backs like a pig
 

"Matt O'Toole" wrote in message
g...
On Fri, 12 May 2006 10:30:00 -0700, 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?

Prop walk is caused by the design of the boat, mostly the downward angle
of the prop shaft. The more downward angle, the worse the walk will be.
Other factors contribute too, but that's the main one.

Changing the prop may cause a noticeable difference, but not enough to
matter.

Folding props reverse poorly, and won't help. Feathering props, such as
Max-prop's, actually reverse better than fixed props. This won't stop the
walk but it will give you more control.

On some boats I just put the wheel hard over and pulse the throttle, or
goose the tranny in and out of gear. The alternate turning forces cancel
each other, and with luck (and no wind) the boat goes straight back.

Practice!

Matt O.

Matt,

Thanks for the comments and comparisons between two type of prop. I'll take
it under advisement, and I don't actually know if what is in the locker is
folding or feathering.

Jonathan

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

backs like a pig
 

"Matt O'Toole" wrote in message
g...
On Fri, 12 May 2006 10:30:00 -0700, 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?

Prop walk is caused by the design of the boat, mostly the downward angle
of the prop shaft. The more downward angle, the worse the walk will be.
Other factors contribute too, but that's the main one.

Changing the prop may cause a noticeable difference, but not enough to
matter.

Folding props reverse poorly, and won't help. Feathering props, such as
Max-prop's, actually reverse better than fixed props. This won't stop the
walk but it will give you more control.

On some boats I just put the wheel hard over and pulse the throttle, or
goose the tranny in and out of gear. The alternate turning forces cancel
each other, and with luck (and no wind) the boat goes straight back.

Practice!

Matt O.

FWIW, I have a Catalina 30 and have had both a fixed 2 blade and a fixed 3
blade prop on it. The prop walk is definitely and noticeably worse with the
3 blade. The diameter of both props is the same. Others on the Catalina 30
list claim that when they switched from the standard-issue 2 blade fixed
prop that usually comes from the factory to a Martec folder that the prop
walk goes down.

--Alan Gomes

backs like a pig
 

"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

backs like a pig
 

On Fri, 12 May 2006 10:30:00 -0700, "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?

I think in the end that the best cure is technique. Once water starts
flowing along the keel and rudder, prop walk is minimized. Give the
boat a quick burst of power in reverse to get it moving a little and
then shift to neutral. Apply more reverse as needed in short bursts,
and use the rudder to compensate for additional prop walk.
Many people are reluctant to build too much boat speed in reverse but
it really does a lot to minimize control issues of al types.

backs like a pig
 

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?

The simple type of folding prop which opens by centrifugal force has about
as much stopping power when reverse is engaged as a car with silcone-coated
tyres on sheet ice. Folding props of this type have one purpose and one
purpose only, to minimise the prop-drag on a racing boat. If you minimise
the drag you also lower the forward thrust of the prop, hence the maximum
speed under engine at a given revs.

Efficient props have more prop-walk than inefficient props, so you have a
price to pay for maximum thrust. Most sailors get used to the prop-walk of
their particular boats and allow for it. In most cases they learn to make
good use of it, such as when backing into a marina berth, the angle of
approach being controlled intitially by the prop-walk factor. Once the boat
gathers way, the prop walk is minimised and the rudder takes over.

If you use the boat only once a week or less, you would take about 3 years
to learn the secret, so practice is essential, which is why professional
fishing-vessel skippers are so good at it.

It would be possible to design a prop which did not "walk". The same prop
would have little or no forward or reverse drive, and would therefore be
useless. The answer can be seen in new liners like the QM2, 4 independently
rotatable pods, each powered by it's own motor. Such technology is rather
expenssive for a small boat, but you can fit a bow thruster, which is a big
help.

backs like a pig
 

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

backs like a pig
 

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

backs like a pig
 

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

backs like a pig
 

" 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

backs like a pig
 

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......