Site preparation
3-10
Chapter 3: Installation
98-146706-A
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.
The tables in the next sections give suggested design values for the free mast length.
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.
Figure 3-10: Free mast length and bracing for a tall mast
Note
Make sure that there is free space below the drain tube. See
also
Condensation, water intrusion and deposits
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.
Note
Bracing and rigid masts can still not prevent vertical vibration 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.
Free
m
a
st
le
n
g
th
(m)
SAILOR900Ka-IM-98-146706.book Page 10 Thursday, July 16, 2015 11:07 AM
