Thanks Rick.
I spoke to Sailspar and they wanted the measurement from the bottom of the forestay, along the port side to the helmsman. I ended up printing out the Catalac layout drawing from your website
Catalac 8M Catamaran information which printed out to be a very convenient scale of 1 inch = 1 metre and posted it to them.
The original Rotostay was forever jamming, I think there was a piece missing when I bought Sea Spirits that was supposed to hold the rope on the drum. The bottom bottle screw was bent which made it difficult to adjust tension on the forestay. Also when I tried to remove the forestay for renewal it was jammed solid in the
furling foil, after lots of pushing and shoving and
heating up the bottom of the foil (which was the
advice from my local riggers) I gave up and cut the foil to release the forestay.