High performance outrigger part 2
GALLERY | Click images to enlarge
Sam Frosh’s practical sailing experience leads him to believe that the tacking proa is not a realistic or sensible design when used in higher winds.
In September I had my contribution appear in Proafile regarding the design and construction of my tacking proa or more correctly, outrigger sailing craft. Since that article I have sailed my boat in the strongest wind conditions that I had taken it out thus far, around 18 to 20 knots. Apart from an impending structural failure in that the 50 mm aluminium tubes could not stand the rig load from the side stays and bent permanently beyond their pre-bent shape, it was very instructive at a design level for this type of craft.
It is a given that when the float is leeward on starboard tack and to windward on port, that the boat behaves very differently on each tack. With the float to leeward it is not practical to attempt to fly the float in strong winds as the smallest mistake by crew or skipper leads to an immediate capsize to windward. Therefore the trim for safety becomes such that the float is allowed to press well into the water; which is not ideal for a very low buoyancy float, being less than half the sailing displacement of boat and crew. The main hull is long and narrow and designed to plane with it’s flattish bottom but is being held back considerably by a float that is well on its way to being fully immersed, and creating considerable drag.
On the opposite tack, one encounters a new set of circumstances, and this in itself creates a major problem, as you need to remember that suddenly your boat has completely new handling characteristics. This I knew from the outset even before construction, and it sounded to me that it would be challenging and also fun. This was true in light and moderate wind, but when sailing in overpowering conditions such dramatic differences are the last thing the crew need when really only desiring to stay upright.
When sailing with the float to windward, in stronger winds, the float is flying well clear all the time which means that crew balance is critical as the main hull is the only thing in the water. At 40 cm. wide or a little over one foot, this is a lot like walking on a tight rope as the crew is hiked out on the trampoline wings. The boat feels as though it could capsize readily to leeward or windward as it powers on as if it has a mind of it’s own. In fact it can only capsize to leeward, but it will topple the crew out of position if suddenly the windward float comes down into the water unexpectedly.
My inescapable conclusion is that such an asymmetric configuration is fundamentally flawed and serves only to frighten the crew into not wanting to go sailing except in light conditions. Therefore my choices are now to either abandon the design or to try to solve the design problem as best as is practical without discarding everything that I have already built. The only solution that I can see is to convert to a trimaran, which overcomes several deficiencies in the original design. It would achieve the following improvements.
- Identical handling on both port and starboard tacks.
- A more stable wider platform that would be less intimidating for the crew in strong winds.
- The ability to hike out further, onto the windward float, and develop greater righting moment, and simultaneously be sailing a boat that is much less likely to capsize.
- The ability to carry more sail as currently we are reaching the limit of righting stability long before reaching the limit of longitudinal stability. That is we have not experienced yet any tendency for the hulls to nosedive.
Whether the floats should be increased in buoyancy to able to float the entire displacement of boat and crew while essential in a larger craft is optional in an off the beach trimaran where crew weight is the main factor to balance the power of the sails. My current thinking is that large highly buoyant floats would create a situation akin to a super wide catamaran which is not at all challenging to sail, so I intend to use the current float as a male mold to create two new super light weight floats in carbon fibre.
