I contacted Carbon Fibre Tubes and asked them if they could build something suitable without it costing too much.
They were very friendly and helpful. The design was based around existing tooling (new tooling would be very expensive) and using glass-fibre where possible (much cheaper than carbon-fibre).
The design consisted of:
- 61mm parallel tube at the base
- 61 – 26mm tapered tube at the top
- Sleeves to join the sections together.
Weight would be around 4kg (fantastic!). Strength would easily achieve 2500Nm with a safety factor of 2.3 (fantastic!). The mast would be a bit flexible – deflection would be 442mm at 2500Nm but that would be ok. Main disadvantage is the price – over £1000. Not bad for a carbon mast and possibly worth going for given the other advantages.
Why not a carbon-fibre windsurf mast?
Windsurf masts are carbon-fibre and are available in about the right length. Would a windsurf mast work in a dinghy?
In practice they are too flexible. The flexibility is indicated by the IMCS number on the mast, so a high IMCS number (38+) might just be practicable; however long masts with high IMCS are expensive even second hand, so this is an experiment that will have to wait.
It might be possible to use a Standard Diameter Mast (SDM) in combination with a Reduced Diameter Mast (RDM) – the RDM inside the SDM. If both masts are stiff then the overall combination should be ok. However, again the cost of building an experiment is too high!
If anyone has access to such masts and wants to test them please report back!
DIY carbon fibre mast?
It is theoretically possible to make a carbon-fibre mast:
- Make a former out of something – foam, Paulownia wood, balsa wood, a windsurf mast.
- Cover this in layers of carbon fibre sleeves and epoxy.
The main issue is keeping the fibres aligned. The fibres must be straight up and down the mast as accurately as possible. Any deviation from this will result in the fibres buckling on the compression side of the mast. Thus creating a rigid, strong and light carbon fibre tube requires tooling and experience – it isn’t really a DIY job.
I did consider using pultruded carbon fibre strips. Here the fibres are already aligned so the result should be much better than just using a sleeve. However the strips are only readily available in lengths of 2m, and anyway they need fixing to something else to hold them all together.