Propellor Pitch

[skier]

Have a 9.9 Evinrude (1983) as an aux. motor on a 26 Ft. Pearson Sailboat.
What pitch prop should I be using?
thanks

[Wgoodrich]

There is no given pitch for a certain horse power outboard. What I normally do is go to my dealer. He is a friend of mine. I pick up three props of different pitches. If you look at your manufacturer manual it will tell you the maximum RPM allowed to operate safely for that motor. Then install the different props until you get the full throttle and the RPM is just short of that maximum RPM suggested by the manufacturer. You then will have the optimum prop for your motor in your certain installation pattern.

I see you nickname as skier. Example of what you can do with props having an experienced operator with the motor to pull the skiers. Normally say an 80 horse power outboard on a 15' fish and ski boat using a 19" prop and you can barely get on plane unless you walk to the front of the boat to get to plane. That is a pain but if you use that prop and a single person in that boat you can run almost as fast over the water top speed as a 150 outboard. Problem is you will never pull up one skier but you will also never reach maximum RPM rated for that motor either no fear of damage. This compared to a car manual transmission would be like taking off in 4 gear. You could do it but from zero you would have to double clutch a long time to get rolling but then again your top speed could break the speedometer of the car. Now if you change to a 15" prop on the same motor it would be like having a tractor gear on the outboard. You could pull up three skiers but your top speed would be real slow compared to the 19" prop. The 15" prop would have one heck of a lot of pulling power to pull skiers and will pull them at great comfortable skie speed even with three skiers. Problem is that operator would have to watch the RPM because the motor can easily reach past maximum rated RPM and blow the motor. On this certain motor the 17" prop would be the comfy prop having ability to plain out and even pull a skier or two with a bit slower top end speed and never have to watch the RPM because the torque would hold the motor below top RPM. Good comfy prop sizing over all.

Your motor does not have concern of plaining out so you would want to set the prop type and design to limit RPM from passing safe maximum RPM level same as that nice comfy prop size above mentioned.

HOpe this helps

Wg

[gbynum]

Have a 9.9 Evinrude (1983) as an aux. motor on a 26 Ft. Pearson Sailboat.
What pitch prop should I be using?
thanks

What was answered is correct in theory, and sometimes in practice. However, for a sailboat auxiliary, max EVER speed will be 10 knots, and probalby more like 6. The motor reduction in 1999 was 2.42:1. Figure spinning the prop at 2000 rpm at 10 knots; you'd like a prop with about 6 inches. You also want as large a diameter as you can swing. Realistically, 10 dia, 5 pitch would likely be ideal.

I always found it interesting to look at real auxiliary engines, those British Seagulls ... huge diameter for 3 or 4 HP, fairly low pitch, but geared to turn slow. Better than "normal" 9.9's.