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GUIDANCE ON DP SET UP AND WORKSITE APPROACH
It has become apparent that there is an inconsistent approach
within our industry to setting
up vessels in DP and approaching installations. The purpose of
this guidance is tohighlight best practice in this area.
DP SET UP
There is no common expectation amongst the client organisations
on when the vesselshould be under DP control.
Some require the vessel to be in DP when entering the 500m
exclusion zone; othersaccept that DP can be engaged at a closer
range.
Whatever the requirement, the overriding consideration is the
development of the DPmodel and the impact of a change of
operational mode on the modelling process.
The modelling time varies from manufacturer to manufacturer and
will vary depending onprevailing conditions. The approximate model
development time for Kongsberg K-Pos andRolls Royce Icon systems is
approximately 8 to 10 mins. For Kongsberg SDP systems aminimum of
20 minutes should be allowed.
The modelling process starts as soon as either DP Joystick or
Auto Position mode isselected.
Be aware that a high DP current and a degraded DP model are
likely to develop if themodel is developed in DP Joystick mode.
Development of the model in DP Joystick modeshould be avoided
DP Auto Position shall be engaged to develop the model.
Note that once the model is developed, the DP system updates the
model every second.
A change of operational mode out of DP to Manual control will
erase the DP modeltotally at any time.
The modelling process is not dependent on multiple position
references. There is nocommon expectation amongst clients on when
different numbers of position referencesshould be selected into the
DP system. Some clients require three to be selected whenentering
the 500m Exclusion zone; others accept that the shorter range
references can beselected nearer to the installation.
WORKSITE APPROACH
The model shall be developed in a safe position. This position
should be at least 200mfrom the installation.
At this safe position, a number of actions shall be carried
out:
Allow appropriate time for the DP model to develop (As above, if
not alreadydeveloped at 500m)
Place vessel on final working heading (This is to allow position
keeping evaluation) Evaluate position keeping performance in DP
operational mode Evaluate position keeping performance in Worst
Case Failure condition
(Deselect appropriate propulsion units from the DP desk)
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If the vessel position keeping is poor, a risk assessment shall
be carried out before movingcloser to the installation.
When it has been confirmed that the vessel is set up in
accordance with the FMEA,position keeping is within accepted limits
and checklists have been completed, the finalapproach to the
installation can be made.
Note: This shall be carried out in Auto Position Mode, switching
to DP Joystickmode is not recommended. Switching to Manual mode
will erase the DP modelentirely.
Irrespective of the distance at which the above takes place, we
recommend that theapproach to the installation involves relatively
small moves.
The size of the position moves and the speed should be reduced
as the rangecloses with the installation.
The DP position keeping should be evaluated after each move.
Large position moveswithout evaluation should be avoided.
The moves do not necessarily have to be sideways moves. The DP
model will bemaintained if the heading is changed during the
approach.
Note: This shall be carried out in Auto Position Mode, switching
to DP Joystickmode is not recommended and switching to Manual mode
will erase the DP modelentirely .
The short range position references can be selected at any time
without impacting thequality of the DP model.
DEPARTURE FROM WORKSITE
The initial move away from the worksite should be small. This is
to ensure that thedirection has been correctly entered.
