On Mon, 30 Aug 2004 09:39:46 -0400, Glenn Ashmore
wrote:

Auto-Prop: Blades are pivoted similar to feathering props but are
independent of each other and can rotate a full 360º. The offset
geometry of each blade is designed to find its own most efficient pitch
by balancing torque against water pressure. Auto-Props can give close
to optimum performance in most conditions in forward or reverse. They
are not truly feathering however.

They are close enough in function to use the term constructively. I
don't think Autoprop's self-description of their product as a
"feathering prop" constitutes trade fraud in this instance.


With no torque water pressure forces
the blades back slightly which results in considerably more drag than
normal feathering props. Also they have considerably more mass which
puts a lot of strain on the drive train when shifting from forward to
reverse and back.

Agreed. As noted, my friend accepts the wear as adequate pay-off for
the motoring performance enhancements he was seeking. I wouldn't put
an Autoprop on a J-Boat, for instance, or any racer-cruiser. It's a
good compromise if you understand the pros and cons, not a universal
panacea for prop drag.

If left idle for any length of time they require
considerably more maintenance than the others to keep the blades
rotating freely.

He hauls in a TraveLift once a year (luckily his club possesses one)
and inspects and adjusts then as part of his general yearly hull
maintenance/cleaning/repainting. He says it's pretty straightforward
so far, but he acknowledges that they are complex pieces of machinery
for props.


Auto-Props are best where powered performance takes
precedence over sailing performance.

Debatable, if you consider the alternative as being a fixed prop or a
folding prop. I think you have to consider hull type, displacement and
engine output along with intended use. My friend takes his large steel
ketch out alone a great deal, and while he is fine sailing it solo, he
appreciates the degree of control his Autoprop gives him in tight
situations and in solo docking. Certainly that aspect--the degree of
control of a 15 ton boat-- is quite noticeable and is obviously worth
it to him in his use of a heavy displacement cruiser.

That's why I tried to give both pros and cons, as the Autoprop isn't
particularly well-known, being British. Getting one personally would
be senseless for my current boat, but seems a good compromise for him
and has bought him a few more years out of his 35 HP Volvo, even if he
has to rethink transmission isolation and so on.

But it's not for everyone. No "marine solution" is, except maybe for
those wooden tapered plugs people hang off seacocks. G

R.