On Thu, 18 Oct 2007 11:22:19 -0700, druid
wrote:

Hi,

My new-to-me boat (Crown 28) has a Volvo 10hp MD6A, and it's way
overpropped with a Campbell Sailor 11x6 3-blade (gets 1500 WOT instead
of 2400). The Campbell Sailor dealer says his calcs recommend a 12x8
(ie much MORE pitch). Now, my experience with CS props is you take the
calculated pitch and subtract 2", but I donno...

Engine IS very "tired" but it pushes the boat at 5+ knots with the
over-pitched prop, so it can't be TOO bad.

Those with MD6A's - what prop do you have on it?

druid
http://www.bcboatnet.org

You need to post the loaded displacement of the boat, the water line
length and the gear box ratio.

For example: if a LWL of, say 22 ft., a loaded displacement of 2,000
lbs. and a 1:1 gearbox then the prop should be about 9 X 6.

With a 1.5:1 box the prop is about 12 X 9

and with a 2:1 box about 14 X 13.

There various propeller calculation programs on the Net. Try a google
for "propeller calculations".

The calculator I used for the above is "PropCalc" from Marine Castle -
freeware - which seems compare favorably with other programs.


Bruce-in-Bangkok
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