Site preparation
2-10
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. It is recommended to 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 some suggested design values for the free mast length.
Figure 2-10: Free mast length and bracing for a tall mast
Make sure that there is free space below the drain tube. Read
also Condensation and water intrusion on page 2-17.
The tables list the values for steel masts. For aluminium
masts, the free mast length is reduced to 75% of the values
for steel.
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 mast length (m)
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