Iridium Pilot Installation Manual page 20

These factors will be discussed in the following paragraphs. The mounting bracket and pole must be capable
of supporting the weight of the unit. Consideration should also be given to accessibility for installation and
service work, and the task of lifting and supporting the size and weight of the equipment safely whilst all the
connections are being made. The mounting bracket and pole must be capable of supporting the lateral loads
caused by the wind. For example at 60 mph the lateral force on the ADE alone (ie. excluding the pole) will be
approximately 3.5-4.5 kgf. This load will generate shearing and bending forces in the mounting bracket and
pole which must be distributed safely into the vessel's structure. Since this loading will vary continuously with
time, the structure must not only withstand the static loading but also the fatigue loading over the lifetime of
installation.
When selecting a suitable mounting pole it is important to consider resonance as well as strength. The ADE will
be subject to vibrations caused by oscillating aerodynamic forces due to vortex shedding from the ADE itself
(in the range 0 – 10 Hz for wind speeds up to 60 mph, or storm force 10), and any upstream objects even if they
are outside the zone shown in figure 7.
The ADE will also be subject to vibrations transmitted through the vessel's structure (from engines, propellers,
motorized equipment, cable stays or guy ropes). Careful consideration must therefore be given to minimize the
potential for vibration causing damage to the ADE, by careful choice of the mounting position, pole diameter,
pole length, and any necessary supporting structure. If necessary modify the design of the mounting pole to
move its natural frequency (with ADE fitted) away from the frequency of the source of vibration. For example,
increasing the stiffness of the mounting pole will increase its natural frequency – this might be achieved by
using a shorter or thicker pole, but note that adding mass will have the contrary effect of reducing the natural
frequency. If the pole cannot be shortened, then consider adding rigid support struts or tensioned guy ropes
to reduce the effective length. The following guidelines are recommended:
• Minimum pole diameter: D = 60.3 mm (2.38 in.)
• Minimum wall thickness: t = 3.2 mm (.125 in.)
• Maximum unsupported pole length, L = 2.0 m (6.6 ft)
For 100 mph winds (hurricane force 12) the unsupported length should be reduced to 1.0 m (3.3 ft.). Longer
poles are possible if additional support is provided such as guy ropes. More sophisticated mounting designs
may be necessary to deal with vibrations in some installations. The design of vibration reducing or absorbent
mountings is critically dependent on many installation specific factors that are well outside the scope of this
manual. Hence for any such an installation, consult specialist suppliers of marine antenna mountings, to obtain
professional advice.
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Iridium Pilot™ Installation Guide
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