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Wing masts on R-Class & 12ft Skiffs.

by Alex Vallings, C-Tech Ltd 

It's been tried before: The first mast
20 years ago legendary 9 times winner of the National R-Class Trophy Paul Macintosh built a wing mast.  250mm x 90mm, strip-planked cedar and carbon with a pocket luff sail.  The sail plan was originally designed with a single sail and no jib.  This was a dismal failure! The main was cut down and a jib fitted, but first time out in any breeze the mast snapped.

Repaired, it showed good enough performance in a very light weather contest and Paul came away with a lucky win.  Next time out in some breeze, splintering wood and carbon - again! That was it - it went in the rubbish, with the general feeling that it was not worth pursuing.

A brief second try
1985 - a wing mast 300mm x 100mm was made by 12 foot Skiff guru Tim Bartlett.  Constructed from tortured ply and carbon, this proved a bit heavy and hard to control and only showed any performance advantage when reaching.  This mast was burnt.

Third time lucky
With this record, why would you bother? But my thinking was that, with the measurement rules of the R-Class allowing 100mm free (unmeasured) area in the mast, it was worth having if you could make it work.  The advantages of less windage, more power and a little extra area seemed attractive.

One of the key developments that made the concept more simple than in earlier years was that the skiff configuration had changed so that the boom was mounted on the boat, rather than the mast. This was of major benefit with a wing mast because there was no forward load from the boom to affect rotation. The mast could therefore be designed with no mast spanner so the mast was allowed to float.

I really wanted this to work, because it made the boat a lot less complicated - but I wasn't sure if it was going to.  A large amount of deliberation and thought was put into a mock-up: broom-stick, sticky tape and sail-thread drawing-pinned to my lounge floor.  The problem being, to have a floating wing mast that could carry a mast-head spinnaker without breaking it.

Construction
With a lot of expertise gained from building all the Kiwi 12 foot Skiff carbon masts it was logical to use a male-mandrel wrapped in pre-preg carbon uni, shrink-wrapped, vacuumed and heated.  This proved harder than it sounds, but the end product turned out well. The idea was to laminate the mast in such a way as to give maximum bend fore and aft, depowering the sail.

Due to weight constraints the section size was the smallest that I thought would be effective - 120mm x 45mm aerofoil section with a plastic track glued on the back.  The mast turned out about 9 kg rigged, which proved to be a bad handicap when compared with the 5 kg, round-profile, non-rotating C-Tech flexi-tip spars dominating the fleet.

Handling issues
The main problem was controlling the boat when gybing in fresh conditions.  The straight luff meaning that the sail tended to rotate too far forward in the head.  To control this, the vang had to be on while gybing - not something we were used to in the skiffs.  We learned the hard way.  There was another problem - it was hard to keep in the groove upwind, with the flow of the jib woolies crucial.  The rig showed very good power until the leeward wooly on the jib broke - then there was none! Skipper and crew had to dive off the wire to compensate.  This resulted in very fast bursts of speed - but only an average performance overall.

After coming 5th in the R-Class Nationals the mast was put away until the next year.  During winter I ground 2 kg of carbon off the mast. This made the boat feel totally different.  It was a lot smoother upwind because the mainsail was opening and closing as it should - and not static.  Unfortunately, while wave-jumping downwind in 20 knots I found that I'd ground a little too much carbon off!

2001 Leander Trophy (R-Class National Contest)
After the repair it was National Contest time again.  Not really knowing whether the wing mast would perform or last the distance we decided to use it for the Invite race, then re-assess the situation.  Pleasantly surprised, we sailed away out of the start and led for the entire race.  Despite an unpromising weather forecast for the next day (Tropical Cyclone Sose) we decided to take a chance (remembering that only 1 rig is allowed during the Leander Contest).

The next day was very fresh and lumpy, and to everyone's surprise the wing-mast performed and we won 2 from 2 races.  It seemed to be very quick upwind into the chop.  The mast tended to lift from the pressure of the jib, decreasing the draft and power automatically.  Although it wasn't very good when the main flogged, as the mast flogged too.

The main advantage we had was the height the wing mast gave us.  We were able to go higher, and at the same speed as other boats.  Given the approaching cyclone, and the subsequent very light weather days, the wing-mast showed very good performance through the whole range of wind conditions.

The future?
Being impressed with the relatively un-tuned mast and sail, I'm thinking about trying it on the 12 foot Skiff as a 3rd rig, and perhaps stumping it up for a 2nd rig as well.  A big call, because the next 12 foot Skiff Interdominion Contest is in Wellington - well known for its wind!

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