In article ,
"R.W. Behan" wrote:

Alan:

Yes, that's what I was taught in the Navy's aviation machinist's mate school
(some years back, obviously, when most of the Navy's planes were still
propeller driven). We can argue nuance here, but do you agree that an
auto-rotating prop will create more drag than one locked in position? I
know this to be true from flying experience. One of the engines of our R4D
(that was a DC-3 in civilian configuration: see how far back I'm talking?)
quit one time, and the drag was enormous, slewing the airplane severely,
until we feathered the prop. I presume the fluid dynamics for boat props is
the same. But decreasing drag is just one reason to shift a boat
transmission into reverse: another good one is to reduce wear on the gear
train and bearings. Agree?

No. First: your example in the DC-3 included *feathering*; changing the
AOA to zero.

Ask yourself: how could it make a difference to drag to have such a prop
locked or free to spin?


Cheers,

Dick

"Alan Baker" wrote in message
...
In article ,
"R.W. Behan" wrote:

Marty:

Can't tell you why your transmission is getting stuck in reverse, but I
would heartily recommend PUTTING it in reverse while you're sailing.
That
isn't boat-specific, it is common-sense specific. An auto-rotating
prop,
whether on an airplane or a boat, creates drag that is equivalent to
towing
a disk of the prop's diameter, and that's a LOT of drag. When you
"freeze"
the prop by shifting to reverse (the equivalent of feathering an
airplane's
propeller) you lower the drag to what is caused by the area of the
prop's
blades--probably a third or so of the area of the prop's diameter.

Can you start your engine in reverse and then shift to neutral--and then
forward? If so, do that, and don't worry.

Do you really think it's that simple?

So regardless of the angle of attack of the blades, the "auto-rotating"
prop is creating the same drag?


Cheers,

Dick Behan


"Marty" wrote in message
...
Is it boat specific, or does it apply to all boats, that the
transmission should be put into reverse when the motor (inboard
diesel)
is off during sailing?

Even when the boat manual says to do so, I frequently find the tranny
stuck in reverse when attempting to return to neutral before starting
the motor.

So, let the prop spin freely while under sail or lock it in place with
reverse?

And why is the tranny getting stuck in reverse?

Thanks,

Marty




--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."



--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."