Ventilators | Cutting New Holes

I explained in a previous post how I cut the holes for the ventilator cowls in the wrong place and had to do a lot of work to fill them and refinish the tops of the Dorade boxes.

This really annoyed me, but these things happen and we have to press on regardless. Which entailed cutting new holes in the cabin roof. Not something I was looking forward to ...

First I used masking tape to outline the cleats inside the Dorade boxes; where the halyard cheek blocks would be located; and lastly where the new holes should be cut.

Here I am making the first hole with the Japanese keyhole saw.

It's much easier to drill holes and cut the hole like this than using a jigsaw.

The roughly cut holes were then shaped with a rasp and an abrasive cylinder in the drill. Here they are.

A test fit of the ventilator followed, like this.

It became apparent that there was a problem here.

The inner piece screws into the outer flange from inside the Dorade box to close the ventilator, and I had assumed that it would bear directly onto the roof to make a seal.

However, the outer flange is secured with machine screws and locknuts which protrude into the Dorade box and prevent the inner piece from closing. It simply grinds against the locknuts.

I will have to give this some thought to find a way around the problem.

On the face of it seems that the ventilator is badly designed. To allow it to be closed fully there cannot be any fastenings inside the box, which would mean using very short wood screws which would not be strong enough.

I contemplated making a gasket to go inside the box which would allow the locknuts to be recessed, out of the way. I even started to make it, as here.

I soon realised that the gasket would not allow the inner piece to be screwed up because its thread is too short!

So I can't see how this can work at all.

More thought required.