Two things. First some technical stuff as to
why a stern lifting prop is better, then my credentials for saying so.
A technical note about the difference between stern lift and bow lift in props. A bow lifting prop produces more of it's thrust out toward the tips of the blades. A stern-lifting prop produces more toward the hub. The effect of a stern lifter is actually to lessen "P" factor, or sideways thrust (which torques the hull to the left), and to lift both bow and stern together. (That's why the best stern-lifters are cleaver-type blades.) It also affects the attitude of the hull on plane. More rake + more "P" factor= greater angle of attack of the planing surfaces.
Because the SeaCraft Hull has no "pad" upon which to ride, "P" factor is always an important consideration, except with counter-rotating twins. And because it is a deep V, the wetted area at the stern is always protruding below the surface tension of the water rather than riding upon it. The goal is to get the minimum amount of hull depth, at a minimum angle of attack, especially at the stern. To do that, you must lift the stern.
How I know what I know
(1)I have owned SeaCraft boats for 23 years.
(2)I have rigged many as I once was the Dockmaster at a SeaCraft dealer.
(3)I was active in powerboat racing from 1968 through 1986, from driving B outboard hydroplanes, to throttleman on 22' and 30' Velocity offshore powerboats.
(4)In '87-'88, I was part of the team that selected oem propeller choices for Wellcraft boats performance division: Scarab, Excaliber, Eclipse, Nova, and Nova III boats. We tested a lot of props during the development of these boats.
Finally, I own a 20' '72 Seafari, with a '92/'02 Merc 150, that I have had up to 55 mph while selecting a prop for it. That's with bottom paint, too.
After having the engine remanufactured, I tested the following props: Rapture, Mirage Plus, Stilletto Bay II 4 blade, Quicksilver 4 blade Cleaver II (over-hub), Yamaha SWS, and PowerTech. I was looking for the best top speed with easy planing capability. I also had a nose-cone on my lower.
- The Mirage Plus 17P planed the hull in about 3 seconds flat, with a top end of 46 mph at 5600 rpm
The SWS and Stilletto Bay, both 17P, planed in about 4 seconds, but the Stilletto only gave me 42 mph, and the SWS about 44 mph, both at about 5700 rpm.
The 19P 4 blade Cleaver II gave me a top end of 55 mph at 6100 rpms, but planed in a very long 8-10 seconds.
The Rapture 18P planed in 4-5 seconds, with a top speed of 45 mph at 5400 rpms.
Finally, I called the engineers at Powertech. I gave the all the info on the hull and weight, and after some computer modeling, they custom-designed and manufactured a 15"X16.5P 3 blade based upon the stern-lifting Offshore series.
I planed in 4 seconds, with a top speed of 52-53 mph at 6150 rpms.
The prop cost me $700. It was worth every penny.