Mystery leak/wet patch

[AnnieRose]

22 minutes ago, beerbeerbeerbeerbeer said:

everything is worth a look at,

even if it’s to only to cancel it out,

if it’s the window (which seems most likely ) then there are sealants you can run around the frame to get you through the winter,

come summer you can remove and do a proper repair,

 

Thanks, do you mean on the outside frame? Could you recommend what kind of sealant would do the job? I need to do this on a few other windows too

[Arthur Marshall]

3 hours ago, AnnieRose said:

The cavity behind appears to be quite rusty, although I don’t know if this is normal? 

If the cavity behind it is rusty, I would assume it aint got no insulation, and it's condensation.

I found a patch under the front bulkhead that I'd missed insulating somehow and took about five gallons of condensation out of the boat plus replacing rotten floorboards.

[Peanut]

If you put dry paper towel down where you think it could be coming from, it might help indicate the source. You can wrap small bits around pipes to see if a joint is leaking, or if it is running down or along a pipe. If it is wringing wet or only slightly damp also helps.

[AnnieRose]

53 minutes ago, Arthur Marshall said:

If the cavity behind it is rusty, I would assume it aint got no insulation, and it's condensation.

I found a patch under the front bulkhead that I'd missed insulating somehow and took about five gallons of condensation out of the boat plus replacing rotten floorboards.

Interesting, how would I go about insulating it? What would you use and where does it go? The rear bulk head is also quite rusty and the floor is damp in that area for sure!! 

[Tony Brooks]

12 minutes ago, AnnieRose said:

Interesting, how would I go about insulating it? What would you use and where does it go? The rear bulk head is also quite rusty and the floor is damp in that area for sure!! 

 

Find out how to take the lining panel off and see what, if anything, is underneath it. If there are battens the panel s fixed to, you could push board insulation between the battens to a tight fit, tape over the battens and tape the joints with self-adhesive aluminium tape, and refit the panel. You could use Kingspan, Celotex, or if on a budget, expanded polystyrene, but try to get the so-called self extinguishing version.

 

If you can keep warm cabin air away from the metal bulkhead it will help, so if you find Rockwool insulation, I would tack heavy-duty polythene over the battens as a damp proof layer. The idea is to keep warm damp air away from cold metal. The insulation board will do the same job. 

[Arthur Marshall]

24 minutes ago, AnnieRose said:

Interesting, how would I go about insulating it? What would you use and where does it go? The rear bulk head is also quite rusty and the floor is damp in that area for sure!! 

Absolutely anywhere you've got vertical bare metal you're going to get condensation, and in a boat it's got nowhere to go except to rust, which you really don't want. For the bit I couldn't reach under the bed at the front I just used spray foam and hoped it stuck, which it did, as well as expanding rather too much! Where I could reach as Tony suggests, I used Celotex. 

I never understood why you don't get condensation forming on flat surfaces like the baseplate, which isn't insulated at all in my boat, though I know some are. But it seems you don't. Someone will know why.

[Tony Brooks]

1 minute ago, Arthur Marshall said:

 

I never understood why you don't get condensation forming on flat surfaces like the baseplate, which isn't insulated at all in my boat, though I know some are. But it seems you don't. Someone will know why.

 

Possibly because in winter, the baseplate and the lower hull sides are in water that is warmer than the air around and inside an unoccupied boat. The upper part of the vertical hull side and cabin side, exterior bulkheads and roof will be at the outside air temperature, so can be far colder than the baseplate.

[MtB]

20 minutes ago, Arthur Marshall said:

I never understood why you don't get condensation forming on flat surfaces like the baseplate, which isn't insulated at all in my boat, though I know some are. But it seems you don't. Someone will know why.

 

I get massive condensation on the underside of the hatch/slides, and they are flat (and horizontal)! 

 

 

[Tony Brooks]

4 minutes ago, MtB said:

 

I get massive condensation on the underside of the hatch/slides, and they are flat (and horizontal)! 

 

 

 

Oh yes, in winter it would be dripping from the cruiser stern deck boards, probably made worse by the wet bilge.

[beerbeerbeerbeerbeer]

2 hours ago, AnnieRose said:

Thanks, do you mean on the outside frame? Could you recommend what kind of sealant would do the job? I need to do this on a few other windows too

personally I’d buy a transparent silicone sealant and push a  beading of it into the inside and outside of the frame,

as a temporary measure to get though winter,

others on here with better experience might well advise better,

 

I have small portholes and have done this in the past to get me by,

 

but at some point it’s likely the frames will need to come apart to sort it properly

 

 

[Tony Brooks]

3 minutes ago, beerbeerbeerbeerbeer said:

but at some point it’s likely the frames will need to come apart to sort it properly

 

More likely that the frame will have to come out of the bulkhead for resealing in my view. 

 

Personally, I would avoid silicon in case it made painting difficult, and use a silicon free sealer.

[AnnieRose]

31 minutes ago, beerbeerbeerbeerbeer said:

personally I’d buy a transparent silicone sealant and push a  beading of it into the inside and outside of the frame,

as a temporary measure to get though winter,

others on here with better experience might well advise better,

 

I have small portholes and have done this in the past to get me by,

 

but at some point it’s likely the frames will need to come apart to sort it properly

 

 

thanks, the plan will be to take them off and reseal them properly in the spring, but if this will keep me going until then, great. Thank you! 

[Arthur Marshall]

1 hour ago, MtB said:

 

I get massive condensation on the underside of the hatch/slides, and they are flat (and horizontal)! 

 

 

Of course. That's why we insulate the damn roof. it's just the baseplate that stays dry, everything else, vertical, horizontal or at the usual weird angles, drips if it can. And Tony's explained that.

[Peugeot 106]

On 17/11/2025 at 18:13, AnnieRose said:

will certainly try the window with a hose next time. I’ll also see what happens with the incoming rain later on in the week with the turf removed. 

I’ve had success with houses tracing leaks like this. Windows and slate roofs. Not infallible but certainly worth a try. Spray in sections starting at the bottom. If you use paper the blue dyed paper shows leaks very well