DUDLEY DIX YACHT DESIGN

FAQ - Steel Boats

You specify steel masts for your steel gaff rigged cruising boats. I have spoken with a rigger and he said that a steel mast is very heavy and has big problems with corrosion. He recommends a solid wooden mast. Is the change of material a problem, what is better?

Your rigger is not correct in his perceptions of steel masts. A steel tube mast is lighter and smaller than a solid wood mast of equal strength.

I will use the Hout Bay 30 gaff cutter as example.To satisfy my mast strength calculations, a steel mast could be 120mm diameter with a 2.8mm wall and weighing 8.1kg/m. Such a size is not available commercially so I went up to the nearest commercial size, which is 127mm diameter with 2.8mm wall and weighing 8.6kg/m.

For strength equal to the 120mm diameter steel mast, a solid spruce mast will have to be 166mm diameter and will weigh 8.7kg/m. It is 30% larger than the specified steel mast so there is more windage and the sails will not work as effectively because of increased turbulence and wind shadow. A hollow spruce mast can be lighter but it also gets larger.

An aluminium mast of the same diameter as the specified steel mast would have to have 8mm wall thickness to equal the strength and weigh 8.1kg/m, so it is not much lighter. To get appreciable weight saving it would have to be 145mm diameter with 5mm wall and weigh 6kg/m, so it is also considerably larger.

Corrosion is not a problem. I have seen steel masts that are 15 years old and still have another 15 years life in them. It needs a good paint system similar to what the hull needs and leather inside the gaff jaws to prevent chafe. The mast is sealed so there can be no corrosion inside. The lighting wires and halliards must all be external and led down the shrouds, not down the mast.

I have used steel masts on all of my gaff designs since the early 1980s, with good success. I researched all of the options very early on and found that steel is the best option for a gaff rig. Other designers have also said to me that they will not use steel masts because they are too heavy. I tell them to do the sums, not make incorrect assumptions.

What are your recommendations for a compass on a steel boat.

What compass to use will depend mainly on your budget. The cheapest will be a conventional magnetic steel boat compass, mounted on a pedestal in the cockpit. It must be a proper steel boat compass with large compensating weights and it must be correctly adjusted.

Other types of compasses like gyro compasses and fluxgate compasses are available and will give better accuracy. A gyro compass is really only suited to very large yachts because of cost and mounting problems. A fluxgate compass is probably the best solution if your budget will allow.

There is an excellent article on the problems and solutions of compasses on steel boats on the W-H Autopilots website at http://www.whautopilots.com/Application%20Notes/ that is worth reading as part of your decision making process.

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This page was updated 24 July 2004

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