Ventilating a Non-Thru Hu Prop

[Fastjeff57]

Gentleman (and the rest of you):

Is there a way to "ventilate" (deliberately cause cavitation on plane off) of a non-thru hub prop? I know how easy it is to leak exhaust through the prop hub on thru-hub exhaust type props and get the rpms up, but I don't have one of those--I run a Mark 55 type LU set up.

As many of us have experienced, the prop we need for top speed has too much pitch to get the boat on plane without a struggle. Like to change all that.

Thanks,

Jeff

PS: My ocean racing buddy had the same problem; even with over 3,000 hp (twin, blown Rat Motors) he could not get is boat on plane without ventilating the props.

[MN1]

Raise the motor up off the transom 1/8" at a time. This will start the ventilation of the prop.
Mark N

[Fastjeff57]

Understood, but I'm trying to avoid that since I use the boat as a "utility" (transporting grand kiddies about and other non-racing duties).

Jeff

[Dan M]

Jeff, just a wild thought. Lower units are streamlined to keep the prop from "ventilating". Mount a retractable Water "upsetter" to the transom to disturb the waterflow in front of the LU and to the prop. A piece of 1/2" pipe through some transom mounted guides to somwhere in front of the LU would allow you to "dirty up the flow of water to the prop causing some ventilation. Once on plane, retract and run as normal.

Again, just a wild thought.

Dan

[Fastjeff57]

And a good one! Thanks.

I had another wild idea that I might try: Drill a good sized hole in the cavitation plate right above the prop. Exhaust from the tower would exit here (as well out the spout in back) and cause cavitation--similar to what happens with holes in front of the hub (thru hub exhaust props).

Anyone ever try that?

Jeff

[sheuninck]

the opa offshore racers have ventilation tubes coming down thru the cavitation plate to give the props some air during take off