Is there a cure for glassfibre with a wet wood core?

[Greenheart]

A chunk of cracked glassfibre broke off one of my lateral centreboard supports. I had always thought there was probably some slender metal stiffening in there, but it seems to be wood, and it's apparently crumbling, sodden with water.

What worries me, is that it may not be localised - there are lots of ribs under the glassfibre deck, and presumably they're all wood and all connected - so possibly the whole wooden skeleton of the boat is wet.

I guess I can drill out the wet wood from the centreboard support and replace it with thickened epoxy...but what if the damp (it's more than damp, it was dribbling) is in all the wood inside the GRP? Is it a long expensive process to correct...

...or isn't it worth worrying about?

 

[William_H]

The GRP would have been laid up around the wooden centre. Now yes it is likely that the wood has rotted due to ingress of water. Quite likely fresh water as that causes rot. I think if you are concerned about the structural integrity of the CB case support you should lay more GRP around the support so relying on the GRP and not the wood in the centre for strength.
In the case very common of decks on Keel boats with balsa core it is more appropriate to remove the rotten wood and fill with epoxy. But this is a special case where the deck collapses or flexes where the core is rotten. It would take a lot of GRP to stiffen the deck.
I imagine your ribs etc would be well stiffened by more GRP on the outside. Use epoxy to get a good bond to the old GRP. Then use a tape or quill weave cloth which can follower tight curves better than straight weave. Or use straight weave but bent on the bias. ie diagonal to warp and weft. it will be important to have the new GRP closely bonded to the outside of ribs etc. So you may need to put in a layer of resin and filler to level the surface for the new cloth.
Yes it is going to increase the weight of the dinghy. So maybe there is enough strength in the GRP anyway. Only you can decide what to do. Much depends on whether you have a wooden boat with GRP protective layer or whether you have a GRP boat where wood was used as a kind of male mold that is not removed. The former will fall apart if wood rots. The latter will not matter if the wood rots as it is the GRP that does all the work. Or is it somewhere between these 2? good luck olewill

 

[Scotty_Tradewind]

The first problem before doing anything is to ensure that everything is bone dry around the area to be worked with any resins.

I had to do some work on the fore foot of my keel and made a mini tent around it with a hot air blower and an industrial dehumidifier for some days before I could start work.

Good luck
S.

 

[Greenheart]

Thanks gents. I'll hopefully take a more detailed look at the problem today.

I'm sure the boat is primarily GRP, rather than wood that has been lightly encapsulated for its protection.

I like the idea of getting the core dry enough at the damaged spot to allow thickening of the glassfibre with epoxy, to make it stronger...

...so I guess I'll just try to keep sailing without thinking about the fact that there may be quite a weight of water in the core.

I suppose I was worrying that the constant presence of water within the fabric of the hull might greatly increase delamination.

 

[dylanwinter]

Thanks gents. I'll hopefully take a more detailed look at the problem today.

I'm sure the boat is primarily GRP, rather than wood that has been lightly encapsulated for its protection.

I like the idea of getting the core dry enough at the damaged spot to allow thickening of the glassfibre with epoxy, to make it stronger...

...so I guess I'll just try to keep sailing without thinking about the fact that there may be quite a weight of water in the core.

I suppose I was worrying that the constant presence of water within the fabric of the hull might greatly increase delamination.

If it were my boat I would just carry on sailing

the wood inside is likely to be just something around which to wrap the GRP

the strength will be in the matting

the slug had some strengthening members across the cabin roof - drill inside and it is some sort of really light roll of papery stuff that is there just to give a shape to the GRP

sail now - fettle later

D

 

[jwilson]

On many small boats the "wood cores" are not structural, just a way of getting a shape to lay up GRP over to form top hat and other sections as structural stiffeners. Some builders even used rolled cardboard as cores for ribs. The best material was closed-cell foam but that cost more than strips of rubbish quality wood or cardboard.

On a similar boat with sodden and rotten soft wood cored ribs I drilled quite a few 1/4" holes in the sections, mopped up the drips from the holes, then let it more or less all dry out in a shed over winter, then laid up more GRP tape over the top to seal the holes and add slight reinforcement. Probably ended up slightly lighter and slightly stronger overall than the starting point of sealed in sodden wood.

 

[Greenheart]

I do love the forum. Even before reading your reply Mr Wilson, I did exactly as you suggested yesterday...drilled a hole as low as I could get in the section below the centreboard case...and the result was startling. It was like I'd struck oil - or water - a little deluge.

But what that showed, to my relief, was that the majority of the 'ribs' aren't cored at all, they're just hollow - so maybe as you suggest, the fibreglass was laid over cardboard tubes. Certainly there's no need for me to worry about a sodden wood framework.

I think I managed to get all the wet out of the cavity below the wood-cored section, which is just that lateral centreboard support.

The GRP there had become damaged, and in the course of several summers with water in the cockpit, the wet wood must have dripped steadily into the 'rib' cavity below. I'll give it time to really dry out, then epoxy-tape round the damage and plug the holes.

I drilled test-holes in other rib-sections and was relieved to find the voids inside were bone-dry. Quite a relief. :encouragement: