A brief conversation at the pond-side reminded me to mention why you might
want to choose a different length backstay crane. The diagram gives
Put simply, the longer the crane, the more it'll bend the
mast because of its leverage. An estimate of its leverage is given
by imagining where the backstay would attach to the mast if the crane were
not present, yielding an "effective" mast height.
Usually, you'll not want a particularly long crane;
in fact you'll probably want the shortest crane that will allow the
backstay to clear the mainsail leech. The reason is that you'll
probably want as much backstay tension as possible, so as to obtain as
much jibstay tension as possible, while bending the mast as little as
possible. If you are running a minimum diameter mast, you'll
probably want to be running a minimum length backstay crane as well.
A small detail: to maximise the transfer of the
tension in the backstay to the mast, have the crane meet the backstay at a