MK3 Water tank Rot

MK3 Water tank Rot

Postby benllben » Tue Nov 14, 2017 4:30 pm

After recently purchasing Galini which appears to be in good condition minus a few cosmetical things, i decided to take a look at the water tank which was decommisioned a few owners ago, and was stuck when i inspected the boat. When i managed to get it open with the careful use of a hammer, i located a thick pile of rotting wood hanging from the top of the tank, along with what looks like a bit of fungus/mold and a bad smell. It appears that there could have originally been plywood under the fiberglass cabin floor, but it has fully delaminated and is only hanging on.

Does anyone have experience with this sort of problem, or know if there is any structural concern? It appears the wood is simply a liner for the water tank, but i could be wrong.
I also remember reading a thread on the forum with a similar issue before, but am unable to find it through the search tool, so i could be wrong.

Any help is appreciated.
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Re: MK3 Water tank Rot

Postby Phillip » Tue Nov 14, 2017 8:31 pm

Ben,
Yes the floors are all plywood and as such after all this time some are likely to start collapsing.

Suggest if you want to restore the water tank you strip out all the ply and replace it. {The new one will last for 40 odd years :shock: }

Suggest you use the West System [plenty of links online] to protect the new plywood.

You will have to replace the fibreglass floor as you you need to remove it to replace the plywood.

Nothing in the water tank itself is structural [except the fibreglass hull of course].
You will probably have to replace the water tank rear bulkhead as well.
I would from what I can see in your photo.
Phillip.
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Re: MK3 Water tank Rot

Postby benllben » Tue Nov 14, 2017 10:29 pm

Thank you Phillip, i will likely replace the plywood early next year after completion of this years trip as there is no rush if not structural, but would be nice to get that space back as opposed to a water bladder.

Is it just the floor and rear bulkhead which is plywood, or would i also be looking at some pieces for the side and bottom of the tank?
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Re: MK3 Water tank Rot

Postby Phillip » Wed Nov 15, 2017 4:24 pm

Should be just the floor and bulkhead.

Don't forget to use the West system to impregnate the timber to preserve it.
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Re: MK3 Water tank Rot

Postby Shaun » Wed Nov 15, 2017 7:55 pm

Depending on how tall you are, you could consider simply removing the top of the tank, tidying up the rough edges then painting it. The extra headroom is awesome.
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Re: MK3 Water tank Rot

Postby Phillip » Wed Nov 15, 2017 9:07 pm

Shaun wrote:Depending on how tall you are, you could consider simply removing the top of the tank, tidying up the rough edges then painting it. The extra headroom is awesome.
Cheers


Rather hard walking on the bottom of the bilge Shaun :lol:
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Re: MK3 Water tank Rot

Postby Miker » Thu Nov 16, 2017 12:05 pm

I had a similar problem in my Mark III. The tank was full of flaky paint that was lifting from the underside of the tank - or, if you like the underside of the floor that is also the ceiling of the tank. Apart from the top of the tank and the bulkhead, mine also has a bulkhead across the floor about 2/3 of the way forward from the stern bulkhead. Made it really difficult to get the bladder in, and the hoses through, so I ended up having to cut another inspection hole at the front of the tank.

From what I can see, the timber has now dried out and is still good and solid. So the bladder will do for now, until I can get a decent amount of time to cut out the floor and start again. If I do it, I'll also be using a waterproofing membrane before painting with food grade enamel or epoxy paint. Just to make sure it's all sealed and watertight for the future.....

In reality, I don't think I'll ever get to it until I retire, by which time I may have a different boat..... :D
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Re: MK3 Water tank Rot

Postby benllben » Thu Nov 16, 2017 5:01 pm

Miker, I was thinking about putting a bladder in the spot for now if i could find the tubes going in/out, but i cannot trace where they are coming in/out of the tank. If i could drain the tank and manage to fit in a 100L bladder, i would absolutely go with that option for now as i am struggling to find any other spot to fit the bladder.
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Re: MK3 Water tank Rot

Postby Phillip » Thu Nov 16, 2017 10:29 pm

The water line comes out through the rear bulkhead and the breather can be found rising in the forward cabin on the starboard side for the Mk1, not sure where it is in the Mk2&3
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Re: MK3 Water tank Rot

Postby Miker » Mon Nov 20, 2017 10:36 am

benllben wrote:Miker, I was thinking about putting a bladder in the spot for now if i could find the tubes going in/out, but i cannot trace where they are coming in/out of the tank. If i could drain the tank and manage to fit in a 100L bladder, i would absolutely go with that option for now as i am struggling to find any other spot to fit the bladder.


In my Mark III there is a bung plug in the aft bulkhead that allows water in the tank to be drained into the bilge. I think from memory this is a double skinned bulkhead, it was pretty thick when I bored it out to take the filler pipe. There is an inspection plate about 200mm before that in the cabin sole to allow filling. The pick up for the tap/faucet/pump is at the foreward bulkhead on the port side. I didn't uncover any breather as such, but there was no sealant around the hose rising out of the forward part of the tank.

To get the bladder in, I needed to cut a second inspection hole about 300mm aft of the main bulkhead that goes to the v-berth. I fed a line in as far as I could, then reached from the aft inspection hole and pulled it through. Tied the line on to the bladder and stuffed it into the hole, whilst pulling the line. I had already attached the pump feed, and the filler to the bladder and chased them to where I needed them. The filler is now on the port side step, just behind the tank bulkhead, with a 2 inch pipe going through the bulkhead.

The downside of not pulling the floor up and fitting the bladder that way, is that you can never get all the folds and kinks out, so I don't think I can fill it to it's 100l capacity. I only ever seem to get about 40-50 litres in when it's empty.

My original plan was to cut the floor out leaving about 100mm solid around the cut where it joins the hull. Clean all that up and then brace the piece that was removed so it could be dropped back in place and secured with screws. Thereby allowing the bladder to be seated correctly.

You can get smaller bladders that will hang on the inside of the hull, or can be placed in the forward or midships lockers, though that does add a higher centre of gravity. These would be joined with feeder hoses and at different levels, allowing water to drain to the lowest point where the pump pick up is to the faucet.
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