[Fr. Frank]

Where do you put 6 people on a Seafari?

2 teenage girls (1 mine) suntanning on the cabin topside deck, 1 kid (not mine) sitting on the front of the portside lounge seat reading a book, my wife and I and 1 kid (mine) fishing.

What accounts for the ability of a heavily loaded 90hp to swing a 4-blade 21 pitch prop to 5150rpms while I can only swing a 21 p 3-blade MWC Vortex 4400 rpms and get only 5000rpms in a 17p Black Max.

I have a 2.33:1 gear ratio. You probably have a 2.0:1 gear ratio. My 90 also actually produces 106 hp at the prop. Pre-'84 115 Merc inline-6 motors produced 115 hp at the powerhead and about 105 hp at the prop.

Also, you had steered me to the black max geometry - I'll eventually pickup an ss MQF from PowerTech unless you're thinking the 3 or 4 blade SCDs are better way to go...have you run a Yamaha style semi-cleaver like the SCDs on your Seafari? Are they theoretically a faster or easier to turn wheel than the black max shape? Better stern-lift?

I really like the Black Max props. They just work well. No getting around that. The MQF from PowerTech and the Mirage Plus for V6 motors is variation of that same geometry.
No, I have never run a semi-cleaver like the early Yamaha SWS props on my Seafari. I have run them on a '76 19' Robalo with twin '85 90 hp Yamahas. They provide lots of stern lift.
As I understand it, the PowerTech SCD4's should theoretically be an ideal prop for a SeaCraft Seafari, with the right diameter and pitch, and right height. But I haven't got the money to test one. My last Powertech prop was custom-ordered/custom-made OFS3 for about $700, and I got it with the proceeds from a 16' Blazer bass boat I sold.