Optimum depth setting for an outboard?

[mrmossman]

I have a 9.8merc long shaft on a 17' sailboat, planing type hull with only a 9" draft with my centerboard up. I've got my engine depth set where the top of the prop is just an inch below the bottom of the boat. The water comes up to the small fin 4.5" above the cavitation plate. I don't have a cavitation problem. I'd just like to know what an optimum speed/mileage depth should be.

Thanks

 

[SuperNova]

Re: Optimum depth setting for an outboard?

The cavitation plate immediately above the prop should be lined up with the bottom of the hull.

 

[steelespike]

Re: Optimum depth setting for an outboard?

The cavitation plate immediately above the prop should be lined up with the bottom of the hull.

This should be considered a starting point ideal operation may be higher or lower.Main consideration is "cavitation" more correctly called ventilation.
You say no venting so you may be able to go higher.Try all maneuvers especially reversing before changing anything.You also need to be sure it pumps water.You may find you have venting problems in rough water.
Once you have it setup you should be sure it is propped so the motor operates at its reccomended rpm.Both for ecomomy and the health of the motor.

 

[SuperNova]

Re: Optimum depth setting for an outboard?

"cavitation" more correctly called ventilation.
.

Cavitation and Ventilation are two distinctly different conditions according to Chapman Piloting and are commonly misused. Ventilation is caused by the prop running too close to the surface of the water. Cavitation is caused by the prop blade tips spinning too fast, causing tiny low pressure air bubbles in the water to collapse, sometimes with enough force to remove metal from the prop tips....pp.33-34.