Wood Rot on a GRP boat!!

[BigRoj]

We had a week away in Greece last week, and before I went I checked the boat over to make sure it was safe and secure, no taps on, electric\gas\fuel off, that sort of thing.

So yesterday when I went to check it over I was gobsmacked to find this lot growing out of the transom:

 

 

 

They are growing out of one of the drain holes!

 

Thoughts of chopping them off, putting them under the grill with some garlic butter and Dolcelatte, and having them for supper soon disappeared as I realised that had they been edible the resident wildfowl would have had them before now!!

 

However, it became apparent after I'd removed them that they were growing out of the transom wood itself, as sticking a finger into the drain hole revealed it to be spongy and soft.

 

This looks as if it could be a mammoth task, eradicating the rotten wood, especially if it has spread. With the transom being possibly the most critical structural member on the boat, supporting the engine and transmitting the thrust from the engine to the rest of the boat, it has to be absolutely perfect, with no weak points.

 

Has anyone had any experience of this? And does anyone know of any product that kills wetrot stone dead that ISN'T harmful to the waterways? Cuprinol do some stuff but it is extremely harmful to aquatic life, so it can't be used.

[John Orentas]

"Mammoth tusk", no I'm sure it's not that.

 

Don't eat them though, spouse tells me it is only the red ones with the white spots that are safe to eat, she serves them up most days with my breakfast.

 

Get some of that fungicide stuff they supply for cleaning fridges.

Edited October 31, 2007 by John Orentas

[grahoom]

what does the underside of the fungi look like?

[ChrisPy]

I'm not confused ........ not 'arf I'm not .................... your thread title refers to a GRP boat but it has a wooden transom .... ??

[BlueStringPudding]

Had something similar growing out of the floor of our boat when we bought it. Looked kinda like a human ear though. Perhaps it was a wierd experiment like that freaky mouse with an ear on it's back? Who knows.

 

Anyway, we had all the carpets and floor ripped out and new flooring put in.

 

No help to you, though. Sorry.

[grahoom]

Had something similar growing out of the floor of our boat when we bought it. Looked kinda like a human ear though. Perhaps it was a wierd experiment like that freaky mouse with an ear on it's back? Who knows.

 

Anyway, we had all the carpets and floor ripped out and new flooring put in.

 

No help to you, though. Sorry.

 

was it one of these?

 

[BlueStringPudding]

was it one of these?

 

 

Woah! Similar... but smaller and a pale beigey-grey colour.

[grahoom]

Woah! Similar... but smaller and a pale beigey-grey colour.

 

sounds like it could be the same thing - odd it's growing in your boat? - what wood was it growing on? they generally grow on Elder

[Yoda]

sounds like it could be the same thing - odd it's growing in your boat? - what wood was it growing on? they generally grow on Elder

 

Think you found the source of the spors. Out of the wood pile!

[Teadaemon]

I'm not confused ........ not 'arf I'm not .................... your thread title refers to a GRP boat but it has a wooden transom .... ??

 

Evidently the transom is wood (probably plywood) encapsulated with GRP, a fairly common building technique.

 

Going back to the original post, fixing this is not particularly difficult from a technical perspective, but is potentially quite a big job. First you need to determine how big the patch of rot is, and whether there are any others - sounding it with a coin or a screwdriver handle is probably the easiest way, paying particular attention to any other drain holes. Any areas that sound like they might be rotten are worthy of further exploration with a pocket knife blade or a spike.

 

If this patch of rot is more than a couple of inches in diameter, or there are several patches, it's probably best to replace the entire transom, otherwise removing the rotten wood and gluing in a new piece with plenty of thickened epoxy might be possible. Whatever you do, make sure that all of the drain holes are made in such a way that water cannot penetrate the wooden core (I'd glue small pieces of plastic pipe or something similar into them).

[saltysplash]

My understanding of the Rot treatments on sale today are they tend to make the wood very brittle. Dig out the soft stuff and if not too far gone then epoxy and fix in a new section. Ive replaced a couple of sections of rail using strong fixings and West's epoxy. good strong stuff but use it quick or it heats up and will burn through anything...almost

[Supermalc]

Hi Rog - like all jobs, rotten cars, boats, leaky roofs etc. etc. once you have the rotten bit cut away and can see what's required it's never quite as bad as first appears, although can sometimes be a bigish job (thinking more of cars of course)

 

Two or three of the Norman lads have done this sort of job, and Simon has documented his, with pics very well. See if you can find them on here.

 

http://www.normanboats.co.uk

 

Last year, Martin the chap who came out into the Wash with me the other week had a leak in the back of his boat, that nice old Norman on the end finger at Bardney. Well I organised it with Roy to take his boat out, and they cut the two corners back and filled them, just as you would on a car. He then painted and antifouled his boat as well, and I know it is not leaking now, a year on.

 

Some will say car filler, P40 etc is hydroscopic but I've known people who have used it and had no problems for years. There is also plenty of marine fillers of course, although I suspect these may be just the same with the price trippled.......

 

But even if you have to replace the whole transom is not as frightening as it first appears. Adi rebuilt the whole transom of his 23 Norman to change from inboard to outboard.

[1066]

Some will say car filler, P40 etc is hydroscopic but I've known people who have used it and had no problems for years. There is also plenty of marine fillers of course, although I suspect these may be just the same with the price trippled.......

 

I'm sure that P40 is fine above the waterline ..... and as you say, a lot cheaper than the 'marine' stuff [although I would be inclined to use this below the waterline, just in case]

[RobinJ]

They are growing out of one of the drain holes!

However, it became apparent after I'd removed them that they were growing out of the transom wood itself, as sticking a finger into the drain hole revealed it to be spongy and soft.

 

This looks as if it could be a mammoth task, eradicating the rotten wood, especially if it has spread. With the transom being possibly the most critical structural member on the boat, supporting the engine and transmitting the thrust from the engine to the rest of the boat, it has to be absolutely perfect, with no weak points.

Even full grp boats normally have a transom plate made of wood, you need to be clear whether the boat is grp covered wood (like Dolphin) or solid grp.

The transom plate is normally marine ply (11 or 3/4"), and that should resist any fungal growth! Has it been replaced with sub-standard wood?

My understanding is that fungii spread from spoors (which could have been picked from the water or airbourne) which then grow 'tentacles' into the wood. You would need a good fungicide and a means of getting it into the wood (which is likely covered in grp). Ideally you need to think about replacing the transom plate completely, though not necessarily immediately. It will depend on the remaining strength of the wood, size of engine etc. (assuming outboard), amount of work involved in getting to it!

[ChrisPy]

maybe you don't actually need to replace the transom plate.

 

why not just laminate a thick reinforcing plate onto the back of the transom using several layers of grp sheathing, and then just treat the symptoms of the rotten wood if and when they appear?

[Teadaemon]

Even full grp boats normally have a transom plate made of wood, you need to be clear whether the boat is grp covered wood (like Dolphin) or solid grp.

The transom plate is normally marine ply (11 or 3/4"), and that should resist any fungal growth! Has it been replaced with sub-standard wood?

My understanding is that fungii spread from spoors (which could have been picked from the water or airbourne) which then grow 'tentacles' into the wood. You would need a good fungicide and a means of getting it into the wood (which is likely covered in grp). Ideally you need to think about replacing the transom plate completely, though not necessarily immediately. It will depend on the remaining strength of the wood, size of engine etc. (assuming outboard), amount of work involved in getting to it!

 

AFAIK the specifications for marine ply say nothing about resistance to fungal growth, and I've seen plenty of marine ply boats with rot in them. The only differences between marine ply and exterior ply are that in a sheet of marine ply each layer is a single sheet of wood, and that there are no voids or knots in any of the layers (of course the price is another big difference).

 

why not just laminate a thick reinforcing plate onto the back of the transom using several layers of grp sheathing, and then just treat the symptoms of the rotten wood if and when they appear?

 

The main reason for not doing as you suggest is that the symptoms of rotten wood may be the original transom disintegrating, detaching the 'thick reinforcing plate' from the rest of the boat. On an outboard-powered boat (as I believe the OP's is), all of the thrust from the motor is transferred to the boat via the transom on which the motor is mounted, so this is not an area where it's sensible to take a chance. Much better to do a proper job now and not have to worry about it in the future (unless the new drain holes are drilled straight through and not sealed properly again, which is almost certainly the root cause of the problem).

Edited November 1, 2007 by Teadaemon

[smileypete]

This looks as if it could be a mammoth task, eradicating the rotten wood, especially if it has spread.

 

I'd start by drilling into the transom near the drain hole from the inside of the boat (and to a limited depth!), to see how far the water and rot has gone.

 

cheers,

Pete.

[ChrisPy]

AFAIK the specifications for marine ply say nothing about resistance to fungal growth, and I've seen plenty of marine ply boats with rot in them. The only differences between marine ply and exterior ply are that in a sheet of marine ply each layer is a single sheet of wood, and that there are no voids or knots in any of the layers (of course the price is another big difference).

that's not quite true: please bear in mind that the normal definition of marine ply is plywood made to BS1088.

 

from an authoritative source:

 

A Guide to Marine Plywood

Marine Plywood's manufactured to BS1088 must satisfy a number of minimum requirements, of which the following is a brief summary:

 

 

All veneers, both internally and externally must be free from gaps, sapwood and natural defects.

Internal veneers must be all of a durable species and the same quality as the veneer faces.

Glue line must be Weather and Boil Proof, usually a resorcinol resin. It must be resistant to attack by micro organisms, cold and boiling water, steam and dry rot.

Genuine Marine Plywood should always be stamped with its country of Origin and, ideally, carry Lloyds certification and a BS1088 Kitemark if Manufactured in Britain.

 

 

Aquaply

British Made and guaranteed for 25 years. A multi-laminate board for high loading uses where strength is a prerequisite. Extremely resistant to fungal attack and is ideal for persistently wet and dry environments. It has a superb face veneer quality. Approved for use by the RNLI, Kitemarked BS1088 and Lloyds certified.

Edited November 2, 2007 by chris polley

[BigRoj]

Thanks for all your replys, I've just caught up with them all.Since discovering this problem I've been busy on a plan of action and course of remedial/replacement work.The first thing I did was to make sure no more water could get to the drain holes, and let the air circulate around to start drying out the exposed wood of the transom.The boat is coming out of the water this weekend so that the motor can be removed and the S/S transom plate taken off. I'm a bit concerned also that this plate is screwed to the transom, some screws below the waterline, but having looked at other boats I find this isn't unusual.Once out of the water and under cover, depending on the extent of the fungal/rot depth, if it isn't too bad, ie no more than a 4in diameter, then the idea is to dig the worst of it out, then attach a vacuum pump to the hole, apply a modicum of heat from a hot air blower and suck like billyo for an hour or so and repeat this process for a few days until there is an acceptable moisture content, that is the same as normal wood. Then the idea is to inject a special resin into the wood which not only kills any fungal spores left, but also bonds into the wood to make it as strong as the original structure.If it's very waterlogged then I may have to drill a small drain hole at the lower edge of the transom to allow any free water to drain. Mind you if it's that bad that there is water flowing from the bottom of this drilled hole then it's going to be a new transom. I have access to some inch and eighth 20 layer marine ply which should do the job if required.I think that this has been caused by a manufacturing defect when it was built, as the boat is only 8 years old, and the glass/fibre around the drain hole was cracked or not done properly to begin with.

what does the underside of the fungi look like?

It has what looks like gills, very similar to the underside of an open cup mushroom, but the fungus itself is very dense, took some chopping off!! Edited November 2, 2007 by BigRoj

[smileypete]

Then the idea is to inject a special resin into the wood which not only kills any fungal spores left, but also bonds into the wood to make it as strong as the original structure.If it's very waterlogged then I may have to drill a small drain hole at the lower edge of the transom to allow any free water to drain. Mind you if it's that bad that there is water flowing from the bottom of this drilled hole then it's going to be a new transom.

 

If the rot hasn't gone too far into the ply but it's difficult to dry out I'd look into using boron/borate preservative rods or gel.

 

These are put into holes in the wood, if there is any damp around they dissolve slowly and the preservative goes into the wood.

 

cheers,

Pete.

[Teadaemon]

that's not quite true: please bear in mind that the normal definition of marine ply is plywood made to BS1088.

 

from an authoritative source:

 

A Guide to Marine Plywood

Marine Plywood's manufactured to BS1088 must satisfy a number of minimum requirements, of which the following is a brief summary:

All veneers, both internally and externally must be free from gaps, sapwood and natural defects.

Internal veneers must be all of a durable species and the same quality as the veneer faces.

Glue line must be Weather and Boil Proof, usually a resorcinol resin. It must be resistant to attack by micro organisms, cold and boiling water, steam and dry rot.

Genuine Marine Plywood should always be stamped with its country of Origin and, ideally, carry Lloyds certification and a BS1088 Kitemark if Manufactured in Britain.

Aquaply

British Made and guaranteed for 25 years. A multi-laminate board for high loading uses where strength is a prerequisite. Extremely resistant to fungal attack and is ideal for persistently wet and dry environments. It has a superb face veneer quality. Approved for use by the RNLI, Kitemarked BS1088 and Lloyds certified.

 

Fair enough, I was working from memory and obviously forgot that bit. I would however point out that 'resistant to' is not the same as 'impervious to' - it's less likely to rot, but it can still happen in extreme circumstances, such as when it's used as a core for GRP and then saturated with water (I strongly suspect that the rot in this case is wet rot, not dry rot).

[ChrisPy]

Fair enough, I was working from memory and obviously forgot that bit. I would however point out that 'resistant to' is not the same as 'impervious to' - it's less likely to rot, but it can still happen in extreme circumstances, such as when it's used as a core for GRP and then saturated with water (I strongly suspect that the rot in this case is wet rot, not dry rot).

no wood will be totally impervious to anything, except possibly rust

[carlt]

no wood will be totally impervious to anything, except possibly rust

Greenheart.

[BigRoj]

If the rot hasn't gone too far into the ply but it's difficult to dry out I'd look into using boron/borate preservative rods or gel.

 

These are put into holes in the wood, if there is any damp around they dissolve slowly and the preservative goes into the wood.

 

cheers,

Pete.

 

Thanks Pete, duly noted!! I shall look into this.

[ChrisPy]

Greenheart.

almost but not quite .......................

 

Greenheart Piling stands in a class superior to all other woods used for marine and structural applications. “Greenheart : A Timber with Exceptional Qualities” - U.S. Department of Agriculture, states Greenheart wood is almost immune to decay and is more resistant to the teredo worms and other marine wood borer than any of the hundreds of species of timber so far used for piling.