Dropped Pitch by 4 When I Went Stainless. New Prop Stops Pushing at 3K RPM.

I read all I could on stainless props and used a calculator to determine what would work for my boat--a '97 Maxxum 1900 SR bowrider with a 4.3 V6. The original aluminum prop was a Michigan Wheel three-blade 14x23, but for our use (pulling skiers and wakeboarders) the Mercury calculator said for a three blade we should go 14x19. I also read posts from a number of different people who have a similar set-up to mine and are using 14x19 props. The prop I bought was a Turning Point Express three blade stainless.

I installed the prop and it pulled fine up to 3000 RPM, but then it felt like it was cavitating and just spun freely all the way up to 4800. I thought I had a bad hub kit because it felt like it had spun, but I tried a Mercruiser hub kit and it did the exact same thing. I had the trim down to its normal angle and tried adjusting the pitch, but nothing seemed to make any difference.

I know I took a pretty radical step by going down 4 in pitch, but this seems like way too extreme of a change. Is it possible that Turning Point props have a different blade profile than the Mercury props? Is it normal to have that feel of cavitation if you're underpropped?

One other thing--this prop is vented with a single hole around 1/4". Not sure if that makes a difference, but I've never run a vented prop before.

Re: Dropped Pitch by 4 When I Went Stainless. New Prop Stops Pushing at 3K RPM.

Try plugging the vent hole(s) and see what happens. Vented props are supposed to let the exhaust gases flow past the vent holes at higher speeds, but perhaps your TP prop is still allowing exhaust to enter the prop; which would cause it to ventilate and lose thrust.

Mercury offers a set of different size plug inserts to allow you to "tune" the amount of exhaust entering the propeller stream. I don't know if TP has such a set.

What rpm were you turning with the 23? The extra cupping on the SS prop could make it act like a 20/21, so the rpm change going from an aluminum prop to a SS may not be as much as you imagined it would be.

For what it's worth, I don't recommend using a vented prop for water sports.

Some folks don't recommend vented props for stern drives at all, because of the increased volume of exhaust gases, compared to a like HP outboard motor.

Re: Dropped Pitch by 4 When I Went Stainless. New Prop Stops Pushing at 3K RPM.

Thanks for the response.

I guess I'll have to give it a shot with the vent holes plugged. Now that I think of it, the feel was just like cavitation, so it may be too much exhaust in the prop. I also notice that the casting in the area where the exhaust escapes is very rough with major burrs and raised areas. If plugging the vent holes works, I may try smoothing out that area as well.

Re: Dropped Pitch by 4 When I Went Stainless. New Prop Stops Pushing at 3K RPM.

I would plug the holes like jestor68 said and try it.