Thread: What 4 blade prop?

What is your WOT RPMs with a typical load?

Originally Posted by Traveling Man

What is your WOT RPMs with a typical load?

I took my tac off when I switched to a tiller handle. It was around 5500

More than likely the weight shift rearward is the difference in your holeshot. I'm no expert but if you can't shift some weight to the bow of your boat you will need to go to a 14 pitch 3 blade prop or you can take a chance on a 4 blade 15 pitch prop. If your boat was turning 5500 RPMs rigged with a helm, the most effective change you could make would be a weight shift. Also, invest in a Tach. Tiny Tach makes a fairly inexpensive one and you need to know your loaded RPMs at WOT to accurately chose the right prop.

Originally Posted by Traveling Man

More than likely the weight shift rearward is the difference in your holeshot. I'm no expert but if you can't shift some weight to the bow of your boat you will need to go to a 14 pitch 3 blade prop or you can take a chance on a 4 blade 15 pitch prop. If your boat was turning 5500 RPMs rigged with a helm, the most effective change you could make would be a weight shift. Also, invest in a Tach. Tiny Tach makes a fairly inexpensive one and you need to know your loaded RPMs at WOT to accurately chose the right prop.

what kind of difference would I expect to see if I started to drop from a 13.5 diameter down to a 13.25 or even a 13?

When you switch from a 3-blade to a 4-blade, you normally keep the same diameter but drop down at least 1" in pitch.

The “rule of thumb” is an increase of approximately 200 RPMs for every inch you decrease in pitch. So decreasing from a 14 pitch prop to a 13 pitch prop would raise your typical loaded RPM range by 200.
Your next step should be getting a tach, if you buy a prop without one you are rolling the dice.

Originally Posted by Traveling Man

The “rule of thumb” is an increase of approximately 200 RPMs for every inch you decrease in pitch. So decreasing from a 14 pitch prop to a 13 pitch prop would raise your typical loaded RPM range by 200.
Your next step should be getting a tach, if you buy a prop without one you are rolling the dice.

That 200 RPM per inch only holds true if the number of blades remains constant. Adding one blade is the equivalent of going up 1" in pitch - that's why you have to drop down an inch (or more) when going from a 3-blade to a 4-blade just to keep the RPMs constant (assuming the same diameter prop).