin and micro fibres.
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I've done a fair bit of research on this as I have a lot of foam in my boat. Tests involved sealing samples of foam in a container of water and leaving for a year to check for absorption. Here are my results:
PVC foam (Airex, Herex, Divynicell): no absorption. Only available in sheets so has to be built in during construction.
Expanded polystyrene: no absorption. Can only be inserted as loose material. Destroyed by polyester resin and most adhesives.
REP (rigid expanded polyurethane). Available as sheets or foam-in-place with 2 liquids to mix & pour: Nominally closed cell but requires very little pressure to break down the cell structure. Immersing as little as 2 ft under water can break the cell walls. Once damaged it absorbs enormous quantities of water. Use only in above-waterline applications like fridge insulation. This is the stuff found in countless old waterlogged boats - I suppose it seemed like a good idea at the time.
Builder's foam Marketed as 'expanding foam': Does not absorb water (really, I tested it). sticks to anything even damp surfaces (in fact they tell you to moisten the surfaces first). The down sides: expensive for a large volume, generates great pressure so must be allowed to expand freely or it will burst the container, doesn't flow like REP so can't be poured into a deep cavity.
There are also commercial foam systems used for cavity wall insulation and spraying onto the underside of roof tiles but I haven't researched these.
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Does genuinely closed cell foam exist?
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