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

Generally, whenever this discussion arises we all tend to discuss or
think of our own boat and/or situation rather than talking about it in
a "generic" sense.
Forgetting wind and current for the moment. All propellor driven boats
will have prop walk to some degree, from hardly noticeable to "wowser"
and that difference will include two of the same type being totally
different due to how they are loaded with gear, fuel, people, etc..
If you have wind and current to consider, learn your boats "walking"
characteristics without wind and current first, then learn it with wind
and current, as sometimes one factor will totally negate the other.
Take, for instance, a single screw right hand prop docking stbd side
too (probably the toughest maneuver for this boat). No wind or
current.... use your prop walk to STOP your stern swinging into the
dock.
Now, same setup but port side too..... use your propwalk to START or
make your stern swing into the dock.
Since most boats will want to back into a wind or current you will have
to learn at what point of wind speed or current velocity and from what
directions will your boat be under the control of one factor (propwalk,
wind, current) or combination.
Obviously, no two conditions are the same and no one answer fits all.
I'd hate to tell you how many times I've started backing down expecting
my stern to go to port, only to find out that today it would rather go
to stbd.... and then after the fact, tried to figure out why.

Shen

" wrote:

Generally, whenever this discussion arises we all tend to discuss or
think of our own boat and/or situation rather than talking about it in
a "generic" sense.
Forgetting wind and current for the moment. All propellor driven boats
will have prop walk to some degree, from hardly noticeable to "wowser"
and that difference will include two of the same type being totally
different due to how they are loaded with gear, fuel, people, etc..
If you have wind and current to consider, learn your boats "walking"
characteristics without wind and current first, then learn it with wind
and current, as sometimes one factor will totally negate the other.
Take, for instance, a single screw right hand prop docking stbd side
too (probably the toughest maneuver for this boat). No wind or
current.... use your prop walk to STOP your stern swinging into the
dock.
Now, same setup but port side too..... use your propwalk to START or
make your stern swing into the dock.
Since most boats will want to back into a wind or current you will have
to learn at what point of wind speed or current velocity and from what
directions will your boat be under the control of one factor (propwalk,
wind, current) or combination.
Obviously, no two conditions are the same and no one answer fits all.
I'd hate to tell you how many times I've started backing down expecting
my stern to go to port, only to find out that today it would rather go
to stbd.... and then after the fact, tried to figure out why.

The rule of thumb will be - if your boat usually backs to starboard,
and you want it to go to starboard, it will go to port.


There have been a couple of instances where we wanted to dock to port
(because that is the side the fuel fill is on), and just had to give
up on it and string the fuel hose all the way across the boat because
the engine could not overcome the wind and current (propwalk or no
propwalk).

In some cases the shore people were requiring a port docking, and we
could tell that it wasn't going to be possible. If they still
insisted, we would tell them that they would have to pull the boat in
to the dock by hand. Sometimes they could, and sometimes they could
not. It takes two of us to push the boat out from the dock against
any significant wind or current. (like in the Cooper River or in
Fernandina Beach). It is a heavy boat.

And sometimes they would tell us to do something - not being aware
that we have a modified full keel and not a fin keel - and without
telling us that there was a very swift current - this can result in
some scary situations when the current carries us sideways down the
fairway.

Bob will sometimes ask them to secure a bow line tight on something
and will run the boat forward into it - if there isn't too much wind
against us, that can get the boat swung around into the dock.

In two instances the shore person indicated a space on the face dock,
and Bob lined up the boat even with the space, and the boat was blown
sideways all the way across the channel and into the spot without us
using any engine at all.

grandma Rosalie

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

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

Then I may be reading more or less into your question than I thought.
I don't believe anyone could give you a definitive answer as to whether
a particular prop would reduce prop-walk on your particular boat
without you actually trying it out, and that can get expensive,
especially if you don't like the results in other areas of performance.
If you are generally happy with the overall performance of your prop
then I would look first to the "operator" to solve your possible
problem.
Nine times out of ten, this is where the real problem lies......
course, I couldn't say if this was true in your case unless I road with
you and watched and then I could easily end up agreeing with you......
or not.

Shen

wrote in message
ups.com...
Then I may be reading more or less into your question than I thought.
I don't believe anyone could give you a definitive answer as to whether
a particular prop would reduce prop-walk on your particular boat
without you actually trying it out, and that can get expensive,
especially if you don't like the results in other areas of performance.
If you are generally happy with the overall performance of your prop
then I would look first to the "operator" to solve your possible
problem.
Nine times out of ten, this is where the real problem lies......
course, I couldn't say if this was true in your case unless I road with
you and watched and then I could easily end up agreeing with you......
or not.

Shen


I thought my question was pretty specific:

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?

Perhaps you should re-read the question.

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