T&T: Controllable pitch prop (was Engine loading at low RPM)

[Rock Bradford]

What is the mystery about?  If you have a fixed pitch prop it is only doing
optimal work at one speed.  A controllable pitch prop can be efficient
nearly all the time if one knows how to read a pyrometer or, better yet, can
listen to the sound of his/her engine.  yes, the truth is you can run a boat
quite well with a controllable pitch prop, (especially with one of those old
timey engines like mine  a Gardner).  I suspect, however, the prevalence of
cpp boats in Europe has more to do with fuel costs . . . here in amerika,
where fuel was always cheap (until now), who worried about saving
0.5gallons/hr.  To think otherwise, one would have to admit that those
clever
european yachtsmen are much smarter than american yachtsmen so they can
master the intricacies of changing pitch on a prop.    I think Arild
mentioned Michael Kasten having something on his website.  True, and he also
has a cost comparison between the two if one were starting from scratch.  A
retrofit, however, is an endeavor of greater expense.  The difference,
Marin, between controllable pitch on a boat and that on an airplane is that
a pitch problem @ 200 kts is more likely to end badly than @ 8 kts.

Rock Bradford
44' Cygnus "Magpie"
Georgetown, SC

On Mon, Mar 3, 2008 at 6:26 PM, Faure, Marin <marin.faure at boeing.com> wrote:

> A controllable-pitch prop makes all sorts of sense on an airplane, so it
> stands to reason it would be very beneficial on a boat.  The two issues
> would be system complexity / reliability, and operator training.  If you
> don't operate it properly it can do major damage to the engine.  Judging
> by the difficulty I've seen many flight students have in grasping the
> concept of a controllable pitch prop, I don't think it's the sort of
> thing you want to turn over to Average Joe Boater and simply say "Have
> at it."  Granted, most controllable pitch props on airplanes are
> constant-speed props, which can make the concept even harder for some
> people to grasp.
>
> But a controllable-pitch prop on a boat in terms of operational benefits
> would be great.  You could truly idle through a marina making virtually
> no wake at all.  For people who like to troll for fish that require slow
> trolling speeds, you could do so without running the engine at dead idle
> for hours at a time or using a trolling valve on the transmission.
>
> Grand Banks boats from the factory are almost always over-propped,
> particularly the older ones with lower-power engines like FL120s..
> Since most owners are only going to be running the engines in these
> boats at 1500 to 1800 rpm anyway, overpropping the boat didn't overload
> the engine and it gave a little more speed through the water at these
> lower cruise rpm settings.  Opening the throttle up,  however, starts to
> lug the engines.  I'm sure this same situation exists with other
> trawler-type boats than GBs.  A controllable-pitch prop gives you the
> best of both worlds.  Like a plane, the prop can be increased in pitch
> to give more thrust at lower engine rpm.  When more horsepower is
> needed, the pitch can be reduced to let the engine(s) spool clear up to
> their maximum continuous rpm if that's needed in a particular situation.
> What an operator needs to know, however, is just how much the pitch can
> be increased at any given rpm to avoid lugging, overheating, etc. the
> engine.
>
> ______________________________
> C. Marin Faure
> GB36-403 "La Perouse"
> Bellingham, Washington
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