<..>
> Sorry guys but everything described upto now is Ventilation
> not Cavitation!
Justify!
cav.i.ta.tion (kv-tshn)
n.
1. The sudden formation and collapse of low-pressure bubbles in liquids
by means of mechanical forces, such as those resulting from rotation of
a marine propeller.
2. The pitting of a solid surface.
3. Medicine The formation of cavities in a body tissue or an organ,
especially those formed in the lung as a result of tuberculosis
Read 1, QED!
*Strictly* speaking, when the blades of the prop are running partially
in air that isn't itself cavitation although it will invariably
*produce* cavitation. The noise and vibration that occur when this
happens are, however, the result of cavitation due to air being drawn
into the prop wash
In marine and inland craft applications, the distinction is a moot point
(although it isn't in pumps etc.) and when the prop is running partially
in air and producing a disturbed wash, noise and vibration it is said to
be cavitating.
I have never heard of cavitation being called "ventilation" nor have I
ever heard of it being caused by the weedhatch although it's not
impossible I guess.
Whatever name you want to call it by (and since it's been known as
cavitation since screw props were first fitted to marine craft I'll
stick with that!) the solution is to stop the prop drawing air in and
almost invariably that means getting the stern of the boat deeper in the
water by adding ballast at the stern or possibly by reducing weight
towards the bows
Bru
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