dogon dory
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Sorry, Folks - Post Deleted By Author
Propeller Pitch
- Thread starter El and Bill
- Start date
Al,
Why don't you consult the oracle out at Kitty Hawk and see if Orville can help? I'll let you know what I find.
Bob, I was using a fuel flow meter to determine my fuel efficiency. The reason I was looking at the Glacier Bay and Pontoon boat was the weight and not the hull form. I am at planing speed when the fuel flow spikes as the ECM takes the motor out of the lean burn mode. It also happens to coincide on that particular prop will slip taking a dramatic drop from 46% to 29% or there abouts. Both the Glacier Bay and pontoon boat stayed in the lean burn mode longer due to lighter engine loading. The thought on going to a 13 inch pitch 14 inch diameter prop was to reduce engine loading in the typical cruise rpm range, say up to 4500 rpm. My current WOT RPM with a 15 pitch 4 blade Solas 13.25 inches in diameter is 6300 but that includes another 200 rpm that produced no more speed just more fuel flow. I would consider the WOT in this condition to be 6100 rpm. The specs on the new 90 VTEC place the WOT range as 5300-6300 with 90 HP produced at 5800 rpm.
The VTEC is a strange beast to figure out with lean burn shifting fuel flow around. With a light boat and the 15P prop it stayed in lean burn to nearly 4000 rpm. Add 200 lbs and it drops out at 3600 RPM. The difference between 3900 in lean burn at 12.5 mph and 4100 not in lean burn at 14 mph is 4.3 mph versus 3.1 mpg. It never recovers that back with a 15p prop. With a 17p three blade it reaches 5800 WOT, doesn't stay in lean burn mode once you try to go on step. It does give pretty decent economy at 22-24 mph of 4.2 mpg. What I am trying to determine is the best compromise between higher speed economy 18-22 mph, and low speed economy 10-12 mph. Right now I can have one or the other but not both.
This weekend the test will be a 3 blade 13P 14 inches in diameter and a 4 blade 13.25 inch 16 pitch prop. The last test will be a 4 blade 14 pitch prop. I forget the diameter. After that I quit. I'll just randomly select a prop out of my box and adjust accordingly.
Tom
Now I know why airplanes have variable pitch propellers and mixture controls.
Why don't you consult the oracle out at Kitty Hawk and see if Orville can help? I'll let you know what I find.
Bob, I was using a fuel flow meter to determine my fuel efficiency. The reason I was looking at the Glacier Bay and Pontoon boat was the weight and not the hull form. I am at planing speed when the fuel flow spikes as the ECM takes the motor out of the lean burn mode. It also happens to coincide on that particular prop will slip taking a dramatic drop from 46% to 29% or there abouts. Both the Glacier Bay and pontoon boat stayed in the lean burn mode longer due to lighter engine loading. The thought on going to a 13 inch pitch 14 inch diameter prop was to reduce engine loading in the typical cruise rpm range, say up to 4500 rpm. My current WOT RPM with a 15 pitch 4 blade Solas 13.25 inches in diameter is 6300 but that includes another 200 rpm that produced no more speed just more fuel flow. I would consider the WOT in this condition to be 6100 rpm. The specs on the new 90 VTEC place the WOT range as 5300-6300 with 90 HP produced at 5800 rpm.
The VTEC is a strange beast to figure out with lean burn shifting fuel flow around. With a light boat and the 15P prop it stayed in lean burn to nearly 4000 rpm. Add 200 lbs and it drops out at 3600 RPM. The difference between 3900 in lean burn at 12.5 mph and 4100 not in lean burn at 14 mph is 4.3 mph versus 3.1 mpg. It never recovers that back with a 15p prop. With a 17p three blade it reaches 5800 WOT, doesn't stay in lean burn mode once you try to go on step. It does give pretty decent economy at 22-24 mph of 4.2 mpg. What I am trying to determine is the best compromise between higher speed economy 18-22 mph, and low speed economy 10-12 mph. Right now I can have one or the other but not both.
This weekend the test will be a 3 blade 13P 14 inches in diameter and a 4 blade 13.25 inch 16 pitch prop. The last test will be a 4 blade 14 pitch prop. I forget the diameter. After that I quit. I'll just randomly select a prop out of my box and adjust accordingly.
Tom
Now I know why airplanes have variable pitch propellers and mixture controls.
