FF
Guru
- Joined
- Oct 12, 2007
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The latest issue of Pro Boat Builder has a good article by N. Calder on proper prop selection for max efficiency.
No surprise that a larger diameter prop works better , up to 5-7% if properly sized, the hassle is the deep reduction gears ,< 4.5-1> not usually made for small ,,,100, 150hp engines.
Most interesting was the test tank results from a slight over prop , where the results were a 15% better fuel burn.
This was with the std red. gear on a Volvo 75 HP rated diesel.
The top speed was identical with no overload .
15% is no big deal to most trawler owners , as the use is too few hours to pay for the new prop.
15% of 2 or 3 gph doesnt add up to much .
However to me the prop would easily be worth the bucks as the RPM at most normal cruise was reduced 200 to 400 rpm, and at some speeds more.
I enjoy the smooth QUIET created by lower RPM , and even at only a few hundred hours a year , the time enjoyed is worth far more than just 15% less diesel .
The old concept of propping for full rpm is fine for folks that do cruising /operating AT FULL RPM.
Calder suggests a rethink of this for displacement boats.
Any NYC 7th grader could paper his way into a Free subscription to PBB , perhaps its worth a try?
Many folks like contemplating prop diameters and pitch , the online stuff is easy but does not usually allow for anything but the built in concept of what the programmer though was best.
Skeenes elements of yacht design is at most libraries and will allow anyone to prop their boat.
A fuel map and real HP/ Torque info from the engine builder is also needed.
No surprise that a larger diameter prop works better , up to 5-7% if properly sized, the hassle is the deep reduction gears ,< 4.5-1> not usually made for small ,,,100, 150hp engines.
Most interesting was the test tank results from a slight over prop , where the results were a 15% better fuel burn.
This was with the std red. gear on a Volvo 75 HP rated diesel.
The top speed was identical with no overload .
15% is no big deal to most trawler owners , as the use is too few hours to pay for the new prop.
15% of 2 or 3 gph doesnt add up to much .
However to me the prop would easily be worth the bucks as the RPM at most normal cruise was reduced 200 to 400 rpm, and at some speeds more.
I enjoy the smooth QUIET created by lower RPM , and even at only a few hundred hours a year , the time enjoyed is worth far more than just 15% less diesel .
The old concept of propping for full rpm is fine for folks that do cruising /operating AT FULL RPM.
Calder suggests a rethink of this for displacement boats.
Any NYC 7th grader could paper his way into a Free subscription to PBB , perhaps its worth a try?
Many folks like contemplating prop diameters and pitch , the online stuff is easy but does not usually allow for anything but the built in concept of what the programmer though was best.
Skeenes elements of yacht design is at most libraries and will allow anyone to prop their boat.
A fuel map and real HP/ Torque info from the engine builder is also needed.
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