Would you believe the local hardware store is where I order props from? Not sure if the guy in that department is still alive.
Got a Lowrance LMF-200 gauge, using the EP-10 fuel flow sensor to get the fuel burn numbers.

Thats amazing, guess you haven't had to buy a prop in a bit, huh? Thanks again for the info...

So, it turns out that the old motor I had (91 Rude 200) had a 4 blade prop on it. It says 15x16 on it. I assume that is a 15" blade with a 16 degree pitch!?! :head: If this is the case, I plan on trying it out over this next weekend and see how it performs.

btw, using the 21p prop Saturday I was running 39 mph (gps) at 4200rpm. Seems as though the engine had lots more in it but I didn't push things. Absolutely ran like a charm though. :love:

You're going the right route!
Getting a basis to start makes it a lot less expensive by not buying prop after prop till you find the right diameter and pitch.
The 15x16 sounds like a good compromise. Just be cautious about over revving the engine.
See if FERM can give you the max rpm's intended for that motor.

Tsubaki, I don't get how you went from a 19 pitch to a 17 & didn't increase RPM's or lose speed?

My 200 merc runs a 19 & hits about 5300 at WOT, thats in the mid 40's by GPS.

I've tried a 17 & 17 cupped, the cupped was pretty good, but the 19 is a nicer prop & other than a bit less of a hole shot it hits wot just right.

If you can find a good prop shop most guys will let you try a few props & pick your favorite.

I'll back up the guys saying use stainless, around here an aluminum prop is a sign of a new boater.

Doug

you can also get a non-cupped prop cupped, that adds a bit of push & drops your WOT RPMS a bit, for cheap.

Doug

That would be 4500-5500 for acrossflow OMC, but 5200-5500 is best. Whatever you do do not run it at 5750-5800 for sustained periods of time though. Crossflo engines have an inherent harmonic vibration in them at that speed that has resulted in more than one exploded flywheel from sustained running at 5800 RPM's.

Thanks Ferm...I appreciate the information.

Subtle changes in diameter with the same pitch prop will sometimes achieve your desired performance. Same is true in reverse by changing the pitch but not the diameter. Another facet is a cupped prop, it can make a world of difference.
A good case and point was on a boat my father had years ago. He kept working toward an ideal rpm by buying props then having them repitched, testing them then having the diameter ground. Got it down to two prop sizes, one would overturn the engine, the other would produce slightly less than desirable rpms. I can't remember the size but he ended up getting the same diameter and pitch prop (of one or the other) but cupped. The engine then did what he wanted.
Normally stainless and aluminum props of the same diameter and pitch don't perform the same. There is a relationship (I've forgotten) about matching a stainless props performance to an aluminum one. It seemed like the aluminum props had the ability to flex more, so needing a slightly larger diameter and less pitch to match the stainless props performance.
In my case it turned out that way.

Now, if I will ever get off my butt and get motivated, I'll try to see if I can get mine to the correct rpms with a prop I've had a couple of years.
http://i175.photobucket.com/albums/w.../ssprop005.jpg