centreboard won't stay down

[Overomtimistix]

On my boat, the centreboard seems to have only two positions: fully up or fully down - down only because the rope handle interferes with the top of the case. If I try to set the centreboard partially down, it floats up
It is a carbon fibre board with presumably a foam core. There are pieces of thin plastic glued either side.
On other boats, with wooden boards, I have come across two methods of stopping board rising - adjustable pads either side or a piece of hose on the front edge that is compressed under a plate.
I have tried addiing a gash CD, but that seems to be too thick to fit into the current slot.
Can anyone suggest what I could use with my set up. I don't want to cut into the centreboard case if I can avoid it.
 
thanks
 
dan

[martin 1262]

Cheapest and easiest is shock cord that wraps around the thwart and the centreboard handle. Adjust length so when fully extended the board is about half way down. You simply remove shockcord when you want board fully raised. 
martin

[johnk]

If you run the shock cord to the back of the centreboard case it can be adjusted so that the centreboard stays wherever it is positioned. Use 8mm shock cord with an adjustable 3-4mm rope tail Should you capsize with the board up, the elastic pulls it down for you. How do I know.....