I’ve made some more bits for the mast:

The topmast support bung sits inside the main tube and provides vertical support to the topmast. It also seals the main tube against water in the event of a capsize. In practice I put a recess on both sides of the bung.

The central boss and M5 thread is to provide a handle when trying to position the bung in the tube. The bung is too far down the main tube to reach directly, and if / when it gets pushed too far down then getting it back up again would be hard. The M5 rod makes it easy.

The bung is positioned 200mm down the main tube to ensure that more than 10% of the topmast is inside the main tube.

The topmast foot bung has 3 tasks:

• Supports the bottom of the topmast on the topmast support bung;
• Seals the bottom of the topmast in the event of a capsize;
• Provides a lump of acetal to take the screw that will fix the topmast to the main tube.

My other boat doesn’t have the topmast fixed to the lower mast. In practice this isn’t a problem – the mast lift and other lines effectively secure the two sections together. However, the Wanderer has a tabernacle to aid lowering the mast and this may be useful when passing under bridges. It would be helpful if the topmast didn’t fall off when afloat with the mast lowered, hence a screw is probably a good idea. The screw will also stop the topmast rotating on the main tube.