In article om,
"terry" wrote:

Thinking of changing to a 3 blade prop?
Westerly 26 foot about 7000 pounds when in the water and occupied.
Engine is a Volvo MD1B (9 HP) with maximum speed of 1800 RPM via a 1:1
forward reverse gear.
Reason for change is we need a new prop.
Also advice some years back from a couple who took a similar size boat
cruising the Caribbean and claimed that the 3 blade was much better,
while experiencing no increased drag under sail!

We went from a fixed two-blade to a feathering 3 blade. Both were
matched to the engine and gave a 3400 max RPM, my target. We have
significantly less drag with the three blade than the two; a fixed three
blade on the same hull and engine is pretty awful. The difference is
mostly in light air. We sail at 2-5 knots when most have folded the
sails and are motoring. In trade wind conditions, particularly off the
wind, it matters much less.

BUT, we have 2+:1 gearing and swing a 16" prop. With your 1:1, you're
probably swinging a 13-14", hopefully not a 12". Your difference in drag
won't be as significant, but will be noticeable if you sail boat vs boat.

For best motoring, get the largest diameter that will fit with
appropriate clearance and pitch it to allow your target RPM.

For best sailing, get a folding prop. For the best of both worlds, get a
feathering prop AND you get unbelievable authority in reverse.

I play tugboat every once in a while and dockmates are astounded how
much "tug" we get in reverse.

BTW, see if you can get a CDI prop: http://sailcdi.com/ppmain.htm I
fell in love with their beauty and would have gotten one, but they
didn't perfect the blade we needed and they *refused* to sell me one
that they didn't think was appropriate.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/