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cald said..
>>>>> For sails, imo to go quick two cams is a minimum, i'm sure there are quick no cam sails out there >>>>
The trouble with no cam sails, is they need wind pressure to "set" them. Deep downwind there's less wind pressure and they can loose a bit of shape. I managed 33 knots on wave gear, with a 4.7m sail but the sail was oscillating, as it lost and regained entry shape.
There's different opinions on water state. Some will swear the flatter the better, others that ball bearing chop is faster.
There's a few things at play here, wetted area is less in smooth water with a greater angle of attack, ie mast track back. choppy water needs the mast track further forward to flatten the board out so it glides over the top of the chop. Also glassy water is likely to have lamina wind flow, so the whole sail works more efficiently. If in very choppy water, as long as the chop is organised in lines, I find it best not to go too deep. Often the chop isn't square to the wind, so follow the chop in the direction that's most downwind, sitting on top of the chop gives the best wind. I've done 32knots in open ocean and 20kts like this.
As to what to buy, that depends on your conditions, if you have 25kts regular and flat water, you could go with a semi sinker, ie board just over your kg weight in litres but a little less than total weight, what you're looking for is a straight rocker from back strap for about a metre, with slight rocker behind back strap. On older boards check rocker between fin and front strap. Use quite often compresses the core foam and gives this area negative rocker. In other words if you put a straight edge there you'll see a gap in the middle. This will slow the board down by making lift behind the rider, pushing the nose down and increasing wetted area. It can be bogged out, if you have the ability.