Skybolt
Well-Known Member
- Nov 11, 2014
- 6,479
- Boat Info
- Reel Nauti
460 EC
- Engines
- Detroit 6v92TA
(Low profile's)
Alison Gears
Westerbeke
12.5kw Genset
I am trying to calculate propeller efficiency (Slip), and if my calculations are correct I am running at ~76% efficiency.
I cruise at 1850 RPM and go 23MPH when the bottom is clean.
My transmissions are 1.5:1 ratio, which means the props are spinning at ~1233RPM.
My props are 26"x26" which equals 32,058 inches per minute travel or ~2671 ft. per minute in a perfect world.
My cruise of 23mph = 23 * 5280' or 121,440 ft/hr. which equals 2024 ft/minute real world.
So my prop efficiency would be 2024/2671 which is ~76%.
The reason I went through this exercise is I read on BoatDiesel that the exact same boat and engines took 1/2" of pitch out and gained 2mph or now cruises at 24mph. Which by the above calculation would be ~80% efficiency. Much better performance and less load on the engines.
I am going to change to this pitch this spring when she comes out for new bottom paint etc.
I am curious if anyone else has gone through this for one reason or another and found this to be accurate? Sea Ray's have never been speed demon's but sometimes I can't help but to wonder why things are what they are at times.
I cruise at 1850 RPM and go 23MPH when the bottom is clean.
My transmissions are 1.5:1 ratio, which means the props are spinning at ~1233RPM.
My props are 26"x26" which equals 32,058 inches per minute travel or ~2671 ft. per minute in a perfect world.
My cruise of 23mph = 23 * 5280' or 121,440 ft/hr. which equals 2024 ft/minute real world.
So my prop efficiency would be 2024/2671 which is ~76%.
The reason I went through this exercise is I read on BoatDiesel that the exact same boat and engines took 1/2" of pitch out and gained 2mph or now cruises at 24mph. Which by the above calculation would be ~80% efficiency. Much better performance and less load on the engines.
I am going to change to this pitch this spring when she comes out for new bottom paint etc.
I am curious if anyone else has gone through this for one reason or another and found this to be accurate? Sea Ray's have never been speed demon's but sometimes I can't help but to wonder why things are what they are at times.
