Kukri
Well-Known Member
The latest MAIB report is a bit sobering...
http://www.maib.gov.uk/cms_resources.cfm?file=/SB1-11.pdf
http://www.maib.gov.uk/cms_resources.cfm?file=/SB1-11.pdf
Foam cored hull, anyone?
- Thread starter Kukri
- Start date
exfinnsailor
Well-Known Member
Old sailing club had a Dory for a rescue boat a few years ago . Everyone said it was a bit slow . Came the end of the season they had a look and noticed a damaged area underneath . Must have hit something or been damaged ashore . The foam was saturated . Think they left it to drain over the winter and then repaired the hole.
aluijten
Well-Known Member
Luckily most glass fiber boats with a foam core are not filled with PUR foam, but flat foam panels were used during the glassing process. The core is extremely well bonded to the polyester, if done properly. The foam itself is very much hydrofobic (?) and absorbs no water just money during the boat-building process 
greenalien
Well-Known Member
Foam core or not, any double-skinned tender that gets damage to the outer hull will (obviously!) take in water, and this may not be noticed until too late. Most common problem is rub-strip wearing out unnoticed, exposing the bare GRP to abrasion damage, or the holes for the screws securing the rub strip leaking. They are also a pain in the a**e to repair, you can do a rough patch-up job from the outside, but a proper repair means that the inside moulding needs to be removed.
vyv_cox
Well-Known Member
There's polyurethane, and there's polyurethane. The two-pack stuff sold by DIY glass-fibre suppliers absorbs very badly, being open cell. I built about 30 canoes in the 1970s, filling the ends with this PU foam for buoyancy. Within two years we had to dig it all out, saturated just like the stuff in the report photos. It was also quite white in colour, again like the photos.
Much later I came into contact with professionally sprayed PU foam, initially in the building industry, then as insulation in LNG carriers. This is closed-cell foam with a water absorption of less than 1%, IIRC. The PU in Kingspan, and in the hull of my Sadler 34, seems to be similar, all being brown/yellow in colour.
So far as the Sadler is concerned, I cut some pieces out when installing the hull fittings for my Yacht Legs. I immersed a sample in water under a weight for a week or so and it appeared to have absorbed none.
Much later I came into contact with professionally sprayed PU foam, initially in the building industry, then as insulation in LNG carriers. This is closed-cell foam with a water absorption of less than 1%, IIRC. The PU in Kingspan, and in the hull of my Sadler 34, seems to be similar, all being brown/yellow in colour.
So far as the Sadler is concerned, I cut some pieces out when installing the hull fittings for my Yacht Legs. I immersed a sample in water under a weight for a week or so and it appeared to have absorbed none.
Bosun Higgs
N/A
Interesting that you installed legs Vyv. I've wondered about doing that on my Starl;ight with the same sort of construction as your 34. Care to give a few details of what was involved in the work.
Joker
Well-Known Member
Some of you might be aware of some problems I have been having with a foam sandwich boat.
During the course of the repairs, the boatyard found some water inside. This came from a screw hole for an external hull fitting.
In the normal course of events the water should not have been able to penetrate further, but in this case it went into the voids resulting from the delamination.
The foam itself was fine, and it all dried out quite quickly. I suspect the problem in the case of the rescue boat lies with the foam that was used.
During the course of the repairs, the boatyard found some water inside. This came from a screw hole for an external hull fitting.
In the normal course of events the water should not have been able to penetrate further, but in this case it went into the voids resulting from the delamination.
The foam itself was fine, and it all dried out quite quickly. I suspect the problem in the case of the rescue boat lies with the foam that was used.
seasolutions
Well-Known Member
PVC foam as used in good quality foam sandwich construction is totaly closed cell, so shouldn't absorb any water. PU as vyv-cox say can be good or not so good. the worst of the lot however is balsa this is used in building decks (and sometimes hulls) on many, many yachts and has been for years and years....
the problem is that sooner or later some rain water finds in way past a badly sealed fastening and then rots the core material away.
the only solution is to cut away one skin of the sandwich, scrape out the rotten wood and rebuild. and belive me that job is a LOT LESS fun than it sounds!
the problem is that sooner or later some rain water finds in way past a badly sealed fastening and then rots the core material away.
the only solution is to cut away one skin of the sandwich, scrape out the rotten wood and rebuild. and belive me that job is a LOT LESS fun than it sounds!
