[Fr. Frank]

Blue,
There may be nothing wrong with the prop, it just may be the wrong prop.

My 20' Seafari, used to have a 150 Merc remanufactured to produce about 190 hp, with a Bob's nose cone.

Started with a 17" pitch Laser prop, with which I got 5750 rpm and about 43-44 mph. It took about 8 seconds to plane, and fell off plane below 23 mph. It blew out in any kind of turn, and cavitated badly upon acceleration from a stop. That's WITH the hub vents blocked.

Changed to a 15"x17"P Mirage, planed in 4-5 seconds, and got 5800 rpms and about 46-47 mph WOT. I could trim all the way without blowing out in a turn, slight cavitation accelerating.

I tried several other props, but nothing near the performance of the Mirage. But I knew the boat could do better.

In 2002 I ordered a custom made prop from Power Tech. We spent a couple weeks going over the hull size/shape, weight, CG, etcetera, before I ordered a 15.25"D x 16.5"P polished prop from them. I planed in 3-4 seconds, and achieved a max of 6050 RPM at 53 mph lightly loaded. I could trim completely, and had moderate cavitation accelerating.

As you can see, just a little bit of propeller design change can make significant differences in performance.

If you go the route of ordering a custom prop, expect to pay for the engineer's time. My PT prop cost me right at $700, and was just a modification of an existing prop line. Of the shelf PT props in '02 were about $400 to $450.

I think the extra money spent was well worth it. I can't spend the money today I could then, but if I could, I would order another custom design now that my Seafari is running a 90 hp Optimax instead of a V6 Merc. I'm not happy with my current prop as it ventilates easily. Acceleration, cruise, and top-end performance are good, however.