Unlubberizing the Single Screw, Part II


In last month's installment, we examined the natural forces that will
influence the handling and maneuvering of a single screw inboard
powerboat and the mechanical forces that we can generate to compliment
or counteract these environmental variables.
Now we will examine some of the specific, situational considerations
commonly encountered as well as some of the techniques that have proven
useful to generations of single screw boat handlers.


The Most Important Mechanical Consideration


Handling a specific, single screw boat would be impossible to do
(properly) without remaining aware of the "handing" of the prop. Is
the propeller is a left-hand prop (turning counterclockwise when viewed
from astern with the vessel in forward gear) or a right hand prop
(turning clockwise when viewed from astern with the vessel in forward
gear)? The handing of the prop is one of the few fixed factors in a
complex equation that must be solved to maneuver a single screw in
close quarters. Wind and current change speed as well as direction. The
rudder can be turned to starboard, port, or left amidships. The
throttle can be increased or reduced, and the gears can be shifted into
forward or reverse.
Draft and windage will not change, nor will the handing of the prop. In
practice, a boater will always need to make decisions based directly
upon the handing of the prop, while there will occasionally be those
lucky circumstances in which windage and draft are virtually
non-factors.

Novice boaters, or experienced skippers called upon to operate a boat
with which they may not be entirely familiar, may wonder whether a
specific boat has a left hand or right hand prop. It wouldn't be
advisable to get behind the prop to watch it turn when engaged, and
particularly if single handed it's not always possible to leave the
wheel to open the engine room hatch and examine the direction the prop
shaft is turning when underway.
In some cases, but not all, the rotation of the prop is marked near the
output shaft of a gearbox and can be determined when performing a
routine engine room inspection prior to startup. In some cases engines
are actually "counter rotating" to drive left hand props, but in
most situations change of direction occurs in the gearbox so any marks
on the flywheel housing of an engine should be considered unreliable
indicators of prop handing. Fortunately, there is a reliable way to
evaluate prop handing that doesn't require any marking on the gearbox
or observations of a propshaft.

Shifting into reverse, particularly with no headway, will move the
stern to either port or starboard. It can help to have the rudder
amidships, but if the boat is not making way rudder position will be of
little consequence when first shifting into reverse from idle.
The single prop directs the prop discharge current away from the rudder
in reverse. The prop is shaped to be most efficient when in forward
gear, so when in reverse the side pressure of the prop tends to exert a
greater influence than the low pressure prop suction current passing
with little effect around both sides of the rudder. In some cases, and
depending upon the diameter and pitch of the prop, the movement of the
stern to port or starboard can be immediate and dramatic. In the worst
cases "prop walk" can be ridiculously extreme, and only slightly
less desirable would be a situation where the prop walk to port or
starboard was barely noticeable. A moderate amount of prop walk is a
useful tool when maneuvering a single screw inboard: a vessel that
steers by moving the stern has greater flexibility and will be easier
to handle with more options for moving the stern rather than fewer.

The majority of single screw powerboats use right hand props and will
back to port. The concept of visualizing the prop as a wheel on the
ground to understand how side pressure pushes the stern to one side or
the other (discussed in the last issue) is equally applicable whether
in forward or reverse. A single screw inboard with a left hand prop
will back to starboard. Vessels with the helm on the starboard side
will generally find docking more easily accomplished with a left handed
prop than a right handed prop, but the common disadvantage of the right
hand prop can be overcome with an adaptive technique.

Knowledge of the handing of a boat's propeller and an awareness of
what the stern will do when the vessel is in reverse gear is critical
to successfully handling a single screw inboard.


Backing and filling:

One of the common misperceptions associated with single screw inboards
is that they will always be awkward to turn in tight quarters. It would
be almost impossible for a skilled single screw operator to turn a boat
as tightly as an equally skilled operator would with twin engines, and
for good reason. Twin engine boats tend to "pivot" farther aft, and
with the advantage of one prop in forward gear and the other in reverse
(as well as the judicious adjustment of throttles) it isn't unusual
to turn a twin screw boat practically within its own length. Single
screw boats can often be turned within just a little greater space,
(perhaps 125% of the boat's LOA) but will require the employment of
some specific skills and strategies rather than engaging a second
engine. The general process of making a tight turn from a dead stop in
a single screw inboard boat is sometimes referred to as "casting",
but more commonly called "backing and filling".

Single screw inboards will back and fill more efficiently in one
direction than in the other, for reasons that are very apparent when
considering any single screw's tendency to back to one direction.
Right hand props that back to port will make a tighter turn to
starboard, and the reverse will be true of left hand props.

To back and fill in a tight circle from a dead stop, first put the helm
hard over in the direction you want to turn. To make the tightest
circle with a right hand prop, put the wheel to starboard.

With the helm hard over, engage forward gear and throttle ahead just
enough to get the stern moving to port. Once the stern is moving and
before making any serious headway, shift to reverse gear and turn the
wheel hard aport. The prop walk will continue moving the stern to port,
and the rudder turned to port will capitalize on any slight amount of
sternway that may be generated with the shift into reverse. Before
making any serious sternway, take the wheel hard astarboard engage
forward gear again. Momentum will continue to carry the stern through
its circle during those moments when the gear is neutral. Continue this
process until the vessel has turned almost through the number of
degrees desired, remembering to begin preparing to power off on the new
heading just prior to achieving it.

A preliminary precaution: The back and fill maneuver is always subject
to the external forces of wind and current. A persistent wind or
current will move the backing and filling vessel from the location of
its originally intended circle while the maneuver is being conducted.
Be sure there is enough room "downwind" or "downstream" before
beginning a tight turn.


Going astern:

Many people hold an inaccurate impression that a single screw inboard
cannot be controlled in reverse. There is no doubt that making
sustained and undeviating sternway is more challenging with a single
screw than with a twin engine craft, but the technique to do so with an
acceptable degree of success so can be mastered. Prerequisites include
a basic understanding of the physics involved and the patience to
practice. Various boats have larger and smaller rudders as well as more
or less aggressively pitched propellers, so going astern is a skill
that each boater will eventually refine with additional experience.

A skipper backing a single screw inboard always needs to remain aware
of the bow. Making sternway may be more often interrupted due to the
wind or current pushing the bow off course than by any catastrophic
miscues in controlling the throttles, gearshift, helm, and rudder.

To go astern from a dead stop, first put the helm hard over to the
opposite side from that which the boat will back toward. For a left
hand prop, put the helm hard aport and for a right hand prop, put the
helm hard astarboard. Shift the gear into reverse and apply a quick
burst of power. The stern will begin shifting toward the direction in
which the boat normally backs, but once the boat is moving reduce the
engine speed and the pressure of sternway against the rudder should
begin to "balance" the side pressure of the prop. Some skippers
will shift the propeller in and out of gear to achieve or maintain the
balance of side pressure from the prop and the counteracting pressure
from the rudder. A practiced hand can sustain this balancing act for an
extended distance. As sternway momentum increases, the rudder can be
brought more amidships.

If, (or more commonly "when") the desired track cannot be
maintained by the aforementioned techniques, a correction can be made
by shifting into forward gear and realigning the bow and stern. The
most skillful helmspeople can often apply the occasional corrective
pulse of forward propulsion without entirely sacrificing sternway, but
remaining in control is always far more important than looking
"cool." Even the most experienced boaters will sometimes need to
stop, reposition, and then begin backing up again. It is the prudent
seaman who will take the corrective and restorative actions required,
or even start over again without embarrassment. The lubber, on the
other hand, will often press on after having sacrificed control and
then simply hope for the best.

Head or back into a slip?

Situations will arise when it is desirable to back into a slip.
Examples will include filling slips along a central float with swim
steps and transom doors accessible for friends at a yacht club event, a
boat show, or an owners' rendezvous. It may be necessary to load or
offload some heavy items or machinery from the cockpit to a pier, or
boaters with the master stateroom forward might covet the extra privacy
from most of the marina foot traffic provided by an extra 25-40 feet of
distance. If wind and current conditions are completely benign and
there is adequate room to get positioned for a proper approach, there
is no reason why backing a single screw inboard into a slip should be
difficult. When moderate winds and currents prevail and maneuvering
space is at a premium, any backing in by most single screw inboards
will need to be assisted by skillful line handlers- either standing on
the dock or aboard the boat. (Line handlers aboard the boat will need
to be well trained in some advance spring line techniques).

Even in light of those exceptional considerations, it normally makes
far more sense to take a single screw boat into a slip bow first. The
benign wind and currents that may have made backing in reasonably easy
may be running or blowing with enthusiasm when it's time to depart.
Control of a single screw inboard is primarily established and
maintained by controlling the stern. Backing into a slip, particularly
a typical Pacific NW configuration with a float on one side and another
vessel tied off on the other, restricts any effective movement of the
stern to either side. If a boat is halfway into the slip and a sudden
gust of wind sets the bow off to port or starboard, making the
correction can be extremely difficult, if not impossible. Going in bow
first leaves the stern in the fairway, where it can be usefully
maneuvered, for the longest possible period of time. Emerging bow first
from a tight slip will result in the winds and currents having their
way with the vulnerable bow until the stern has traveled the length of
the slip and is far enough clear of the float and adjoining boat to
begin making corrections.


The bowthruster factor:

It should be recognized that many of the concerns associated with
turning and most particularly with backing single screw inboards would
be alleviated by the addition of a bowthruster. Bowthrusters provide
side thrust to control the bow, just as the prop and rudder control the
stern. A purist would observe that adding a bowthruster takes a boat
out of the "single screw" category, so while bowthrusters are
commonly used by some very experienced boaters, we will reserve a
discussion of bowthruster-assisted techniques until we have examined
fundamental single screw operation.

Next installment: In our next issue, we will examine how the principles
of backing, turning, and maneuvering are essential elements in the
science of docking a single screw inboard.

"Chuck Gould" wrote in
ups.com:

Unlubberizing the Single Screw, Part II


In last month's installment, we examined the natural forces that will
influence the handling and maneuvering of a single screw inboard
powerboat and the mechanical forces that we can generate to compliment
or counteract these environmental variables.
Now we will examine some of the specific, situational considerations
commonly encountered as well as some of the techniques that have proven
useful to generations of single screw boat handlers.


The Most Important Mechanical Consideration


Handling a specific, single screw boat would be impossible to do
(properly) without remaining aware of the "handing" of the prop. Is
the propeller is a left-hand prop (turning counterclockwise when viewed
from astern with the vessel in forward gear) or a right hand prop
(turning clockwise when viewed from astern with the vessel in forward
gear)? The handing of the prop is one of the few fixed factors in a
complex equation that must be solved to maneuver a single screw in
close quarters. Wind and current change speed as well as direction. The
rudder can be turned to starboard, port, or left amidships. The
throttle can be increased or reduced, and the gears can be shifted into
forward or reverse.
Draft and windage will not change, nor will the handing of the prop. In
practice, a boater will always need to make decisions based directly
upon the handing of the prop, while there will occasionally be those
lucky circumstances in which windage and draft are virtually
non-factors.

Novice boaters, or experienced skippers called upon to operate a boat
with which they may not be entirely familiar, may wonder whether a
specific boat has a left hand or right hand prop. It wouldn't be
advisable to get behind the prop to watch it turn when engaged, and
particularly if single handed it's not always possible to leave the
wheel to open the engine room hatch and examine the direction the prop
shaft is turning when underway.
In some cases, but not all, the rotation of the prop is marked near the
output shaft of a gearbox and can be determined when performing a
routine engine room inspection prior to startup. In some cases engines
are actually "counter rotating" to drive left hand props, but in
most situations change of direction occurs in the gearbox so any marks
on the flywheel housing of an engine should be considered unreliable
indicators of prop handing. Fortunately, there is a reliable way to
evaluate prop handing that doesn't require any marking on the gearbox
or observations of a propshaft.

Shifting into reverse, particularly with no headway, will move the
stern to either port or starboard. It can help to have the rudder
amidships, but if the boat is not making way rudder position will be of
little consequence when first shifting into reverse from idle.
The single prop directs the prop discharge current away from the rudder
in reverse. The prop is shaped to be most efficient when in forward
gear, so when in reverse the side pressure of the prop tends to exert a
greater influence than the low pressure prop suction current passing
with little effect around both sides of the rudder. In some cases, and
depending upon the diameter and pitch of the prop, the movement of the
stern to port or starboard can be immediate and dramatic. In the worst
cases "prop walk" can be ridiculously extreme, and only slightly
less desirable would be a situation where the prop walk to port or
starboard was barely noticeable. A moderate amount of prop walk is a
useful tool when maneuvering a single screw inboard: a vessel that
steers by moving the stern has greater flexibility and will be easier
to handle with more options for moving the stern rather than fewer.

The majority of single screw powerboats use right hand props and will
back to port. The concept of visualizing the prop as a wheel on the
ground to understand how side pressure pushes the stern to one side or
the other (discussed in the last issue) is equally applicable whether
in forward or reverse. A single screw inboard with a left hand prop
will back to starboard. Vessels with the helm on the starboard side
will generally find docking more easily accomplished with a left handed
prop than a right handed prop, but the common disadvantage of the right
hand prop can be overcome with an adaptive technique.

Knowledge of the handing of a boat's propeller and an awareness of
what the stern will do when the vessel is in reverse gear is critical
to successfully handling a single screw inboard.


Backing and filling:

One of the common misperceptions associated with single screw inboards
is that they will always be awkward to turn in tight quarters. It would
be almost impossible for a skilled single screw operator to turn a boat
as tightly as an equally skilled operator would with twin engines, and
for good reason. Twin engine boats tend to "pivot" farther aft, and
with the advantage of one prop in forward gear and the other in reverse
(as well as the judicious adjustment of throttles) it isn't unusual
to turn a twin screw boat practically within its own length. Single
screw boats can often be turned within just a little greater space,
(perhaps 125% of the boat's LOA) but will require the employment of
some specific skills and strategies rather than engaging a second
engine. The general process of making a tight turn from a dead stop in
a single screw inboard boat is sometimes referred to as "casting",
but more commonly called "backing and filling".

Single screw inboards will back and fill more efficiently in one
direction than in the other, for reasons that are very apparent when
considering any single screw's tendency to back to one direction.
Right hand props that back to port will make a tighter turn to
starboard, and the reverse will be true of left hand props.

To back and fill in a tight circle from a dead stop, first put the helm
hard over in the direction you want to turn. To make the tightest
circle with a right hand prop, put the wheel to starboard.

With the helm hard over, engage forward gear and throttle ahead just
enough to get the stern moving to port. Once the stern is moving and
before making any serious headway, shift to reverse gear and turn the
wheel hard aport. The prop walk will continue moving the stern to port,
and the rudder turned to port will capitalize on any slight amount of
sternway that may be generated with the shift into reverse. Before
making any serious sternway, take the wheel hard astarboard engage
forward gear again. Momentum will continue to carry the stern through
its circle during those moments when the gear is neutral. Continue this
process until the vessel has turned almost through the number of
degrees desired, remembering to begin preparing to power off on the new
heading just prior to achieving it.

A preliminary precaution: The back and fill maneuver is always subject
to the external forces of wind and current. A persistent wind or
current will move the backing and filling vessel from the location of
its originally intended circle while the maneuver is being conducted.
Be sure there is enough room "downwind" or "downstream" before
beginning a tight turn.

Good article...... naturally I don't agree 100% with everything but the
only item really worth mentioning is that on 999 out of 1,000 boats I
never waste time shifting the rudder in the above maneuver as you will
never (if properly done) have enough sternway to have rudder effect.

otn


Goin

otnmbrd wrote:

Good article...... naturally I don't agree 100% with everything but the
only item really worth mentioning is that on 999 out of 1,000 boats I
never waste time shifting the rudder in the above maneuver as you will
never (if properly done) have enough sternway to have rudder effect.

otn

I tend to agree with you, and I don't move the rudder on my own boat.
Several sources I consulted when researching for this article mention
moving the rudder, so that might be considered the "textbook" version
of backing and filling. It certainly won't hurt to move the rudder, and
it could be useful to do so if wind or current creates a situation when
some extended sternway is required to regain the position where the
manuever began.
But I would in general agree with you.

Glad the rest of the item generally passed muster. :-)

"Chuck Gould" wrote in message
oups.com...

otnmbrd wrote:

Good article...... naturally I don't agree 100% with everything but the
only item really worth mentioning is that on 999 out of 1,000 boats I
never waste time shifting the rudder in the above maneuver as you will
never (if properly done) have enough sternway to have rudder effect.

otn

I tend to agree with you, and I don't move the rudder on my own boat.
Several sources I consulted when researching for this article mention
moving the rudder, so that might be considered the "textbook" version
of backing and filling. It certainly won't hurt to move the rudder, and
it could be useful to do so if wind or current creates a situation when
some extended sternway is required to regain the position where the
manuever began.
But I would in general agree with you.

Glad the rest of the item generally passed muster. :-)


I watched in amazement while a very experienced guy backed a 55 foot
sailboat into the slip beside me. I was on the forward deck of my boat,
ready to assist and watched carefully how he set up as he passed my boat and
I took note of his rudder position which was very obvious being so large.
He made a sharp turn to starboard as he passed my bow with the rudder full
over. After the boat settled from the turn (in neutral) , he put it in
reverse and started backing straight towards my port bow .... his rudder
still full over from the previous starboard turn.

Again, he went to neutral, settled the boat (still coming at my bow) then
popped it into forward. The rudder, still being full over, caused his bow
to swing hard again to starboard .... perfectly lined up parallel and
forward of the finger slip. Threw it in reverse for a couple of seconds and
he was done. The boat gently glided into the slip, a foot or so from the
finger. It really was an impressive display of boat handling (most
blowboaters come in bow first) and I told him how impressed I was. He
laughed and told me that he has been doing it for years. He then nodded at
my boat and said, "Those things with the twin engines and rudders are the
ones that confuse me".

Eisboch

I took note of his rudder position which was very obvious being so large.

That makes all the difference. On most sailboats the size of that rudder,
along with hull design, makes them far easier to dock than a powerboat.

Eisboch wrote:
"Chuck Gould" wrote in message
oups.com...

otnmbrd wrote:

Good article...... naturally I don't agree 100% with everything but the
only item really worth mentioning is that on 999 out of 1,000 boats I
never waste time shifting the rudder in the above maneuver as you will
never (if properly done) have enough sternway to have rudder effect.

otn

I tend to agree with you, and I don't move the rudder on my own boat.
Several sources I consulted when researching for this article mention
moving the rudder, so that might be considered the "textbook" version
of backing and filling. It certainly won't hurt to move the rudder, and
it could be useful to do so if wind or current creates a situation when
some extended sternway is required to regain the position where the
manuever began.
But I would in general agree with you.

Glad the rest of the item generally passed muster. :-)


I watched in amazement while a very experienced guy backed a 55 foot
sailboat into the slip beside me. I was on the forward deck of my boat,
ready to assist and watched carefully how he set up as he passed my boat and
I took note of his rudder position which was very obvious being so large.
He made a sharp turn to starboard as he passed my bow with the rudder full
over. After the boat settled from the turn (in neutral) , he put it in
reverse and started backing straight towards my port bow .... his rudder
still full over from the previous starboard turn.

Again, he went to neutral, settled the boat (still coming at my bow) then
popped it into forward. The rudder, still being full over, caused his bow
to swing hard again to starboard .... perfectly lined up parallel and
forward of the finger slip. Threw it in reverse for a couple of seconds and
he was done. The boat gently glided into the slip, a foot or so from the
finger. It really was an impressive display of boat handling (most
blowboaters come in bow first) and I told him how impressed I was. He
laughed and told me that he has been doing it for years. He then nodded at
my boat and said, "Those things with the twin engines and rudders are the
ones that confuse me".

Eisboch

That very experienced guy may find himself stuck in that slip depending
upon winds or currents when he departs. Assuming he has boats, docks,
or floats to either side He's got to get 55 feet out into the fairway
before he can do much except go straight ahead.

Sailboats with a deep keel will tend to pivot around the keel, usually
more toward the middle of the boat than the common "1/3 of the way aft
general location" of a single screw powerboat. They are in general more
maneuverable. Also, many sailboats carry a lot less prop than an
equivalent size powerboat would, so there can be less prop walk. And
some of the "folding props" that sailors use to minimize drag when
under sail are almost useless in reverse....(you have to start putting
the brakes on really early)

On 13 Oct 2006 07:32:58 -0700, "Chuck Gould"
wrote:

That very experienced guy may find himself stuck in that slip depending
upon winds or currents when he departs. Assuming he has boats, docks,
or floats to either side He's got to get 55 feet out into the fairway
before he can do much except go straight ahead.

No difference there between sail or power. My experience has been
that if you can get in, you can also get out.

"Harry Krause" wrote in message
...
On 10/13/2006 11:46 AM, Wayne.B wrote:
On 13 Oct 2006 07:32:58 -0700, "Chuck Gould"
wrote:

That very experienced guy may find himself stuck in that slip depending
upon winds or currents when he departs. Assuming he has boats, docks,
or floats to either side He's got to get 55 feet out into the fairway
before he can do much except go straight ahead.

No difference there between sail or power. My experience has been
that if you can get in, you can also get out.



Good grief. When I was 13, my old man said "go practice on that Century
inboard." It was a 19' or 20' straight inboard, lapstrake boat, with the
damned steering wheel on the side of the hull and rope steering. Low tech.

About an hour later, I could back it into a slip two inches wider on each
side than the boat. I've driven dozens of single screw inboards since,
power and sail, and after a couple of minutes to acclimate myself, I never
had any serious problems "docking" them. It takes less time to practice
and figure them out than it takes to read how to do it.


I'll pass your expertise on to the owner of the 55', 60,000lb sailboat.

Eisboch

"Harry Krause" wrote in message
. ..
On 10/13/2006 2:45 PM, Eisboch wrote:
"Harry Krause" wrote in message
...
On 10/13/2006 11:46 AM, Wayne.B wrote:
On 13 Oct 2006 07:32:58 -0700, "Chuck Gould"
wrote:

That very experienced guy may find himself stuck in that slip
depending
upon winds or currents when he departs. Assuming he has boats, docks,
or floats to either side He's got to get 55 feet out into the fairway
before he can do much except go straight ahead.
No difference there between sail or power. My experience has been
that if you can get in, you can also get out.


Good grief. When I was 13, my old man said "go practice on that Century
inboard." It was a 19' or 20' straight inboard, lapstrake boat, with the
damned steering wheel on the side of the hull and rope steering. Low
tech.

About an hour later, I could back it into a slip two inches wider on
each side than the boat. I've driven dozens of single screw inboards
since, power and sail, and after a couple of minutes to acclimate
myself, I never had any serious problems "docking" them. It takes less
time to practice and figure them out than it takes to read how to do it.


I'll pass your expertise on to the owner of the 55', 60,000lb sailboat.

Eisboch

My sailboat experience stops at around 36'.

Pansy.

"Harry Krause" wrote in message
...
My sailboat experience stops at around 36'.

Pansy.

No doubt, but the only want to learn how to dock a boat is...to dock it.

That be true.

Eisboch