Ian Aitkens designed and built himself a harryproa on a farm in New Zealand. His description follows.
Gidday Rob, Here is some history and specs.
I was intrigued by the article in Multihulls magazine in 2002 featuring Harrigami. Then a few years later I built a model to see if it worked as well as a regular multi. It did but I could see room for improvement. It evolved over a few more years until I was happy to forge ahead with a full size version.
Specifications of Weight to windward (Harry) Proa
Designed and Built by Ian Aitken
LW hull LOA = 11.0 m one of the bows folds back to facilitate getting it on and off the trailer, this reduces the length to 10 meters when on the trailer. Both ends have 1 m of ‘glass covered foam.
WW hull LOA = 7.0 m The end 0.5 m is closed cell polystyrene with one layer of 200gsm glass cloth skin.
Hull shape underwater is basically semicircular but with a 150mm flat section in the middle, (to make it more comfortable to walk/stand on the inside of the hull bottoms).
There is a small amount of rocker in both hulls, about 100mm in the LW hull and the ends of that hull are flatish to give some dynamic lift to the front and squat to the rear. This is to help counteract the normally nose down attitude of these boats. It still sails with a slightly depressed bow.
The LW hull ends also have a banana shape underwater, (straighter to LW more curved to WW). This is to reduce the weather helm to acceptable levels and stop the tendency to go into irons if the helmsman is not on the ball. I refined these tricks on a 1 metre long model that I made about 10 years ago. It was fitted with RC gear and after trying 4 masts 4 boom designs 3 different rudder sizes and locations 2 different LW hull shapes and 3 different folding geometries I decided to go ahead and do the calcs for a maxi size trailerable one.
I use the term maxi because here in NZ the maximum allowable trailer length is 11.5 metres from towball to rear of load.
Weight = Bare structure = about 1200 kg. The design target was for 1000kg but by the time you put just a bit more here and another layer there just to be sure, it soon grows to 20% over the target.
Weight = 1550 kg With all cruising/camping gear aboard ie sails, portaloo, fridge, inflatable, galley stuff, food, 40 litres water, 2 anchors and chains/rodes, ropes, fenders etc etc. but not including any crew.
Length of mast 11.7 m 1.2 m bury 10.5 metres above deck.
The mast is a whole book in itself. 2 years research and calculations. Then another 2 years admittedly very part time to build. I learnt how to vacuum infuse by making the rudders and beams first. Then made the rectangular spar which is the guts of the mast. Then when that passed its test for strength and deflection. I gave myself the OK to go ahead with the rest of the boat. That was September 2014.
Mainsail 20.0 sq m
Jib 9.8 sq m
Mast 4.9.sq m
Total 34.7 sq m I have a Naish 16 metre kite that I plan to play with in the right conditions and an old 18 sq m lightweight genoa that I could use as a code ‘0’ in light air.
Beam overall 4.7 m
Beam hull centres 3.75 m
Bridedeck clearance 0.700 m
Draft WW hull 280 mm
Draft with rudders down 1.7 m
Rudders are NACA 64a 010 400 mm chord 1.7 m in the water. They rotate 180 degrees when shunting. Have an adjustable latch that allows them to kick back. This latch can be triggered with a short boathook from the deck and the rudders then pop up to the surface (because they are much lighter than water). They can be wound down using a brace/crankhandle from the deck also.
9.9 hp Yamaha 4 stroke outboard motor. Long shaft electric start, high thrust prop. Gives top speed of 8 knots. It purrs along nicely at 6 knots at only 1/4 throttle. The ouboard is raised 800mm on a sliding mount so that it clears the LW hull that folds under the brigedeck.
An electric trolling outboard can be mounted near the middle of the bridgedeck. This can turn full circle and is used to move the boat in any direction.