1353
1 INTRODUCTION
Offshore, in gas and/or oil fields, there are many
different types of terminals that are considered unique,
such as Submerged Turret Loading (STL) [1, 2], Single
Anchor Loading (SAL) [2, 4, 6, 11], Ugland Kongsberg
Offshore Loading System (UK OLS) [2, 8], Single Buoy
Mooring (SBM) or Multi Buoy Mooring (MBM)
offshore terminals with floating or submersible cargo
hoses [11], Hiload unit [10,13] or any other floating
production and/or storage and offloading units (FPSO,
FSO, FSU) used offshore to exploit subsea oil & gas
resources. These units are currently serviced by a fleet
of specialized shuttle tankers (ST) equipped with
various offshore mooring, loading & discharging
systems. The purpose and scope of this paper is to
describe the characteristics of different
loading/discharging systems in particular the Bow
Loading System (BLS), the Stern Discharge System
(SDS), Submerged Turret Loading (STL) and the
conventional Midship Cargo Manifold (MCM) used on
Shuttle Tankers (ST) at open sea and to make
comparison between them with reference to their
operational efficiency, reliability, safety and weather
condition operational limits.
All types of tankers, including shuttle tankers (ST),
are always designed to load/unload liquid cargo by
using a conventional midship cargo manifold (MCM)
[6, 11, 13].
Most modern shuttle tankers are DP class vessels
(DP ST) and are also equipped with BLS used on
terminals such as SAL, OLS, SPM, FPSO, FSO. Some
specialized DP class 2 shuttle tankers are also adapted
to conduct storage and transshipment operations at
STL installations offshore [12]. These ships are then
Comparison of the Operational Performance
of Different Cargo Offshore Loading Systems,
in Particular the Bow Loading System (BLS), the Stern
Discharge System (SDS), Submerged Turret Loading
(STL) and the Conventional Midship Cargo Manifold
(MCM) used on Flex Shuttle Tanker
G. Rutkowski & P. Nowak
1
Gdynia Maritime University, Gdynia, Poland
2
Pilotage Services, Master Mariner Association, Gdynia, Poland
ABSTRACT: The purpose of this paper is to describe the characteristics of offshore loading/discharging systems
used on Flex Shuttle Tankers (Flex ST) at open sea, in particular the Bow Loading System (BLS), the Stern
Discharge System (SDS), Submerged Turret Loading (STL) and the conventional Midship Cargo Manifold (MCM)
and to make comparison between them with reference to their operational efficiency, reliability, safety and
weather condition operational limits. All types of tankers are always designed to load/unload cargo through a
conventional midship cargo manifold (MCM). Most modern shuttle tankers are equipped with BLS used on
terminals such as SAL, OLS, SPM, FPSO, FSO. Some specialized shuttle tankers are also adapted to conduct
storage and transshipment operations at STL installations offshore. These ships are then equipped with
submerged turret mooring and offshore loading system (STL) and sometimes also, but rather rarely with
additional stern discharging system (SDS). Tankers equipped with all the above-mentioned systems (BLS, SDS,
STL and MCM) are called Flex Shuttle Tanker (Flex ST) and they are used for transshipment of crude oil and gas
offshore.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 19
Number 4
December 2025
DOI: 10.12716/1001.19.04.35
1354
equipped with submerged turret mooring and offshore
loading system (STL) and sometimes also, but rather
rarely with additional stern discharging system (SDS).
Tankers equipped with all the above-mentioned
systems (BLS, SDS, STL and MCM) are called Flex
Shuttle Tanker (Flex ST) and they are used in the
offshore sector for transshipment of crude oil and gas
[1, 3, 4, 8, 13, 14, 15].
2 METHODOLOGY
All items described in this paper are based on the
common requirements covered by the specified oil
field offshore operation manuals (e.g. [3, 5, 9, 12, 16,
18]), installation makers operational manuals [6, 7, 17,
19, 20], ship’s operator manuals [15] and the authors
own experience and observation collected on shuttle
tanker fleet in offshore industry since 1997 (e.g. [2, 10,
11, 13]).
3 TANKER RAIL HOSES ON MIDSHIP CARGO
MANIFOLD (MCM)
During offshore cargo handling operations using
conventional tankers and sometimes also shuttle
tankers (ST), the midship cargo manifold (MCM) is
used to handle liquid cargoes such as oil and gas using
flexible and submersible tanker rail hoses that are lifted
from the seabed (e.g. MBM Aracaju terminal, selected
SPM and SAL offshore installations [1, 11]) or floating
hoses lifted from the water level (e.g. SPM Sao
Francisco do Sul terminal, SPM Tramandai in Brazil) or
optionally cargo rail hoses transferred directly from
Stern Discharg System (SDS) located on FPSO/FSO
(e.g. FPSO Campos Basin P-31, FPSO P-38, FPSO P47
[6, 11, 13]).
Figure 1. Schematic diagram of Floating Rail Hoses
connecting Stern Discharg System (SDS) on FPSO with
Midship Cargo Manifold (MCM) on Shuttle Tanker
according to OCIMF guidelines. SDS on FPSO may include
optionally Hose Reel system, Contilevered A-Frame Hose
Hang-Off System or Offloading Hose Chute System. Source:
Own researches based on [16, 21].
Schematic diagram of Floating Rail Hoses
connecting Stern Discharg System (SDS) on FPSO with
Midship Cargo Manifold (MCM) on Shuttle Tanker
according to OCIMF guidelines [21] is shown in Figure
1. Tanker rail hose can be delivered to MCM on Shuttle
tanker from FPSO/FSO Stern Discharge System (SDS)
by using Hose Reel system, Contilevered A-Frame
Hose Hang-Off System or Offloading Hose Chute
System (See Fig.1) [16,21].
Tanker rail floating hose is being used in calm sea
contitions (max. wave height 1 m, max. wind speed 30
kn (≈ 15 m/s). Calm sea in required to avoid hose
vertical jumps during connection/ disconnection and
hose handling crane overweight while keeping hose
weight on crane hook. Offloading hose has at least 250
m in length and has tipically 16”, 20” or 24”. Offloading
hose is taken alongside tanker midship hauled by
standby vessel and picked-up by tanker hose handling
crane and secured over tanker rail to the midship
manifold. Experienced deck crew need to carried out
hose securing, bending over tanker rail and connect
offload hose to tanker manifold. Precautions needs to
be taken to perform that safely and avoid hose snap
forward or aft while hose secured to rail and bended
for end flange disconnection and connection hose to
the vessel cargo system.
Shuttle tanker/conventional tanker shall use tug fast
center lead aft before final arrival to FPSO for mooring.
Tug shall be connected aft and ready for use at least 2
Nm (≈3.7 km) from FPSO/FSO. Shuttle tanker shall
take great caution do not take by thrust hose messenger
into bow thruster while cargo hose is being hauled by
stand-by vessel to ship manifold and do not take hose
messenger into main propeller when hose messenger
incidentally released by stand-by vessel. Start bringing
cargo hose alongside can take place when vessel is
safely moored and assisting tug used for hawser
tension. Fairleads with hose suspending chain at ships
manifold area shall be greased after hose connection to
protect hose chains on fearlead holding vertically hose
from parting.
When cargo loading is taken via midship manifold
cargo max. loading rate depends on piping max.
loading capacity through single tanker manifold
usually not exceed 2500-3000 m3/h. During loading
max. wind speed is 40 kn (≈21 m/s) and max. waves 2-
2.5m. Connection and disconnection of cargo hose shall
take place during daylight and with wave height not
exceeding 1 m in height. When cargo hose is lowered
to the water surface during hose disconnection, hose
weight on hook is reduced by its boyancy and hose
suspending chain is released from the crane hook by
quick release to free hose handling crane from floating
hose weighting during hose ballancing on waves while
hose drifting off ships side. When loading is completed
and sea state is not adequate for hose disconnection
than its reasonable to wait for wave height reduction to
1 m. Connection and disconnection cargo hose is risky
operation and risk mitigation must be taken to prevent
incident/accident occurance. In case wave is too high,
quick release of cargo hose can be tricky, expecially
when quick release messenger could not release crane
hook due to loads created by hose dancing on waves
on crane hook via suspension chain.
4 BOW LOADING SYSTEM (BLS)
Most DP shuttle tankers (DP ST) are equipped with a
Bow Loading System (BLS) which has two parts. One
on top platform is designed for vessel mooring to
offshore terminals such as SAL, OLS, SPM, FPSO/FSO,
and second part inside BLS for connection offloading
hose to BLS cargo manifold using the hose handling
winch to pick-up a cargo hose end flange to BLS
manifold shown at Fig. 2.
1355
When shuttle tanker is loading from FSO/FPSO,
operation is called tandem operation. In the North Sea
the distance between the loading point-base (stern of
the FPSO) and the shuttle tanker bow is typically
between 70 m and 100 m, while in Brazil distance is
typically between 145 m to150 m. Some FPSOs have
active heading control using thrusters while others are
passive, meaning that they are weather-vaning on the
turret. In case wind and current direction changing
rapidly than heading of FPSO is changing rapidly to
creating challenge for shuttle tanker to follow FPSO
heading. For instance, FSU Alba in British Sector was
usually liable to sudden heading changes due to
environmental forces changes.
In Brazil weather vaning FPSO are seldom in use.
Prevailing FPSO ’ s are Spread-Moored FPSO ’ s,
which have fix heading e.g. 210° moored by anchor
chains to sea bottom. Approaching to FPSO starts from
10 Nm zone (≈18.5 km from FPSO) and shuttle tanker
shall follow oil field operational procedures with
regards to offtake tanker speed limits and weather
limitations for approach and loading [13,15]. BLS
tests/checklists shall be carried out by shuttle tanker
personel before arrival 10 Nm zone, and shuttle tanker
shall not have any defects in regards to propulsion,
thrusters, DP system, BLS system and cooling systems
[2]. Average time from arrival 10 Nm zone to
commence loading take arround 5-6 hrs, while time
period of competion loading, disconnection and
passing 10 Nm zone takes around 3,5-4 hrs.
Figure 2. Shuttle tanker Bow Loading System overview.
Source: Own research based on [4, 7, 20].
Shuttle tanker speed limits when approaching an
offshore installation (e.g. FPSO, FSO, SPM, OLS, SAL)
within 10 Nm ( ≈ 18.5 km) zone from the loading
position for DP ST are presented in table 1.
Table 1. Shuttle tanker DP ST speed limits during
approaching to installation offshore
Operational Zones
Outside 10 Nm (distance
≥18.5 km)
10 Nm to 3 Nm (18.5 km to
5.5 km)
3000 m to 900 m
900 m to 500 m
500 m to 150 m
150 m to loading position
Source: Teekay reqirements for Offshore Loading
Operations (Shuttle Tankers). Doc No SP0978, [15].
DP Shuttle tankers use BLS to receive crude oil from
FPSO via FPSO stern discharge system (SDS) to shuttle
tanker BLS manifold through FPSO hose end valve.
Hose end valve is opened by BLS coulper valve while
vessel being safely moored to FPSO and having cargo
hose connected to BLS manifold. Loading though
tanker midship manifold Rail Hoses are taking place
when FPSO using Hose Hang-Off System or Hose
Chute System.
Figure 3. Shuttle tanker during bow loading via BLS on FPSO
P-57 and DP ST operational limit. Source: Own research
based on [7, 13,15].
Loading take place around 15-18 hrs for 100000
DWT tanker, and around 24-30 hrs for 150000 DWT
tanker. Time of loading depends on FPSO cargo pumps
capacity, but in real time rates 6000-6500 m3/h are
possible. Shuttle tanker shall have balast pumps fully
operational to manage discharge ballast during such
fast-loading rates. When weather is touching
operational limits shuttle tanker master shall terminate
loading operation and disconnect from FPSO. Shuttle
Tankers are equipped with telemetry system
integrated with DP system which monitor bow-base
distance safety limits and heading difference between
shutte tanker and FPSO/FSO and also Hawser Tension.
See Fig. 3 for reference.
In case shuttle tanker touch ‘yellow limits’ ESD1-
emergency shut down class 1 – stops pumps on
FPSO/FSO and closes manifold valves while ESD2 ‘red
limits’ – additionally activates fire fighting water
deluge over the BLS area and after water deluge
activation release cargo hose and finally FPSO/FSO
chafing chain from top platform to the water. Before
loading commencement cargo hose and mooring
chaffing chain shall be ready for emergency release,
when activated by telemetry or manually from BLS
accumulators in case of drive-off from DP positioning
or shuttle tanker blackout [13,15]. Steering cabinet for
BLS manifold at righthand side. Ones loading hose is
connected to BLS manifold hold by coulpler claws,
hose messenger shall be released and manifold set to
free wheel. BLS is slightly ballansing with hose weight
gravity. Cargo Hose messenger must be disconnected
from cargo hose and cargo hose bridles taken out of
bow loading structure. Chafing chain messenger line
on top platform shall be diconnected and shackle shall
be removed from the end of chafing chane. Thus,
system is ready for emergency release into the sea.
Shuttle Tanker must perform DP Failure Mode and
Effect Analysis (FMEA) to have proven that all BLS and
DP features are working properly. Shuttle tanker stay
on DP during FPSO approach, mooring, cargo hose
connection, loading. Shuttle tanker weather vaning
behind FPSO during loading using thrusters and
propellers.
Weather operational limits for tandem operations
with DP: for mooring, wave heights 4,5 m; wave period
max. 15 s, wind speed 40 kn (≈21 m/s), for loading:
wave heights 5,5 m, wave period max.15 s, wind speed
50 kn ( ≈ 26 m/s). Weather operational limits for
tandem operations in Taut Hawser (Non-DP): for
mooring, wave heights 3,5 m; wave period max. 15 s,
wind speed 40 kn (≈21 m/s), for loading: wave heights
4,5 m, wave period max.15 s, wind speed 50 kn (≈26
m/s).
1356
5 STERN DISCHARGE SYSTEM (SDS)
Figure 4. SDS Offloading Hose stored on a Reel. A - Hose end
piece with flushing unit. B - Submerged hose.
Source: Photos from the authors' private collections.
Stern Discharge System (SDS) located on FPSO/FSO
can include Hose Reel system, Contilevered A-Frame
Hose Hang-Off System or Offloading Hose Chute
System (See Fig.1, 4 & 5) [16,21].
Many of the modern FPSO’s /FSO have Offloading
Reel Type SDS system. The hose assembly on the SDS
is stored on a dedicated hose reel, enabling rapid and
safe deployment. The system also incorporates a
vertical drum mooring and hawser handling winch
specifically designed for tandem mooring with shuttle
tanker. The mooring operation is significantly
simplified, with the winch storing chain and rope on
the same drum. To avoid wear on the soft mooring
hawser, both chafing chains are stored in a special
recess at the bottom flange. The vertical drum
construction also prevents chain fall-off, a common
problem for horizontal drum winches. The SDS
contains a ball joint for “moment-free” termination of
the loading hose, thus protecting it from excessive
strain
Figure 5. SDS Offloading Chute type.
Source: Based on [4, 6, 11].
SDS Offloading Reel type (See Fig. 4) is most
frequently used on FPSO’s / FSO’s, expecially on new
buidings. Cargo hose is paid out from slowly turning
hose storage drum while shuttle tanker is heaving
cargo hose messenger line with messenger bridles
connected to cargo hose end swivel. Its reasonable to
keep messenger line tensioned to avoid bridles
twisting before final picking -up cargo hose and
connection. Offloading hose can be either submerged
or floating type. Length and diameter are project
specific. Hose end-piece is usually equipped with
flashing unit (See Fig. 4A). Submerged hoses used in
the North Sea and Canada are typically 120 m of 16” or
20” and are stored in one layer on the reel. Offloading
house during cargo operation offshore is connected to
Bow Loading system installed on DP shuttle tanker
(DP ST). Typical seperation distance between DP ST
and FPSO/FSO is 80 m. Floating hoses are typically
used in area with ‘nice’ sea conditions (e.g. Campos
Basin Offshore Brazil). Hose length is typically more
then 250 m of 20”. Floating hoses are stored in two
layers on the reel and can be connected also to midship
manifold on conventional tanker (See Fig.1).
SDS Offloading chute type (See Fig. 5) is met on
older types of FPSO/FSO for instance in Campos Basin
in Brasil (Petrobras-43 and Petrobras-48). Chute type
SDS require proper maintenance. Horizontaly stowed
cargo hose need to be paid out by FPSO hydraulic
rollers. Can be the case when shuttle tanker Master is
being asked to pull out cargo house using some tension
to pull hose out by hose handling winch or combined
traction winch used for mooring and later for cargo
hose heaving.
SDS Offloading hose is usually submerged type and
is stored on a chute. Length and diameter are project
specific. Submerged hoses used in North Sea are
typically 120 m length and 20” diameter, in Brazil 250
m of 20”. Typical separation distance between vessels
is 80 m to 150 m. SDS offloading hose can be connected
to BLS on DP ST or conventional tanker MCM. The
chute is equipped with rollers to enable pull-in and
pay-out of the offloading hose. For enabling connection
of the offloading hose to the coupler, a trolley with a
lifting mechanism is used. The trolley also ensures that
the hose end piece is free from the rollers.
SDS of Reel Type and SDS of Chute Type are used
to be connected to shuttle tanker BLS system. Thus, the
same procedures against weather limitations are used
for shuttle tanker loading via BLS described in
previous chapter. On Spread-Moored FPSO sometimes
2 offloading stations are available Depending on
direction of environmental forces shuttle tanker master
decide which station he is going for use. For shuttle
tanker approach heading 210° (e.g. to the stern of FPSO
P50) or approach heading 030° (to the bow of FPSO
P50). We can add one to two extra hours in
comparision to the North Sea FPSO’s mooring
operations due too longer mooring system and cargo
hose system in Brasil FPSO’s infrastucture. During
loading telemetry system is being used. In case of cargo
green line failure cargo pumps are tripped on FPSO by
telemetry system. After cargo hose connection to BLS,
Shut Down Class I shall be tested against SDS before
loading commencement take place.
1357
6 SUBMERGED TURRET LOADING (STL)
Submerged turret loading (STL) is underwater
instalation designated for DP class 2 Shuttle Tanker
equipped with STL manifold at forward bottom part of
tanker. The STL buoy known as STL system
incorporates a turret spread-moored to the sea floor
and to the riser (see Fig.6). The buoy floats in neutral
position about 30 m to 50 m below water surface. The
buoy is pulled into the keel pool for STL system on
shuttle tanker. The turret is free to rotate inside the
buoy, thus it allows shuttle tanker to bias against
weather within STL base point while STL buoy is
connected to shuttle tanker STL manifold. All STLs are
based on standardized mating cone geometry in the
vessel keel.
DP ST arrives oil field and pick-up STL buoy by STL
pool messenger line connected with STL buoy
messenger line and finally enable to connect STL buoy
to STL manifold, perform loading operation and
disconnecting STL buoy when loading is completed.
STL system with a submerged STL buoy that connects
through a cone-shaped mating cone in the keel of the
shuttle tanker or FSO tanker. STL is also currently used
on LNG STL tankers. STL is best suited for loading in
areas of high sea states.
Figure 6. Shuttle tanker SDS overview. Source: Own research
based on [2, 7, 13].
As an example of loading with extreme weather
conditions experienced at Aasgard C FSO Storage
Tanker. Åsgard is located at Haltenbanken in the
Norwegian Sea, about 200 kilometres from the
Trøndelag coast and 50 kilometres south of the
Heidrun field. Water depth in the area is 240-310
metres [5, 12, 15]. STL require technology, experience
and reliable equipment.
Field specific limits are programmed into the DP
software (buoy selection). Specific limits and
configuration differ from one type of loading
installation to another. For Kongsberg supplied DP
systems the following alarm wording is used: ‘yellow
limits’ (Distance to base too long. ESD I shall be
activated if this limit is exceeded); ‘red limits’ (Distance
to base critically long. ESD II shall be activated if this
limit is exceeded). Teekay reqirements [15] for Offshore
Loading Operations (Shuttle Tankers- Doc No SP0978)
are as follow: For STL connection max. significant wave
height 4,5 m; max. wave period 15 s. For STL loading:
max. significant wave height 10 m. Telemetry shut
down loading, when shuttle tanker touches yellow
limits. However, it must be noted that ESD II was not
applicable for shuttle tanker STL loading at Heidrun oil
field.
On STL buoy only DP class 2 shuttle tankers are
used for operation. The following DP modes are being
used [5, 12, 15]: DP Approach Mode (from 1500 m to 5
m off STL terminal base point), DP Connect Mode and
Go to Base/Buoy (during connection/disconnection
STL buoy to/from ST) are used.
On DP2 minimum two position reference systems
(PRS) are required to be in use by the DP system on the
shuttle tanker and usually there are as follow: one
Hydroacoustic Position Reference system (HPR) and
one (absolute) Differential Global Navigational
Satellite System (DGNSS/DGPS). When DP is prepared
the following apply: Between 3000 m and 1200 m from
the STL base, the pickup line on the ST shall be lowered
trough the mating cone with a sandbag and a floating
element. The ST shall stop and thrust sideways by 0.5
knots (≈0.3 m/s). The sandbag will be hydrostatically
released, and the floating element rise to the surface. It
shall be picked up by the crew and made fast on the
port side, forward. The vessel shall continue its
approach. On 300 meters zone DPO shall select
Heidrun1 or Heidrun 2 on HPR, interrogate LBL
transponders on seabed. When stable HPR, position
drop-out, select HPR as reference origin, select DGPS
as PRS 2. Select Approach mode and continue towards
shooting position, speed 0.4 knots (≈0.2 m/s). When
passing 200 meters zone DPO shall stop vessel in
shooting position. Pick up the messenger line.
Continue towards STL base while picking up slack on
the messenger line. At 50 meters zone DPO shall
activate STL buoy transponders by selecting auto scan.
The system will select the best transponder
automatically. The depth of the STL buoy on Heidrun
oil field was 40 to 45 meters. Shuttle tanker speed limit
was set up to ≈ 0.15 m/s. At 5 meters zone to STL
buoy DPO proceeded towards STL centre if sway and
heading was stable. If not, he shall wait in ‘DP
Approach Mode’ until stable and then select ‘DP
Connect Mode’. DPO shall select ‘DP Go to Base’ mode
and pull STL buoy. Then buoy is locked, it’s displayed
on the DP ‘STL Buoy in Position’.
When the vessel is in ‘Base/Buoy position’ than it’s
ready to hoist the buoy into the mating cone and when
STL buoy is in locked position, a signal is sent to the
DP. The DPO should then select ‘DP Loading Mode’.
In good weather conditions it is most common to stay
in ‘Loading Mode’ with no thruster active and only
DGPS as reference system. When loading is completed,
the vessel shall disconnect from the STL more or less
opposite way of how the vessel connects to the buoy.
The DPO shall select ‘Connect’ and ‘Go to Base’. The
STL shall be disconnected and lowered to its normal
depth. The DP shall be set to the ‘Approach mode’, and
the vessel shall move astern while slacking away on the
messenger line until the marker buoy is in the water.
According to field operator [12, 5] and APL
manufacturer for most of the STL systems [4, 7],
connection can be done in sea states between 5 m to 7
m of significant wave height. Loading is weather
independent, and further disconnection can be
undertaken in any sea state.
7 COMPARISON SUMMARY
A summary comparision between Midship Cargo
Manifold (MCM) used for tanker rail hose loading,
bow loading system (BLS), stern discharge system
(SDS) and submerged turret loading (STL), considering
1358
operational limits, time needed for approach, mooring,
hose connection, loading, hose disconnection and
unmooring had been taken into consideration. With
regards to weather conditions limits STL is the most
realible and sophisticated offshore loading system, BLS
and SDS system are interlocking with each other and
are commongly used by DP Shuttle Tankers allowing
smooth approach, connection, loading and
disconnection when weather window opens. Tanker
Rail Hose manifold loading is uniwersal loading
system for all types of crude oil tankers but mooring
chafing chain via Panama Fairlead and manifold hose
connection require crew experience, proper planning
and carefull tracking of weather forecast. A summary
comparison between BLS, SDS, STL and Tanker Rail
Hose loading were presented in table 2.
Table 2. A summary comparison between BLS, SDS, STL & MCM hose rail loding.
Bow Loading System (BLS)
SDS Stern Discharge System
Submerged Turret Loading
(STL)
Midship Cargo Manifold
(MCM) hose rail loding
1. Approach to FPSO or FSO or FSU// N.A //STL buoy//FPSO or FSO or FSU
DP Approach mode (DP ST)
or manual approach (Taut
Hauser)
Waiting for ST or
conventional tanker
DP Approach mode on
(DP2 ST)
Manual approach with
tugboat fast aft
2.Time for approach
10 Nm till mooring psn at 150 m Off FPSO in Brazil and 80
m Off FPSO in the North Sea: 4 h
1.5-2 hrs on DP2 ST
10 Nm till mooring line
pick-up abt 400 m off FPSO/
FSO: 2-2.5 hrs
3. Tug connection with tugline paying out around 600 m of towline for tow connection: 30 min
N/A
ST:1000 m from FPSO;
Conv.tanker: 2 Nm from
FPSO
4. Type of mooring
chain stopper on BLS with
chaffing chain and hawser
STP-submerged turret
production anchored to
seabed or Spread-Moored
FPSO in Brasil
STL buoy anchored to
seabed
Chain stoper on ST or
chafing chain via panama
fairlead on conventional
tanker
5. Time for mooring
From time of shooting psn
till chain stoper closed: 30
min to 1 hour
From start of mooring
Messenger paying out till
chafing chain paid out from
mooring drum: 30 min to 1
hour
30 min to 1-hour Vsl at STL
base picking up STL buoy
to ST hull mating cone
Mooring tug bringing
mooring messenger: 380 m
from FPSO till chafing chain
received via panama
fairlead – 2.5 hrs
6. Time for cargo hose connection
Heaving and picking up
cargo hose – 30 min in the
North Sea, 1-1.5 hrs in
Brazil
Cargo Hose pay out from
Cargo Hose Rai or from
horizontal chute system 1-2
hrs in Brazil; 30 min in
North Sea
STL buoy turret manifold
connection to vls manifold
by actuators: 15 min
Hose brought by stand-by
tug alongside midship
manifold: 1-1.5 hrs (wave
max. 1 m); Daylight
7. Time for loading
15-18 hrs - 100000 DWT 24-
30 hrs - 150000 DWT
24 hrs-100000-130000 DWT
48 h-60 h
8. Time for hose disconnection
15 min in the North Sea, 30 min in Brazil
10 min, can be performed in
any weather condition
40 min- 1 hrs, daylight
9. Time for unmooring/mooring disconnection
15-20 min
1-1.5 hrs
10. Weather limits – for mooring and hose connection
On DP: wave heights 4,5 m;
wave period max. 15 s,
wind speed 40 kn, On Taut
Hawser mooring: wave
heights 3,5 m; wave period
max. 15 s, wind speed 40 kn
Same as for offtake tanker
via BLS beside
Teekay SP0978 doc max.
sign. wave height: 4,5m;
max. wave per.:15 s, as per
APLsign. wave height: 5-7m
max. wave height 1 m, max.
wind speed 30 kn,
11. Weather limits – for loading
On DP: wave heights 5,5 m,
wave period max.15 s, wind
speed 50 kn, On Taut
Hawser: for loading: wave
heights 4,5 m, wave period
max.15 s, wind speed 50 kn
Same as for offtake tanker
via BLS beside
Same as for offtake tanker
via BLS beside
Teekay SP0978: max. sign.
wave height: 10 m; APL-
weather independent
offshore loading
max. wind speed 40 kn and
max. waves 2-2.5m
12. Weather limits for hose disconnection and unmooring
On DP: wave heights 4,5 m;
wave period max. 15 s,
wind speed 40 kn, On Taut
Hawser mooring: wave
heights 3,5 m; wave period
max. 15 s, wind speed 40 kn
Same as for offtake tanker
via BLS besides,
Same as for offtake tanker
via BLS beside
Teekay SP0978:
disconnection with DP
Mode: Hs=10m; APL maker:
in any weather conditions
Daylight, wave height not
exceeding 1 m, max. wind
speed 30 kts
Source: Authors Own researches.
1359
REFERENCES
[1] Cydejko J., Puchalski J., Rutkowski G., Outline of off-
shore ships and technologies, ISBN 978-83-62227-24-2,
Trademar Publishing House, Gdynia, 2011.
[2] Rutkowski G.: A Comparison Between DP Offshore
Loading Operation on Submerged Turret Loading
System STL, Submerged Single Anchor Loading System
SAL and Offshore Loading System OLS Considering the
Hydro-meteorological Condition Limits for the Safe
Ship’s Operation Offshore. TransNav, the International
Journal on Marine Navigation and Safety of Sea
Transportation, Vol. 13, No. 1, doi:10.12716/1001.13.01.18,
pp. 175-185, 2019.
[3] Marine Insights website:
https://www.marineinsight.com, date of access:
December 2024.
[4] National Oilwell Varco website: https://www.nov.com;
accessed on December 2024.
[5] Equinor: https://www.equinor.com. Accessed on
December 2024.
[6] SBM Offshore, website: www.sbmoffshore.com. Accessed
on December 2024.
[7] APL Advanced Production and Loading, National
Oilwell Varco, website: www.nov.com/fps. Accessed on
November- December 2024.
[8] Subsea Oil and Gas Directory website:
https://www.subsea.org, accessed on November-
December 2024.
[9] EPCM consultants, website: https://epcmconsultants.co,
Accessed on November 2024.
[10] Rutkowski G.: Numerical Analysis for the Dynamic
Forces and Operational Risk Accomplished for a "Hiload
DP1" Unit Docked to MT "Navion Anglia" at Sea Waves.
TransNav, the International Journal on Marine
Navigation and Safety of Sea Transportation, Vol. 8, No.
4, doi:10.12716/1001.08.04.04, pp. 505-512, 2014.
[11] Rutkowski G., A Comparison Between Conventional
Buoy Mooring CBM, Single Point Mooring SPM and
Single Anchor Loading SAL Systems Considering the
Hydro-meteorological Condition Limits for Safe Ship’s
Operation Offshore. TransNav, the International Journal
on Marine Navigation and Safety of Sea Transportation,
Vol. 13, No. 1, doi:10.12716/1001.13.01.19, pp. 187-195,
2019.
[12] Heidrun STL Guideline and Loading, version 1.6, Teekay
internal documentation for Heidrun Oil Field. Accessed
on Nov.-Dec. 2024.
[13] Rutkowski G. (2013), Operation of dynamically
positioned ships, Volume 8 of the series "Contemporary
Maritime Transport Technologies", Trademar Publishing
House, ISBN 978-83-62227-44-0.
[14] Kołakowski P., Rutkowski G.: The Analysis of Offshore
Industry Transition - Acceleration from Oil & Gas to
Wind. TransNav, the International Journal on Marine
Navigation and Safety of Sea Transportation, Vol. 16, No.
2, doi:10.12716/1001.16.02.20, pp. 375-384, 2022.
[15] Teekay internal document No.: SP0978 ver. 10, Teekay
Requirements for Offshore Loading Operations (Shuttle
Tankers). Accessed on Nov.-Dec. 2024.
[16] Denia Link S.L, website:
https://denialink.net/oil_loading_rubberhoses_ocimf.ph
p. Accessed on Dec. 2024.
[17] CROSS maker, website:
https://www.cross.com.gr/product/ocimf-hoses-and-
ancillaries. Accessed on Nov.-Dec. 2024.
[18] Offspring International LTD, website:
https://www.offspringinternational.com. Accessed on
Nov.-Dec. 2024.
[19] HEES internal document No.: DOM-SA-P-001B, Oil
Pipeline and Loading Operating Procedure, Rev.
71.12.2015. Accessed on October-November 2024.
[20] Pusness Maritime, Website:
https://pusnesmaritime.com. Accessed on Nov.-Dec.
2024.
[21] The Oil Companies International Marine Forum
(OCIMF) Website: https://www.ocimf.org. Accessed on
Nov.-Dec. 2024.