Site considerations
98-175666-A
Chapter 2: Installation
2-6
2.2.3 ADU mast flange and mast length
The system is designed for harsh environmental conditions at sea, both in regards to
vibration amplitude and speed. The antenna system performs optimally when mounted on
a properly designed foundation. When mounting the antenna the overall goal is to establish
a foundation which is as rigid as possible. However, in some scenarios establishing a very
rigid foundation can be difficult. This section aims at defining the minimum design criterion
for the mast. In addition, some specific design suggestions are presented. Note that the
design values given below depend on rigid interfaces between antenna and ship, the values
are furthermore given based on a standard steel type (e.g. S235JR, S355JO).
The placement of the ADU must ensure a rigid structural connection to the hull or structure
of the ship. Parts of the ship with heavy resonant vibrations are not suitable places for the
ADU. A small platform or short mast must provide rigid support for the ADU fastening bolts
and a rigid interface to the ship. If it is necessary to use a tall mast, you must stabilize the
mast with bracing. In regards to stiffness the overall criterion is that the first structural
mode of the mast or foundation (where the antenna system is mounted) should be above
30 Hz. All the designs presented in the following sections respect this standard.
The ADU mast must carry the weight of the ADU unit, that is approximately105 kg (+ the
weight of the mast flange) for the 100 cm antenna, and 37 kg (+ the weight of the mast
flange) for the 60 cm antenna. The mast must also withstand on-board vibrations and wind
speeds up to 110 knots on the radome, even in icing conditions.
Figure 2-4: Blocking zone with no-transmit zones, elevation angle (example)
Important
An antenna mounted on a less stiff structure might be functional, but
could lead to a decrease in the operational lifetime of the antenna
system and possibly a decreased performance under operation
CAUTION!
Avoid sharp edges where the flange is in direct contact with the
radome. Round all edges as much as possible to avoid
damaging the surface of the radome.
