Free-standing mast: Aluminium Tubes

Aluminium tubes are easily available in the UK and fairly cheap. Aluminium is strong, light and has very predictable properties.One issue is that aluminium is only available in lengths of 5m, so we can’t make the mast out of a single tube – we’ll need to extend it somehow.

Another issue is that cutting and welding aluminium destroys the properties – you are likely to end up with a very soft material. So we can’t cut and weld the tube to create a tapered tube – we’ll have to stick with the tubes as delivered.

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Free-standing mast: Wooden Mast

I like making things in wood, so it is worth working through the design of a wooden mast.

A mast needs to be as light and thin as possible so large defects in the wood such as knots cannot be allowed. This means most wood in the retail market in the UK isn’t suitable. I eventually tracked down two suppliers: Robbins Timber and Sykes Timber.

There are a few types of timber that could be used, but when availability of the necessary grade is taken into account it comes down to two:

The figures for Douglas Fir are as follows:

  • Sitka Spruce. This has the highest strength to weight ratio of any wood so is the traditional wood for boat spars. However it is expensive, a bit soft and not as strong as…
  • Douglas Fir. A bit heavier for the same strength but cheaper, harder (less chafe from yard and battens) and stronger for the same size.
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Free-standing mast – Requirements

Following on from my previous post I thought I would describe the design process for the free-standing mast. Any design process needs requirements, so here goes:

  1. Strong enough to capsize the boat, with a safety factor. Normally expressed as a righting moment in Nm. For a yacht this will be approximately 1/4 of the beam (width) of the yacht multiplied by the displacement (weight). A dinghy is trickier since the crew move around to balance the boat – two crew hanging over the side can provide a large righting moment.
  2. As light as possible. A heavy mast will tend to capsize the boat. It also will be harder to raise and will make moving the boat on land harder. The weight of the bottom section doesn’t matter too much, but the top 1/2 or 1/3 should be as light as possible.
  3. As thin as possible. The mast will catch the wind with the sail up and down. When the sail is up a thin mast will improve performance. When the sail is down a thin mast will have less drag when rowing and manoevering the boat.
  4. I want to be able to sell the Wanderer eventually. There isn’t much of a market for junk rigged boats so the hull must be able to use the bermuda rig with as few changes as possible. This means that the mast must fit through the existing hole in the deck which imposes a maximum mast diameter of around 71mm. It must also use the existing mast foot.
  5. Cheap. This is a hobby.
  6. Easy to make, if necessary.
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Junk rig conversion

I’m considering converting my Wanderer dinghy to junk rig from the existing bermuda rig. This obviously raises the question why! It is a lot of work and the existing rig has a very good reputation.

Reason number 1 is I like tinkering with things.

Reason number 2 is that I sail with two small children. Normally, when sailing, one has 100% concentration on the weather, waves, wind, what the boat is doing and how the sails are responding. This is great fun. However, with my current sailing, one child has just dropped something over the side and the other is making a spirited attempt to drop themselves over the side. I need 95% of my attention on the kids, and the remaining 5% is mostly making sure that I don’t hit anything. Both children also want to steer and this is to be encouraged as I want them to learn and to enjoy themselves. With a child steering a boat with a bermuda rig I would always be worried about a gybe – where the sail flicks across the boat with the wind behind the boat – as a bad gybe can damage the rig or capsize the boat.

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Wanderer dinghy centreboard repair

My Wanderer is about 40 years old. The centreboard isn’t the easiest thing to inspect or get out, plus it is deep so hits things. Overall the condition was fine but the tip had seen better days. The wood was starting to go soft where it had been immersed in water without any varnish. I probably could have just varnished it but being me I wanted to fix it up.

My experience with the rudder meant that I didn’t want to try fibreglass tape and epoxy. Instead I thought I’d try some iroko on the leading edge and tip.

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