Furuno FELCOM251, Installation Manual

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2. INSTALLING THE SYSTEM
2-9
Mast length and diameter
The placement of the antenna 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 antenna.
A small platform or short mast shall provide rigid support for the antenna fastening
bolts and a rigid interface to the ship.
If it is necessary to use a tall mast, use the tables on page 2-10 and page 2-11 to ob-
tain the maximum free length of the mast. Note that these values depend on rigid an-
tenna-ship interfaces. The cross-sectional properties and the corresponding
maximum free length give a natural frequency above 30 Hz.
It is recommended to shorten the mast length as much as possible to obtain higher
frequencies. Alternatively, mount stays or wires to stabilize the mast further.
Note: Make sure that there is free space below the drain tube of the FB-1501.
Make sure there is free space below the drainage hole in the bottom centre of the FEL-
COM251 Antenna Unit.
Please refer to "Condensation" on page 2-17.
The tables in the next sections give some suggested design values for the free part of
the mast (shown on this page).
Note: The tables list the values for steel masts . For aluminium masts , the free mast
length is reduced to 75% of the values for steel.
FB-1501
Drain Tube
OD (mm)
Free mast length (m)