Coachroof insulation?

[KenMcCulloch]

The coachroof on Border Maid is ½in ply with 1in square oak reinforcing ribs at 6in centres. Enough condensation forms on this surface, when conditions are suitable, to cause a significant nuisance. It runs down the insides of the coamings and drips onto the bunks. The paint on the inside of said coachroof needs renewing, however I wondered if there might be mileage in some improved insulation. Cork would look reasonably traditional but would it make any difference to the condensation problem? Has anyone else succesfully treated a similar problem?

 

[Poignard]

That's odd. My Twister also has a 1/2" ply coachroof and I don't get condensation on it. It is painted with Dulux emulsion paint. On top it is sheathed with something [Cascover, I think] and painted with International deck paint.

The only explanation I can think of is insufficient ventilation. When we sleep on board we have at least one companionway door open and the forehatch raised a couple of inches. There is also a ventilator in the coachroof doors and a mushroom vent above the galley stove. Cosy it aint, but it's dry.

 

[Seanick]

Agree with Twister owner. Ventilate more until it stops.
We recently had a similar question from a customer who owned a 40' motorboat. It was dripping wet down below. We simply opened all the port lights half open, fitted a small cover over the wheel house to keep the rain out, propped open fopre and aft hatches. and pumped her dry. Two days later the whole boat was dry and fresh. This works most of the time, however if its been really cold, and a warm/damp front comes through you will get some condensation untill the structure warms up.
The other way is to close all ports and vents and fit a mains dehumidifier.
Steer clear of cork tiles. They are hell to remove,and wont help much with the drips!
Another trad solution is a timber gutter on the bottom edge of the cabin side. If made large enough, it can be a handhold too.
A drain hole at one end clears water from the bunk.

 

[Gordonmc]

The coachroof on my Hillyard is of similar construction and while ventilation helps it doesn't erradicate condensation entirely. Despite leaving portholes open with flower-pots tied over to stop rain and beasties getting in, the drips appear as soon as the air temperature goes below freezing, probably because the water temperature is higher.
One thought I had was to use thinsulate between the beams, then cover with something like flotex, a thin foam cored plastic sheet material. For now the charcoal heater dries off the condensation efficiently enough, but that's only of use when I am on board.