Foam Cored Hulls

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purplerobbie

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What is the benefit of a foam cored hull
Is it possible for foam cored hulls to get water in the foam? or would it just sit around the foam?
If it is is it possible to get it out?

I seen a boat for sale a while ago wit a foam core (a morgan 38 i think) and it had water in the core

How would you go about curing this if indeed you could?
I suppose you would have to stop it getting back in if you could find where it go in the first place.

wouldnt you just be better off with a normal hull?

Rob
 
I'm no expert but foam cored hulls seem to offer great stiffnes and lightness when new, but long term their integrity depends on the foam not getting waterlogged and not degrading........How can you tell when its had enough, and is the boat then effectively a dangerous liability, and how can you repair it?

I don't know the answers, but its what would concern me. Maybe I've got it all wrong, but i'd always be suspicious of a hull where you can't examine inside the inside effectively..if you get my drift.

Tim
 
A foam cored hull bonds the inner and outer skins together. So in effect they work on the same engineering principle as an I beam and you get a much greater stregth for a given weight of lamination. Once the bond is broken, however, you have two independant floppy thin skins

Anything in fibreglass is repairable as long as it isnt burnt - all it requires is the application of money. So you can dry out a foam core and the question is how much it will cost and is it worth it.

Most boats have balsa cored decks and the same principle / problem applies, except that balsa unlike foam can rot and problkems are more likely because there are more potentially leaky fittings through a deck than a hull..
 
There're foam cores used for buoyancy, like Etaps, and there're structural foam cores to reduce hull weight, often used on multihulls and some of the whizzier monos like X-Yachts. I don't know anything about the Etap kind, but have lived with a couple of the latter types.

If foam cores are going to be used by the manufacturer, it has to be done properly. A problem that can occur in manufacture is a lack of bond between the outer skin of glass and the foam core. It's not easy to get this right and neither is it possible to tell how good the bond is either. There are some horror stories on this website...

Foam cores

A technique that helps here is called vacuum bagging. It's slow, messy and expensive, so not all foam core manufacturers do it. X-Yachts don't. Quorning who make Dragonfly trimarans and Corsair who make Farrier-like tris both do.

As already mentioned in another post, the problem is getting water in the foam. Although foams are closed cell, water can still play havoc and wreck the foam. See the Yacht Survey site for examples. Water can get in where holes have been made in the inner skin for fittings. Good manufacturers will avoid this, and provide areas of solid laminate where skin fittings need to penetrate the laminate. Many problems are caused by owners fitting something later and not sealing the hole correctly, allowing water in.

One method of avoiding water ingress problems is not to use solid sheets of foam core, rather sheets made of small biscuits with gaps between. When manufacturered using vacuum bagging, resin completely fills these gaps isolating each small area of foam. Any water ingress causes much less problem as it's isolated to a small area of foam. But it all adds to the cost again. Quorning and Corsair use this technique.

As for is a (structural) foam cored hull worth the expense and risk? I'd say for most monohull sailors no. The weight saving won't make much difference when you're dragging around a big lump of lead anyway. It really comes into it's own on multihulls, especially tris, and that's where it's found most often. But done properly (as the 2 main tri manufactures do) it comes at a price, and is one of the reasons tris are so expensive for their size.
 
All very interesting to the owner of a Sadler. I can't decide exactly where the foam is located in our S29. Certain areas seem to be very thick-walled e.g. the grid structure which supports the cabin soles and the supports for the berths but I don't know whether the foam in these areas is all connected. Anyone know?
 
Slight digression
It's my experience that collisions with foam cored hulls generally seem to result in more extensive damage. A Sigma 33 I know hit a mark on the beam which punched a massive open hole in the side. Solid GRP seems to crack but basically holds together. All depends on the severity of course.
 
My only personal experience was, 2 Dellquay 17' Dories I used for work. They both got waterlogged, its pretty well impossible to get the water out, they weighed a collosal amount, personally I would be very very wary of a foam (or balsa) core anything.
 
G'day Evening Star,


Some very good responses on this thread, well done.

But to answer a couple of questions you asked.

<<<What is the benefit of a foam cored hull>>>

Items not listed include: Less noise, no condensation and good thermal insulation.

<<<Is it possible for foam cored hulls to get water in the foam? or would it just sit around the foam? and If it is is it possible to get it out?>>>

Replacing wet or degraded foam is possible but expensive as it involves the removal of one skin, stripping the old foam preparing the remaining skin and installing new foam. The common method is to locate the wet area with a moisture meter and drill out plugs to establish the extent.
Once foam has been wet it will almost certainly have lost it's bond or the foam dissolved to a mush if not of the closed cell variety. Bottom line here is that is not possible to remove the moisture and be confident in it's structural integrity.

<<<wouldnt you just be better off with a normal hull?>>>

There are a few systems that will provide the same or better strength to weight ratios, like carbon fibre and other exotics, however their cost puts them out of reach but for racers with very deep pockets.

Never purchase a foam cored boat that has foam below the water line, this asking for trouble.

Our 42 foot Cat is foam cored, and was made in the USA then sailed to Australia, the bulk heads to the forward compartment were never cut to provide access as cabins. Each hull was fitted with fresh water tanks against the bulkhead and collision bulkheads in the bows. We plan to strip the tanks and open the bulkheads next winter and add more accommodation taking us from 8 to 10 capacity.

Hope this helps.

Avagoodweekend......
 
"Never purchase a foam cored boat that has foam below the water line, this asking for trouble."

I'm in trouble then both my hulls are foam cored !
/forums/images/graemlins/laugh.gif
 
[ QUOTE ]
Never purchase a foam cored boat that has foam below the water line, this is asking for trouble.


[/ QUOTE ]

Or at least not a hand laid-up one. I used to have an X99, which had hand-laid foam core construction below the waterline. It got water in its core, and it cost a lot to fix.

A vacuum-bagged or resin-infusion constructed hull is less prone to problems when a core is used below the waterline. Dragonflies are built like this and don't seem to suffer. But I would agree with oso that it's a risk too far unless you want a high speed racer or a tri.
 
Howdy,

My main interest is wood, but there have been large numbers of Foam Glass boats in existance from dinghies through to ferries and large commercial ships.

Military vessels as well.

There are some that have had problems but there are many more that haven't.

Otherwise Lloyds and other bodies would not accept it as a construction method.

That doesn't mean that there are not disasters out there, but there are with trad timber, aluminium, modern timber, composite.

We have all heard of problems with all of these. Buy any second hand boat carefully. If it is surveyed and OK after 10 years there is not likely to be any sudden problem with no warning.

Best wishes
Michael Storer
 
Rob

Etap have already been mentioned by others. Etap use closed cell foam, so water in the void between the two skins will not be absorbed by the foam. Our first Etap bought in 1992 was 20 years old, we carried out various modifications which dictated that foam be cut away. There was NO signs of any water absorption into the foam.

You may want to visit the Etap web site:

Etap Yachts

This may not apply to all 'foam cored' boats however.
 
[ QUOTE ]
Or at least not a hand laid-up one. I used to have an X99, which had hand-laid foam core construction below the waterline. It got water in its core, and it cost a lot to fix.

[/ QUOTE ]
Could you have still used this boat?
If it has water in will it cause problems?
Rob
 
The X99 with water in its core got stern heavy - it was noticeably down on its normal waterline. It was still useable, but left it would not get better on its own. Eventually it would have spread and/or weakened the structure.
 
[ QUOTE ]
Slight digression
It's my experience that collisions with foam cored hulls generally seem to result in more extensive damage. A Sigma 33 I know hit a mark on the beam which punched a massive open hole in the side. Solid GRP seems to crack but basically holds together. All depends on the severity of course.

[/ QUOTE ]

Is a Sigma 33 foam cored? I didnt think it was.
 
Our Island Packet is foam core above the water line, solid lay up below. Proprietary closed cell foam so no water ingress. Hull comes with 10 year warranty. Have looked at IP's 20+ years old and they look fine. Trust this far more than balsa/ply core. Also warmer, drier etc etc but not unsinkable like Sadler/Etap.
 
It seems to me that the thicker the outer layer of fibreglass the better chance you have of resisting water ingress. So I have seen a few small dinghys with foam in the bottom that did not last very well with the natural abrasions of a long hard life.

On the other hand my 21fter seems to have bottom solid skin about 8mm thick and if that were in a bigger boat over a foam sandwich I can't imagine water getting through 8mm.

So I would tend to worry a bit more with an old boat with foam under water. but if it is not subject to abrasion it is probably OK.

Many years back I built a little 14ft catamaran of fibreglass. Now perhaps I was not the most diligent skilled f/g layer upper but he end result with about 3mm thick of polyester resin was appalling porosity. Not good when it went into foam. Or in another case without foam it simply ran into the bilges. I am sure a commercial boat builder would do better but it seems on thin lay up there is plenty of scope for unwanted porosity. olewill
 
As I said earlier, I would be very wary of foam, it must eventually be a problem, more complex than a single GRP solid lay up. Any breach of the skin will allow water ingress.
 
[ QUOTE ]
I would be very wary of foam, it must eventually be a problem

[/ QUOTE ]

No, your wrong "it must" is not true. Some manufactures who have chosen to use cheaper, non closed cell foam etc may have problems, but your statement is a general rule which is incorrect. I refer my earlier post, which may also apply to other makes:

[ QUOTE ]
Our first Etap bought in 1992 was 20 years old, we carried out various modifications which dictated that foam be cut away. There was NO signs of any water absorption into the foam.

[/ QUOTE ]

Etap have been using foam core since 1970, with great long term success. I have been very close to Etap and their owners for 10years now and have heard no such reports that you suggest.
 
It all depends on the type of foam and the construction method inc quality of lay up.
Obviously the foam must be in close contact with curing resin to get a good bond.
Using PVC closed cell foam creates an inseperable bond with the resin.
Balsa is less reliable since punctures lead to core softening.
It's best to plan ahead especially with regards to posn of later thro hull fastenings so as not to crush the foam. However with a good system you end up with several waterproof layers and it's very strong for the weight. The later honeycomb cores got a very bad reputation for delaminating. And you need to differentiate between structural foam and foam added later for buoyancy which is unlikely to bond well.
My cruising tri with GRP/Airex PVC foam is thirty years old and still tough.
 
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