Free standing aluminium mast – design tweaks and cutting the tubes

Right – time for a deep breath. This is where the designs become reality. First stage is check the design to get it as good as possible.

Mast head

The topmast tube needs to be extended a bit for the mast head fitting. The length for the stress calculations remains the same – 5.6m – but the overall length is a bit longer to allow for the masthead bung and the loops for the masthead blocks

Topmast

The main 2 3/4″ x 10swg tube is heavy when 5m long. To make the mast lighter where it counts I tweaked the topmast length and made it a bit longer and the main tube shorter. The trade off is that this reduces the strength at the base of the topmast. This should be ok as some of the load is distributed over the length of the mast plus as soon as the sail is reefed the load in the topmast decreases dramatically.

Mast foot

I’ve tweaked the design of the foot. The main tube (2 3/4″ x 10swg) will go all the way down to the heel fitting. The strengthener will stop a bit above the heel fitting. Theoretically the strengthener could stop at 395mm above the heel, but in practice I’m going to take it down to 100mm above the heel. The primary reason is that I want lots of strength at the mast pivot point.

Mast pivot

The Wanderer features a tabernacle with a pivot that makes putting the mast up much easier – a one-person job. Given that it will just be me on my own putting the mast up it makes sense to keep this feature. The similar GP14 without a pivot requires two people to put the mast up safely.

The issue is where to put the pivot on the mast tube. Drilling a hole through the tube is by far the simplest route but will weaken the mast in a highly stressed location. Ideally the pivot should be clamped to the mast but this raises other issues:

  • The mast might hit bits of boat as it goes up and down. Clearance in the hull was designed for a centre-pivot.
  • It is a lot more work unless I can think of a clever way to do it.

I’m going to reinforce the mast at the pivot point with some internal Scots Pine. This shouldn’t be too hard to do and means if I need to drill right through it should be strong enough. I need to have a play with a section of tube in the boat to find out how it will all fit together.

Cutting tubes

I dragged my metal-cutting bandsaw outside (after first cleaning it down to avoid metal filings in the carpets…) and set to work.

Check and check again

After a few cuts I ended up with this:

Beginning to look like a mast!

Woo! Instead of a couple of tubes I have something I can pretend is a mast! The main tube and strengthener is at the bottom of the picture with the topmast at the far end.

I also cut the taper sleeve and topmast head fitting:

Mast head fitting and taper sleeve

All tube cutting now done – just need to fit it all together.

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