more than a tug. voith water tractor
TRANSCRIPT
II
More than a Tug.Voith Water Tractor
2
3
This concept has revolutionized ship-handling worldwide.
More than 900 Voith Water Tractors in more than 200 ports
are the hallmark of safety today. Reliability, speed and preci-
sion in towing and escorting service, salvaging, fi refi ghting,
oil pollution control and offshore supply have led to the
classifi cation: “Best Available Technology!”
Voith Water Tractor (VWT) Best Available Technology
Voith Water Tractor means: Logical correlation of the main systems –
propellers with all-round protection, towing gear, skeg and integrated
control station – for all duties in the wide fi eld of ship handling.
4
The task of the ship-handling vessel is to bring the tow to its
destination:
• Rapidly and by the shortest route.
• With minimum power requirements but with optimal
utilization of the installed power.
• While ensuring maximum safety for the tow, the tug,
the crew and the port facilities.
Design Criteria.
For the successful performance of this task the ship-handling
vessel must satisfy the following requirements:
• Fast and safe takeover of lines, even at high speeds
outside protected harbor waters, in adverse wind
conditions, swell and currents.
• Immediate function after taking over the lines, with
active braking and steering to ensure a smooth transition
from free movement of the incoming vessel to the towing
operation.
• Substitution of the tow’s own controls in the event of
rudder and/or engine failure.
• Continuous transmission of forces with no long delays
while the tug changes position in relation to the tow.
• Maximum maneuverability to facilitate operation in
restricted spaces with very quick and precise changes
in position.
Ship handling is an important link between
overland and waterborne transportation to
ensure fast, smooth traffi c fl ows.
5
The VWT is driven and controlled by the Voith Schneider
Propeller (VSP), which integrates propulsion, steering and
optionally active roll damping of the Voith Water Tractor into a
single system. The VSP sets outstanding standards of propul-
sion efficiency and precise maneuvering at extremely high
safety levels.
• Swift, sensitive, stepless thrust variation in direction
and magnitude, independent of the VWT’s speed.
• Thrust variation according to X-Y coordinates.
• Easily controlled, redundant steering, logically
related to VWT movement.
• Robust, slow-running marine engineering using
top-quality materials.
• High degree of resistance to external stresses in
rough ship-handling operations and extremely long
service life.
Features of the Voith Water Tractor
6
5
4
3
6
2
1
The logical arrangement of the basic components
1. The VSP is located in the forebody, with
free infl ow and outfl ow in all directions.
The thrust forces act ahead of the vessel‘s
axis of rotation.
2. Fitted underneath the propellers is a pro-
peller thrust guard that exerts a nozzle
effect and increases propeller thrust.
It also protects the propeller blades against
running aground and supports the vessel
in dock.
3. The hull is an integrated part of the system,
creating lift for the indirect steering principle
and ensuring low resistance in transit.
4. Located underneath the aft body is an
effective skeg for steering and braking
assistance of the tow, shaped to create
lifting force. The skeg shifts the center of
lateral resistance aft, thus increasing lever-
age between propeller thrust and pivot
point. It also ensures adequate course
stability when running either bow or skeg
fi rst.
5. The towing gear (staple and winch)
is located aft of the vessel’s center of
rotation.
6. The VWT is operated from the control
stand in the wheelhouse. One or several
synchronized control stands, depending
on the size of the vessel, can be installed.
There are two key control options:
– mechanical control
– electronic control
The mechanical control is a well-recognized
reliable system based on mechanical linkages.
The electronic control is designed
fully redundant. It allows Dynamic Position-
ing, combinator control for optimum fuel
effi ciency and/or active roll damping.
7
Control of the Voith Water Tractor is direct. The direction of
the steering force coincides with the desired direction of
movement, since the steering forces act ahead of the vessel’s
axis of rotation. This form of control results in the smallest
possible turning circle, i.e. on the spot.
The direction of the tug’s movement is the same as the move-
ment made at the control stand. This enables the tug master
to devote undivided attention to the tow-handling operation.
Changes in position are extremely quick and precise due to
the unrivalled steering times of the Voith Schneider Propeller.
This allows more time for effective work and keeps the tow
under more effective control.
Since the Voith Schneider Propeller is driven at a constant
engine speed due to its controllable pitch characteristic, it is
possible to use the free fl ywheels of the main engines to drive
auxiliary units such as fi refi ght-ing pumps.
The Voith Water Tractor remains fully operational when fi re-
fi ghting even with a fi re-pump capacity of more than 70% of
the rated engine power.
The Voith Water Tractor can also be used in a similar way as
an oil pollution control vessel, or in combination.
Excellent Maneuverability
8
21
Taking over lines without risk at high speed.As soon as the forces deviate from the VWT’s longitudinal
direction, they create a reversing torque about the vertical axis.
The tractor turns its longitudinal axis in the direction of the
towline before the vessel reaches a critical heeling movement.
In other words, even without the assistance of thrust, the
vessel stabilizes itself.
This eliminates a major risk normally associated with ship-
handling. Thanks to this principle, ship-handling maneuvers
can be performed far more safely, directly and smoothly. Voith
can offer pure mechanical control or electronic control. Con-
trol elements are logically arranged. No mental reorientation of
the helmsman at change over from one working direction to
another.
Taking over lines between an in-coming vessel and a tug in-
volves considerable risk. The procedure frequently takes place
at a relatively high speed and the tug has to come very close
to the vessel that is to be handled.
Safety
The Voith Water Tractor concept averts the risk of capsizing, which is
a constant fear with any stern-driven tug when working with a towline.
The steering force (propeller thrust) acts ahead, and the towline force
always astern of the vessel’s pivot point.
9
43
In particular at the bow of the in-coming vessel, the tugboat
passes through a negative pressure fi eld which, in addition to
other external forces such as wind and current, can cause
a collision or lead to the tug being overrun by the tow. This
risk is minimized by the Voith Water Tractor. Full power is avail-
able instantly for a steering maneuver thanks to the Voith
Schneider Propeller propulsion at the forward end of the tug,
enabling the VWT to free itself from such critical situations.
The sensitive thrust control provided by the Voith Schneider
propulsion system allows the tractor to keep close to the
vessel being assisted, thus permitting safe and rapid transfer
of the line.
10
“Butterfl y” diagram for Voith Water Tractor escort “Direct” and “indirect” methods
Ajax, Ostenjsjö Reederi A/S, Norway
Contemporary ship-handling operations cover the entire
speed range from the vessel at rest to the tug’s free-running
speed. In stationary operation, the “direct” method of working
is used.
In this mode, engine power generates the necessary forces
through the propulsion system. In dynamic operation, the
“indirect” working method is applied. In this mode the hydro-
dynamic force of the hull is utilized.
There is a smooth transition between the “direct” and “indirect”
methods. The Voith Water Tractor performs this transition
continuously and without risk.
A further improvement is possible without undue complexity
by installing the Voith Turbo Fin (VTF), a rotating tube at the
leading edge of the skeg. The VTF exerts a specifi c boundary
layer infl uence on the fl ow acting on the ship’s hull and gener-
ates a considerable increase in lift. With VTF installed, steering
forces can be increased by 18 - 20 %. Escort forces of up to
two times of static bollard pull have been certifi ed by all major
classifi cation societies.
Dynamic Ship Assistance and Escort Work
Forces, longitudinal [t]
Fo
rces,
tran
svers
e [
t] -160 -120 -80 -40 0 40 80 120 160
100
50
0-50
-100
-150
-200
–––– At speed = 0 kn
–––– At speed = 2 kn
–––– At speed = 4 kn
–––– At speed = 5 kn
–––– At speed = 6 kn
–––– At speed = 8 kn
–––– At speed = 10 kn
Direct ~ 0 - 5 kn Indirect ~ 3 - 10 kn
With VWT double static bollard pull in escort mode possible.
11
The Voith Water Tractor with its unique capabilities can be a
key element of the complex safety system of any port.
The VWT’s superior dynamic ship-handling characteristics
reduce expenditure on shore-side facilities, such as break-
water extensions and channel dredging.
The VWT fl eet increases and maintains the existing traffi c
density and permits an approach to harbor in poor weather
conditions at all ports that serve merchant vessels.
Economy and Environmental Protection
Most damage to vessels occurs in bad weather conditions.
In such poor operating conditions, it is essential for effective
ship assistance to be available. Protection of human life,
awareness of environmental protection needs and ship handling
in an emergency are some of the critical tasks that must be
accomplished by marine support facilities.
This is possible with the VWT because precise thrust control
is available from the Voith Schneider Propeller to counteract
external forces with no delay and minimal risk.
Voith Turbo Schneider
Propulsion GmbH & Co. KG
Alexanderstraße 18
89510 Heidenheim, Germany
Tel. + 49 7321 37-4099
Fax + 49 7321 37-7105
voith.com
G 1
81
0 e
n
ak/S
VG
1
00
0
20
14
-06
S
ub
ject
to m
od
ific
atio
n d
ue t
o t
ech
nic
al d
evelo
pm
en
t.