Symmetric Spinnaker size

[neilsty]

I am looking at buying a used S2 symmetric spinnaker and am unsure about sizing. It will only be used occasionally so I don't want to pay for a new one. I know to be IRC legal the foot has to be no more than 180% x J. My question is on the leech/luff length. My I = 61 feet, but my spinnaker pole is about 5 feet off the deck, so going with a 61 foot luff/leech would seem to put too much curvature in the luff. Obviously going with 61-5 = 56 feet would be too tight. What should is a usual luff/leech length - on line sail makers just ask for the I and J.

[Stumble]

Racing spinnaker luffa are typically 100% the I, a cruising spin luff really should be no smaller than 95% I. Height of the pole does not factor into the luff length of the spin, unlike on a asym there should be a significant amount of luff curve (slack) in the sail. Obviously spinnaker trim includes adjusting the pole height, but it's not critical for a cruiser, it just means the sail will be a little less stable than it should be.