Sonardyne UK (Head Office)
T. +44 (0) 1252 872288
F. +44 (0) 1252 876100
E. sales@sonardyne.com
www.sonardyne.com
Datasheet
BOPNav Acoustic Transceiver
Description
The BOPNav System is a powerful
enhancement to Sonardyne’s Long
and Ultra-Short Baseline (LUSBL)
positioning system for drilling rigs in
deep water. On very noisy vessels
and when drilling in the deepest
water, the performance of the vessel-
mounted transceiver can suffer
degradation due to low acoustic
signal from the seabed transponders
compared with the high ambient
noise from the thrusters.
An additional feature of the BOPNav
is that it can be used as a
Responder. This allows the stack to
be tracked during deployment, while
it is still too high to have sight of the
replies from the seabed
transponders. It can also be used to
locate itself over the stack in USBL
mode without the need to deploy any
transponders (see diagram B). Such
a system is intended to provide a
coarse position for temporary use
while the transponder array is being
deployed and calibrated.
Conserves Transponder Battery Life –
Again, if transponder reply signals
are only received at the BOPNav,
the power transponder level can
often be reduced, so conserving
battery power.
The BOPNav is mounted on the stack
and electrically connected via the
riser to the surface system
Navigation Processor. Transponders
are triggered by an interrogation
signal from the surface as normal but
the transponder replies are received
at the BOPNAV unit as well as at the
surface (see diagram A). Operating
in this way dramatically improves the
system redundancy and allows a
number of signals to be lost at the
surface without degrading the
computed vessel position. In fact it
allows the system to operate even if
no transponder replies are detected
at the surface at all.
BOPNav provides the following
advantages:
The BOPNav is enclosed in Stainless
Steel housing. Two Acoustic Remote
Transducers are used to provide
additional redundancy and avoid
any possible shielding by the riser.
Both Transducers are connected to
the BOPNav by armoured cables
and are normally mounted on arms
extended to the side of the BOP
stack.
Stable Position Fixes – The stability
and reliability of the signals received
at the BOPNav are improved
because the ranges are relatively
short and the noise level at the BOP
is normally low. If the BOPNav
receiver is combined with the surface
receiver, system redundancy is
greatly improved. This also allows
good positioning to continue even
after the loss of signals received at
the surface.
A LUSBL system with Version 6
software is able to position both the
vessel and the stack simultaneously.
Interrogations can be transmitted
from either the vessel transceiver or
the BOPNav and transponder replies
are received at both systems. This
allows the stack to be positioned
accurately for re-connection. In
addition, if the BOPNav has two
transducers, the orientation of the
stack can be determined.
Increased Update Rate – If the
receipt of signals at the surface is
disabled in favour of receipt at the
BOPNav, the system does not need
to wait for signals to return through
the water column, saving time in the
cycle and allowing an increase in the
update rate.
The BOPNav itself takes 24 V DC
power from the BOP stack and this
cable (optionally a PBOF - Pressure
Balanced Oil Filled - cable) carries
the comms lines (RS-485 half-duplex
is standard) to the riser cable. Future
enhancements will include internal
Dual Axis Inclinometers and an
interface for an external Dual Axis
Inclinometer Module. When the
external inclinometer module is
mounted on the riser above the flex
joint, this will allow the inclination of
the riser, the BOP and the differential
angle to be monitored over the
comms link, providing an Electrical
Riser Angle (ERA) function.
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