In the 49er, Julian has achieved an outstanding harmony of visual appeal, physical parts and dynamic ratios to achieve a miniaturized design of a new level of efficiency.
The drag of the 49er shape and assembled parts is lower by far than the drag of any previous skiff. This is partly hydrodynamic – the shape of the wet part of the hull, and the successful transfer of the dynamic-hump less feature.
It is partly aerodynamic. The hull is lower. The hull not only has no vertical bulkheads, it has no external bulkheads at all. Its wings are small – tiny by skiff standards – and these small wings are slender and blend smoothly into the hull, with no bulky tube outlines nor bulky plug-in points. An important point is that the wings are low – well below the meter height above the water where the wind speed is slower because it is slowed by surface friction with the water.
The unusual design of the forward end of the mainsail foot both cleans up a usually draggy area and it greatly improves the efficiency of the jib/mainsail slot interaction. The diameter of the longer FRP topmast is smaller than is possible with spun alloy. Foils are state of the art. All these features reduce the drag.
The 49er s final ratios are impressive. The modern Eighteen plus crew weighs about 990lbs (450kg). Its crew of 3 weighs 510lbs (230kg) on average and trapeze with their weights at 11.75ft (3.58m) from the centre of buoyancy, so develop a righting moment of 5992 lbs/ft. The arm between the centre of effort of the centerboard and the centre of effort of the rig is about 12ft. so the side force the boat can sustain – its ‘sail carrying power’ – is 5992/12 or 500lbs app. As a fraction of its total weight this is 500/990 or 0.505.
The same calculation for the 49er gives 256lbs side force and a total weight (with a 330lb crew) of 595lbs. Its ‘sail carrying power’ is 256/595 or 0.43. This is only 85% of the Eighteens power. Yet the 49er sails almost as fast as the Eighteen.
All observation of the 49er’s performance among the Eighteens on Sydney Harbor is that the 49er sail about as fast straight-line as the Eighteens. (They are slower around the corners and with spinnaker hoists and drops as is to be expected with their smaller crews.) The true surprise of the 49er is that its miniaturized and simplified design has achieved the superb performance level only recently achieved by the Grand Prix Eighteen footers in a boat which is affordable and easy to sail and is so efficient that it needs only 85% of the Eighteen s relative power to achieve the same speed.
