Which Prop and WOT Fit My Situation Best?

[R H Cotton]

My motor is a E-Tec 75hp on a 20 Ft. pontoon. WOT is rated at 4500-5500 rpms. After adjusting the motor to the maximum height that I could run it without slippage a 14x11 prop would turn 5300 rpms. A 14x13 prop will turn 4600 rpms. It will run 20 mph with either prop. I know that I am saving gas with the 14x13 prop. Is it good to run this motor on the lower rpm wot as long as it doesn't go below 4500?

 

[steelespike]

Re: Which Prop and WOT Fit My Situation Best?

I'm not an expert but it seems to me something is amiss.
A 50 Etec on a 20 ft Premier runs a 14 X 13 prop at 5,500 wot rpm 21 mph.
on a 23 ft Sunset bay a 50 runs a 13 3/4 X 13 at 5,375 and 19.5 mph.
I wonder if a more efficient prop (SS?) or a 4 blade might help.Pro pulse props are a 4 blade adjustable composite prop that I have seen and read some amazing reports on.Also maybe a careful adjustment of trim.
It would seem to me running at 4,600 is too low with no room for an rpm drop with a load or rough conditions.

 

[R H Cotton]

Re: Which Prop and WOT Fit My Situation Best?

The two props 14x11 and 14x13 are SST props. I tried a piranha composite in a three blade that was 14x11 and got 5350 rpms out of it. I threw it away because I barely touched a underwater wood post at idle speed in gear and knocked half of all the blades off of it. It is not the prop that Piranha makes it out to be. They advertise it to be the strength somewhere between aluminum and SST. Buyer beware. This forum has been very helpful to me. I thought after I moved the motor up as was suggested I got 5350 rpms with the 14x11 sst prop that the 14x13 would be somewhere in the middle of the wot range. I was surprised that it will only get 4600 rpms. I have tried trimming but there is no difference in rpms until it starts to slip. The throttle linkage was checked and I am getting all it will give. I am estimating that my total weight with one passenger and gear is 2500 lbs. I can live with this 14x13 prop; it's just that I want to know that everything about my motor is okay to run at this low end wot without any harm. Thanks for all the help.

 

[R H Cotton]

Re: Which Prop and WOT Fit My Situation Best?

My main concern now is my wot at 4600 rpms. I just want to know if this is okay. any response or suggestions appreciated.

 

[Silvertip]

Re: Which Prop and WOT Fit My Situation Best?

I would suggest you look at 4 blade "pontoon" props which have much more blade area. A pontoon is not a planing hull and generally calls for lots of blade area. Running the engine at the low end of the rpm band may be fine if the "toon" is lightly loaded. But get a bunch of folks on it and you are now lugging the engine. Always prop for average load.