Greg's thread made me think about my old Chris-craft Cavalier and how it was set up. It had solid shaft propulsion. And looking from the back, it had the rudder just left of the prop. I wonder why it was set that way instead of being directly behind the propeller instead of offset the way it was. Also I wonder why only one prop instead of two. It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of speed or direction.
Any ideas?

On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how it was set up. It had solid shaft propulsion. And looking from the back, it had the rudder just left of the prop. I wonder why it was set that way instead of being directly behind the propeller instead of offset the way it was. Also I wonder why only one prop instead of two. It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.

On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.

On 3/18/15 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how it was set up. It had solid shaft propulsion. And looking from the back, it had the rudder just left of the prop. I wonder why it was set that way instead of being directly behind the propeller instead of offset the way it was. Also I wonder why only one prop instead of two. It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of speed or direction.
Any ideas?


Offset rudder. First time I saw that was in the late 1950s. It wasn't
uncommon on inboard runabouts that "wandered" into my dad's shop.

--
Proud to be a Liberal.

On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



Moving to the left (or right, depending on whether the prop design is LH
or RH rotation) is a result of "prop walk". A RH prop will tend to move
the stern to port in reverse while a LH prop will tend to move the
stern to starboard.

The technique used for backing a single (fixed) screw with rudder boat
is called "Back and Fill". It's a combination of short forward thrusts,
then backing depending on the prop walk to maneuver into the slip. You
also have to take into account wind and current if they are present.
Backing a single screw boat with rudder is a challenging technique to
learn. It's one of the reasons I enjoyed the Grand Banks we had. It was
different and required much more skill than docking a twin engined boat
or even a I/O that has the advantage of vectored thrust, forward or
backward.

On 3/18/2015 7:28 PM, Keyser Söze wrote:
On 3/18/15 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?


Offset rudder. First time I saw that was in the late 1950s. It wasn't
uncommon on inboard runabouts that "wandered" into my dad's shop.


I think even in larger, twin engined boats with rudders, the rudder is
not necessarily dead center to the prop. It's usually offset, not by
much, but is not perfectly centered. I remember this on the Egg Harbor
I had. When it was being launched but still on land I was standing
behind it and noticed that the rudders where not perfectly in line with
the center hub of the props. They were offset by about an inch, one in
one direction, the other opposite.

On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

On Wed, 18 Mar 2015 16:14:51 -0700 (PDT), Tim
wrote:

Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

===

That issue is known as "prop walk" and it is most apparent at very
slow speed before the boat gains momentum. Prop walk is caused by the
propellor acting as a paddle wheel. Since the prop/paddle wheel
rotation is perpendicular to the center line, a side thrust is created
instead of forward motion. The direction of "walk" depends on the
direction of shaft rotation. Since your boat is walking to the left
we can assume the shaft is rotating counter clockwise in reverse (when
viewed from behind the boat). Remember to think of the prop as a
paddle wheel at low speed. There are other more complicated
explanations for why prop walk occurs but the paddle wheel analogy is
the most intuitive to understand and the easiest to apply to problem
solving.

As Richard pointed out, the rudder has very little effect in reverse
until the boat gains some speed and creates water flow past the
rudder. This is not a problem in forward because the prop creates
plenty of water flow even when the boat is standing still.

Backing up a single engine boat is an art form not a science. Every
boat is a little different but some basic priciples apply. The best
strategy I've found is to apply a quick burst of power in reverse and
then shift immediately into neutral. Once you are in neutral there is
no more prop walk, and if you have built a little speed, you can steer
with the rudder. Sometimes you have to do this more than once.

Another strategy is letting the prop walk work in your favor and just
let the stern "walk" in the direction it wants to go. This implies
some maneuvering room of course.

On Wednesday, March 18, 2015 at 5:16:48 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

Speaking of 'trim' this boat had stationary trim tabs on it. They were cushioned by what looked like big shock absorbers.

For an old 27 ft. wooden cabin cruiser, it plowed water really hard till you got it up on plane and then it was really quite agile.
Speaking of getting up on plane it kinda reminded me of a fully loaded PBY trying to take off out of the water.

It seemed like it fought hard to plane out for quite a distance, but really it didn't take that long.

Too bad the plywood hull was starting to delaminate on the thing. I really had a lot of fun on that old tub.