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TRANSIT FROM ONE LOCATION TO ANOTHER
The Transit Mode occurs when a Jack Up Unit is to be
transported from one location to another. Transit can occur either
afloat on the Jack Up Unit’s own hull (wet tow), or with the Jack
Up Unit as cargo on the deck of another vessel (dry tow).
Main preparations for each Transit Mode address support
of the legs, support of the hull, watertight integrity of the unit, and
stowage of cargo and equipment to prevent shifting due to
motions. Though the Unit’s legs must be raised to ensure they
clear the seabed during tow, it is not required that the legs be fully
retracted. Allowing part of the legs to be lower than the hull
baseline not only reduces jacking time, but it also reduces leg
inertia loads due to tow motions and increases stability due to
decreased wind overturning. Lowering the legs a small distance
may also improve the hydrodynamic flow around the open leg
wells and reduce tow resistance. Whatever the position of the legs
during tow, their structure at the leg/hull interface must be checked
to ensure the legs can withstand the gravity and inertial loads
associated with the tow. Field Tow corresponds to the condition
where a Jack Up Unit is afloat on its own hull with its legs raised,
and is moved a relatively short distance to another location. For a
short move, the ability to predict the condition of the weather and
sea state is relatively good. Therefore, steps to prepare the Unit for
Field Tow are not as stringent as for a longer tow. Most
Classification Societies define a “Field Tow” as a Tow that does
not take longer than 12 hours, and must satisfy certain
requirements with regards to motion criteria. This motion criterion,
expressed as a roll/pitch magnitude at a certain period, limits the
inertial loads on the legs and leg support mechanism. For certain
moves lasting more than 12 hours, a Unit may undertake an
Extended Field Tow. An Extended Field Tow is defined as a Tow
where the Unit is always within a 12-hour Tow of a safe haven,
should weather deteriorate. In this condition, the Jack Up Unit is
afloat on its own hull with its legs raised, similar to a Field Tow.
The duration of an Extended Field Tow may be many days. The
motion criteria for an Extended Field Tow is the same as for a
Field Tow.
The main preparations for a Unit to undertake an Extended
Field Tow are the same as those for a Field Tow with the
additional criteria that the weather is to be carefully monitored
throughout the duration of the tow. A Wet Ocean Tow is defined

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