Back to more questions somewhat related to the Perkins 4-108. This sailboat
is a pig to back up. It really wants to prop walk to starboard. According to
the owner, it's got a fixed, 3-blade prop. I believe the boat also has a
folding prop aboard in a locker. Would that help? Would tuning help? What do
you think?

--
"j" ganz @@
www.sailnow.com

"Capt. JG" wrote:

Back to more questions somewhat related to the Perkins 4-108. This sailboat
is a pig to back up. It really wants to prop walk to starboard. According to
the owner, it's got a fixed, 3-blade prop. I believe the boat also has a
folding prop aboard in a locker. Would that help? Would tuning help? What do
you think?

We have a Perkins 4-154 which had a fixed three blade prop. It also
backed poorly and had a prop walk. We replaced the prop with a Max
Prop (not because of that, but because the noise made by the shaft
spinning when we were under sail sounded like we were next to an
expressway). The Max Prop feathers (doesn't really fold), and the
blades are flat instead of cupped so that it will feather flat. This
meant that the boat backed better - the cupped blades only increase
the bite of the water when going forward. So

Not being an engineer or anything, and not even playing one on TV ...

My guess would be that yes the folding prop would help. Why is it
stored in a locker?



grandma Rosalie

S/V RosalieAnn, Leonardtown, MD
CSY 44 WO #156
http://home.mindspring.com/~gmbeasley/id1.html

"Rosalie B." wrote in message
...
"Capt. JG" wrote:

Back to more questions somewhat related to the Perkins 4-108. This
sailboat
is a pig to back up. It really wants to prop walk to starboard. According
to
the owner, it's got a fixed, 3-blade prop. I believe the boat also has a
folding prop aboard in a locker. Would that help? Would tuning help? What
do
you think?

We have a Perkins 4-154 which had a fixed three blade prop. It also
backed poorly and had a prop walk. We replaced the prop with a Max
Prop (not because of that, but because the noise made by the shaft
spinning when we were under sail sounded like we were next to an
expressway). The Max Prop feathers (doesn't really fold), and the
blades are flat instead of cupped so that it will feather flat. This
meant that the boat backed better - the cupped blades only increase
the bite of the water when going forward. So

Not being an engineer or anything, and not even playing one on TV ...

My guess would be that yes the folding prop would help. Why is it
stored in a locker?



grandma Rosalie

S/V RosalieAnn, Leonardtown, MD
CSY 44 WO #156
http://home.mindspring.com/~gmbeasley/id1.html

I guess the owner felt that coming up the west coast he would have more
power with the fixed prop. That was the reason he gave, although I'm not
sure that makes sense.

Thanks for the thoughtful response. I appreciate it.

--
"j" ganz @@
www.sailnow.com

Capt. JG wrote:
Back to more questions somewhat related to the Perkins 4-108. This
sailboat
is a pig to back up. It really wants to prop walk to starboard.

Try pulsing the prop when in reverse.

Set engine speed relatively low, then shift into reverse for maybe
5-10 seconds, then back to neutral for maybe 30 seconds.

You will have to experiment with times.

Place rudder in desiored position.

Not perfect, but it will help.

Lew

"Lew Hodgett" wrote in message
nk.net...
Capt. JG wrote:
Back to more questions somewhat related to the Perkins 4-108. This
sailboat
is a pig to back up. It really wants to prop walk to starboard.

Try pulsing the prop when in reverse.

Set engine speed relatively low, then shift into reverse for maybe 5-10
seconds, then back to neutral for maybe 30 seconds.

You will have to experiment with times.

Place rudder in desiored position.

Not perfect, but it will help.

Lew

Lew, I'm familiar with this technique. My question was how to correct it
from a mechanical view, not how to correct it by technique. Thanks though.
It's nice to hear the technique mentioned.

--
"j" ganz @@
www.sailnow.com

"Capt. JG" wrote

My question was how to correct it from a mechanical view, not how to
correct it by technique.

It's very difficult to correct mechanically. Physics are against you.
Open wheels are always going to walk. Variations in size and number
of blades with change the degree but the psychological effect of
spending a grand or more to reduce the problem will often be greater
than the actual change in forces.

The difference in water density with depth makes the wheel act like a
paddle wheel (grossly oversimplified explanation warning).

Three things you can do:

Put the prop in a nozzle. You really won't be happy with the drag
under sail of this arrangment!

Twin props. Not much better from the drag standpoint.

Angle the shaft to counteract the effect and normal backing speed.
Going forward faster and with more rudder authority, the off center
thrust will not be as noticeable.

Neither of these are practical as a retrofit.

--

Roger Long

As long as you treat "propwalk" as the enemy, you will continue to have
problems with it and never learn to handle your boat well.
Learn to use it, treat it as your friend, compensate for it, and you'll
soon be wondering what all the fuss is about.
Accept it..... single screw or twin screw..... prop walk is an
important consideration to your boat's handling.

Shen

Roger Long wrote:
"Capt. JG" wrote

My question was how to correct it from a mechanical view, not how to
correct it by technique.

It's very difficult to correct mechanically. Physics are against you.
Open wheels are always going to walk. Variations in size and number
of blades with change the degree but the psychological effect of
spending a grand or more to reduce the problem will often be greater
than the actual change in forces.

The difference in water density with depth makes the wheel act like a
paddle wheel (grossly oversimplified explanation warning).

Three things you can do:

Put the prop in a nozzle. You really won't be happy with the drag
under sail of this arrangment!

Twin props. Not much better from the drag standpoint.

Angle the shaft to counteract the effect and normal backing speed.
Going forward faster and with more rudder authority, the off center
thrust will not be as noticeable.

Neither of these are practical as a retrofit.

--

Roger Long

I agree. Having no ability to make the stern go sideways with minimal
forward or aft motion would complicate almost as many single screw
maneuvers as it simplified for the person who knows how to use the
prop force. It's almost like having a stern thruster.

It does mean though that the boat has a good side and a bad side in
many docking situation. I have a slip on the difficult side. 75% of
the time, the wind is quartering off the dock and half the time, the
current is as well so stopping the boat with three forces pulling the
stern away is an adventure. We've got it down pat though and I even
manage it single handed very often.

That said, the tiny propeller, large lateral plane, and high windage
of the typical sailboat make the propwalk force minimally useful
except in very calm conditions. When there is any wind, you can't
make our boat do the fancy things you see the lobster boats doing.

--

Roger Long



wrote in message
oups.com...
As long as you treat "propwalk" as the enemy, you will continue to
have
problems with it and never learn to handle your boat well.
Learn to use it, treat it as your friend, compensate for it, and
you'll
soon be wondering what all the fuss is about.
Accept it..... single screw or twin screw..... prop walk is an
important consideration to your boat's handling.

Shen

Roger Long wrote:
"Capt. JG" wrote

My question was how to correct it from a mechanical view, not how
to
correct it by technique.

It's very difficult to correct mechanically. Physics are against
you.
Open wheels are always going to walk. Variations in size and
number
of blades with change the degree but the psychological effect of
spending a grand or more to reduce the problem will often be
greater
than the actual change in forces.

The difference in water density with depth makes the wheel act like
a
paddle wheel (grossly oversimplified explanation warning).

Three things you can do:

Put the prop in a nozzle. You really won't be happy with the drag
under sail of this arrangment!

Twin props. Not much better from the drag standpoint.

Angle the shaft to counteract the effect and normal backing speed.
Going forward faster and with more rudder authority, the off center
thrust will not be as noticeable.

Neither of these are practical as a retrofit.

--

Roger Long

Shen, it's not really helpful to tell me stuff I already know. Anyone who's
been around boats for any length of time knows that prop walk can be used to
advantage. That has nothing to do with my question.

--
"j" ganz @@
www.sailnow.com

wrote in message
oups.com...
As long as you treat "propwalk" as the enemy, you will continue to have
problems with it and never learn to handle your boat well.
Learn to use it, treat it as your friend, compensate for it, and you'll
soon be wondering what all the fuss is about.
Accept it..... single screw or twin screw..... prop walk is an
important consideration to your boat's handling.

Shen

Roger Long wrote:
"Capt. JG" wrote

My question was how to correct it from a mechanical view, not how to
correct it by technique.

It's very difficult to correct mechanically. Physics are against you.
Open wheels are always going to walk. Variations in size and number
of blades with change the degree but the psychological effect of
spending a grand or more to reduce the problem will often be greater
than the actual change in forces.

The difference in water density with depth makes the wheel act like a
paddle wheel (grossly oversimplified explanation warning).

Three things you can do:

Put the prop in a nozzle. You really won't be happy with the drag
under sail of this arrangment!

Twin props. Not much better from the drag standpoint.

Angle the shaft to counteract the effect and normal backing speed.
Going forward faster and with more rudder authority, the off center
thrust will not be as noticeable.

Neither of these are practical as a retrofit.

--

Roger Long

yea, you just need to "get to know: the boat and how
she acts whilst backing down...all sailboats will want
to walk to one side at different rates...ist the "p factor"
we see in airplanes also...esp the single engine prop
planes...the torque from the spinning blade causes it...
just practice and get to know your vessel......