Just a quick question..
When conditions dictate and i am running larger sails it seems when i push the boom to a downward acute angle for maximum power over jump and bump swell(keeping sail square to board.) i seem start sliding out.I can shake it off by changing direction and pumpin the deck.
I was just wondering is this a fin size problem or is board problem.
it happens on my wave board aswell. dosent seem to happen on my big tugboat 130 litre though fin size is same on freeride and tugboat board width is different?
that makes sense mucksy. 
another thing is to not bag out your bigger sail just because the wind is light.
tension for the apparent winds.
mucksy........do an experiment next time your sailing - when fully powered up, can you take your back foot out of the foot strap? if not then you are applying too much back foot pressure.
i must be doing something wrong then, i sail with maximum back foot pressure on all points of sailing.
i dig back foot toes in [lifting heal] to lift up windward rail. this helps to stop board spinning out.
a wider tail board, you need a little bigger fin.
use half a metre smaller size sail [rigged fuller] should solve the problem.
After reading a very good thread from Roo, I adjusted my rear footstraps to their forward position and have not managed to cavitate since.
Following the guidelines of a previous sail to fin ratio thread/guide I've noticed that I'm actually keeping up with people instead of being left behind.
bottom line is in lighter winds you need to use a bigger fin to stop spin outs.
in stronger winds as you go faster the fin generates a lot more lift countering the back foott presure so you can drop down a few sizes . In light winds there simply isnt enuf speed for the fin to generate that same amount of force.
Think of it as a wing on a plane - it requires a certain amount of speed before there is sufficient lift to take off. A glider with huge wing span requires very low velocity in comparision to a jet fighter which requires a lot of velocity for the small wings to take effect.
