FAST FRED
10-01-2004, 07:09 AM
Our current boat is a lobster style house built on a Navy 50 ft Launch.
Since 1967 it probably had a half dozen engines .
Built with a 6-71 of 235hp/2100 and a 1.5 to one tranny it worked great for Uncle Sam.
Unfortunatly in its last repower (before we purchased her) a very newish Grey Marine 6-71 was installed with a 3 to 1 tranny.
The orig prop was 26 X 17 (with orifgtranny),
with only E bay the best the owner could find was a 30 X 26 to use with the 3-1 tranny.
The engine easily loads this prop and never break a sweat.In fact its so lightly loaded at 1500engine 500shaft that it still smokes a bit of white , sure sign of underloading.
As a loading help I installed HN60 (instead of HN90's) which reduces the HP to 180at 2000rpm.
At the boat yard a fellow has a 32X30 that has a reasonable price ($600 , used excellent cond).
2 inches more dia and 4 more pitch sounds great!
Does anyone have a sugestion on the power required to turn this prop at 150rpm to 700rpm shaft speed?
My goal is to load the engine a bit more at 1500 rpm (normal cruise)and perhaps go from 7K to 8K at this rpm.
Hopefully the top rpm would still be avilable for emergencys , but at 10 to 12 GPH ,high cruise wont be often!!
Engine loading is so light now that only 3.5 GPH are burned at 7K -1500rpm.
A second question , Does anyone have a DOD or other website that might be able to locate an operators manual for this 50ft Navy Personelle Launch?
Have been quite unsucessful with Google search.
Thanks all,
FAST FRED
Since 1967 it probably had a half dozen engines .
Built with a 6-71 of 235hp/2100 and a 1.5 to one tranny it worked great for Uncle Sam.
Unfortunatly in its last repower (before we purchased her) a very newish Grey Marine 6-71 was installed with a 3 to 1 tranny.
The orig prop was 26 X 17 (with orifgtranny),
with only E bay the best the owner could find was a 30 X 26 to use with the 3-1 tranny.
The engine easily loads this prop and never break a sweat.In fact its so lightly loaded at 1500engine 500shaft that it still smokes a bit of white , sure sign of underloading.
As a loading help I installed HN60 (instead of HN90's) which reduces the HP to 180at 2000rpm.
At the boat yard a fellow has a 32X30 that has a reasonable price ($600 , used excellent cond).
2 inches more dia and 4 more pitch sounds great!
Does anyone have a sugestion on the power required to turn this prop at 150rpm to 700rpm shaft speed?
My goal is to load the engine a bit more at 1500 rpm (normal cruise)and perhaps go from 7K to 8K at this rpm.
Hopefully the top rpm would still be avilable for emergencys , but at 10 to 12 GPH ,high cruise wont be often!!
Engine loading is so light now that only 3.5 GPH are burned at 7K -1500rpm.
A second question , Does anyone have a DOD or other website that might be able to locate an operators manual for this 50ft Navy Personelle Launch?
Have been quite unsucessful with Google search.
Thanks all,
FAST FRED