2018.02.05 - Cockpit Tent and Latex
So, what to do about leaky canvas? I looked at waxed canvas previously which would seem to do the trick but is quite difficult to apply especially since I'll be making the cockpit tent soon and that has a lot more canvas to waterproof, so I wanted something a little easier.
I remembered that the old cover for Shoal Waters was rubberised canvas and a quick trip to Google showed that rubberising canvas is not a difficult task. You get some latex, actually lots of latex, brush it on, wait for it to dry and brush on a second coat to complete the waterproofing, then a third coat for additional strength and Robert is your mother's brother. Now Latex, when dry, is tacky even though it's dry, and sticks to itself readily, a feature that is used to great effect in the hour-move industry but not something that you want o happen with a cockpit cover or tent. There are two main ways to prevent this. One is to coat the whole thing with talc, or Baby Powder which is the same thing and the other is to use silicone spray.
The problem with talc is that you have to shake it on and rub it in until the latex stops being tacky and then, if that were not bad enough, you have to do it regularly as the latex seems to either absorb the talc or let it drop off.
Silicone spray, however, is very easy to apply and although it will eventually wear off, it's the eventually that is the good bit and it's easy to apply again.
So, I have a gallon of latex, silicone spray, lots of 2" brushes ready for the rubberising to begin. The cockpit cover was removed and dried but before I could work on it I had to cover the boat with a tarpaulin to stop the water going in as it's precipitating a lot at this time of the year. While I was doing that I decided that I might was well start work on the cockpit tent. The idea is that I'll use a tarp to make a pattern and then make a canvas one from the pattern.
And here we are with the first part.
This has to run far enough forward so that the companionway is covered when the hatch is open, but not too far forward that it touches the flue which may get hot enough to melt/burn it.
Then it has to go back far enough to enable a funny shaped piece to be attached that goes around behind the crutches. This is about right but I sat in the boat yesterday afternoon for a couple of hours and found that although the tent give plenty of cover above, you stay nice and dry, the gap between the cover and the deck allows the wind to low through and the Northerly wind yesterday was just a tad cold. I was cold on one side from the wind and toasty on the other side as I had the heater going.
Making the tent from canvas will be an interesting exercise. Ideally the tent is made oversize by 10% or so, so that when it is soaked in cold water in order to swell the fibres and also to close the holes made by the sewing, and then dried, it shrinks and ends up the correct size.
But that's way too complicated for me so I'll just soak, dry and shrink it first and then sew the bits together for an exact fit. The underside will be rubberised like the cover which will take care of the waterproofing.
The downside here is that the latex will make the canvas lightproof and thus the inside very dark, especially with the front and back piece on. Now I could put in a couple of "windows" made from a thick (~1mm) flexible, soft, clear plastic but I'm not sure if I want to do that. I probably will otherwise the inside will be very drear!
The white semi-transparent tarpaulin that you seen in the photos above is really good for this, it's a shame that it is so vulnerable to UV degradation.