pvanv
Admiral
- Joined
- Apr 20, 2008
- Messages
- 6,573
This may be a little unusual, but here goes:
I am using a Nissan NSF 9.8 A3 long electric remote on a 7,000-pound sailboat. It replaces an old, tired, points-and-condenser 2-stroke Evinrude 15.
I bought the rather radical-looking High-Thrust 4-blade 5-pitch prop that Tohatsu sells for this motor. The low-speed maneuvering is spectacular. Much better that the old 15 with a "sail" 3-blade 5-pitch prop. And it backs up -- something that a typical 3-blade prop does not do well on a sailboat. I've got to say that overall, everything is a great improvement. Lower vibration, much quieter, starts and runs very smoothly, and double the fuel economy.
Of course, "high speeds" are not part of this picture. The hull speed of this displacement-hull boat is about 6 knots. It doesn't go faster than that unless it's surfing.
My tach shows that I am turning 6200 or so at full throttle, while making a boat speed of 4.5 knots. I would like to go 5 or 6 knots, but don't want to sacrifice too much of that wonderful low-speed responsiveness. Stands to reason that I probably want the RPM down about 750 or so at WOT. I am thinking that I could stand some more pitch. So then the question becomes, how much more?
My local prop shop says that they aren't sure exactly how much to increase the pitch, but that they can re-pitch my prop, say to 6 inches, for a good price.
I see that Tohatsu now sells a 7-pitch version of the High-Thrust 4-blade prop, in addition to the 5-pitch that I have. Will that be too much pitch? Maybe I should buy a new 7-pitch prop, and if that lowers the RPM too much, or hurts the low-speed thrust too much, then I will know that the "magic" pitch is 6. Of course, then I will have an extra prop...
I am using a Nissan NSF 9.8 A3 long electric remote on a 7,000-pound sailboat. It replaces an old, tired, points-and-condenser 2-stroke Evinrude 15.
I bought the rather radical-looking High-Thrust 4-blade 5-pitch prop that Tohatsu sells for this motor. The low-speed maneuvering is spectacular. Much better that the old 15 with a "sail" 3-blade 5-pitch prop. And it backs up -- something that a typical 3-blade prop does not do well on a sailboat. I've got to say that overall, everything is a great improvement. Lower vibration, much quieter, starts and runs very smoothly, and double the fuel economy.
Of course, "high speeds" are not part of this picture. The hull speed of this displacement-hull boat is about 6 knots. It doesn't go faster than that unless it's surfing.
My tach shows that I am turning 6200 or so at full throttle, while making a boat speed of 4.5 knots. I would like to go 5 or 6 knots, but don't want to sacrifice too much of that wonderful low-speed responsiveness. Stands to reason that I probably want the RPM down about 750 or so at WOT. I am thinking that I could stand some more pitch. So then the question becomes, how much more?
My local prop shop says that they aren't sure exactly how much to increase the pitch, but that they can re-pitch my prop, say to 6 inches, for a good price.
I see that Tohatsu now sells a 7-pitch version of the High-Thrust 4-blade prop, in addition to the 5-pitch that I have. Will that be too much pitch? Maybe I should buy a new 7-pitch prop, and if that lowers the RPM too much, or hurts the low-speed thrust too much, then I will know that the "magic" pitch is 6. Of course, then I will have an extra prop...
