The mast on any of the late Watsons and Barnetts is designed as the exhaust as well as needing to fold to fit into the boathouse. It also carries the radio wires and various lights. It is made up of two diameters of tube with various collars and platforms fitted to it. Starting from the bottom these are:
The plate that makes a seal between the mast and the rest of the exhaust system;
The locating cheeks;
Screw seal (holds the mast tightly back, and is a vaguely U shaped bar with a large screw in the centre)
Emergency pin tube (holds the mast in the general position, while it is fixed with the screw seal)
Hinge Collar clip (essentially a large jubilee clip that holds the hinge collar on)
Hinge collar and hinge
Hinge collar clip
Wiring loom collar
Decklight collar
Wiring loom collar
Horn platform
Forward mast light platform
Radio wire yard
Masthead light platform and exhaust outlet.
This was mainly worked out from the plans, I hope a photograph of the model explains a bit more.

The bottom of the mast is missing the fastening points and the hinge collar clips, and the wiring loom collars and decklight collars are also missing. The large cheeks at the bottom of the mast were from balsa, these were used to keep the mast a tight fit in the tabernacle to stop lateral movement. The lower section of mast is thick aluminium tube, while the upper section is brass tube (They were the right diameter) The collars and platforms were all plastic, while the yard was carbon fibre. (It was handy).