New boat, new Nissan O/B, new skipper. Came with 14 pitch prop, top RPM's about 3100. Changed to 11 pitch, now kicks right up to 5900 rpm but top speed with no ballast about 14 knots. Supposed to be 24+?
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Steve Cameron
Not 24 mph
First, don't mix knots and miles per hour. Isn't it something like 1 knot = 1.3 mph. Several things affect the top speed. MacGregor puffery is a big item. I've never heard of anyone getting to 24 mph in their own boat. It might be possible, but only with the perfect engine in perfect conditions. Check your weight. To get to 24 mph you will need to gett rid of all the "stuff" that makes cruising safe and enjoyable, especially the people. I understand the Mac loses at least 1 mph for each 100 lb. of weight gained. Next is the engine. You don't say what engine you have. Is it the 50hp? Is it properly tuned? Remember, a 2-stroke engine usually weighs less than a similarly powered 4-stroke. Next is the prop--depending on the pitch you are trading rpm's for volume of water moved. You might be churning 5900 rpm, but are you really "digging in." At what rpm does your torque fall off? Can you change the prop pitch to move more water while maintaining a relatively high rpm? What's the altitude? Your engine may make less power at high altitude (less dense air/fuel mixture) than at sea level. Finally, what are the conditions? Smooth water with the wind at your back and 60-70 degree weather should give you optimum performance.
First, don't mix knots and miles per hour. Isn't it something like 1 knot = 1.3 mph. Several things affect the top speed. MacGregor puffery is a big item. I've never heard of anyone getting to 24 mph in their own boat. It might be possible, but only with the perfect engine in perfect conditions. Check your weight. To get to 24 mph you will need to gett rid of all the "stuff" that makes cruising safe and enjoyable, especially the people. I understand the Mac loses at least 1 mph for each 100 lb. of weight gained. Next is the engine. You don't say what engine you have. Is it the 50hp? Is it properly tuned? Remember, a 2-stroke engine usually weighs less than a similarly powered 4-stroke. Next is the prop--depending on the pitch you are trading rpm's for volume of water moved. You might be churning 5900 rpm, but are you really "digging in." At what rpm does your torque fall off? Can you change the prop pitch to move more water while maintaining a relatively high rpm? What's the altitude? Your engine may make less power at high altitude (less dense air/fuel mixture) than at sea level. Finally, what are the conditions? Smooth water with the wind at your back and 60-70 degree weather should give you optimum performance.
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L. Tower
Thanks Steve
All good questions but my answers don't make me feel better. The 50hp is new, (broke-in) and tuned. Wind, water, temp. conditions optimum and weight only about 300# over bare bones. Mac specs say 24MPH (not knots)with 50hp. If prop pitch was wrong, rpm's wouldn't be right where they should be? Only thing not sure if speed indicator is right? What am I missing?
All good questions but my answers don't make me feel better. The 50hp is new, (broke-in) and tuned. Wind, water, temp. conditions optimum and weight only about 300# over bare bones. Mac specs say 24MPH (not knots)with 50hp. If prop pitch was wrong, rpm's wouldn't be right where they should be? Only thing not sure if speed indicator is right? What am I missing?
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billy w
Prop Pitch
Something is drastically wrong. There is no way RPM should increase by 2,800 with a 3 reduction in pitch. In best or worst case, a change of each 1 in of pitch should only effect RPM between 100 & 300. I run a Merc 50 with 11.25 x 10 prop and cruise at 18 mph (per GPS) @ 5500rpm with crew of 4, empty ballast. My spare 11 pitch drops RPM to 5300 and speed drops off very little. With just me on the boat and no supplies, the 11 pitch actually performs better with more speed (20+) @ 5500rpm. I always limit my RPM to 5500 and usually power for extended time between 45 & 5000. I would definitely consult the dealer about the rpm's and the ideal operating range for your motor.
Something is drastically wrong. There is no way RPM should increase by 2,800 with a 3 reduction in pitch. In best or worst case, a change of each 1 in of pitch should only effect RPM between 100 & 300. I run a Merc 50 with 11.25 x 10 prop and cruise at 18 mph (per GPS) @ 5500rpm with crew of 4, empty ballast. My spare 11 pitch drops RPM to 5300 and speed drops off very little. With just me on the boat and no supplies, the 11 pitch actually performs better with more speed (20+) @ 5500rpm. I always limit my RPM to 5500 and usually power for extended time between 45 & 5000. I would definitely consult the dealer about the rpm's and the ideal operating range for your motor.
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Dave
Sounds like cavitation
I'm not a 26X owner (yet), but from my experience with outboard powerboats (I have owned several since childhood as well as a Catalina 30), it sounds like what most people call cavitation. Could your prop be suckin down air and spinning in a bubble? That small change in pitch should not have changed RPMs that much. Technically drawing down air is NOT cavitation, it's ventilation, but most seem to confuse the two (true cavitationis where the prop develops such low pressure on the low pressure side that it actually lowers the boiling point enough to boil the water causing bubbles. This is VERY bad for the prop but is also VERY rare. But, I think you might be ventilating...
I'm not a 26X owner (yet), but from my experience with outboard powerboats (I have owned several since childhood as well as a Catalina 30), it sounds like what most people call cavitation. Could your prop be suckin down air and spinning in a bubble? That small change in pitch should not have changed RPMs that much. Technically drawing down air is NOT cavitation, it's ventilation, but most seem to confuse the two (true cavitationis where the prop develops such low pressure on the low pressure side that it actually lowers the boiling point enough to boil the water causing bubbles. This is VERY bad for the prop but is also VERY rare. But, I think you might be ventilating...
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Jim Hughes
RPM
I would worry about the rpm.Sounds like an awful lot for a 4stroke.I had a 125HP on a ski boat and the recomended rpm was 5600.Thats what the motor was balanced for.You're sure your motor mount is in the down position.The motor is a long shaft motor.Good luck and let us know when you find the answer.
I would worry about the rpm.Sounds like an awful lot for a 4stroke.I had a 125HP on a ski boat and the recomended rpm was 5600.Thats what the motor was balanced for.You're sure your motor mount is in the down position.The motor is a long shaft motor.Good luck and let us know when you find the answer.
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Bob Cardoza
Same story with the Tohatsu (sister engine)
I have a 50 Tohatsu TLDI... Same story... Went from top RPM 4100 at 14mph with 12.5 Pitch to 5900 with cavitation on an 11 pitch top speed 14 mph. Two people on board no mast or any gear. If ever I hit the lottery I'm buying a BigFoot like I wish I did in the first place.
I have a 50 Tohatsu TLDI... Same story... Went from top RPM 4100 at 14mph with 12.5 Pitch to 5900 with cavitation on an 11 pitch top speed 14 mph. Two people on board no mast or any gear. If ever I hit the lottery I'm buying a BigFoot like I wish I did in the first place.
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Bob Cardoza
Same story with the Tohatsu (sister engine)
I have a 50 Tohatsu TLDI... Same story... Went from top RPM 4100 at 14mph with 12.5 Pitch to 5900 with cavitation on an 11 pitch top speed 14 mph. Two people on board no mast or any gear. If ever I hit the lottery I'm buying a BigFoot like I wish I did in the first place.
I have a 50 Tohatsu TLDI... Same story... Went from top RPM 4100 at 14mph with 12.5 Pitch to 5900 with cavitation on an 11 pitch top speed 14 mph. Two people on board no mast or any gear. If ever I hit the lottery I'm buying a BigFoot like I wish I did in the first place.
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