| Tomarack, looking at the drawings it would seem to be a pretty normal conical cap arrangement with the added complexity of the funnel not being round.
I have included a couple of period tug pictures and a couple of shots of my model Envoy Class tug for your reference.
I would suggest that you make a cone shape by wrapping either thin metal sheet or plasticard into the appropriate conical shape then joining the material along its edge. Once you have the cone you can then cut the thin slice of the cap out of the cone shape.
If you look closely at the tugs you will see that the cap is open underneath and not joined to the funnel along it's lower edge as you might first expect. This is to allow air to flow up inside the cone and help to carry the exhaust gas clear of the vessel.
As for the spark arrester gauzes, I couldn't find any pictures of that so a bit of digging around the internet may bring up something. The trouble with such items was that they were made up on the spot rather than to a specific drawing and were pretty much open to interpretation of the yard workers at the time. Having said that the advantage is that no-one could say what you create is wrong. You could make a very simple open gauze from something like thin brass rod and solder the rods together to form a lattice. This can then easily be glued onto the inside of the cone.
Looking at your drawing I think the top right hand side detail is a plan of the gauze as fitted, which gives you something to copy with your brass rod and the elevation to me indicates that the gauze is curved in section and fitted to a raised part in the centre of the cone. That's just my interpretation of it.
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“Dirty British coaster with a salt-caked smoke stack, Butting through the Channel in the mad March days" |