Etec 50 prop help

[JC21]

Hey guys Im posting for a buddy who's needing help with his prop choice I've gave him what little help I could and figured I could get better answers on here. He has an etec 50 on a light semi v #425. I ran the boat with him recently and here were the performance numbers. Running with an average load top speed is 38 on GPS turning 5600 Rpms on the tiny tach with a solas Rubex aluminum 19" pitch prop. He's wanting to go to a powertech stainless will the sst prop in 19" allow for higher Rpms and more speed? Or should he go to say a 17" to achieve higher Rpms and maintain speed. He said he would like to allow for a little more weight in the boat without sacrificing much top end. We just don't know what size he needs. Any help would be greatly appreciated.

 

[jestor68]

Re: Etec 50 prop help

The full throttle operating range is 5500-6000 rpm. Since he is near the bottom of the range at 5600, he needs to drop pitch going from aluminum to SS if he expects to be able to have the ability to carry more weight. The 17 pitch SS sounds like a viable choice.

 

[steelespike]

Re: Etec 50 prop help

Before making any changes the numbers don't quite add up.You can't go 38 with a 19" prop at 5600.
Assuming the gps is correct we have to suspect the tach. Using a 2.67 gear ratio,19" prop 8% slip at 38 mph calculates to 6100 rpm.
I don't have a tach or gps on my 88 50 tiller Evinrude on a 395# 18ft Crestliner. With a 19" al prop.
Hole shot is excellent,excellent speed and Never had any indication I need less pitch and I've carried many loads up to and beyond
capacity.Before any prop change maybe you should verify the tach.

 

[JC21]

Re: Etec 50 prop help

Thanks for the help. All I know is that the tach was installed by the dealer I would assume that they knew what they were doing. My GPS read a consistent 38 mph. Is there anyway to check the tach to ensure its correct?

 

[steelespike]

Re: Etec 50 prop help

Perhaps the dealer will let you borrow a shop tach to run a test.
Was there any current where you ran? I think you could check current simply by drifting with your gps.
The Etec 40,50 and 60 have a somewhat numerically high gear ratio 2.67:1
For instance the 75 and 90 have a 2.00:1 ratio.

 

[JC21]

Re: Etec 50 prop help

No current we were in a lake. Ill see if I can have the dealer run it with his diagnostic tach and see what we come up with. Thanks for the help.