I have some questions. I asked in the prop forum, but didn't get a good answer. I have a 20' Lowe sf214. 90 hp 1979 merc I-6. I can run by my self and I get 18 mph @ 5000 rpm, very high prop slip. I figured around 48%. I can pull 2 tubers with 4 other people in the barge and I get 18 mph...