Site preparation
98-166784-A
Chapter 3: Installation
3-7
3333
Install
ation
3.2.6
ADU mast design: Mast foundation and height
The antenna 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 is difficult and inappropriate. This section aims at defining the
minimum design criterion for the mast. In addition, some specific design suggestions are
presented. In order to keep the presented designs to a manageable size only a sample of
design suggestions is 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 shall 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 stabilise the mast with bracing. Note that the
design values given below depend on rigid ADU-to-ship interfaces. The cross-sectional
properties and the corresponding maximum free length give a natural frequency close to
30 Hz. Shorten the mast length as much as possible to obtain higher frequencies. Preferably,
mount stays or wires to stabilize the mast further.
The ADU mast must be designed to carry the weight of the ADU (38 kg), plus the weight of
the mast flange. The mast must also be able to withstand on-board vibrations and wind
speeds up to 110 knots on the radome, even in icing conditions.
Follow the guidelines in the sections:
•
•
ADU mast flange
For best performance provide a mast flange with a minimum of four gusset plates. To
prepare the mast flange do as follows:
1. Fit the top of the ADU mast with a flange with clearance holes matching the bushings in
the radome and with minimum 4 gusset plates. No center hole is necessary in the flange.
•
Flange thickness
: Minimum 5 mm.
•
4 gusset plates
: Minimum 5 mm thick, must be placed as close as possible to the
holes in the mounting plate and evenly distributed.
Important
An antenna mounted on a less stiff structure might be functional, however,
this could lead to a decrease in the operational lifetime of the antenna system
and possibly a decreased performance under operation.
