The reader will now be aware that the stability of the vessel depends on the righting moment
which can be varied either by changing the GZ or the displacement. A change in either of these
can also affect the rolling period of the ship and some notes on this follow.
Wave period is the time in seconds between successive crests, or troughs, passing a fixed point.
Apparent wave period is the time in seconds between successive crests or troughs, passing an
observer on board ship.
Ship’s period is the time in seconds taken by a vessel doing a complete roll (e.g. Port-Starboard
- Port). This is denoted by TR.
A dangerous state of affairs can arise if the ship’s still water period and the apparent wave
period are equal. This is known as Synchronism and, if allowed to continue, it could capsize a
vessel.
It should be noted that the movement of a vessel when rolling is similar to that of a pendulum,
this being so, an expression can be formed for the vessel’s period when in still water as follows:
The reader will now be aware that the stability of the vessel depends on the righting momentwhich can be varied either by changing the GZ or the displacement. A change in either of thesecan also affect the rolling period of the ship and some notes on this follow.Wave period is the time in seconds between successive crests, or troughs, passing a fixed point.Apparent wave period is the time in seconds between successive crests or troughs, passing anobserver on board ship.Ship’s period is the time in seconds taken by a vessel doing a complete roll (e.g. Port-Starboard- Port). This is denoted by TR.A dangerous state of affairs can arise if the ship’s still water period and the apparent waveperiod are equal. This is known as Synchronism and, if allowed to continue, it could capsize avessel.It should be noted that the movement of a vessel when rolling is similar to that of a pendulum,this being so, an expression can be formed for the vessel’s period when in still water as follows:
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