5.44 MULTIPLE PORT OR DOCK DISCHARGES
The cargo may be designated for discharge at more than one dock or
port. This intention will normally be indicated in the original loading
orders, but may not be received until the ship is making its loaded
passage. How the chief officer arranges the cargo to permit a multi-port
discharge depends on the nature of the cargo.
5.44.1 Single grade cargo
When the cargo is a single grade, the chief officer need only calculate
a discharge plan which offloads the designated quantity of cargo at
the first port and leaves the tanker with acceptable trim, stress and
transverse stability conditions for the passage to the second port.
The offloading programme for the first port should provide enough trim
for stripping the discharged tanks to a consolidation or slop tank,
however the trim should be limited to the maximum for which volume corrections
are provided in the ship's calibration tables.
If the vessel is discharging heated cargo, all discharged tanks should
be stripped. Adequate trim should be provided for good drainage. After
discharge is complete, cargo may be gravitated or pumped from an aft
tank to a forward tank to adjust the trim for the second part of the
With unheated cargo, the discharge may be completed without stripping
tanks, maintaining the trim near even-keel and leaving sufficient cargo
in the tanks discharged so that the cargo volumes can be accurately
5.44.2 Multi-grade cargoes
When a tanker carrying a multi-grade cargo is ordered to conduct a two
or three port discharge, the problem of planning the cargo loading arrangement
(see section 2.20), is compounded
by the need to achieve acceptable stability, trim and stress conditions
during the passage(s) between discharge ports. This additional requirement
may indicate the need of a different arrangement than would otherwise
be used and may require some consultation with the shipper to modify
the quantities and arrangement of the cargo parcels. The SBT tanks may
be used, if hull stresses permit, to assist with the trimming of the
ship after discharge at the first berth. Correct separation of cargo
grades and protection of cargo quality remain the most important considerations.
When the ship has been loaded for a single port discharge and the orders
are changed en route to offload at two or more terminals, the chief
officer may discover that it is impossible to complete the first discharge
with acceptable stability, stress, or trim for the voyage to the next
port. In this case, he must develop a two step discharge plan which
safely discharges the first parcel(s), then transfers cargo within the
ship to achieve acceptable stress, trim and stability for the following
The cargo transfer programme must be approved by the shipper and owners
before it is carried out. After the first parcel is discharged, the
ship must be gauged by an independent inspector to provide a record
of cargo discharged and cargo on board after discharge. Cargo is then
transferred within the ship as agreed and the independent inspector
again gauges the ship to provide a report of cargo on board at departure.
Ship's pipeline volumes must be properly accounted for in this report.
5.44.3 In-port movements
The hull bending and stress limitations are more stringent for a tanker
at sea than for the ship in port. If the multiple dock discharge point
delivery involves only a shift within a port, (as opposed to a voyage
between ports), then only the harbour stress limitations apply. The
ship need only have suitable trim and list for un-berthing and manoeuvring
to the next terminal.