c) lifelines (guardlines) supported on stanchions, which, with pulpits, shall form an effectively continuous barrier around a working deck for man-overboard prevention. Lifelines shall be permanently supported at intervals of not more than 2.20m (86.6") and shall not pass outboard of supporting stanchions.
If you want to read the whole thing look here
Category 3 with liferaft is for RORC's cross channel races; to give you a sugesstion as to which section to look in
Often the spacing is not decided by you - but by boats toe-rail ... especially if its a moulded one with freeing ports at intervals .... the other is of course the shrouds / stays .
If you don't put them at equidistant intervals, taking into consideration above - your eye will notice it everytime you look at the boat .... it's like the fence post that isn't quite vertical - the eye sees it everyday !!
I am pretty certain that the RCD specifications are the same as the ISAF. They also specify the height of the guardwire(s) and determine the number of gaurdwires needed.