Performance numbers

[Fr. Frank]

Props confuse me
A 13.75 x 19 or a 13.5 x17? The second is less RPM and less pitch than the first. Maybe this is the range you think I will be in?

There is a 4 blase SS Yamaha 13.75 x 18 for sale locally. $275 asking price. Not sure if it will fit my gearcase. It fits the F150.

Also, how do you like the hydroshield?

Yes, I think you'll be in the 17" to 19" pitch range on your prop. However, there is absolutely no substitute for trying out a prop. I don't know if the 18" you mention will fit your gearcase or not.

The 19"P prop will turn less rpms than the 17"P.

As to the architecture, generally speaking, the greater the pitch of a prop, the smaller the diameter. A 13.5"D x 19"P propeller is 13 and a half inches in rotating diameter, and without slippage moves a theoretical column of water 19 inches long with each rotation; i.e.; twisting it one complete rotation in a block of gelatin would cause it to move 19 inches.

Because of the greater number of blades effecting water moving, the effective pitch of a four-blade is greater than a 3 blade. In other words to maintain applied torque when changing from a 3-blade to a 4-blade prop, you usually need to reduce the pitch by 2 inches. A motor that turns a 19"P 3-blade to max of max at max will not be able to turn a 19"P 4-blade to the same point, but would need to drop to a 17"P in a 4-blade. There are some very important variable that can change all of that, but generally speaking, that's the way it works.

As for the HydroShield, I cannot speak highly enough about it.
I have no trim tabs, and prior to installing the HydroShield, I would fall off plane at about 19-20 mph, and took 6-7 seconds to plane with my current 90 hp Optimax.

WITH the HydroShield I can stay on plane down to about 14-15 mph, and I get on plane in about 4-5 seconds. The boat is also more responsive to changes in thrust trim, enabling a much softer ride in a chop.

This is the 3rd motor I have put a HydroShield on. I really love it, AND it protects my prop and skeg in shallow water, which I frequent.