Self rightable Unicorn

I had long considered the Unicorn as being one of the best single handed catamarans.

However I had restrained from buying one because of the difficulty in self righting after a capsize. I sail mainly in the North Sea, where in a westerly wind there is no safe shore, until you reach Norway. Under these circumstances, the ability to right a high performance boat by one's self, comes high up the list of desirable attributes.

I came into Unicorns from the Catapult, which has an excellent righting system. The Catapults designer Jon Montgomery designed a system, that appears complicated but which is in effect very easy to use. The Catapult mast is of a larger sealed section. However even this will not always prevent total inversion particularly in a gale and the crew's weight in the wrong place. Jon has got over it by having a 6-1 purchase between the shrouds and the hulls, which allows the mast to be heeled over to either side. If the mast is totally inverted, heeling the mast to one side allows the mast to float to the surface. Reversing the mast heel, rotates the hulls around the bottom of the mast until the hull is inclined away from the mast giving a positive heeling moment. The helm then climbs up the toe straps and the boat rights its self without any great physical exertion. Jon's system is th basis of the system I have adapted for the Unicorn.

For the Unicorn where there is no buoyancy in the mast some form of buoyancy in the sail seemed to be the best answer to prevent total inversion. After weighing and measuring all the components on my Unicorn, I calculated that the buoyancy to keep the mast head floating would have to be 30 lbs, but if there were a 20 mph wind blowing on the underside of the trampoline, then 55 lbs of buoyancy would be required. However to right the boat from it lying on its side with the mast in the water, the crew needs to exert a turning moment of 731 lbs ft. In my case weighing 10 stone, I would need all my weight at more than 5 ft from the hull. However if the shrouds are adjustable by +- 30" then by shortening the lower shroud and simultaneously lengthening the upper shroud then a crew weight of 100 lbs on the upper hull will right the boat.

   If the boat is totally inverted by combined action of wind and wave, then with this degree of shroud adjustment and 40 lbs of buoyancy at the masthead, it is possible for a 10 stone helm trapeezing off the opposite side of the inverted boat, to bring the mast head back to the surface.  Forty pounds is a good compromise between 30 lbs and 55 lbs mentioned previously to prevent the mast sinking.

   To provide the buoyancy I have used closed cell foam attached to the top panel of the sail. The foam needs to be flexible, light and tough. Low density closed cell polyethylene foam is a suitable material. One supplier of this foam is BXL Plastics Ltd of Croydon,(01816641600), who's trade name for the foam is Plastazote, it is available in densities from 18 to 70 k gms/M3. However for our use we should aim at 18 to 24 Kgms/M3 or 33 Kgms/M3 at the most, these grades are designated LD18, LD24 AND LD33 respectively. BXL would not supply me directly in the quantities I needed, but passed me on to a local converter (Plasmore 01902307711) who in turn gave me the name of a local user, who uses it in road bridge joint construction. I bought an 8' x 4' x 20 mm sheet of LD33 foam for £7-50. It is also used by manufacturers of  buoyancy aids, gymnasium mats and mainly high quality packaging.  I shaped the foam to give a rounded leading edge and a tapered trailing edge. A sail cloth bag was maid shaped to the same section as the foam and attached to the sail by 1" wide velcro. I have not noticed any loss of sail performance due to the buoyancy bags in light or heavy weather. Indeed the extra confidence it gives allows me to sail nearer to the edge of the boat's stability envelope.

     The mast heel system follows closely the catapult system, except that a greater length of adjustment is required by the Unicorn, due to its much longer shrouds. I would recommend a minimum of 30" adjustment. To adjust the shrouds a 6-1 purchase is required on each side. Triple ball or roller blocks are necessary. One block of each pair needs a becket, to secure the ends of the control line. The line goes forward from each lower block to a turning sheave (also  ball bearing) on th forward beam through a cleat and across to the other side of the boat where every thing is repeated. It is convenient to have enough line in the system to be able to cleat and uncleat from the opposite side of the boat, but not too much spare line. It is essential to have a tie from the cross beam close to the mast to a plastic eye about 12" up the mast and back down to the other side of the beam. This needs to be tight enough to allow the mast to rotate but not enough to allow the mast foot ball to disengage from its socket. The lower end of the fore stay should end in a sheave. The bridle needs a short length of  braided line in its center that passes through to sheave to allow the fore stay to slide along the bridle as the mast heels. On the pictures of my boat, there is a line running forward from the heel system to a  purchase on the starboard  bridle, this is this was to allow easy adjustment of the mast rake. Ignore this, it is not necessary.

At the 98 Nationals at Stone I demonstrated the mast float to some of the class committee. It certainly stopped the mast head sinking, but I did not have the bottom of the mast tied down and forgot to detach the inner shroud as a result mast fell down whilst re-righting. I have used it twice after a capsize. In the fist event I had still not made proper provision for releasing the inner shrouds, so I did not use the heeling system.

The wind was F4, and the mast did not sink despite me walking around on the boom. The rescue boat towed my mast head around until it was across the wind, and let it go. The sail lifted the mast about 10-12 ft, but the boat swung quickly with the mast down wind and the mast dropped back into the water. At a second attempt the rescue boat took the mast head further into wind, on release the sail immediately righted the boat. Since then I have fitted quick release shackles to the inner shroud, which release by means of a cord and are retained by light shock cord. The next capsize was on purpose and again in a force 4 wind, after releasing the upper inner shroud, I stood on the lower hull, grasped the control line running across the forward beam, flicked the line out of the upper cleat and pulled the line through the lower cleat, it took about 5-6 seconds completely heel the mast. I then climbed on to the trampoline and the boat righted just as I reach the upper hull. All that remained to do was to pull the vertical again by the control line and re-secure the inner shroud. In all it took about two minutes, with some practice it should be possible to right the boat in about one minute.

     Should anyone think of fitting a similar system and if this article is not fully self explanatory, I would be pleased to advise further.  My personnel view is that some system similar to this one, would make the class more popular with newcomers and certainly safer for those who sail without rescue facilities.