Leaking gunwhales

[RoseB]

key point - what do I clad the underside of the gunwhale with? 
So, I’ve been re-doing my boat. Initially took out everything from the bedroom at the back (furthest end from the fire) which included a large wardrobe. Had to replace the insulation and cladding where it had been. Replaced the polystyrene like for like but foamed it in to give better seal. I’ve also added some polystyrene to the gap in the gunwhale, and then put mdf up.

sadly, within weeks, the mdf is getting soggy and mouldy. 
So I guess condensation is forming on the walls, running down and dripping in the gunwhales. The old material put there seemed to be a veneered mdf and was stained heavily, but never dripped. My flooring is now dark where the drips have accumulated and pooled. 
 

Other than a dehumidifier, I’m not sure how to stop the condensation being this bad? This bit of the boat isn’t well heated. 
and what better material to fix to the underside of the gunwhale is? 
 

thanks a bunch!

[Arthur Marshall]

I used rockwool insulation and screwed cut to size tongue and groove under it to hold it in place, varnished on both sides. Still there thirty years later.

MDF is a disaster on boats, it doesn't like damp, falls to bits and, I believe, gives off poisonous fumes. Plywood is much more resilient.

If you've got any bare metal at all, you're going to have rivers of condensation this time of year. It'll come off the windows, anyway.

[BEngo]

The key thing with insulatingvsteel 8s to provide a vapour barrier.  Either as an integral part of the insulation as in kingspan/celotex or to add one as a separate layer over the top of polystyrene or rockwool.  Builders merchants sell 100 micron polythene sheet, which is idea.  Tape the joins.

 

Under the gunwales use the same insulation sheet as on the sides, then put a vapour barrier over if not celotex and tape the vapour barrier to the ones on the cabin sides and hull sides.

 

The other advantage of a poly sheet is  that it separates your cables from the polystyrene.

 Arthur is bang on about mdf.

 

N

[Tony Brooks]

Are you sure it is not window or roof vent leaks running downwards.

[David Mack]

You need to work out whether this is leakage (e.g around windows or through the gunwale/hull joint if timber or grp cabin top) or condensation. 

Also consider that any water originating on the cabin top or cabin side may well be running down unseen behind the lining and only appearing at gunwale level.

[blackrose]

1 hour ago, Tony Brooks said:

Are you sure it is not window or roof vent leaks running downwards.

 

That was my first question too.

 

2 hours ago, BEngo said:

Arthur is bang on about mdf.

 

 

Well that really depends on which type or grade of MDF we're talking about. It's not all the same.

 

I built a bathroom counter and cupboard from green waterproof MDF 15 years ago and despite the splashes and steamy conditions it's still fine. In fact I left an offcut outside on my pontoon for 6 months over winter until a neighbour asked if he could have it to make something. It was still solid and hadn't warped but had turned a bit yellow from UV exposure.

Edited February 2 by blackrose

[Peugeot 106]

If you play a hose over the suspect area you may well see a stream of water on the inside  where it is (if it is) leaking. Start at the bottom and work your way up the windows finishing at the vents then hopefully if does leak you can see where the leak starts. Condensation won’t stream in but water from a hose pipe most likely will

[RoseB]

4 hours ago, Tony Brooks said:

Are you sure it is not window or roof vent leaks running downwards.

Could be a window leak, but it seems to be a long stretch along the gunwhale, not just under the window.

Thank you all for your answers.

vapour barrier and better treated sheet material seem to be the answer. Thank you!

[Tony Brooks]

1 hour ago, RoseB said:

Could be a window leak, but it seems to be a long stretch along the gunwhale, not just under the window.

Thank you all for your answers.

vapour barrier and better treated sheet material seem to be the answer. Thank you!

 

As narrowboats tend to trim down by the stern, the water can run down hill for a fair distance, especially if you have a board of wood or insulating panel horizontally under the gunwale. Water leaks are notorious for appearing somewhere other than close to the actual lea.

[Bee]

Firstly, is this an all steel boat or does it have a wood or fibreglass top? If its wood or f/glass then it is probably leaking from the joint. If it is all steel then it is most likely to be condensation , outside possibility of rust holes and some likelihood of leaky windows. Condensation is an absolute sod, I would peek behind the cladding to see if there is any insulation  at all (!)  If it is soggy fibreglass wool it is doing nothing except keeping everything cold and wet. There are many opinions on insulating materials but whatever is used it must cover all the steel - no gaps - and be a couple of inches  thick. Same with under the gunwhale.,   Good luck with it, most of us have wrestled with these problems and in the end the thickest normally wins - thats the insulation - not the boat owner.

[Arthur Marshall]

2 hours ago, Tony Brooks said:

 

As narrowboats tend to trim down by the stern, the water can run down hill for a fair distance, especially if you have a board of wood or insulating panel horizontally under the gunwale. Water leaks are notorious for appearing somewhere other than close to the actual lea.

My tub has alumininimumum window frames, and the weld at the corner of one had stopped being a weld. The soggy insulation and stained wood were a good yard from the leak, took me ages to find. The only other time I had water dripping off the gunnel turned out to be a screw hole rusted through where the cutout for the hatch is - there's a bit of a lip to stop the water running under the hatch because of the slope of the boat, water always pools there. Leaked into the roof with no sign on the ceiling cladding , and dripped out by the stove.