Thanks Bill,
Since the spinnaker doesn't generate lift the same way the foils do, I can't use the formula they talk about there to calculate spinnaker loads. I sent harken an email asking for info. Using the compu-spec tool for a J/30, they recommend a mast base block with a working load of 792 lbs, which is in-line with what I was guessing. Disqualifies that harken ball-bearing sheave everyone's been talking about...
-g
