Originally Posted by jwalker
The vent holes allow exhaust gasses to aerate the water in the vicinity of the prop at low speed so the engine has less load to drive, its revs therefore increase so provides more power to drive the high pitch prop.
Correct .. on Mercury props its called the PVS system, and as you say allows the prop to spin more freely at lower revs until it bites and when it does, and the boats on the plane, water pressure seals in the gasses which then vent normally through the arse end of the prop .. sorry.. was that a minor colloquialism?
With their system you can actually vary the size of the holes and so help the prop grab faster and tailor it to the load of your hull
and no I'm not a merc salesman cos heres the science .. no fooker ever does adjust the size of the vent holes
.. however.... this is ribnet, and I await correction