Following Skydive130’s tutorial on the making of the roof vents for his Pilot Boat I had several attempts to make the roof ventilators using his method, none of which I was entirely satisfied with and so I decided to adopt a slightly different approach.
I did some research into the actual size, shape and workings of these things and found sufficient information on the web about them 🤓.
Known as ‘Dorade Box Ventilators’ they are designed to admit air flow and funnel it through the device to the cabin interior and at the same time to block the ingress of water by using a clever valve mechanism with the water draining away through slots on the base.
Not that much of that was relevant to making them but identifying the type, and then the manufacturer, and finding drawings was a great deal more help than the grainy low resolution photographs that I was looking at previously.
With a much clearer idea of what they should look like from the info I found I started by laminating some square section styrene for the bases and cutting them into blocks of an approximate length.
There’s a raised circular section at each end of the ventilators and I simulated those with some 8mm and 6mm styrene rod and then trimmed the blocks to a rough tapered shape with a knife using the circular pieces as a guide.
Further shaping was done using a sanding plate, file and abrasive to shape the bases with a taper in length and in height. I also filed some bevels on the underside of these bases to simulate the water drainage slots.
The bases for the two ventilators on the forward engine room roof are circular in shape and were easily made from some 10mm diameter rod that I was able to ‘turn’ to a tapered shape in the chuck of my makeshift Black and Decker ‘lathe’.
A distinctive feature of these ventilators is the air intake funnel that has a particular shape which I wanted to look as realistic as possible and involved multiple experiments to get a repeatable method.
These parts were made from 8mm styrene tube and being a thermoplastic it can be readily heated and formed and to form the distinctive mouth shape of the intakes I made a wooden former suitably carved and shaped that could be pushed into the end of the styrene tube during the heating stage and using finger pressure mould the walls of the styrene tube around the wooden former.
The end of the former has a rounded end that will stretch and distort the plastic so that the tubing can be bent to 90 degrees while maintaining the curved shape.
The styrene cools and hardens very rapidly and so it took many attempts to form the desired shape successfully and I must have used almost a complete 300mm length of 8mm styrene tube perfecting a technique to form the piece in a repeatable way.
Probably a dozen or more such pieces went into the bin until I was happy with a repeatable process 😥.
As I need six of these ventilators I was very careful to perfect this without running out of material 😮.
Each piece needed to be trimmed at each side of the bend and the ‘mouth’ heated and refined on the wooden former. The base end of the piece was re-heated and reformed into a roughly circular shape so that it mounts neatly on the 8mm raised disc at the large end of the tapered base.
This was not a particularly easy process at all and a few ended up in the bin after the repeated heating and forming rendered them irretrievably miss-shaped as can be seen in one of the pictures ☹️.
I probably spent a whole day making eight usable pieces (six to use and two for spares) but I was determined to see it through despite aching and burnt fingers 😢.
After a final trim and clean-up with file and abrasives they were glued to the ventilator bases and left to set.
I used a ‘ScotchBrite’ type abrasive pad to clean the completed parts and to provide a key for the white gloss paint.
One good thing about styrene is that it’s not always necessary to spray a primer coat if the surfaces are well keyed.
The mouths of the vents were painted inside with satin matt black as a finishing touch and a 1.5mm brass rod superglued into the base as a fixing pin.
After careful measurement and positioning the roof was drilled to take the brass fixing pins and a dab of canopy glue used to secure them in place.
The forward vents on the engine room roof are fixed in the same way but I had to add a reinforcing piece of ply on the inside as the roof there is only a 1.5mm ply panel.
I had been putting off making these vents for a while and now that they are made and fitted they do look quite good and I’m very satisfied with the end results 😊.