So I've spent a couple years now completely restoring my 1985 Chris craft catamaran. Its now back on the water but I'm not completely satisfied. Both engines are now running good but I'm having issues planning out when I have multiple people on the boat. I have 502's with ssm2 drives. I'm running 28x16" clever style props. I switched to these props hoping it would help me as I was running 30x15" before. The boat holds about 1400 rpm and just plows. If I put a few people in the cabin and can break the 1500 mark it will instantly blow the props out and take off like its suppose to. My question is do I need to target the larger diameter of my props as being the issue or should I look into ways to get more bottom end out of my engine's. I don't know if this is a lack of power issue or props. Just looking for suggestions on where to start. If I'm alone on the boat I have no issues. However I usually have a full crowd.

Are you saying its full throttle and stuck at 1500RPM ? What is your max rpm full throttle once on plane?

You think aerating the props will help ?

Yes I can put the throttles through the fiberglass and hold 1400 rpm. If by chance I hit 1600/1700 it will break the props loose and plane me out.

Full speed I'm running about 74 @ 4800

Sounds like you're over propped, have you tried a 24