transmission in reverse during sailing
 

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

transmission in reverse during sailing
 

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.

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

transmission in reverse during sailing
 

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."

transmission in reverse during sailing
 

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?

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."

transmission in reverse during sailing
 

"R.W. Behan" wrote...

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.

Not quite...

Feathering an airplane's prop also includes turning the blades within the hub so
they are faired into the air stream, more like the folding/feathering props
available (at high cost) for sailboats. Simply stopping the prop will slightly
reduce drag, compared with autorotation, but will not reduce it anywhere near
that of a feathered prop. There is still the turbulence created by the unfaired
blades, and that creates drag.

OTOH, putting the prop in gear may reduce wear on the transmission, shaft seal,
and cutless bearing...

transmission in reverse during sailing
 

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."

transmission in reverse during sailing
 

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?


Alan, look. Feathering an airplane propeller does indeed change the angle
of attack to zero, but that is how you STOP the autorotation. In a boat,
you stop the autorotation by shifting to reverse. The purpose in either case
is the same: to reduce drag.

Your second statement is a non-sequitur. There's no way in the world a
feathered prop CAN spin, right?

Cheers. It's a lively discussion.

Dick

transmission in reverse during sailing
 

"John R Weiss" wrote in message
news:cjcVa.168299$H17.60017@sccrnsc02...
"R.W. Behan" wrote...

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.

Not quite...

Feathering an airplane's prop also includes turning the blades within the
hub so
they are faired into the air stream, more like the folding/feathering
props
available (at high cost) for sailboats. Simply stopping the prop will
slightly
reduce drag, compared with autorotation, but will not reduce it anywhere
near
that of a feathered prop. There is still the turbulence created by the
unfaired
blades, and that creates drag.

John, you're dead right. My statement was a bit ambiguous. By "equivalent"
I meant that feathering and shifting to reverse are "equivalent" in terms of
stopping the autorotation. They are not equivalent in terms of reducing
drag.


OTOH, putting the prop in gear may reduce wear on the transmission, shaft
seal,
and cutless bearing...


Yep, and that's reason enough, right?

Cheers,

Dick

transmission in reverse during sailing
 

Hey, Howard, not a bad idea: let's hear from someone who REALLY knows what
they're talking about. My information, from the Navy training, is half a
century old.

Cheers,

Dick



"Vito" wrote in message
...
John R Weiss wrote:

OTOH, putting the prop in gear may reduce wear on the transmission,
shaft seal,
and cutless bearing...

I suspect that's the main reason. As you said, "feathering" a prop is
very different than simply stopping it from turning. In fact, intuition
says simply stopping the prop would cause more drag than letting it "do
its thing" but I've never researched it. Anybody working at the USN's
David Taylor Model Basin or equivalent care to comment?

Regards
Howard

transmission in reverse during sailing
 

"R.W. Behan" wrote in message
...
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?

Cheers,

Dick

No, disagree. I purchased a Gori folding prop this season after some
experimenting last season with the prop in neutral vs. reverse. The manual
that came with the boat recommends locking in reverse to prevent
transmission wear, shifting from reverse to neutral while under sail
resulted in a 1/2 increase in boat speed. Did this on several occasions,
just to verify. I figured a folding prop should be worth at least 1/2 knot
also.
John Cairns