Tips on Thruster Installation
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Thrustmaster tunnel thrusters are easy to install. The
whole unit has already been installed in a section of tunnel
and all you need to do is install this section of tunnel in the
hull.
With hydraulic tunnel thrusters, orientation is not critical.
You can direct the strut opening straight upward, down,
fore, aft, or at any angle that optimizes the hydraulic piping
layout. With engine or electric drive thrusters,
the lube oil vent port to the head tank should be as high as
practical.
The tunnel length can be extended by butt-welding pipe of
the same material, diameter, and wall thickness to the ends of
the standard three-foot tunnel section of the thruster.
As an alternative, order your thruster with extended tunnel length
(specify total tunnel length with your order) to save time and
money during installation.
When adding a tunnel thruster to an existing vessel, cut tunnel
openings in the hull plating and longitudinal bulkhead (if any)
and slide the thruster into the hull from one side until it is
in the desired position. Weld the tunnel ends to the hull
plating or fairing pieces and weld the tunnel to longitudinal
structural members so that the tunnel becomes an integral part
of the vessel structure.
Proper submergence of the tunnel entrance is necessary to
prevent vortexing and air entrainment. When air is entrained
in the tunnel flow during operation, the thruster will cavitate,
resulting in excessive noise, vibration, substantial reduction
of thrust output and possible damage to the thruster. As
a minimum, the top of the tunnel must be one tunnel diameter
(1D) below the minimum light draft waterline of the vessel.
If two or more tunnel thrusters are installed in tandem, the
center of each tunnel should be two times the tunnel diameter
(2D) apart (see Fig. 1 below).
Figure 1: Typical
tunnel thruster location
Tunnel thrusters for bow and stern maneuvering applications
should be installed as far forward or aft in the vessel as possible.
This increases the effective turning moment lever arm around
the vessel's natural center of rotation. It is generally
recommended that the propeller be placed near the ship's centerline
so that equal thrust is available to port and starboard (see
Fig. 2 below).
Figure 2: Typical tunnel thruster
placement
For maximum thrust production, fairing of the tunnel entrances
with the hull shell plating is strongly recommended. Fairing
the tunnel with the shell plating will substantially improve
the thruster's efficiency. The recommended tunnel entrance
fairing is chamfered. Chamfer fairing should be 45 degrees
and ten percent of the tunnel diameter (0.1D). (see Fig.
3 below).
Figure 3: Typical tunnel fairing
chamfer
In addition to fairing the tunnel entrances for thruster performance
improvement, the tunnel entrances may be faired back conically
to reduce drag or hull resistance (see Fig. 4 below).
Figure 4: Typical conical hull
fairing
Inlet grids are generally not required on hydraulic tunnel
thrusters. The torque limiting hydraulic drive design and
low rotation of inertia of hydraulic tunnel thrusters allow them
to be stalled without damage. The absence of inlet grids
allows easy access to the propeller for inspection and removal
of debris. However, if frequent operation in waters with
substantial floating debris is anticipated, inlet grids are recommended.
Grids are also recommended if the thruster may be used in waters
where swimmers or divers are present. Depending on tunnel
size, use two to four grid bars evenly spaced at both tunnel
entries. Grid bars should be made of flat bar with round
edges and spaced with round bar (see Fig. 5 below).
Figure 5: Typical tunnel entrance
grate
The flat bar should be aligned parallel to the predominant
water flow direction generated by vessel bow wave for least resistance,
typically about 15 degrees (see Fig. 6 below).
Figure 6: Typical tunnel grid
installation
The tunnel section provided with the thruster may be extended
by butt-welding to pipe of compatible material. After
welding in place, the tunnel inside wall must be sand blasted
and painted with a suitable marine coating system to prevent
corrosion. Please note that the inside of the tunnel has
been provided with a special ceramic coating to prevent erosion
by entrained particulates such as sand and silt. Pay special
attention to sand blasting to prevent removal of this coating.
Do not aim the sand-blasting stream towards the propeller shaft
seal of the thruster.
If sacrificial anodes are used, they should be Mil-Spec MIL-A-18001
for zinc anodes, Canada Metals or equal. These type anodes
contain additional cadmium (~0.1%), which causes the anode to
erode from the surface inward, giving a sand blasted appearance
to the surface as the anode is consumed. When the anode
is ten percent or less than its original size, it should be replaced.
If anodes are installed, they must be placed in the tunnel lengthwise.
Anode cross section should not exceed 1 by 2 inches (25 by 50
millimeters).
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