Copernicus

FREE-STANDING MASTS

COPERNICUS

Fig. 1. Copernicus originally rigged. Fig. 2. Copernicus' new free-standing mast.

Bryan and Carey Pollock lived aboard Copernicus, their Spencer 42 sloop, a traditional CCA rule type of boat, in Vancouver, British Columbia. When it came time to replace the rigging on the mast, they considered doing away with the rigging entirely and going free-standing. A phone call from Bryan in August, 1996, led to my very first, and so far only, free-standing mast design that is a replacement to an existing stayed rig. Usually, the cost of reinforcing the hull and deck in an existing boat for a free-standing rig involves more cost than it is worth, particularly on an older boat. But Bryan and Carey were committed to doing the best mast construction job possible.

Fortunately, the original hull lines and a stability test were available from the designer of the boat, so I was able to get an accurate number for Copernicus’ maximum righting moment. All rigs, whether free-standing or stayed, are designed to a load which is a function of the boat’s maximum righting moment, so this is an essential number to have.

Fairly early in the design process, Bryan and Carey decided they wanted to build the mast in pre-preg materials. These are fabrics, carbon fiber in this case, which are pre-impregnated with resin. They are usually used in autoclave/heat cure systems, but Bryan and Carey had to opt for vacuum bag/heat cure. The mast was built on the stage of a theater where Bryan built theater sets for a living. Between plays, the mast took center stage. But during shows, the mast was lifted up to the rafters out of the way of the actors. It was the only place in town long enough and cheap enough to build the mast.

I designed the mast using my wood-epoxy and carbon fiber technique, in which a wood-epoxy form is built first ,and this remains captive in the mast. This makes mast building relatively easy for amateur construction, and it allows me to tailor the diameters of the mast to suit the loads of the boat, rather than having to rely on some existing form of tooling or pole that may not be ideal. This method also allows for internal reinforcing to be placed anywhere in the mast for the various fittings, such as sheaves, tangs, gooseneck, etc., as the wood-epoxy form is being built. Carbon fiber is laminated on the outside to form the structural skin that takes all the bending loads.

Fig. 3. Wood pre-form of mast. Fig. 4. First layer of carbon fiber over wood.

The mast turned into a two-year project with quite a number of ups and downs. As luck would have it, Sebastian Reidl, the owner of my free-standing open class 60 design Project Amazon and a former resident of Vancouver, looked in on Bryan and Carey during their mast construction. A particularly difficult problem to overcome was to get the right amount of hot air circulation in the curing oven (also built of wood-epoxy) for curing the pre-preg carbon fiber laminate at the correct heat rate. Sebastian saved the day by bringing in a mining engineer friend who knew about air circulation in deep mine shafts, to solve the problems.

In the end, the new free-standing mast weighed almost exactly the same as the original rig with all its associated rigging. It probably could have been lighter as I think we could have used less wood. Bryan and Carey report that the boat sails faster, points higher, balances better, and is just a lot more fun to sail than it ever was before. It is a completely different boat. With the old stayed rig, they could never catch a friend’s Beneteau 37 before. Now they sail past him with only the mainsail up, and they point 5° higher. In gusty conditions, the mast bends just the right amount to spill the wind, and as the mast straightens again, the boat accelerates ahead. This phenomenon is common to free-standing rigs; Sebastian Reidl reported the same effect on Project Amazon.

Bryan Pollock wrote a very nice article about their experience building the mast for Ocean Navigator magazine, issue #98, May/June 1999, pages 90-97.