[PUP] PUP:PMM controllable pitch prop

[Bob Frenier]

There seems to be lots of agreement that a controllable pitch propeller will
not pay for itself in fuel savings. Are we using for that comparison
mechanically controlled engines, $3 per gallon fuel and a Hundstat
propeller? If so, then an electronically controlled engine running at low
rpms on $6 per gallon fuel and spinning a less expensive Saab CPP may alter
the equation.

But I am attracted to a CPP for our "perfect passage maker" regardless of
the ultimate cost for the following reasons:

1. the fun of trying to squeeze out a remarkable nmpg with a smallish,
electronically controlled, turbo-charged diesel engine running at the proper
temperature despite very low rpms. When installed in a long, narrow hull
designed to run best at VL 1.2, this drive train would seem to approach the
only "perfection" open to us.
2. the impact that combined system will have on range and, thus, tank size.
3. the ability to have as much thrust in reverse as in forward to pull our
PMM off the reef without a tow.
4. the ability to "down shift" to a finer pitch when running uphill and thus
wring acceptable performance from that smallish engine in conditions that
would, otherwise, make it "too small."

BTW, I think a controllable pitch prop is different from a variable pitch
prop in that the VPP changes its configuration automatically but the CPP
pitch selection is done by the captain.

And finally, would someone please comment on the propeller efficiency charts
the engine companies produce that have tilted me towards a CPP? Is that
fixed prop really working at such great disadvantage just when the engine is
at its most efficient?


Regards,
Bob Frenier
Advantage Apparatus, LLC
Chelsea, VT

I  agree that a VPP is a luxury on a passagemaker. Unless  your lifestyle is

to live aboard and cruise very long distances, I don't believe  you will
ever 
recoup, in fuel savings, the cost of a VPP.