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gigamurph
06-02-2001, 10:35 AM
Okay, no laughs! Am "old school" and currently own a 1979 17ft. Witchcraft Banshee with a 1980 90HP in-line 6 Merc. It's paid for and "mint" and gives me plenty of thrills for the buck. Am looking for info on prop section. My current prop came with the motor and appears to be a 12", 19 pitch three blade aluminum prop. With this prop, I am only turning 4600 rpm at full throttle (on Havasu). Don't know the speed due to the fact that I have no speedo. This prop gives me a decent hole-shot and adequate top-end. What I am looking for is a prop that will get me closer to the factory recommended rpm (5200) without sacrificing either my hole-shot or top-end. Possible? Thanx for any help!

BillyD
06-14-2001, 12:12 PM
First, I would definitely recommend a stainless steel prop. They are much more efficient that the aluminum ones (albeit, more expensive). I am more familiar with the props out there for V-6s, but Merc makes several props for your engine. Best top speed and best hole shot are almost impossible to have together, so you may need to compromise one for the other (at least a little bit, anyway). However, compared to that aluminum prop, you may be able to find a prop that does both better than what you have now. I would go to a three blade if you want best top end and a four blade if you want best acceleration and load carrying ability. Get a copy of Hot Boat magazine and call some of the companies in the back that advertise props. They will make specific recommendations. Also, Merc now has a set of props that you can try before you buy (they are painted blue). Ask your local Merc dealer if he participates in that program. You may be able to stay with about a 19" pitch prop since the increased speed of a stainless should actually help you to get some "free rpm". Only way to be sure, however, is to try. For best acceleration, a 17"-18" four blade (properly selected) would really rocket you out of the hole and maybe still give you more top end than your current aluminum. Good luck!

Bliz
07-25-2001, 07:32 AM
Here too is the rule of thumb when selecting props. When you decrease your selection of pitch, for every one inch of pitch decrease, you will raise your RPM by between 150 and 200. Likewise, when you increase pitch, you decrease rpm. The resulting formula would be as follows for your scenario
MFR Rec. WOT RPM =5200
subtract
Current WOT RPM =4600
=600rpm difference
dived by 200
Pitch change = 3"
Current pitch =19"
Theoretically, you should be running about a 16" prop, but I dont think Merc makes one that size for that motor, although i cant be sure. You should also make sure your prop isnt damaged. Look it over and make especially sure your hub isnt spun, if it is, your just spinnin your tires. I assume you probablly have the FLo-Torq 1 hub on that prop, which would still be available, but you can also upgrade to the Flo-Torq2 hub, which is much more practicle and eliminates the problems with spun hubs(the hubs are easily replacable in the FT2)
One thing also to remember is that Merc lists a "range" for WOT to run at. It is essential to fall in this range, but you do not have to be at the top end of it. If I recall, I think the range on that motor would be between 4800 and 5200, so if thats the case, you are close to the parameters, but still falling short. Have fun!!

dragally
07-26-2001, 07:49 AM
Call Kevin at R and R prop shop in Hendersen, Nv. He is THE propman.
dragally