3 October 2005
PASSING SHIP EFFECTS ON MOORED SHIPS
INTRODUCTION. A ship moving through the water generates several
types of waves that may have an effect on moored ships, structures, shoreline erosion,
etc. One type of wave generated is a long-period pressure wave that may be very
small. However, this long wave (together with Bernoulli effects) may have a major
influence on moored ships.
PASSING SHIP EFFECTS ON MOORED SHIPS. A ship navigating in a
harbor or channel can produce major forces/moments on a nearby moored ship. The
moored ship is forced through a combination of wave, long-wave and Bernoulli effects
(NFESC TR-6027-OCN). NSTB Marine Accident Report, PB91-916404, NSTB/MAR-
91/04, for example, discusses a case where a nearby passing ship caused a moored
tanker to break its mooring and fuel lines. The resulting fire caused loss of life, in
addition to total loss of the pier and tanker.
The forces and moments acting on the moored ship depend upon a great
number of parameters including, relative size of the two ships, water depth, as well as
passing ship speed and separation from the moored ship. Figure 9-1 shows an
example passing ship case for parallel ships. This figure shows that the forces and
moments acting on the moored ship are highly time-dependant. Therefore, dynamic
programs, such as AQWA DRIFT (Century Dynamics, Houston, TX), are used to
determine the response of the moored ship to the passing ship.
Parallel passing ships are discussed in detail in NFESC TR-6027-OCN. An
associated spreadsheet PASS-MOOR.XLS is available that aids in predicting passing
ship forces and moments. Figure 9-2 illustrates example predictions. These examples
show that peak forces and moments applied to the moored ship in various degrees of
freedom occur at different times and highly dynamic.
A study is now underway (2004) at the U.S. Naval Academy to further refine
predictions of forces and moments on moored ships due to passing ships.
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