2-blade vs 3-blade with more pitch??

[dhonda]

Hello, i recently found a old 10 1/2"x16" 2 blade prop made for 1960's evinrude 40hp motors. My boat currently has a 10 3/8"x13.5" 3 blade prop. My question is would that 2 blade be beter for more speed or would it probly be too much pitch? My boats a 1957 crestliner viking 14" and rite now the prop seems to push the boat pretty good provided theres only 2 people in it pulls about 4500rpms. I just dont know if the added pitch will kill it altho its got 2 blades instead of 3, any opinons? Think i should buy it and see what happens?

 

[steelespike]

Re: 2-blade vs 3-blade with more pitch??

The prop is intended for a light fast boat. A 2 blade 16" prop might turn slightly faster than a 3 blade 16 but not going to make up for almost 3" pitch difference. If its not too expensive it might be fun to strip all the weight out of your boat and see what it will do.
The biggest prop available in the 64 motor brochure was a 14.Each inch of pitch is about a 200 rpm change.
The motor is rated for 4000 to 5000 rpm.The 16 will make it pretty guttless but if you can get enough rpm
might be fun.
Your 13.5 gives about 29 mph at 4,500 rpm and a guess of 10% slip.
Assuming 4000 and 16" at 10% speed is about 31.2.
Thats a lot of assuming Usually as prop speed goes down slip goes up.
The 16 will just be a lark; hole shot will disappear and you will have to eliminate a lot of weight.

 

[dhonda]

Re: 2-blade vs 3-blade with more pitch??

The prop is intended for a light fast boat. A 2 blade 16" prop might turn slightly faster than a 3 blade 16 but not going to make up for almost 3" pitch difference. If its not too expensive it might be fun to strip all the weight out of your boat and see what it will do.
The biggest prop available in the 64 motor brochure was a 14.Each inch of pitch is about a 200 rpm change.
The motor is rated for 4000 to 5000 rpm.The 16 will make it pretty guttless but if you can get enough rpm
might be fun.
Your 13.5 gives about 29 mph at 4,500 rpm and a guess of 10% slip.
Assuming 4000 and 16" at 10% speed is about 31.2.
Thats a lot of assuming Usually as prop speed goes down slip goes up.
The 16 will just be a lark; hole shot will disappear and you will have to eliminate a lot of weight.

Thanks for your quick comment! The boat i figured would most likely run 4000 rpms but my motor cavitation plate is mounted 3" below the bottom of the boat so i figured if i raise that up a few inches i could gain around 200-300rpms wich would bring up my 13.5" prop up to 4800rpms and if i used that 16" prop and could turn 4000rpms it would now be 4300rpms rite? Although im sure your rite about the acceleration being eliminated. I just figured its only $25.00 and its been used 2 times and looks like new but if its going too much like u say then i probly should pass.

 

[steelespike]

Re: 2-blade vs 3-blade with more pitch??

Yeh,if you can raise it 3 inches or to a point just before venting(cavitation) becomes a problem you could gain rpm and speed.
maybe enough so you can experiment.That 2 blade might even allow more height.