Under floor condensation

[lewisericeric]

Hi Everyone

 

Hope you're as well as can be. I'm just wondering if other people have 'damp' bilges, in the living space of their boat? 

 

I have two access holes to under the floor where I can check in the bilge for leaks etc. One is in the kitchen steps at the back of the boat and another is under the false floor in the wardrobe at the front of the boat. I was doing a check today and noticed that the steel is damp in the bilge. I took some video footage, wedging my phone down there and there is some rusting and the steel under flash light looks quite, erm, 'moist'. There's no accumulated water and it's not possible for it to be a leak as there are  steel support beams so each 'section' would have to fill up before it poured into another one and the level of dampness is the same at the very back of the boat as well as at the front of the boat.

 

 

Is this normal? I don't remember if my old narrowboat had the same issues to be honest, but that was a long time ago. 

 

Is there any way to eradicate this? I thought for the bilge to be damp or condensate like that, the moist air would have to have got underneath that space somehow? More to the point, how can I dry it out? Obviously I can't wedge a dehumidifier down there but I was thinking of maybe fitting an extractor fan into one of the access holes (perhaps in the kitchen steps) to 'pull' out the damp air and that would dry? Is it maybe a seasonal thing as we're moving from winter into spring and the warmer weather we've been having.

 

Rattling now, I'll head off and see if you geniuses can solve it!

 

Thanks!

 

Edit - Boat is a 60ft widebeam, modern, two years old. Engine bilge can't leak into living space - it's separate. 

[David Mack]

1 hour ago, lewisericeric said:

There's no accumulated water and it's not possible for it to be a leak as there are  steel support beams so each 'section' would have to fill up before it poured into another one

Are you sure? It is normal for the ends of the transverse stiffeners across the bottom plate to be cut away at the bottom where they meet the hull sides, leaving a triangular hole through which any bilge water can run towards the back of the boat (assuming it is trimmed stern down).

[blackrose]

Yes, they're called limber holes. I think it's more likely to be a leak somewhere or perhaps condensation dripping down from above than condensation forming on the base plate.

Edited April 5, 2021 by blackrose

[Tony Brooks]

Window to cabin side leaks can be difficult to find because they tend to just run down behind the lining.

 

Yes, a fan is a good idea and will help but see if you can get a vent into the opposite end of the boat so air is drawn through the bilge. Its another advantage of floor fans used to keep electric fridge radiators cool.

[lewisericeric]

14 hours ago, David Mack said:

Are you sure? It is normal for the ends of the transverse stiffeners across the bottom plate to be cut away at the bottom where they meet the hull sides, leaving a triangular hole through which any bilge water can run towards the back of the boat (assuming it is trimmed stern down).

 

The reason I've saisd I don't think it's a leak is the base plate is 'moist' to the same degree through all different places. So right at the front of the boat (bedroom) where I can access it from the front step. Inside the wardrobe, abutting the bathroom and gives me access to the shower drainage (that's not leaking) and then right at the back stern steps. There's not one place which is more damp than the other.

 

As the boat also has a natural tilt back as my water tank is often half empty(!) if it was a leak, I also wouldn't have thought it would 'spread' to the front of the boat? 

[nicknorman]

I would say a bit of condensation in the bilge is quite normal at this time of year. The canal water 2’ down is very cold, the air has recently been fairly warm and although the relative humidity hasn’t been particularly high, once that air is cooled down to canal water temperature it seems highly likely that it will be cooled below its dew point and condensation will occur.

 

This is why forced ventilation of the bilges isn’t a good idea - the more air you force over the baseplate, the more moisture you are transporting onto the base plate. Ventilation only dries stuff if the relative humidity of the air in contact with the moisture, is below 100%. If the air cools to saturation, all you do is add more water!
 

Even worse would be to force cabin air into the bilges, in an occupied boat that will have more moisture than outside air. It may feel drier because it is warmer, but as soon as it cools in contact with the baseplate, even more water will condense out.

 

Its all about relative humidity vs absolute humidity.

Edited April 5, 2021 by nicknorman

[lewisericeric]

1 minute ago, nicknorman said:

I would say a bit of condensation in the bilge is quite normal at this time of year. The canal water 2’ down is very cold, the air has recently been fairly warm and although the relative humidity hasn’t been particularly high, once that air is cooled down to canal water temperature it seems highly likely that it will be cooled below its dew point and condensation will occur.

 

This is why forced ventilation of the bilges isn’t a good idea - the more air you force over the baseplate, the more moisture you are transporting onto the base plate. Ventilation only dries stuff if the relative humidity of the air in contact with the moisture, is below 100%. If the air cools to saturation, all you do is add more water!
 

Even worse would be to force cabin air into the bilges, in an occupied boat that will have more moisture than outside air. It may feel drier because it is warmer, but as soon as it cools in contact with the baseplate, even more water will condense out.

 

Its all about relative humidity vs absolute humidity.

Thanks Nick

 

What's the answer then? Just leave and monitor? Just not a nice thought thinking that the floor is damp underneath me 

[Tracy D'arth]

5 minutes ago, lewisericeric said:

Thanks Nick

 

What's the answer then? Just leave and monitor? Just not a nice thought thinking that the floor is damp underneath me 

Yes, its life on a boat in winter. Condensation is natural, it will dry out when the water under the boat warms up and the relative humidity of the air decreases.

[Tony Brooks]

But organising  a through draft helps.

[nicknorman]

1 hour ago, Tony Brooks said:

But organising  a through draft helps.

Yes some ventilation is necessary.   Under the wrong conditions ventilation actually makes things worse, but overall for most of the year it helps.

[cuthound]

1 hour ago, lewisericeric said:

Thanks Nick

 

What's the answer then? Just leave and monitor? Just not a nice thought thinking that the floor is damp underneath me 

 

If you have access to shore power, then a dehumidifier, like a Meaco DD8l https://www.meacodehumidifiers.co.uk/products/meaco-dd8l-8-litre-desiccant-dehumidifier?gclid=CjwKCAjw6qqDBhB-EiwACBs6x_yWlD2Tvv1plJPX-UGKhEvYYWbKAm70mYfj2TXDRFnCnsU7GBTeVhoC1VQQAvD_BwE

 

will remove the excess moisture from the air.

 

If you do use one, don't forget to close all windows and block the high and low level ventilation (I use bath sponges for the mushrooms and cardboard for the low level vents), or the dehumidifier will try to dry out the world.

 

If you live aboard, then using the solid fuel stove 24/7 in cold weather will quickly dry the boat out, unless their are leaks introducing more water.

Edited April 5, 2021 by cuthound
Clarification

[nicknorman]

1 hour ago, lewisericeric said:

Thanks Nick

 

What's the answer then? Just leave and monitor? Just not a nice thought thinking that the floor is damp underneath me 

Well, the floor is a lot damper under the floor under the floor (aka the canal!). Yes I think it is just a feature of steel hulls and winter boating. It will dry out when the canal temperature increases. Hopefully the inside of the boat has some corrosion protection, not just bare steel. Even if  bare steel, you need a hell of a lot of rust to penetrate 10mm of steel, so I wouldn't worry about it.

[blackrose]

4 hours ago, nicknorman said:

I would say a bit of condensation in the bilge is quite normal at this time of year.

 

I can only go by my own experience and it's never been normal on my boat. My cabin bilges are bone dry even in winter.

 

The only place where I've found any dampness was where condensation was dripping down from an exposed part of the BT tunnel close to the water outlet pipe from the tank that wasn't covered in foam. My baseplate itself doesn't form condensation. I don't really know why that would be different on different boats.

 

1 hour ago, nicknorman said:

Well, the floor is a lot damper under the floor under the floor (aka the canal!). Yes I think it is just a feature of steel hulls and winter boating. It will dry out when the canal temperature increases. Hopefully the inside of the boat has some corrosion protection, not just bare steel. Even if  bare steel, you need a hell of a lot of rust to penetrate 10mm of steel, so I wouldn't worry about it.

 

That will be the test. If it dries out over summer then it's condensation, if it doesn't it's a leak.

Edited April 5, 2021 by blackrose

[Jackofalltrades]

On 05/04/2021 at 16:15, blackrose said:

 

I can only go by my own experience and it's never been normal on my boat. My cabin bilges are bone dry even in winter.

 

The only place where I've found any dampness was where condensation was dripping down from an exposed part of the BT tunnel close to the water outlet pipe from the tank that wasn't covered in foam. My baseplate itself doesn't form condensation. I don't really know why that would be different on different boats.

 

Is your floor insulated? Are the insulated walls and floor sealed together at the joint?  Do you use a dehumidifier or heat recovery/ventilation system? Are your bilges ventilated passive/forced? Is your heating (what type?) on a lot in winter?

 

edit: Lots of questions there, sorry!

 

Edited April 6, 2021 by Jackofalltrades

[Jackofalltrades]

Jackofalltrades, killing threads since... Tuesday ?