Performance Factors

A what?????

Someone mention SCHRS

Hang on, this is turning into a skiff-only thread!

The reason the 400 is relatively good in the light airs is that it has an "old-style" hull-plan - one that compromises between displacement and planing sailing. In the light stuff it's hull is sufficiently hydrodynamic to cut the water better than a 4000. However, when the wind gets up a bit, its rounded aft section doesn't pop onto the plane as quickly as a skiff with a ultra-wide chined stern. Now all things are relative and the 400 has a more of a planing hull than, say, an Albacore.

The amount of sail you carry is relatve to the righting moment you can produce. The most efficient sails are those with a high aspect ratio as they minise drag against lift. However, they also the least forgiving of inappropriate sheeting angle. The same is true for foils. Long skinny boards and rudders are the most efficient but you have to be moving fast for them to work. And they stall more easily than chubby centre-boards.

Once you get your weight out-board on the wire, you are loading up the foils, forcing them to work harder and produce more lift. At that point a lighter craft will be more responsive. When you are in-board however, all-up weight of crew plus boat is what matters and a carbon tiller can be offset by a full bladder !

Catamaran's break most of the rules above as they are generally displacement-only craft. They go very fast for their length due to the narrow section of their hull which allows a higher hull-speed. However, their designs are now starting to look towards some element of a planing hull in their designs - I know this is true of the F18 Capricorn and there must be others. But, for the geeks amongst us, it's well worth looking at how the SCHRS cat handicap formula works. It's fairly reliable for all cats and shows where the emphasis of weight vs sail area vs hull length goes. Although SCHRS doesn't cover monohulls the laws of physics are the same so you should be able to get some idea of the importance of the various factors.

The other good source for anyone wanting to bluff their way in marine architecture is "Sailpower - The Science of Speed" by Laurie Smith and Andrew Preece.

Foiling boats like the Moth occupy the same sort of lack of compromise as the 12'. Dogs in displacement mode but lighting fast once up to the speed at which they are designed to sail. The problem lies in getting them to that speed and then keeping them there.

Appologies if I have got anything wrong but I think it's generally correct.

Would have been interesting to have had a bit of a race with the 12 on sunday to see how the different advatages would have worked out over the course. From our perspective (in the 14) we certainly pointed higher up wind at a similar boat speed until the wind piped up - then needed more rake!

The bit I thought was the most interesting was how high you were sailing down wind even with the bigger kite. We just could not wind the 14 up that high without the apparent wind pushing us way off to leward? An example of a more efficient kite shape?? I don't know.

The thing that makes the biggest difference to our speed is our T foil - let it off up wind and the boat feels like its stopped! Pull it on down wind and again you can really feel the boat lower it nose and accelerate, or alternativly, as we were doing sunday afternoon leave it off for the more impressive ride (or lazyness - afterall we weren't racing). 

If we were racing a windward leward somewhere small, I'd certainly favour the chute option over the bags... plus easier when swimming