Purpose - Primarily to investigate problems of proa handling, secondarily to provide a larger, more stable, family boat! Speed was not a consideration.
Restrictions - To be low cost - the hull for preference to be made from two sheets of plywood.
Description - The hull is of hard chine form, of fairly conventional glued clinker ply, with a slightly curved bottom, built over sawn softwood frames. The outrigger float, which is only eight foot long, is of stitch & glued ply. Connecting beams were aluminium scaffold poles (cheap, but thick and heavy, so now replaced with timber) arranged in a triangular planform to minimise torsional stresses on the main hull. Due to the low cost limit, Nimanoa has insufficient freeboard to be used on the sea without either a deck or washboards fitted.
Originally, she was rigged with a mast and 80 sq. ft. sail off my Solo class dinghy. Eventually, she will be re-rigged with a 100 sq. ft. Pacific Lateen set on a swinging mast stepped amidships, with the yard tacked down to the current "bow". Staying is to the apexes of the outrigger booms.
Lateral resistance and steering are provided by two linked side rudders mounted on cross beams about a foot from each end of the hull. The rudder blades are arranged to trail a little to avoid overbalancing the helm. In shallow water, when the rudder blades are partially or completely lifted, the tiller links must be disconnected as rudder movement is otherwise restricted.
Performance - With the Solo rig, and once under way, the boat is well mannered, light on the helm, although neither especially fast nor close winded. The biggest problem is spray from under the main hull chines, although the outrigger seems to have too much wavemaking drag. At times, it seems to be "bow-down" in the wave from the main hull.
Stopped, the boat rapidly turns beam to wind (outrigger to windward) and lies quietly. The rate of drift can be readily controlled by the angle of the side rudders. In fact she is too stable in this position, as it is very difficult to move off again without lifting the "bow" rudder. Any attempt at sheeting in merely changes the angle of the boat to the wind as the main hull pivots around the outrigger. We have never yet completed a shunt without resorting to a paddle. This is undoubtedly due in part to the aft C of E of the rig, and it is hoped this will improve when the lateen is fitted.
Update - That was the position in September of 1990. Things have moved a little since then, but not as much as I had then hoped. The lateen sail still has not been made, but instead I am using a 6.4 sq. m sailboard sail that is suspended from the masthead by a halyard at about 2/3 of its height. The tack is hauled down to the lee gunwale at the current bow. The mast, which is off a Mirror, is stepped on the weather gunwale, and stayed to the float, and the current stern. It leans forward, and when I "shunt" moves to lean the other way. The rig is sheeted to the current stern with a twin sheet to the current bow. (I'm too lazy to do it standing up.) In this way the Centre of Effort of the rig has been moved somewhat forward, and is about 1/3 of the boat's length from the bow when the sheets are slacked.
Handling has improved. The boat will now bear way from beam to wind quite happily and shunting is no longer a problem. It still would not point very well, and it became clear that the forward rudder/leeboard was stalling. This will not have been helped by the foil section which was a simple ogive with sharp leading and trailing edges.
After some experiments I now use a leeboard fixed amidships, and raise the forward rudder. There has been a marked improvement in pointing and manoeuvrability, and I can now pivot the rudder at its leading edge so improving feel. (Previously the rudder was pivoted in its centre, for symmetry.) I have yet to try it in a really strong wind as I am a little concerned about the strength of the leeboard which bends alarmingly!
The next generation boat will have a lighter hull, with a bilgeboard instead of a leeboard, a lighter and longer outrigger, the rudders mounted on the stems, retractable upwards, with locks to fix the idle one, and a larger sail area!
Lessons Learned
1. A boat may be balanced dynamically, but not be manageable when at rest. Rudders are no good then, turning has to be achieved by changing the relation of Centres of Effort and Lateral Resistance.
2. Bow rudders are not a good idea. Though they can be very effective under normal conditions, when they stall they are useless. A stern rudder, when stalled, still has some use as the drag acts in the right direction. For directional stability, the forward foil needs to be more heavily loaded then the after. This increases the tendency of a bow rudder to stall.
3. Weight is only needed in a proa outrigger if there is enough sail to pull it out of the water in the first place!
4. I still do not know if a hydrofoil proa could
be made to fly on a canted leeboard. At least, by separating lateral
resistance and steering functions I have neatly side-stepped the
problems of interacting lift and directional control that I expected
to have to face.
