Furuno FV-110GX Operator's Manual page 34

Site preparation
Mast length and diameter
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-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.
Make sure that there is free space below the drain tube. See
Note
also Condensation, water intrusion and deposits on page 2-
16.
The tables in the next sections give suggested design values for the free mast length.
The tables list the values for steel masts. For aluminium
Note
masts, the free mast length is reduced to 75% of the values
for steel.
Bracing and rigid masts can still not prevent vertical vibration
Note
if the mast is attached to a deck plate that is not rigid. Make
every effort to mount the mast on a surface that is well
supported by ribs. If this is not possible, provide extra deck
plate propping.
The following tables show the minimum dimensions for a ADU mast with and without
stays or wires. Note that the values are only guidelines - always consider the environment
and characteristics of the ship before deciding on the mast dimensions.
2-10
Figure 2-10: Free mast length and bracing for a tall mast