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Taisei Engineering Consultants, Inc.
Tokyo Japan
When many
barges are operated in a short route of service, such as lighterage
service, the conventional rope-towing is used as a common practice in most
cases. But, in such a service, introduction of the pushing system,
particularly mechanically connected one, can improve the operational
efficiency remarkably through raising the running speed and saving the
time needed for berthing, unberthing and exchanging barges, and, at the
same time, the safety of operation is likewise improved.
The merits of pushing over towing can be easily understood from the
comparison stated below.
Pushing versus Towing
 (a) The pusher-barge combination is much shorter in length than
the tug-barge train towing by a rope. This shortness means a higher
safety.
(b) The pusher-barge combination can stop itself by its own power,
while the towed barge has no power to stop itself.
(c) The pusher-barge combination can choose its running course by its
own power, while the towed barge cannot do it. The combination of (b) and
(c) above assures a much higher safety and a much better maneuverability
of the pusher-barge combination.
(d) As a result of (b) and (c) above, the pusher-barge combination can
berth and unberth itself by its own power in a short time. As is well
known, berthing and unberthing of a towed barge requires much longer time
and troublesome works.
(e) The speed of a pusher-barge combination is higher than that of a
towed barge when the deadweight and engine power are the same.
(f) The pusher-barge combination has a better course-keeping quality
than the towed barge which often swings to the left and right when being
towed. This is because the pusher hull connected at the stern of the barge
functions as an enormous skeg for keeping straight course of the barge.
(g) When several barges must be operated alternately in a short route,
the time needed for exchanging barges is very important. Exchange of towed
barges will need 20-30 minutes, while a pusher having a mechanical coupler
needs 30-40 seconds only for disconnection and connection respectively and
the exchange of barges can be finished in several minutes. This difference
has a considerable influence on the available number of services per day.
(h) Small barges often have rudders and, accordingly, need helmsmen on
board. Most bigger barges have no rudder and, accordingly, are very
difficult in maneuvering. On the contrary, the maneuverability of a
pusher-barge combination is same as that of a conventional self-propelled
ship.
There are two types of connection in pusher-barge combinations -
rope-connection and mechanical connection. The merits of the latter over
the former are easily understood from the comparison stated below.
Mechanical Connection versus Rope-Connection
(a) The seaworthiness in wavy sea of the rope-connected pusher-barge
combination with the most advanced method of connection has an absolute
limit, while the mechanically connected pusher-barge combination can be
designed and constructed for unrestricted service if so desired. In
sheltered waters a fairly simple method of mechanical connection can be
applied to assure a satisfactory performance.
(b) The rope-connected pusher-barge combination requires 5-8 crew
members and 10-20 minutes of long time for connection, and even the
disconnection requires similar number of crew and 5-15 minutes of time.
The work of connection and disconnection is muscle work to be carried out
even in rainstorm on the slippery wet deck. Particularly when a pusher is
required to operate several barges alternately in a short route, the long
time needed for connection and disconnection for repeated exchange of
barges is a big problem affecting the available number of services per day
and, in addition, an increased number of crew members may be required for
efficient exchange of barges.
In mechanically connected pusher-barge combination, connection and
disconnection are affected in 30-40 seconds only by the captain's
remote-control from the bridge.
(c) In the rope-connected push barge combination, crew members must go
to the barge for handling ropes before connection and return from the
barge after handling ropes after disconnection, even when the pusher is
oscillating due to waves.
In the mechanical combination, connection and disconnection are
effected one-sidedly from the pusher and crew members have no need of
going to the barge.
(d) The inevitable looseness in connection of the rope-connected push
barge combination permits angular deviation (loss of coincidence of
centerlines) of the pusher and barge, and this phenomenon occurring at the
first stage of steering will cause delay of response of the barge to
steering of the pusher. In other words, the pusher deviates first relative
to the barge and, thereafter, turning the barge begins.
In the mechanically connected P/B combination, such a delay of response
does not occur and the motion of the combination is same as that of a
self-propelled ship.
As may be clear from the above statement, the operational efficiency of
the pusher-barge combination, particularly mechanically connected one, is
so high as compared with that of rope towing that the additional cost for
the introduction of pushing system can be recovered in a short time.
Classification of Systems
Taisei Engineering's mechanical couplers for sea-going pusher-barge
systems are classified into two main categories --- 2-Pin supported
articulate connection, Series ARTICOUPLE, permitting free relative
pitching and 3-Pin supported rigid connection, Series TRIOFIX, not
permitting any relative motion, as follows:
2-Pin Supported Articulate Connection:
ARTICOUPLE: K
Multi-step tooth-engagement,
FR Combined friction- and
tooth-engagement,
F Stepless pure friction engagement.
3-Pin Supported Rigid Connection:
TRIFIX TK Multi-step
tooth-engagement (bigger units),
TR Multi-step tooth-engagement
(smaller units),
TRF Combined friction- and
tooth-engagement.
Each of these types is designed to realize connection practically at
any point within the connectable range of draught relationship of the
pusher boat and the barge. Further, for simple cases that connection is
needed at one point or two points, or even three points, there are much
simpler couplers of Series Articouple B or Triofix TB.
The ARTICOUPLE coupler for 2-point supported articulate connection is
simpler in construction and the wave-excited load acting on the coupler is
generally smaller, and, as  the result, the cost is lower. However, it permits
free pitching of the pusher relative to the barge and, accordingly, needs
some wider clearance between their hulls to avoid hitting of the pusher's
stem against the wall of the stern notch of the barge. This wide clearance
causes heavy eddies which will increase resistance and affect the running
speed seriously. The generation of eddies in the barge stern is the very
reason why the speed of a pusher-barge train is unexceptionally lower than
the speed of a conventional ship of same loading and same engine power. In
addition, the pusher swung by the oscillating barge is subjected to heavy
pitching and, as the result, the articulately connected pusher cannot be a
ship comfortable to the crew on board.
On the contrary, the rigid connection by Triofix 3-point supporting
coupler does not permit any relative motion of the pusher and the
clearance between two hulls can be reduced to the minimum to lower the
eddy resistance remarkably. Therefore, the 3-pin supported rigid
connection involves a possibility of getting a much higher propulsive
performance - speed - than the 2-pin supported articulate connection, and
this is a important particularly when higher speed is desired in longer
routes. further, absence of relative pitching assures same comfortableness
to the crew on board as a conventional self-propelled ship. But, on the
other hand, the TRIOFIX-coupler has a greater number of components and the
wave-excited load acting on the coupler is generally larger and, as the
result, the cost is somewhat higher.
In addition, the barge with rigidly connected pusher must have a
greater longitudinal strength than a barge with articulately connected
pusher, because the former, in combination with the pusher, will move as a
single body in waves.
Thus, the rigidly connected pusher-barge train having a better
operational performance is somewhat more expensive in building cost
inevitably. But, if an excellent propulsive performance can be realized
through adopting good hull forms, the engine power required for getting a
same speed can be reduced or a higher speed can be got with the same
engine power, and such an excess performance is often more than sufficient
to cover the difference of the building cost.
When running in waves, the characters of wave-excited loads are much
different between 2-pin supported articulate connection and 3-pin
supported rigid connection - - the longitudinal load component is largest
in the former, while the vertical component is largest in the latter, and
the coupler constructions should be adapted to such characters of these
primary load components.
Further, the coupler load varies with the longitudinal position of the
coupler main bodies on the pusher hull. In 2-point supported articulate
connection, if the coupler position is moved aft to get near amidships,
the longitudinal load component will decrease and the vertical component
will increase, and the pitching angle will increase as the coupler
position approaches amidships - - nearer to the center of gravity.
Therefore, 100% advantage is not probable. In 3-pin supported rigid
connection, somewhat similar variation of coupler loads occurs.
Types having friction-components, having names with 'F', can permit
'Draught-adjustment' during cargo-handling work so that the draught of the
pusher boat can be adjusted, manually or automatically, while the draught
of the barge gradually changes due to loading or unloading and the pusher
boat can remain connected while cargo-handling. These couplers with F can
also be used for operating dumping barges, bottom-door dumping or
split-dumping, which will change draught abruptly when dumping load, while
the pusher can be kept connected to the barge.
One of the great merits of the friction-connection consists in the fact
that the connection is 'stepless', different from multi-step
tooth-engagement connection. Utilizing this merit, these couplers with 'F'
can realize connection under influence of waves of a certain height. The
first contact of friction components stops vertical motion of pusher
relative to the barge. In Articouple F-coupler, this friction-connection
becomes the final connection, and in Articouple FR- and Triofix
TRF-couplers, it becomes the provisional or preparatory connection, and,
then, transition to the next final combined friction- and tooth-engagement
connection will take place under automatic control.
For simple transport services among sheltered harbors, it is
recommended to use types without 'F' (friction component) because the
models with 'F' have, as their vital components, 'Pressing shoes'
with high-friction rubber lining which needs periodical replacement at
intervals of 2-7 years, depending on the roughness of use, and this
replacement needs high-grade technique and a certain cost. Couplers
without 'F' have no parts needing such a periodical replacement, while the
pusher boat must be kept disconnected during cargo-handling in
harbors.
2-Point Supporting Articulate Couplers
The 2-point supporting articulate couplers, Articouple, are classified
into the three series - - K, FR, and F.
 The type Articouple-K of pure multi-step tooth-engagement
principle, having practically no wearing parts, is a reliable coupler
system particularly suitable for large sizes and services in rough sea.
For connection and disconnection, Articouple-K is remote controlled by the
captain's finger-tip from the bridge and accordingly, no muscle work is
needed. These functions need about 30 seconds only. Connection by
Articouple-K can take place without difficulty even when a slight relative
heel is found between the pusher and barge or the pusher is slightly
oscillated by waves. Articouple-K contains practically no wearing parts
needing periodic replacement. When converting a harbor tug by addition of
an Articouple-KD coupler, the coupler main bodies installed at deck sides
just abaft the windlass will not cause any change of the bow contour so
that the function of the boat as a tug can be maintained even after
conversion.
 The
type Articouple-F of pure friction engagement principle might, at the
glance, seem quite insufficient in seaworthiness. In practice, however,
this type can generally assure safe navigation up to a wave height of
about 3 meters, or somewhat higher. The seaworthiness of small F-couplers
is particularly good. The best merit of Articouple F-coupler is the
simplest process of connection that it is possible at the point of the
first contact of pressing shoes to the barge. The F-coupler was first
developed primarily for operating dumping barges and, now, it is employed
also for ordinary cargo transport in bays, harbors and similar
comparatively calm waters because of its fairly good seaworthiness.
Articouple-F series are classified into two sub-series, deck-mountable
FD-Series for small foc'stles and side mountable FC-Series for medium and
large sided pushers with long foc'stles.
The type Articouple-FR of combined friction- and tooth-engagement
principle is widely used when the dumping barge must run in rough area or
when the owner prefers a coupler capable of automatic draught adjustment
during cargo-handling, though its maintenance cost is somewhat higher
because of the need of periodical renewal of rubber lining. 
3 Point Supporting Rigid Connection Couplers
The 3-point supporting rigid connection couplers, Triofix, are
classified into three services - TK, TR and TRF.
The type K used the Articouple K-coupler as the side coupler units and
a simple wedge-shaped unit is the bow coupler. The type Triofix- TK is a
reliable coupler system particularly suitable for large sizes and services
in rough sea.
In the type Triofix-TR, all the side and bow coupler units are simple
wedge-shaped units, and the manner of handling the longitudinal load is
different from other types. The TR-coupler is simple and cheap in cost,
but is not suitable for larger coupler.
The type Triofix-TRF is combined friction and tooth-engagement
principle and its side coupler units may seem similar to Articouple-FR.
But the arrangement of the main structure carrying the primary load
component - vertical load - is different. The construction of the side
coupler of Triofix TRF-series is fairly complicated while the bow coupler
units is of simple wedge-shaped type same as the bow coupler of
TRIOFIX-TK. TRF-couplers are used in operation of the dumping barges when
higher speed is desired for long-distance run in rough sea, and also for
ordinary cargo transport when the owner wants to have the performance of
automatic draught adjustment during cargo-handling.
The couplers with friction components, having names with 'F', have some
limits to their realizable sizes. Articouple-K and Triofix-TK series of
pure tooth-engagement principle have no such limit of size, and they are
the most reliable couplers suitable for big sizes applied to long-distance
services in rough sea.
Selection of Coupler Model
 As
for the navigability in rough sea, the rigid connection with
Triofix-coupler might, at a glance, seem superior to the articulate
connection with Articouple coupler. In practice, however, these two series
can realize a same level of seaworthiness if the model is properly
selected on the basis of reliable analysis of coupler loads and the pusher
boat and the barge are properly designed.
As may be obvious from the above explanations, Taisei Engineering's
Articouple and Triofix can cover all probable types of needs for the
pusher-barge systems, and the above-mentioned various models were
developed for the purpose of complying with multifarious types and modes
of demands.
The coupler model should be selected to suit to the character and use
of the barge and, then, to keep necessary navigability in the probable
heaviest sea state expected in the service routes or areas intended.
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