A Skylight and Forward Hatch

The Bowmar metal hatches on Ruth Avery's coach roof work just fine, but a wooden skylight and forward hatch would look so much better ...

I will use a box join for the sides of the skylight. First I set up a jig so that it can be done accurately using a table saw.
The notches will be made using a dado blade. The two adjoining boards will then be cut simultaneously using the jig shown, where the first board is notched onto the stick (which exactly fits the notches) ...
And the second board is set one notch to the right. In this way they will fit together nicely ...
The skylight is then roughed out. I use a mortise and tendon to join the rails and stiles into which translucent Lexan panels will be inserted, along with some sealant, to form the roof.
This will not be a traditional opening skylight, sometimes called a butterfly hatch, in which the roof panels are hinged along the ridge pole at the apex so that they can be opened to allow air in. Instead, the skylight will be divided into two sections, one open to the cabin, the other with an oval airhole, a glass floor and drains ...
Since the baffle in the center does not reach up to the roof, air passing through the big oval can reach the cabin. Water, on the other hand, will likely be stopped by the baffle and, unable to penetrate the glass floor, drain out the small holes in the sides. This kind of skylight--basically a big dorade vent with windows--is recommended by nobody less than Bud C. MacIntosh as being not only easier to build, but less prone to leaks.

With all the pieces cut out, including the Lexan windows and floor, it merely requires assembly. Easier said than done! For starters, all the windows need to be sealed. I used 3M 5200 for the roof panels, since they will be permanently glued together as one piece. In the process, yours truly used Interlux 216 solvent to clean up the windows which I did not mask off. Two lessons: first, make sure to mask everything within 100 meters of the sealing/seaming site ... the stuff gets all over everything! ... could be used to catch thieves ... The other lesson being to never use solvents on polycarbonate. I spent a (classified) number of hours with plastic cleaners and scratch removers trying to correct my mistake.

Finally I have to seal around the glass floor. Since this is not a permanent installation, I used Life Caulk, which is not so sticky but just as evil as far as the application goes. And I managed to foul it up too and had to pull the whole thing out and do it over. Got it the second time.

So finally we are up to the easy assembly stage, screwing the roof panels down onto the sides ...
After that I give everything seven coats of varnish (except the Lexan windows!):

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