Bob Curry's articles in Catamaran Sailor published by Mary Wells, stated "Start by marking off in 1" increments from behind the rear beam 5 through 10 inches. We will want to set the rake at 7" behind the rear beam for starters. This will allow the sailplan to generate lots of lift in the lulls. This is a great setting because it doesn't hurt in puffs near 25 mph. If the sustained wind was in the mid-20 range, then we would want to begin our mast rake at 10" behind the rear beam. If the sustained winds are upper 20's with gust in the 30's, rake all the way back (Remember to set your rig tension to your racing setting before you check your mast rake.)" General rigging and tuning guide by Steve Leo as published in Hobie U from NAHCA has the mast rake at 6" from tip of rudder. Rudder should be up and locked. So we have the range 7" from the rear beam to 6" from the rudder tip. If testing with other boats make sure weight (boat & crew), sails and other variables are accounted for. Maybe you could switch boats after a lap and see if you have the same out come.