earlier in this thread you quote drag due to centreboards as 21%, is this the figure an average for upwind and downwind or is it the upwind drag.
This data comes from miss Nylex C-class design article. The text with the table says :
Approximate drag values for the following conditions :
Boat speed - 12 mph
40 degrees from true wind
true wind speed 15 mph
apparent windspeed 25 mph
They have more or less optimized the Miss Nylex cat for these conditions as they found the C-class boats on the C-class course to spend at least 43 % of the time on such a leg. Therefor most gains were to be had with improvements here.
Also remember that Miss Nylex had a solid wing sail and those rigs produce more thrust for a given drag and side force. Therefor you can expect the dominance of the rig to be larger on soft cloth beach cats this means that the drag numbers given for hulls drag etc (precent wise) probably can be considered as upper limits for those found in beach cats.
Seems to me that this drag must be mainly caused by the leeway a boat going upwind makes so that the boards are slanting through the water, I would have thought that the downwind component induced by boards must be far less than the upwind since the board is travelling parallel to it's centreline(pretty much).
I expect as much as well.
But also note that boats under spinnaker achieve higher speeds then when going upwind. Wave-making drag becomes increasingly less important relatively to wetted surface area drag with increasing speeds. As such downwind legs can actually favour shorter hulled boats more then upwind legs, meaning that when a shorter hulled boat is found to be favoured on the upwind (which is not a certainty) then it is logical that under spinnaker it will be favoured even more.
I hope this helps.
All very interesting stuff really.
Wouter
