The rules require the mainsheet exit to be mounted on the keel just aft of the centreboard case.
This can result in the mainsheet chaffing on the toe strap .
There is nothing in the rules defining how this block should be mounted or the type of block to be used.
The practice for many years has been to mount the exit block on length of tubing or a cord/wire strop.
Recently some owners have been bracing the tube using shock cord or stainless steel rod attached to the thwart.
I have taken the view that providing the vertical component of the force developed by the exit block is transferred to the keel this system complies with rules and the accepted practice within the class for many years.
Phillip Johnson
National Measurer