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

I swapped a large blade two-bladed fixed prop for a smaller blade Gori
folding prop of the same pitch and diameter. I didn't notice any
change in the walking behaviour. (But the boat sailed faster... )

Ryk


--
NewsGuy.Com 30Gb $9.95 Carry Forward and On Demand Bandwidth

I was in Port Townsend, WA about 5 years ago. Talking to a guy who had
same problem so he called the designer of his production boat. Can not
remember the designer's name but he was someone legendary type.

The designer's response was, "I did not design my boats to sail
backwards."
Bob

Prop walk is a function of 'tip clearance' to the hull and other hull
projections (aperture, etc.) , blade tip shape, , etc. etc. etc.

Just learn to 'back and fill' to steer going in reverse when there is
NO flow over the rudder ... and be prepared to use your rub-rails.
Especially if this is a full keeled boat with an aperture, you will
need LOTS of practice in 'backing and filling' to get it right; but,
once you 'learn', you will not want less prop-walk.

If you want to see exactly how to use prop-walk, go down to the
commercial docks and watch the prop-walk wizards / watermen fishermen
when they are about to land with a single screw boat -- always in a
hurry, LOTS of 'rpm burst', and precise maneuvering ... and all without
touching the wheel !!!!!.



In article , 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?

"Rich Hampel" wrote in message
...
Prop walk is a function of 'tip clearance' to the hull and other hull
projections (aperture, etc.) , blade tip shape, , etc. etc. etc.

Just learn to 'back and fill' to steer going in reverse when there is
NO flow over the rudder ... and be prepared to use your rub-rails.
Especially if this is a full keeled boat with an aperture, you will
need LOTS of practice in 'backing and filling' to get it right; but,
once you 'learn', you will not want less prop-walk.

If you want to see exactly how to use prop-walk, go down to the
commercial docks and watch the prop-walk wizards / watermen fishermen
when they are about to land with a single screw boat -- always in a
hurry, LOTS of 'rpm burst', and precise maneuvering ... and all without
touching the wheel !!!!!.



In article , 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?

Rich, as I mentionen in a previous response, I'm familiar with the
technique. I was looking for a mechanical solution. Thanks though.

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

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 O'Toole" wrote in message
news
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

"Matt O'Toole" wrote in message
news
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

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.

On Sat, 13 May 2006 14:30:49 -0400, Wayne.B
wrote:


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.


I know the OP wanted physics and not art, but the prop walk of my old
fixed two-blade was so nasty (and contrary to my port side docking
situation) that I learned quite early to just walk the boat off the
dock in neutral and "coast" until I could put it in forward, and to
"dead stick" the boat back to dock by throwing it into neutral,
bleeding off speed in a sharp S turn and basically crabbing right into
my slip.

So even though I can back down straighter (after a slight pause as the
blades open), I still don't use a lot of reverse thrust. I fell out of
the habit.

R.

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.