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Wet Cabin Under Floor


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Hi. 
Can you help with a wet under floor please? 
2008 65 foot narrow boat. The cabin bilge is always wet. I suck out about 5 litres per month. 
There was a small leak in the bathtoom 2 months ago but it’s been fixed. 
Still seeing some wicking up the base of the wooden bulkheads so I drilled some inspection holes. Photos attached. The whole floor is like this. 
Could this be condensation? 
Do I need to force ventilate under the floor? 
Having been searching for a leak for a month and not found conclusive evidence of one anywhere I’m at a loss. 
Your advice very gratefully received. Thanks. A8FBA3C6-1F34-41E4-B9F0-6396BAD22AA2.jpeg.e7724ad115edf52c5e608934623facf8.jpeg

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Always tricky to pin these things down! There can be some condensation because the canal water cools the steel hull, and then if you add in some warmer moister air from the cabin, condensation forms. But it usually isn't a lot. What is perhaps more likely are leaks from windows. Windows are typically aluminium framed and attached to the outside of the steel sides and sealed with some mastic type stuff. Over time and with the sides of the boat getting very hot in summer, the sealant can go brittle and then with the differential expansion /contraction of steel vs aluminium, cracks in the sealant can open up and water can leak in. This water can sometimes run down behind the cabin lining and not be at all obvious, but of course it makes its way into the bilge eventually.

 

Forced ventilation may not be a good idea especially if it is cabin air. Ventilation works by evening up the relative humidity, so for example if you introduce cold air into the warm cabin, the relative humidity of that air once warmed, is very low and has a drying effect. Conversely if you introduce warm air of moderate relative humidity, into a cold space, the air cools and moisture may condense out. So force ventilating a bilge can actually make matters worse especially in winter.

 

In reality you may have a combination of a bit of condensation and bit of a leak from some of the windows.

Edited by nicknorman
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may I recommend cutting several circular holes in the floor in various unseen locations and fitting 12v computer fans, all either sucking or pushing air out of or into the underfloor space.  These have tiny current demand but will keep the air moving.  Without forced ventilation it is unlikely that the baseplate will ever dry out. 

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I wonder what that white felt stuff is? Not sure if I am interpreting the pictures correctly but most boats have transverse angle iron frames along the bottom and the floor laid on wooden bearers above that. There is usually bricks or slabs under there as ballast too. In the meantime I would do as Murflynn suggests and see if it dries out.

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Thanks so much everyone. I’m going to suck it to death with a wet and dry vac this weekend and I’ve also bought a dessicant dehumidifier to try and manage the condensation level. The fans idea is a good one. Thanks. Should I get them sucking out into the boat or sucking from the boat into the baseplate do you think? Many thanks. 

The White stuff you refer to by the way is a thin sheet of what looks like insulation. It’s all over the boat. On top of that are concrete blocks like block paving which is the ballast. 

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9 hours ago, David Mack said:

But without ventilation it has no chance of drying out.

Yes but it is a balance and forced ventilation when the hull is colder than the air, risks making the problem worse. I suggest that ventilation, as opposed to forced ventilation, is the answer - along with fixing any leaks.

1 hour ago, Murflynn said:

may I recommend cutting several circular holes in the floor in various unseen locations and fitting 12v computer fans, all either sucking or pushing air out of or into the underfloor space.  These have tiny current demand but will keep the air moving.  Without forced ventilation it is unlikely that the baseplate will ever dry out. 

Pumping warm cabin air which has added moisture from humans and cooking, into a cold bilge, will make the problem worse. Any bilge ventilation should involve outside air not cabin air.

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Wet concrete brick ballast can take months to dry out even in summer. The water will migrate to the back of the hull most likely as most boats are a bit bow up.

Does the water pump ever have a little go even when you have not drawn water off? If so you have a leak.

If the pump stays off all night, check the plumbing between the water tank and the pump inlet, leaks here will not cause the pump to run and are hard to pin down.

Does the shower tray leak around the edge?

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45 minutes ago, Floatymark said:

The White stuff you refer to by the way is a thin sheet of what looks like insulation. It’s all over the boat. On top of that are concrete blocks like block paving which is the ballast. 

 

 

It may be worthwhile looking at ways of removing all that 'white stuff / insulation'.

It won't be an easy job and may involve lifting latge sections of the floor.

If the insulation is sitting on the base plate and below the ballast it may be acting as a huge sponge and holding all of the moisture, just using ventilation could take years to dry out.

 

It seems very strange - was it a 'self-fit-out' boat or was it built and fitted out by a boat builder ?

 

 

1 minute ago, Tracy D'arth said:

Wet concrete brick ballast can take months to dry out even in summer. The water will migrate to the back of the hull most likely as most boats are a bit bow up.

Does the water pump ever have a little go even when you have not drawn water off? If so you have a leak.

If the pump stays off all night, check the plumbing between the water tank and the pump inlet, leaks here will not cause the pump to run and are hard to pin down.

Does the shower tray leak around the edge?

 

 

The OP has said there was a leak in the bathroom (now fixed) that could / would be a source for the water.

Edited by Alan de Enfield
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In answer to ‘was it a 'self-fit-out' boat or was it built and fitted out by a boat builder ?’ Its an Aqualine Manhattan. 
In its life it’s had a water pump leak, a calorifier leak and a leak in the bathroom. 
The bathroom one ended up with about 200 litres of water under the floor, thanks to a dodgy bilge pump. That was around 2 months ago.
I have heard that large quantities of water can take a long time to filter down to the bilge at the stern especially with concrete blocks. But I’d have thought by now it would have drained to the stern? 
what do you think? Thanks for all your advice. It’s very helpful. 

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3 minutes ago, Floatymark said:

In answer to ‘was it a 'self-fit-out' boat or was it built and fitted out by a boat builder ?’ Its an Aqualine Manhattan. 
In its life it’s had a water pump leak, a calorifier leak and a leak in the bathroom. 
The bathroom one ended up with about 200 litres of water under the floor, thanks to a dodgy bilge pump. That was around 2 months ago.
I have heard that large quantities of water can take a long time to filter down to the bilge at the stern especially with concrete blocks. But I’d have thought by now it would have drained to the stern? 
what do you think? Thanks for all your advice. It’s very helpful. 

In winter 2 months is nothing. I have known boats that have been wet take all year to lose all the water out of the ballast and run to the stern. You will be adding to it with the unavoidable condensation too. 

I may be worth hiring a proper de-humidifier if you are on a shore supply, its incredible how much water these will extract in a day running constantly. The absorption crystal type are toys compared. 

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6 minutes ago, Floatymark said:

In answer to ‘was it a 'self-fit-out' boat or was it built and fitted out by a boat builder ?’ Its an Aqualine Manhattan. 

 

Maybe they have very different build methods in Poland.

 

It seems very odd to put 'matting' on the base-plate which can only cause problems when you get the inevitable leak.

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3 minutes ago, Alan de Enfield said:

 

Maybe they have very different build methods in Poland.

 

It seems very odd to put 'matting' on the base-plate which can only cause problems when you get the inevitable leak.

We often came across roofing felt under brick ballast, presumed it was to avoid the bricks scratching the paint off. It could be geotextile matting, looks like it.

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1 minute ago, nicknorman said:

Steve Hudson put roofing felt on the baseplate of his boats (including ours). Not quite sure why, but he made a couple of hundred boats and as far as I know, none have yet sunk due to rusty bilges.

 

I have seen non-absorbant roofing felt used, but never seen 'fluffy duvet / Sponge' material used

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But even non absorbent felt will trap water against the bottom plate, and stop it drying out quickly.

I wonder how the consequent increase in baseplate corrosion compares with that resulting from damage to the paint film if ballast is placed directly on the baseplate.

Best of both worlds is to place ballast on non-metallic spacers, allowing drainage and ventilation and minimising damage to the paint film.

Probably all a bit academic if you have 10mm of baseplate (unpainted on the underside).

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21 minutes ago, David Mack said:

But even non absorbent felt will trap water against the bottom plate, and stop it drying out quickly.

I wonder how the consequent increase in baseplate corrosion compares with that resulting from damage to the paint film if ballast is placed directly on the baseplate.

Best of both worlds is to place ballast on non-metallic spacers, allowing drainage and ventilation and minimising damage to the paint film.

Probably all a bit academic if you have 10mm of baseplate (unpainted on the underside).

Don’t forget that for corrosion, you need two things ie water and oxygen. Even though it might be damp under the felt, access to oxygen is pretty limited.

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