Leak from freshwater tank - woodcore epoxy boat

[KompetentKrew]

I have quite the photo essay for you here. I've only owned my boat for about 3 years and, after discovering this, I thought "I'd better take this to the forum" and took lots of pics. Having done so, I'm not sure you need so many photos, but I'll add them to this post in case you're interested and to maximise the information I provide.

My boat is a Van De Stadt Caribbean 40, which was built in epoxy composite as a one-off by the Jachtbouw Johan Vels (which was pretty much Johan's back garden at that time) in the early 90's.

The freshwater tanks appear to be simply part of the hull, formed between one rib or bulkhead and the next with a lid on the top. Presumably they have been painted with epoxy on the inside?

Yesterday whilst cleaning I noticed this black stain on the plywood beneath the chart table:

I believe this indicates water intrusion into the plywood?

The layout of the boat is that next to the chart table is an armchair:

And underneath the armchair is a water tank.

I have circled some black staining that matches on this side of the ply:

Fortunately the tank is empty at the moment, so I put a couple of flashlights inside and waved my phone around taking photos.

From starboard to port, looking aft:

This seems like a crack where the top of the tank meets the sides, and that I can just paint it over with epoxy sealer?

I've never done this before and am mostly just going off a half-remembered conversation with a neighbour who has rust pin-holes in his boat's steel water tank. I believe he bought some kind of epoxy paint / sealer to fix these, and if it works on a steel tank then it must surely work on an epoxy boat, right!?

Does this seem like a sensible way forward? Do I need to use any particular brand of epoxy, to make it food safe? Or is my regular West System boat-fixin' epoxy adequate?

The last pic makes it look like the previous owner was in this tank doing the same thing before, but I don't see any evidence of a previous leak. Maybe is just the corner that Herr Vels finished up in when he was building the boat, and it's messy due to poor access.

I am grateful for any thoughts or comments you may be able to share.

 

[KevinV]

I know you don't want to hear this, but I don't think painting over the crack is going to be good enough - the lid looks like it's loose, possibly because the support is not properly sealed and therefore waterlogged.
I'm looking at in on my phone, so I could easily be wrong, and hope I am - looks like a bit of a PITA with that armchair surround in the way.

 

[Bajansailor]

The first few photos posted show the water staining just above the sole under the chart table - does this correspond in height to the water staining shown (highlighted by an orange ellipse) in a later photograph in way of the top aft edge of the tank?

 

[coopec]

Is epoxy safe for water tank?

A commonly used polymer is epoxy resin consisting of monomer bisphenol A (BPA). Leaching of BPA from epoxy lining to drinking water has been a concern among public and authorities. Currently epoxy lining is not recommended in some countries.15 Oct 2016
Drinking water contaminants from epoxy resin-coated pipes: A field study - PubMed

Considerations for potable water
tanks
We have adopted the broad policy of not
recommending epoxy for drinking water
tanks because of regulatory and safety is-
sues. The potential problems outweigh
the benefits. To date, none of Gougeon
Brothers’ epoxies meet FDA regulations
or any other drinking water certified ap-
proval. The major long-term concern
with any plastic wate ..........

Epoxy Composite Tank Guidelines - Epoxyworks

 

[Boathook]

The best way of repairing I feel is either to fit a flexible tank in, get a stainless steel one fabricated to fit the space or get a plastic one from TekTanks for example. Either of these is likely to reduce the amount of water you can carry.

 

[Tranona]

Built in tanks are invariably problematic whatever the material. They are attractive in theory but as you have now discovered when the sealing at the edges fail serious repairs are needed. If that were my boat I would do as Boathook suggests - cut the top out and fit a custom made plastic tank in the space. The only proviso is that the top could be structural. If you can't can't face that, still remove the top, build a ledge around the perimeter and screw the top down on with a sealer. Water has got into that cracked seam and the ply bulkhead and I don't think you will ever be able to seal the crack even by laminating over it without removing the top. You can't tell how far the crack has gone and the ply will be damp.

 

[vyv_cox]

Might be worth asking these people. I think some epoxies are too brittle for applications where there is some wall movement, such as on a boat where it is inevitable. More flexible epoxies do exist and might be useful here.
Cleanwater 5000 Drinking Water Approved Protective Epoxy Coating | Cactus.

 

[Concerto]

I would fit a flexible tank as the easiest and simplest solution as Boathook and Tranona have suggested. I would be reluctant to try any repair or disturb the broken joint without talking with Jachtbouw Johan Vels.

With regard to the water staining of the plywood, you must dry the plywood out. Remove the surface finish, it is probably a lacquer not epoxy, and direct a gently air flow from a fan at it. This may take weeks at this time of year. If the dark staining remains, then you will need to bleach the plywood. Use cheap supermarket bleach as it has no perfume added and dilute it by 4 parts water to 1 of bleach. Brush on and cover with some polythene or cling film for about half an hour. Check the stain after allowing to dry out. You may need to do this several times and the stain will become less apparent but unlikely to be removed completely. Finally reinish the plywood.

 

[coopec]

I've painted the inside of my water tanks with Crommelin's Water Base bitumen which satisfies AS 4020 for drinking water.

What is as NZS 4020 drinking water?
AS/NZS 4020 prescribes tests for analysing the suitability of products for use in contact with drinking water, with regard to their effect on the quality of the water. It is a requirement in the application for WaterMark™ certification. Testing focuses on wetted parts only.

In the UK you may have to go for a different brand.
crommelin water based bitumen AS "4020:" - Google Search

 

[KompetentKrew]

The first few photos posted show the water staining just above the sole under the chart table - does this correspond in height to the water staining shown (highlighted by an orange ellipse) in a later photograph in way of the top aft edge of the tank?

Yes, apologies for being unclear - the sole beneath the chart table is on a step about 6 inches above the main cabin sole, and then the top of the tank is about an inch below the bottom of the armchair, so the two stains do match up.

The tank has been dry for probably at least 18 months now, and I don't care about the appearance of the stains (which are normally hidden).

 

[jwilson]

Different construction, but these photos are of a strip planked wood epoxy boat where the water tanks were the inside of the hull epoxied over......

 

[Tranona]

The stains are an indication that the core is wet. Use a simple moisture meter to find if the ply is dry. I am refitting a boat with an epoxy ply deck and coachroof which has had historic (and current) leaks and use the meter regularly to check before I do any repairs plus afterwards to determine that the repair is not leaking. You are looking for moisture content of below 20%, although just because it is now dry does not necessarily mean the core is srill sound. It can be dry and like a cornflake packet inside! 40 years of owning epoxy ply boats!

 

[KompetentKrew]

The stains are an indication that the core is wet. Use a simple moisture meter to find if the ply is dry. I am refitting a boat with an epoxy ply deck and coachroof which has had historic (and current) leaks and use the meter regularly to check before I do any repairs plus afterwards to determine that the repair is not leaking. You are looking for moisture content of below 20%, although just because it is now dry does not necessarily mean the core is srill sound. It can be dry and like a cornflake packet inside! 40 years of owning epoxy ply boats!

Is there a model of meter you recommend, please?

I thought moisture meters couldn't give absolute readings, but only relative to elsewhere on the boat.

 

[Tranona]

This stanleytools.co.uk/product/0-77-030/moisture-meter is the one I have. Commonly used in the building trade for timber. Seems effective in identifying areas of ply with high water content and in areas where I had stopped leaks and allowed to dry out showed a reassuring steady reduction in % age . About £30 . Many other similar products at around the same price or a bit more.

 

[penfold]

Doesn't look like the tabbing was very well applied, although doing so through such a small hole it's a wonder a seal was achieved at all. It almost looks as if the plywood top is a replacement that's been bonded onto old tabbing with bog or polyurethane goop.

If I wanted to continue using the tank or there was an imperative to do so, I'd cut as large an opening in the top as possible and use the remainder as a flange to bolt a hatch to. The larger opening would allow grinding back of all the tabbing to dry out the joint and then relaminate it with new tabbing.

 

[KompetentKrew]

Doesn't look like the tabbing was very well applied, although doing so through such a small hole it's a wonder a seal was achieved at all. It almost looks as if the plywood top is a replacement that's been bonded onto old tabbing with bog or polyurethane goop.

Off-brand Sikaflex was the PO's favourite. I shall have to investigate further tomorrow.

 

[Refueler]

Personally ? I would cut away the tank top and clean up as best ......
The plywood bulkhead - may be saved by using a water absorbant product .... or seal with something like Burgesseal - which uses the water content.

Then install a Tektanks or other tank into the space. That way you have a completely new tank and you can remove / service later if needed.

I would not waste time on the old tank trying to repair. Built in tanks like that suffer the 'movement' of hull over the years .... which I suspect yours has finally said 'enough' ....

 

[geem]

Built in water tanks are great if they are constructed properly and to a high standard. Ours have been trouble free. 1980 boat.
It appears that you have two small access hatches in the top of the tank. I would cut the largest circular hole you can accommodate in the top of that tank to give you good access. Get in there and grind out the crack and repair the with several layers of glass cloth and epoxy and use peel ply over the repair. Once you have done the repair you can paint the epoxy (or the whole tank if you prefer) with a potable 2 pack polyurethane tank paint. To make a new access lid, lay up 10mm of epoxy and glass on a waxed flat surface. Paint the underside with the same polyurethane paint. You can glass M10 bolts to the underside of the tank in a ring to make fixing for the new lid. Use a cork/rubber gasket and some CT1 sealant when you fit thr new lid. The photo attached is from when we repainted the inside of our tanks. We have two 600mm diameter tank access lids in our 800 litre tank under the saloon floor

 

[Spirit (of Glenans)]

I would fit a flexible tank as the easiest and simplest solution as Boathook and Tranona have suggested. I would be reluctant to try any repair or disturb the broken joint without talking with Jachtbouw Johan Vels.

With regard to the water staining of the plywood, you must dry the plywood out. Remove the surface finish, it is probably a lacquer not epoxy, and direct a gently air flow from a fan at it. This may take weeks at this time of year. If the dark staining remains, then you will need to bleach the plywood. Use cheap supermarket bleach as it has no perfume added and dilute it by 4 parts water to 1 of bleach. Brush on and cover with some polythene or cling film for about half an hour. Check the stain after allowing to dry out. You may need to do this several times and the stain will become less apparent but unlikely to be removed completely. Finally reinish the plywood.

Wood bleaches, based on hydrogen peroxide are available from woodwork suppliers, or from specialist suppliers of wood finishes. Would be less aggressive on your woodwork than household bleach.

 

[Spirit (of Glenans)]

The first few photos posted show the water staining just above the sole under the chart table - does this correspond in height to the water staining shown (highlighted by an orange ellipse) in a later photograph in way of the top aft edge of the tank?

Looks like the tank is under the armchair, or perhaps under the whole structure into which the armchair is set.
I would concur with the opinions expressed above regarding replacing the built-in tank with a plastic or s/s alternative.