A Journey Into the Emotions of Software Developers
Anchor Handling Stability
1. Formulating Stability Requirements for
Anchor Handling Tug and Supply
(AHTS) Vessels
Dephne Chea Wei Peng, Arun Kr Dev, Ivan Tam, (Newcastle University)
Kenneth Hanks, Kalyan Chatterjea (EMAS Training Academy & Simulation Centre)
1
2. BACKGROUND
No specific internationally applicable stability requirements for
AHTS vessels.
After AHTS “Bourbon Dolphin” tragedy in April 2007, initiatives
were taken for improving
Design
Operational safety & specifically
Stability and the performance of anchor handling winches.
Probably the most important initiative is from the
Norwegian Maritime Directorate (NMD):
NMD Circular - Series V, RSV 04-2008, 14 July 2008.
2
3. IMO Guidelines…BV Presentations, 2010 @ KL
Refer to Intact Stability Code, 2008, IMO Res. MSC.267(85).
Code covers
intact stability criteria &
addresses offshore supply ships & special purpose ships,
requirement for a minimum freeboard at the stern of at least 0.005L
to be maintained in all operating conditions.
Code does not include any specific stability criteria for towing and
anchor handling operations
Minimum required GM0 = 0.15 m should NOT be considered
as sufficient stability margin for towing and anchor handling.
.3
4. IMO Criteria for OSV
Max GZ of an OSV is allowed to
occur at much smaller angle of
heel than normal, providing
that the positive stability up to
this angle of heel (area A) is
greater than for a cargo ship
This requires a large upright
GM
Minimum freeboard criteria for
OSV is inadequate for anchor-
handling operation
Clark & Hancox (2012)
4
5. Recommendation from
Marine Safety Forum (MSF)
Quoting from Anchor-handling Manual template by
Marine Safety Forum (MSF), incorporating
recommendations from NMD.
Prior to sailing, a document must be displayed on the
bridge, where it is visible to be navigator on duty, to
show the acceptable vertical and horizontal transverse
force/tensions to which the vessel can be exposed.
This should show a sketch of the GZ curve and a table
of the tension/forces which give the maximum
acceptable heeling moment. 5
6. Further quoting from the Anchor-handling Manual
template by MSF incorporating recommendations from
NMD.
Calculations must show the maximum acceptable tension in
wire/chain, including transverse force, that can be accepted
in order for the vessel’s maximum heeling to be limited by
one of the following angles, whichever occurs first:-
o Heeling angle equivalent to a GZ value equal to 50% of GZ max.
o The angle of flooding of the work deck – i.e. the angle which
results in water on working deck when the deck is flat.
o 15 degrees.
Recommendation from
Marine Safety Forum (MSF)
6
7. NMD Criteria
1. Heeling angle
equivalent to a GZ
value equal to 50% of
GZ max.
2. The angle of flooding of
the work deck – i.e. the
angle which results in
water on working deck
when the deck is flat.
3. 15 degrees.
Vessel‟s Maximum
Heeling to be limited by
one of the following
angles, whichever
occurs first:
Heeling moment must be
calculated as the total effect of
the horizontal & vertical
transverse components of the
force /tension in the wire/chain
The torque arm of the
horizontal components shall
be calculated as the distance
from height of the work deck at
the guide pins to the centre of
the main propulsion propeller
or to the centre of stern side
thruster if it projects deeper
The torque arm of the vertical
components shall be
calculated from the centre of
the outer edge of the stern
roller & with a vertical straining
point on the upper edge of the
stern roller
7
8. External Acting Forces & Healing Moments
…NMD Proposal to IMO
α – angle between towline & ship’s centre line
β – angle between towline & the waterplane
y & v – refers to application point of the of the
line tension
Ft – towline tension
Unified Stability Criteria & Operational Guidance for AH Vessels
Application Point & Direction
of a Towline in the Stern of a
multi-operational mode vessel
8
9. External Acting Forces & Healing Moments
…NMD Proposal to IMO
Heeling Moment MH = (Ft .sin α.cos β x v)+(Ft .sin β x y)
Application Point & Direction
of a Towline in the Stern of a
multi-operational mode vessel
Transverse
Component
Vertical
Component
Unified Stability Criteria & Operational Guidance for AH Vessels 9
10. Tension Directions vs Healing Moments MH
…NMD Proposal to IMO
A typical example
of Heeling Moments
with some specific
‘y’ & ‘v’ levers
β
α
So, in general,
As ‘α’ increases
MH is increasing
As ‘β’ increases
MH is decreasing
Unified Stability Criteria & Operational Guidance for AH Vessels
10
11. Influence of ‘α’ & ‘β’ on MH
…NMD Proposal to IMO
α
As ‘α’ is increased
MH could reach to
an unacceptable
level!
β
MH
Unified Stability Criteria & Operational Guidance for AH Vessels
11
12. Concept of Constant Heeling Moment
…NMD Proposal to IMO
The Norwegian proposal is based on a concept of α constant
heeling moment MH , providing limits
to the line tension only dependent on sideways angle ‘α’
Vertical
Component
Transverse
Component
Unified Stability Criteria & Operational Guidance for AH Vessels
12
13. Fixed Moment vs Tension
…NMD Proposal to IMO
Tension
distribution with a
constant Heeling
Moment
Unified Stability Criteria & Operational Guidance for AH Vessels
13
14. Operating Tension vs Angle Alpha
…NMD Proposal to IMO
Finally, a
simplified Angle
Alpha vs Tension
could be created
For use by the
operators
15 30 60 90
Unified Stability Criteria & Operational Guidance for AH Vessels
14
15. Graphical Presentation
…NMD Proposal to IMO
A simplified graphical
presentation on bridge
T1 – 0 to 150
T2 – 15 to 300
T3 - 30 to 600
T4 - 60 to 900
Unified Stability Criteria & Operational Guidance for AH Vessels
DF – 1.4 to 1.6 times
the static load is common
Sector-1
Sector-2
Sector-3
Sector-4
15
16. Stability Limiting Curves
…NMD Proposal to IMO
Unified Stability Criteria & Operational Guidance for AH Vessels
For AH-Operations,
the stability limiting
curves should be
developed as a
function of
draught/displacement
against initial KG or
GM & applied tension
Covering lightest
anticipated draught to
Summer Load Line &
trim range
Heeling Angle Flooding Angle
16
17. Stability Limiting Curves
…NMD Proposal to IMO
Unified Stability Criteria & Operational Guidance for AH Vessels
The minimal residual
area between the
righting lever curve
and the heeling lever
curve ≥ 0.055 m-rad
[θe to θf or θc
whichever is less]
17
19. Ultra Deep Water Multifunctional AHTS Vessel
LOA – 93.4m
LBP – 82.0m
B – 22.0m
D – 9.5m (main deck)
Design Draught – 6.5m
Bollard Pull – 300 tonnes
AH/Towing Winch – 500 tonnes pull [600 tonnes brake]
Propulsion - 23,467 BHP
DP II
Deadweight Approx. 4,700 T
GRT Approx. 6,000 T
Lewek Fulmar
19
20. Lewek Fulmar uses AUTOLOAD 6
AUTOLOAD 6 ASUMPTIONS:
Tension from chain is placed at the full breath of aft roller, & the chain
angle (tension) is calculated from 0o(vertical) to 90o(horizontal)
The vertical moment arm from main thrusters (or aft side thrusters if
existing) and up to aft roller is kept constant, independent of vessels
heel angle.
The horizontal moment arm from end of aft roller to centerline is kept
constant, independent of vessels heel angle.
Both the effect of the horizontal forces and the tensions offset from CL
is converted to an external moment acting on the vessel.
To keep correct displacement during all calculations, the vertical
tension component (the weight) is placed at centerline on top of aft
roller. 20
21. Lewek Fulmar uses AUTOLOAD 6
Tank Sensors in AUTOLOAD 6:
Autoload installations can be fitted with a Tank Sensor
program that interfaces directly with Autoload
Thus providing immediate tank loadings for an accurate and
up-to-the-minute analysis of the vessel’s stability.
21
25. IMO 469 Intact Stability in AUTOLOAD 6
Righting Arms vs. Heel - IMO 469, INTACT STABILITY
Heel angle (Degrees)
A
r
m
s
i
n
m
0.0 10.0p 20.0p 30.0p 40.0p 50.0p 60.0p
0.0
0.5
1.0
Righting Arm
R. Area
Flood Pt
25
26. NMD Criteria in AUTOLOAD 6
Righting Arms vs. Heel - NMD ANCHORHANDLING CRITERIA
Heel angle (Degrees)
A
r
m
s
i
n
m
0.0 10.0s 20.0s 30.0s 40.0s 50.0s 60.0s 70.0s
-0.5
0.0
0.5
1.0
Righting Arm
Heeling Arm
Equilibrium
Crit. Pt
26
27. NMD Criteria in AUTOLOAD 6
Righting Arms vs. Heel - NMD ANCHORHANDLING CRITERIA
Heel angle (Degrees)
A
r
m
s
i
n
m
10.0s 20.0s 30.0s 40.0s 50.0s 60.0s 70.0s
-1.0
-0.5
0.0
0.5
Righting Arm
Heeling Arm
Equilibrium
Crit. Pt
27
28. NMD Criteria in AUTOLOAD 6
Righting Arms vs. Heel - NMD ANCHORHANDLING CRITERIA
Heel angle (Degrees)
A
r
m
s
i
n
m
10.0s 20.0s 30.0s 40.0s 50.0s 60.0s 70.0s
-1.5
-1.0
-0.5
0.0
0.5
Righting Arm
Heeling Arm
Equilibrium
Crit. Pt
28
29. Conclusions
Recommendation for Stability Requirements during Towing &
Anchor-handling Operations are likely to be covered by the Par „B‟
of the Intact Stability Code, 2008, IMO Res. MSC.267(85) in
2014
We should be prepared with a suitable course to support the
professionals at the operational level
We hope there will be continuous support from the academia
29
Good afternoon…ladies & gentlemen!This work was done by Dephne Chea Wei Peng as her Final Year Project! The project was supervised by Dr Ivan Tam & Dr ArunDevThe topic was proposed by the EMAS Academy.As Dephne is not here, Dr Ivan Tam asked me to make the presentation!If you have any queries, kindly direct them to Dr ArunDev and Dr Ivan Tam after my presentationIn her project Dephne traced the work that is being done in AH stability and hopefully her findings will update us in this area!
Neither the IMO’s regulatory system nor Norwegian regulations have concrete requirements for the stability of anchor-handling vessels.The Commission of Enquiry for BD has acquired information from British and Danish authorities confirming that they do not have separate stability requirements for anchor-handling vessels either.Dephne has looked only into the stability aspects in her studies
The 2008 IS Code is divided into two parts: Part A, which is mandatory, contains general intact stability criteria for cargo and passenger ships. Part B, which is recommendatory, contains intact stability criteria for certain types.
Max GZ of an OSV is allowed to occur at much smaller angle of heel than normalAs per Clark & Hancox (2012) Minimum freeboard criteria for OSV is inadequate for anchor-handling operation
Each AH Vessel should have its AH Operation ManualAs per Marine Safety Forum it should incorporate the NMD recommendationsPrior to sailing, a document must be displayed on the bridge, where it is visible to be navigator on duty, to show the acceptable vertical and horizontal transverse force/tensions to which the vessel can be exposed.This should show a sketch of the GZ curve and a table of the tension/forces which give the maximum acceptable heeling moment.
AH Manual Template also incorporates the NMD recommendations, which is explained in the next slide
3 NMD CriteriaHeeling Moment Levers should be ‘h’ is distance from the CL to the end of the Stern Roller ‘v’ is the distance from top of stern roller to CL of Thrusters.
NMD Proposal to IMO for Amendment of the 2008 Intact Stability Code Part B providesInformation on Application Point & Direction of a Towline in the Stern of a multi-operational mode vessel alpha - beta
Heeling Moment has two main components as shown
Values from a typical example show the effects of sideways angle ‘alpha’ & downward angle ‘beta’
Then it is possible that as ‘α’ is increased MH could reach to an unacceptable level!
Norwegian proposal is based on a concept of αconstant heeling moment MHLine tension only dependent on sideways angle ‘α’
Line Tension vs sideways angle ‘α’ for a fixed moment
Finally, a simplified Angle Alpha vs Tension could be createdFor use by the operatorsMark the angle segments which are made specially for the operators!
This visual could be put on the bridge for the benefit of operators.This one also includes the dynamic factors.
Finally, stability limiting curves also have to be made
With its specific requirements
These amendments are expected in 2014
Now will show you some screenshots of theAutoload Software on one of the EMAS vessels
Autoload 6 Assumptions
Anchor handling inputs to the software!
One can choose the NMD Anchor-handling criteria.
General Interface of AUTOLOAD 6 – Hydrostatics, Anchor Handling & Margins
This is IMO Intact Stability Analysis
NMD Anchor Handling Criteria line tension 250 t alpha – 10 degrees
NMD Anchor Handling Criteria line tension 350 t alpha – 10 degrees
NMD Anchor Handling Criteria line tension 650 t alpha – 10 degrees