Re: Stainless Prop gains on a 89 Force 150 outboard?
Well, when you take a trip, in order to know how to get where you are going, you need to know from where you are starting.
You need to know what your current set-up is doing at full throttle in RPM and MPH. You should be turning about the 5000-5500 RPM range. This tells you if you are correctly propped or not.
Regardless, specifics aside, there are some generalities for these engines. They are not really high horespower machines and gains due to prop changes (assuming you are correctly propped now) are minimal.
There are not many props to choose from--Michigan branded, and I think Vortex and one other brand.
The equivalent prop in stainless will run 200-400 RPM more than aluminum because the blades are thinner and there is less resistance through the water. This would translate into 2-4 MPH more than the aluminum prop. However, The Michigan branded stainless props are cupped. This reduces the rpm by about 200-400. The advantage to a cupped prop is that it has better "bite" in the water and tends to cavitate less. Thus you can run it trimmed a bit higher and lift the bow up a bit. This usually results in lower wetted surface area and more speed. You can also run the engine a bit higher on the transom and this also results in less drag.
If you are incorrectly propped, you could see gains as high as 8-10 MPH. But again, if you are propped correctly now, a stainless prop is not going to turn your rig into a fire-breather. A couple of MPH is really all you can expect unless you get aggressive with jackplates, low water pick-ups, and other hardware. Now you are putting big money into an engine that was never designed to be anything else other than basic transportation--you still will be disappointed at the performance.
