Draft for Public Consultation
CentrePort Harbour Deepening Project:
Assessment of Environmental Effects
NAVIGATION REPORT
Date: April 2016
Prepared by:
Captain Charles Smith,
Marine Services Manager/Chief Pilot
CentrePort Ltd
Version status:
DRAFT FOR PUBLIC CONSULTATION
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Glossary of terms
AIS
Automatic Information System - vessels equipped with this equipment
broadcast positional and movement information via a VHF radio band
to other vessels and stations in the locality
B
Beam - ship's width
cable
Measure of distance - 185 metres, or 1/10 of a nautical mile.
CD/Chart Datum
Chart Datum - zero of all tide predictions
Draught
The amount of ship in the water in a vertical sense
Drift angle
The angle between the vessels head and her course made good in
response to wind pressures on the side
DUKC System
Dynamic Under Keel Clearance - a propriety system to calculate under
keel clearance using real time parameters
Dynamic Underkeel Clearance
Underkeel clearance of a ship when moving (as distinct from a DUKC
system)
Front Lead
Outer beacon and light, when aligned with the Rear Lead, gives the
alignment and centre of safe water when entering the port
Falcon Shoal
A navigational beacon marking the eastern edge of a shoal. Ships
inward bound with a draught over 7m always pass this to the east of
the Beacon and vice versa.
Heel
Angular body movement from the vertical in the transverse plane
HWN
High Water Neaps
HWS
High Water Springs
knot
Unit of speed at sea - 0.5144m/sec or 1 nautical mile per hour
LW
Low water - tide height (may also be LWS or LWN which refers to the
spring or neap cycles)
LAT
Lowest Astronomical Tide - tide will not normally fall below this level
Maximum draught
The draught to which a vessel can be loaded to in a given set of
conditions whilst maintaining enough under keel clearance to ensure
safe passage
m
Metre
mb
Millibar - unit of pressure
MHWS (HWS)
Mean High Water Springs - average height of high waters when
heights are highest around new moon and full moon - about 14 days
apart
MHWN (HWN)
Mean High Water Neaps - average heights of high waters over a
period when tides are lowest - about 14 days apart when moon is in
quadrature
MSC
Mediterranean Shipping Company
nm
Nautical mile - 1.852 kilometres
NIWA
National Institute of Water and Atmospheric Research
Optimised depth/profile
The minimum depth allowing for squat and ship dynamic motion
factors, which allows a vessel to just make a transit of the channel, but
without any safety factor.
The profile are the calculated optimised depths for any point of the
channel
Over dredge
The amount allowed for to take account of variations in the dredging
process - normally 0.5m.
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Period (of a wave)
The time in seconds between two following crests or troughs of a wave
system
Pilot Exemption Certificate
A certificate awarded to a ship’s master after examination allowing him
to operate his vessel without a Pilot on board
PIANC
Permanent International Association of Navigational Congresses
PPU
Pilots Portable Unit - navigation computer
Rear Lead
Inner beacon and light, when aligned with the Front Lead, gives the
alignment and centre of safe water when entering the port
RAOs
Response Amplitude Operator: engineering statistics that are used to
determine the likely behaviour of a vessel and calculated for all ship
motions and all wave headings
Scend
A combined ship motion of roll, pitch and surge
Significant wave height
The average height of the highest 1/3 of all waves (sea and swell)
passing a given point in a given time - it is not the maximum height
which may be nearly double this height
Shoaling
Gradually decreasing depth
Slot
A space aboard a container ship to hold a container
Squat
The change of draught and trim when a moving vessel reacts with the
proximity of the harbour bottom. It is a downward displacement of the
vessel due to the accelerated flow of water between the hull and the
bottom causing a low pressure zone below the vessel
Static draught
Draught of a ship when stationary - dependant on local water
properties
Static UKC
Under keel clearance when the ship is at rest - dependant on local
water properties
Swell
Water motions not described as sea waves - usually a longer period
than sea waves. Primarily generated by wind forces outside the local
area
TCW
Thorndon Container Wharf
Tide cycle
For this report - between two high waters - approximately 12 hours
Tidal windows
1. A tidal window is a period of time when a vessel can set sail and safely
complete the desired transit in the expected wave climate. The
opening and closing of the window is associated with changing tide
heights
TEU
2. Twenty Foot Equivalent Unit - The twenty-foot equivalent unit is an
inexact unit of cargo capacity often used to describe the capacity of
container ships and container terminals. It is based on the volume of a
20 foot long (6.1m) intermodal container. Containers come in different
sizes (ie 20 foot, 40 foot, 45 foot, hi-cube) but they are always
referenced back to a 20 foot equivalent
UKC
3. Under Keel Clearance - distance allowed for from the bottom of the
vessel to the sea floor when the ship is at rest (see also Static UKC)
Yaw
4. Swinging each side of course line in response to swell waves from the
stern
Zero Crossing Wave Period 5. A time measure - often taken as the time between the peaks of
successive waves
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1.
EXECUTIVE SUMMARY
1.1
Key characteristics of Wellington harbour and container operations at CentrePort are:
(a)
it has a harbour entrance which is 750m metres wide at its narrowest point (near Steeple
Beacon) and is 7,400 metres long from Pencarrow Light to Falcon Shoal;
(b)
having navigated the entrance, and once north of Falcon Shoal, the harbour opens up to be a
large basin with depths of about 21m; and
(c)
Aotea Quay has a total length of 1700m (TCW has 560 metres of crane rails and is used as
the container wharf for CentrePort).
1.2
Wellington harbour entrance shipping channel has a minimum depth at Chart Datum is 11.3 m. In
terms of shipping the channel has the following depth limitations:
1.3
(a)
maximum ship’s draft at High Water Spring (maximum) tide of 1.8m is 11.6 meters; and
(b)
maximum ship’s draught on a normal Low Water tide of 0.4m is 10.2 meters.
Any vessel with a draught greater than 10.2m can be expected to have some delay for tide due to
the restrictive depth in the shipping channel.
1.4
CentrePort is using a 14.5m laden draught container ship of modern design with a beam dimension
for its channel dredging design purposes. This is the same draught as being used by the ports of
Tauranga and Otago for their dredging projects. The dimensions of the model design ship for the
project, the MSC Antalya, are:
(a)
Length: 299.9m.
(b)
Beam: 48m.
(c)
Design loaded draught: 14.5m.
(d)
TEU capacity (at 14t average weight per container): 9400.
(e)
Built 2013.
1.5 The larger ships will transit through the shipping channel at the same speeds (8-12 knots) as
current vessels. At this speed limitation there will be negligible variation in wake or noise compared
to existing vessels.
1.6
1
The proposed channel has been designed to satisfy the PIANC Guidelines 2014 ("PIANC
Guidelines") which provide for international best practice for shipping channel design. By applying
the PIANC Guidelines I consider that a channel width of 217 metres is required.
1.7
A multifaceted process has been used to establish the optimised channel configuration with the
design profile being narrowed down and improved through a series of iterations based on both
theoretical and practical inputs. The following steps were involved:
(a)
determining the physical environment that has the potential to affect the navigation of vessels
using CentrePort;
1
PIANC: Permanent International Association of Navigational Congresses.
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(b)
establishing the behavioural and navigational characteristics of the design vessel, such as
hull shape, and responses;
(c)
establishing underkeel clearance ("UKC") and understanding vessel motions that can affect
UKC along the transit and at the berth;
(d)
preparing a preliminary design profile in the first instance using PIANC guidelines;
(e)
checking the preliminary theoretical design against computer simulations using 10 years of
hindcast data and confirming the channel concept design for further testing; and
(f)
refining the design using real time simulation exercises in the ship simulator in Launceston,
Tasmania, using experienced pilots.
1.8
The simulator enabled the behaviour of the model vessel in various environmental conditions to be
observed and underkeel clearances closely monitored until the vessel touched the harbour bottom
(or not). The required depth of the optimised channel varies according to its position measured
from the inner (harbour) end of the shipping channel. This is because of the changing vessel
responses to the increasing wave energy along the channel and the angle and period of encounter.
1.9
To enable the design vessel at 14.5m draught to undertake a safe transit of the harbour entrance at
all tides and during a 6m swell height necessitates the seabed at the outer end of the channel to be
deepened further to approximately 17.2 mCD - whereas it will only be 16.5 mCD at the inner end.
1.10 Thordon Container Wharf ("TCW") is CentrePort’s main container berth. Once a vessel has
navigated the channel it must be berthed at a working berth which can also accommodate the
vessel at all stages of the tide cycle. As a vessel is in a static state when berthed the UKC is
reduced to 0.6m as there are no dynamic factors to be allowed for, only possible rare negative tidal
factors. Therefore, a maximum depth of 15.2 mCD is required for the berth pocket.
1.11 To enable bigger vessels the berth must be able to be approached from both the north and the
south to suit varying wind conditions, particularly in strong winds, as well as stevedoring
requirements resultant from the stowage of cargo aboard the vessel. The approaches to TCW must
be at the same depth as the berth to ensure that the vessel can safely access and leave the wharf
at all times (both to meet shipping schedules and to enable the evacuation of the berth in an
emergency).
1.12 The present approach from the south is in water deep enough to safely accommodate the design
vessel's draught. However, the seabed shoals to the north to a depth that cannot accommodate the
design vessel's draught. This means that to be compatible with the designed channel depth both
the berth and the northern approach to the berth have to be deepened.
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1.13 All vessel activity associated with the dredging and disposal activities will be managed by
CentrePort and the Regional Harbourmaster and any changes to the current navigational
requirements and procedures will be less than minor, although temporary Operational Rules will be
developed. Ultimately the navigational environment will be improved as a new sector light will be
fitted on Pencarrow Lighthouse. Following a Risk Assessment process, specific operating
procedures will be developed once the size and type of the dredger is known. However, in general,
the contents of any Operational Rules will cover:
(a)
consent requirements and conditions;
(b)
managing shipping conflicts during dredging and at the disposal sites;
(c)
weather limitations; and
(d)
navigational aspects other than that contained within the examination for a Pilotage
Exemption Certificate.
1.14 The MetOcean Reports identify that the deeper and wider channel will result in changes to the
hydrodynamics of the harbour entrance, however they will not have any effect on vessel navigation.
1.15 As the port has a 24 hour Local Port Service station on Beacon Hill which overlooks the harbour
entrance and the channel management of the navigational aspects of dredging in the shipping
channel will be readily achieved. All shipping, including recreational harbour users, which transit
through the harbour entrance are managed or monitored through this Station.
2.
INTRODUCTION
2.1
As explained in the Operations and Commercial Report there is a global trend to larger container
vessels. As a consequence New Zealand ports are preparing for the arrival of larger vessels with
deeper drafts. The Operations and Commercial Report records the dredging that has commenced
for the Ports of Tauranga and Otago, and considers it likely that 6,500TEU vessels will visit New
Zealand waters from the end of 2016. Those ports which cannot accommodate the larger vessels
will either become feeder ports or miss out on future container trade altogether.
2.2
New Zealand ports planning to accommodate deeper draught vessels and have obtained or are
seeking consents to dredge to chart datum depths as follows:
(a)
Tauranga: depths of 16.5 to 18.5m (including overdredge allowance and deeper in the
entrance). Spring tide range 1.78m
2.3
(b)
Otago: depths of 15 to 17.5m (deeper in the outer channel). Spring tide range 2.08m
(c)
Lyttelton: depths of 17.8m. Spring tide range 2.39m
(d)
Auckland: depths of 12.5m. Spring tide range 2.98m
Key characteristics of Wellington harbour and container operations at CentrePort are:
(a)
it has a harbour entrance which is 750m metres wide at its narrowest point (near Steeple
Beacon) and is 7,400 metres long from Pencarrow Light to Falcon Shoal (see Figure 1
following);
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(b)
having navigated the entrance, and once north of Falcon Shoal (see Figure 1), the harbour
opens up to be a large basin with depths of about 21m; and
(c)
Aotea Quay has a total length of 1700m (TCW has 560 metres of crane rails and is used as
the container wharf for CentrePort).
2.4
The areas proposed to be dredged, and the disposal areas, are shown in Figure 1 below. As can
be seen from Figure 1 the shipping channel is aligned through the very centre of the harbour
entrance. Vessels navigate the entrance using the two leading lights.
Figure 1: Plan showing extent of project
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2.5
Falcon Shoal is a shallow area to the west of the main channel that is not navigable to ships of deep
draught. Falcon Shoal Beacon marks the eastern edge of this area.
2.6
CentrePort has been very careful to align the proposed dredged channel close to existing shipping
routes which are safe and efficient from a ship handling perspective.
3.
PURPOSE
3.1
The purpose of this report is to:
(a)
describe current and future vessel characteristics;
(b)
identify current navigational and safety requirements;
(c)
identify the navigational and other (ie safety) requirements of larger ships using Wellington
harbour; and
(d)
describe the weather and wave environment, how this affects large vessels and how this is
related to channel optimisation to determine and efficient and safe channel design.
4.
EXPERIENCE AND EXPERTISE
4.1
I have a Master Foreign Certificate and an Unlimited Pilot’s Licence for the Port of Wellington.
4.2
I have been employed by CentrePort and its predecessors since 1972 as Pilot Launchmaster,
Tugmaster and since 1975 as a Pilot. I was promoted to Marine Services Manager/Chief Pilot in
1996.
4.3
I have piloted over 7000 ships of all sizes (up to Queen Mary 2 size - 148,000 tons gross and 345m
in length) in all weather conditions into and out of Wellington harbour.
4.4
My present duties include:
(a)
managing CentrePort’s marine activities;
(b)
co-ordinating the activities of pilotage, towage, launch and mooring services;
(c)
ensuring that CentrePort’s marine operations meet all industry standards, best practice and
Code/Rule requirements; and
(d)
liaising with the Harbourmaster in matters of daily operations and the Port & Harbour Safety
Code.
5.
THE CURRENT SHIPPING CHANNEL
5.1
Wellington harbour entrance shipping channel is shown in Figure 2 below. The entrance channel is
well marked and identified by a set of main leads, an entrance buoy, a lighthouse at the entrance
and a beacon at Steeple Rock. There is also an up harbour light on Matiu / Somes Island which is
a visible light when entering the harbour.
5.2
The shipping channel is on an alignment of 016.5/196.5 degrees. The shipping channel centreline
is marked by the transit of two lights (labelled "Front Lead" and "Rear Lead" in Figure 2 below)
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which are located 1.3nm (nautical miles) apart. The centreline has ships taking a central position,
equidistant from dangers on both sides, in particular from Barrett Reef and Pencarrow Head.
5.3
An inward bound vessel navigates with the lead lights in line until abeam of Steeple Light (labelled
on Figure 2 below), when the inward course is altered to approximately 005 degrees. Outward
bound vessels in general use the reverse of the inward tracks but positioned westward of the inner
tracks so that passing ships always pass port to port.
5.4
The main lights are illustrated in Figure 2 below.
Figure 2: Wellington harbour shipping channel - key features
Somes/Matiu Lt
Rear Lead
Falcon Shoal Bcn
Front Lead
Steeple Bcn
Pencarrow Light
Pilot Stations
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5.5
Although not entirely constraining for vessels of lighter draught, the length of the channel for deeper
vessels (presently deemed as vessels over 10.2m in draught) extends between Pencarrow Light
◦
(Lat 41◦ 29.9’S) and Falcon Shoal Beacon (41 18’S). This distance is 3.6 nautical miles (7,400
metres). Once north of Falcon Shoal Beacon the harbour opens out to become a wide basin with
depths up to 21 metres (in general) until the berth margins are reached.
5.6
Currents through the shipping channel flow predominately NNW/SSE x 0.5 knot at Steeple Beacon
and mainly N/S near Pencarrow Light.
5.7
Wellington harbour entrance channel, and the harbour itself, is of sufficient scale that there are no
restrictions to the length of any vessels. CentrePort’s Pilots regularly handle cruise liners in the
315m length range and the Queen Mary 2 (which has visited the port on three occasions) is 345m
in length. Longer vessels are planned from 2016.
5.8
At its narrowest point the width of the present shipping channel is 750 metres. This is situated
adjacent to Steeple Beacon.
5.9
In terms of depth, the shipping channel the minimum depth at Chart Datum is 11.3 m. In terms of
shipping the channel has the following depth limitations:
(a)
maximum ship’s draft at High Water Spring (maximum) tide of 1.8m is 11.6 meters; and
(b)
maximum ship’s draught on a normal Low Water tide of 0.4m is 10.2 meters.
5.10 Any vessel with a draught greater than 10.2m can be expected to have some delay for tide due to
the restrictive depth in the shipping channel.
6.
CURRENT SHIPPING CHARACTERISTICS
6.1
As already mentioned, for the reasons set out in the Commercial Report, the size of international
vessels (both container and bulk) continues to increase. In relation to vessels entering CentrePort
this is illustrated in Figure 3.
Figure 3: CentrePort's average ship size 2009 - 2015
35000
Gross Tons
30000
25000
20000
15000
10000
5000
0
FY-09
FY-10
FY-11
FY-12
FY-13
FY-14
FY-15
Average Ship Gross Tonnage
25475 25887 25792 28746 32840 31072 32995
Piloted
6.2
In considering the present situation the existing channel depth is limiting for vessels with a draught
greater than 10.2m. In the period of 1 January 2010 to 31 December 2014 two hundred and
seventy one (271) vessels visiting CentrePort had a draught of 10.2m or greater and had to time
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their arrival for the high tide. In this same period from a total of 6120 piloted vessels nine had a
draught exceeding 11m, with the maximum draught being 11.5m.
6.3
Not only are container ships affected by draught limitations. In March 2015 Queen Mary 2 which
had a draft of 10.3m had to abort her call as there was not enough water to safely transit the
channel in a swell condition which was about 6m high at the entrance.
Deep draught tankers
going to Seaview may also be subject to delays on account of lack of depth. There is 11.1m of
depth at the Seaview berth but vessels arriving with a draught greater than 10.2m have to wait for
the tide to rise to pass through the harbour entrance. Import tankers arriving from an overseas port
generally have to discharge at Lyttelton or Tauranga first if they are not prepared to wait off
Wellington.
6.4
The vessel ‘Kota Loceng’ pictured in Figure 4 below has called at CentrePort numerous times. It is
typical of a current modern container vessel which comes in and out of the NZ trade as arranged by
the respective shipping line. Her parameters are:
6.5
(a)
Length: 266m.
(b)
Beam: 32m.
(c)
Design loaded draught: 12.7m.
(d)
TEU capacity (at 14 ton average weight per 20’ container): 4335.
Although her design draught is 12.7m, when she visits Wellington she is at an interim stage of her
NZ rotation so not heavily laden. This means that she sits higher in the water. Her draught when
she visits CentrePort is between 9.0 and 10.6m, depending on the export season.
Figure 4: Kota Loceng
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7.
DESIGN VESSEL AND CHARACTERISTICS OF THE LARGER SHIPS
7.1
The Shipping Channel Deepening Project has a planning horizon extending well into the future to
enable a 'generational' change in ship sizes to visit CentrePort. Approach channels to a port are
designed using the concept of a ‘design vessel’. A design vessel is chosen to ensure that the
channel, post dredging, will allow the design vessel and similar vessels to navigate in safety.
7.2
2
The proposed channel has been designed to satisfy the PIANC Guidelines 2014 ("PIANC
Guidelines") which provide for international best practice for shipping channel design.
7.3
As explained in the Operations and Commercial Report CentrePort is using for channel dredging
design purposes a container ship of modern design with a beam dimension not yet calling at New
Zealand ports but one that is likely to within the term of the consents sought. As described in the
Operations and Commercial Report a 14.5m laden draught is a common draught across a wide
range of larger container vessels (excluding the mega-vessels) and is the same draught as being
used by the ports of Tauranga and Otago for their dredging projects.
7.4
The dimensions of the model ship for the project, the MSC Antalya, are:
(a)
Length: 299.9m.
(b)
Beam: 48m.
(c)
Design loaded draught: 14.5m.
(d)
TEU capacity (at 14t average weight per container): 9400.
(e)
Built 2013.
Figure 5: MSC Antalya
2
PIANC: Permanent International Association of Navigational Congresses.
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7.5
Apart from its beam the MSC Antalya is similar in draught to vessels chosen as the model design
3
for other ports. For example the port of Tauranga used the Susan Maersk. Her details are:
(a)
Length: 347m.
(b)
Beam: 42.8m.
(c)
Design draught: 15m.
(d)
TEU capacity (at 14t average weight): 8,160.
(e)
Built 1998 (ie an older vessel).
7.6 For the reasons explained in detail in Section 8 below, key for channel design in Wellington Harbour
is the MSC Antalya's design draught of 14.5m and beam of 48m. This is wider than any vessel that
presently visits CentrePort (and New Zealand). CentrePort has deliberately chosen a beamier
vessel to provide it with future proofing in its channel design. The Port of Tauranga is currently
investing in two super post-Panamax gantry cranes capable of servicing vessels with this beam.
7.7 The larger ships will transit through the shipping channel at the same speeds (8-12 knots) as
current vessels. At this speed limitation there will be negligible variation in wake or noise
compared to existing vessels. An examination of the design vessel’s trial data shows that the
engine will be on revolutions of only 34 rpm to give 9.2 knots. Full speed is 84 rpm. Thus only a
small fraction of the vessel’s total power is required to undertake the channel transit. In effect the
engine will be only idling, and therefore the noise output will be low. CentrePort has never received
any complaints about ship noise or wake in the channel (other than small fast ferries). Figure 6
4
below shows how the hull is fine lined . This allows an easy passage through the water and in my
opinion the wake characteristics will be comparable to existing vessels entering the harbour as
illustrated in Figure 7.
3
Taken from http://www.maersk.com/en/hardware/fleet/maersk-line/sovereign-m%C3%A6rsk-class/susan-m%C3%A6rsk noting the
draught of 15m is not consistent with the draught of 14.5m in the Environment Court's description at paragraph [63] of Te Runanga o
Ngai Te Rangi Iwi Trust and Others v Bay of Plenty Regional Council and Others [2011] NZEnvC 402.
4
Her block co-efficient, as provided by the master of the vessel, (shape of hull compared to a block of same dimensions) at light
draught is 0.632 and loaded 0.712 so this confirms her fine lines.
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Figure 6: The fine hull shape lines of a typical larger container vessels
Figure 7: wake emanating from the 3,500 TEU container ship MSC Banu at a speed of 15 knots
7.8 Figure 7 above shows the wake emanating from the 3,500 TEU container ship MSC Banu at a
speed of 15 knots when at a draught of 9 metres. It is not significant and illustrates the point made
above that wake effects will be minimal at a slower speed. The photo was taken between the Front
Lead and Steeple Beacon.
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8.
CHANNEL REQUIREMENTS FOR THE LARGER SHIPS
Channel characteristics
8.1
The proposed channel for larger vessels generally retains the orientation of existing vessel tracks
with a minor variation only of the alter course position (the elbow in the shipping channel shown in
Figure 1).
8.2
It is anticipated that an additional lead mark will be needed on the eastern shore of the harbour to
assist outward transits in particular. Following the June 2015 Optimisation Tests in the Ship
Simulator in Launceston Tasmania, this additional navigational mark (in the form of a sectored light)
will be fitted to the existing Pencarrow Head Lighthouse.
8.3
To enhance precision navigation, Pilots will be utilising portable piloting units (PPUs) which derive
positional information and heading from GPS satellites to provide positional, speed, heading and
rate of turn information. PPUs allow Pilots to make complex manoeuvres in confined spaces with
accuracy and in adverse conditions, including fog.
8.4
The proposed channel will be a one way channel. That is only one large vessel will navigate in the
channel at a time with appropriate traffic controls to avoid conflicts with other shipping.
8.5
Figure 8 shows the difference between a channel and fairway width.
Figure 8: Channel and fairway widths
Line of leads/channel
centre
Width of fairway
Width of channel
8.6
The width of a proposed shipping channel is determined by applying the PIANC Guidelines as
shown in Table 1. The PIANC Guidelines provide international best practice for the safe navigation
of ships into and out of ports. I therefore used the PIANC Guidelines in determining the
characteristics of the shipping channel required to safely allow larger vessels to enter Wellington
Harbour (see Table 1).
8.7
The PIANC Guidelines set a number of criteria which, apart from a 1.5 factor for a basic 1 way
manoeuvring lane, are each given a factor rating (of between 0 and 2 times the vessel’s beam)
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depending on the characteristics of the chosen port. I have applied my experience and knowledge
of navigating Wellington harbour to determine what I consider to be the appropriate factor for each
criterion. For example Wellington Harbour has very low cross current speed so that criterion is
given a low factor of 0.2.
8.8
The PIANC Guidelines also allow port specific criteria to be added to reflect specific risks. For
Wellington harbour the only additional criterion I consider necessary is an allowance for yaw. Yaw
(swinging each side of course line) can occur when entering Wellington harbour with a larger
southerly swell to the stern. As shown in Figure 9 below, this causes the stern of the vessel to be
displaced with the momentum of the wave further away from the course line than the bow of the
vessel. The design vessel length (299.9m) with a 3 degree drift angle results in the stern using an
additional 16m of channel width when the wave conditions apply. As a result, for safety reasons I
have factored an additional 20m for yaw or drift angle. This allowance for a drift angle may also be
applicable when a very strong wind comes from a relative direction rather than from directly ahead
or astern.
Figure 9: The effect of yaw on vessel drift from the channel centre line
5
PW= path width. The vessel
pivots about her natural pivot
rd
point which is about 1/3 of
her length from the bow
8.9
By applying the PIANC Guidelines I consider that a channel width of 217 metres is required. This is
calculated as set out in Table 1 below. As can be seen from Table 1 the key to determining
channel width is the beam of the vessel. As set out above the beam of the design vessel, the
MSC Antalya is 48m.
Table 1: Application of the PIANC Guidelines to determine channel width for the design
vessel (MSC Antalya) with a beam of 48m
6
Basic for manoeuvring lane
Speed 8-12 knots
Cross wind between mild and moderate
Cross current - low, moderate speed
Longitudinal current - low, moderate speed
Quartering stern wave 1-3m
5
6
1.5B
0.0
0.3
0.2
0.1
0.5
This pathwidth is calculated by the formula: PW=(length*SINdrift angle)+width*COSdrift angle)
PIANC Guidelines - page 85.
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Aids to navigation - good
Depth - smooth and soft
Depth of waterway
Bank slope - port - mod speed, sloping sides
Bank slope - stbd - mod speed, sloping sides
4.1 x 48
0.2
0.1
0.2
0.5
0.5
4.1B
197m wide
Add 20m for Wellington harbour channel yaw effect
217m wide
8.10 The design channel will have sloping sides of up to 1:5 for the section north of the Front Lead and
up to 1:9 for the central and southern sections of channel.
Channel depth and optimised channel profile
8.11 From a navigational point of view there are no constraints for bigger ships using Wellington Harbour
other than depth in the harbour entrance channel and the approach/berth at TCW.
8.12 The design vessel illustrations and all project documentation refer to a depth capable of handling a
vessel of 14.5m laden draught plus allowances as described elsewhere in this report. This resultant
depth is the depth of water required for safe navigation. In addition an over dredge allowance of
0.5m is required. As explained in the Dredging Report this is an accepted international measure
and safety margin which allows for the difficulties arising from accurately positioning the dredge
drag-head and in survey.
8.13 The decision as to the channel depth required is a technical navigation and safety decision, as well
as a commercial and environmental decision, which strikes a balance between the amount of
material to be removed (and its effects), the operational window selected (98%) that has been
chosen for vessels to safely transit the channel. This is called the optimised channel profile.
8.14 A multifaceted process has been used to establish the optimised channel configuration with the
design profile being narrowed down and improved through a series of iterations based on both
theoretical and practical inputs. The following steps were involved:
(a)
determining the physical environment that has the potential to affect the navigation of vessels
using CentrePort;
(b)
establishing the behavioural and navigational characteristics of the design vessel, such as
7
hull shape, and responses (RAOs );
(c)
establishing underkeel clearance ("UKC") and understanding vessel motions that can affect
UKC along the transit and at the berth;
(d)
preparing a preliminary design profile in the first instance using PIANC guidelines;
(e)
checking the preliminary theoretical design against computer simulations using 10 years of
hindcast data and confirming the channel concept design for further testing; and
(f)
refining the design using real time simulation exercises in the ship simulator in Launceston
using experienced pilots.
7
Response Amplitude Operators - see glossary.
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8.15 The required depth of the shipping channel to accommodate larger vessels was determined by the
following need factors:
(a)
the draught of the design vessel (14.5m); and
(b)
provision for a static UKC of 1.5m.
8
8.16 Described simply, UKC is the gap between the bottom of a vessel and the seabed. The UKC
required varies as to whether the vessel is stopped (static UKC) or moving (dynamic UKC). This is
because a vessel sits deeper when it is moving through the water - this is known as squat and it
varies according to the square of the vessel’s speed (see Figure 10). The increased draught when
the vessel is moving is known as the dynamic draught.
8.17 The key factors relevant and affecting UKC for ships transiting the channel are:
(a)
tides (as measured along the channel);
(b)
vessel motion (as caused by wave responses);
(c)
squat (how the ship sits in the water when moving); and
(d)
heel (caused by turning, wind or yawing).
8.18 Each of these factors is discussed below and the combined effect is shown on Figure 10 below as
'sinkage'.
9
8.19 One calculation to obtain this is to use Barrass' formula (Cb x v2/100) where Cb is the vessel's
2
block co-efficient and v is the speed squared. Research however suggests that the largest draft
increase in a wide bodied ship may actually be at the ship’s widest part where 2 degree of list or
heel for a vessel of 48m beam will increase the draught by 0.84m. This shows the importance of
allowing sufficient UKC when assessing proposed channel depths.
Figure 10: Vessel’s sinkage allowance to arrive at dynamic UKC.
Static condition
waterline
Tides
Dynamic condition
Static draught
Dynamic draught
Sinkage
Static UKC
Dynamic UKC
Bottom
draught
8
9
This UKC level is determined as safe through my experience of piloting vessels through the Wellington harbour shipping channel.
Ship Dynamics for Mariners - Nautical Institute P.188. Formula by Dr Barrass.
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8.20 A ship moves in six planes (see Figure 10 below) and these movements are described:
(a)
pitch - fore and aft changes caused by how the sea or swell supports the vessel, will increase
the draught;
(b)
roll - caused by wind, waves or turning where draught at the bilge (outside corner) will be
increased;
(c)
heave - a bodily lift up and down;
(d)
yaw - swinging each side of course line;
(e)
surge - fore and aft movement; and
(f)
sway - sideways movement.
Figure 10: Illustration of ship movements
8.21 As shown in Table 2 below, Wellington's tidal range of about 1.36m is low and the smallest range of
any main port in New Zealand.
Table 2 and 2a: Tides and tidal ranges for Wellington harbour
10
Chart Datum
Low Water
High Water
Range
Spring tide
0.0
0.45
1.81
1.36
Neap tide
0.0
0.73
1.49
0.76
Nautical Almanac 1914.
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8.20 The small tidal range makes it difficult for CentrePort to take advantage of significant increases in
tidal levels to 'work the tide' with acceptable entry or departure windows as shown in Table 3.
Table 3: Periods of availability of the channel if dredged to accommodate 14.5m at HW only
(along with maximum draughts at intermediate stages of the tide cycle)
Period in tide
cycle
HW
LW + 5 hours
LW + 4 hours
LW + 3 hours
LW + 2 hours
LW + 1 hour
LW
Permitted
draft
14.5m
14.4m
14.1m
13.8m
13.6m
13.4m
13.3m
Total period of availability in the tide cycle
HW only - twice in each 24 hr period
Across 2 hours of each 12 hour tide cycle (ie 4 hrs/24hrs)
Across 4 hours of each 12 hour tide cycle (ie 8 hrs/24hrs)
Across 6 hours of each 12 hour tide cycle (ie 12 hrs/24hrs)
Across 8 hours of each 12 hour tide cycle (ie 16 hrs/24hrs)
Across 10 hours of each 12 hour tide cycle (ie 20 hrs/24hrs)
Available all tides
Table 3 is calculated on a tidal range of 1.2m - approximately the spring range. During neap tides
the maximum draft at HW would be 14.2m (Spring HW - Neap HW = 0.32m).
Harbour entrance weather
8.21 The primary source of sea and swell data is from a Waverider buoy operated by NIWA under
contract to Greater Wellington Regional Council since 1999. The buoy is located close to the main
pilot boarding stations: Alpha, Bravo & Charlie. CentrePort also sources data from logging devices
on the Front Lead Light structure in the channel. Wind data is also used from the closest
meteorological monitoring site, which is at NIWA’s research station at Baring Head.
8.22 The entrance area is highly exposed to southerly sea and swell, with an extremely large fetch for
these conditions. 5.9% of the wave records have a significant wave height in excess of 3m. The
average number of days in a year when the significant wave heights exceeds 3m is 56. On average,
9 days per year exceed 5m. In terms of the maximum individual wave, H max, 61 days per year on
average exceed 5m. During a storm in June 2013, Hmax exceeded 15m three times in the course of
a day. Wave heights in general are greater in winter months when southerly storms are most
prevalent.
11
8.23 The onset of a high sea state with the arrival of a southerly front is often very rapid, and it poses a
potential hazard to mariners. Southerly sea and swell dominates the sea state at the Waverider
buoy.
8.25 Tidal currents modulate the significant wave height by as much as a metre. Within the harbour
entrance itself, the shoaling (reducing) depth also significantly shortens the wavelength and
steepens the waves.
8.26 Strong winds are common from both north and south. The mean wind speed at Baring Head is
19 knots with a 90 percentile wind speed of 33 knots and a maximum of 77.5 knots.
Vessel Motions
Introduction
8.27 Vessel motion is affected by the sea state with swell and sea waves causing reduced depths in the
troughs of waves. The resultant motions are further affected by the angle at which the waves strike
11
NIWA Report (Wave Climate of Wellington Harbour Entrance) for CentrePort July 2014.
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the vessel and the period of encounter of the waves. Pitching and rolling along with vertical heave
increases the draught of a vessel. It is therefore important that these motions are clearly identified
in the design of a safe channel.
8.28 Although Wellington Harbour experiences a high frequency of strong winds the limited fetches
12
available in the harbour restrict the growth of sea waves. The exceptions to this are:
(a)
near Steeple Beacon when wind and tide oppose; and
(b)
at the harbour entrance itself as there is considerable fetch to the south, which may extend
up to 1,500 kilometres.
8.29 Northerly winds are the prevailing winds, accounting for about 60% of all winds. Northerlies are
most frequent during the period October to January and least frequent between May and August.
Southerly winds account for about 30% of all winds and are most frequent between May and
August.
8.30 The Waverider buoy is 3 nautical miles south eastward from the harbour entrance. The entrance
itself has distinctive wave and current properties. Outside of the harbour entrance the tidal streams
are generally along the coastline and across the orientation of the entrance. However, once within
the entrance, the ebb and flow of the waters in and out of the harbour dominate the flow so it is
essentially in a north-south orientation. The southward ebb tide through the harbour entrance can
reach rates of 0.9 knots. While not large, this flow compounds the shoaling (or reducing water
depths) effect at the harbour entrance and changes the wave profiles in this area by about a metre
in height.
8.31 On approaching the harbour entrance itself, the depths shoal from 40m to 20m and then to about
11m over a short distance in the narrowest part of the channel. This shoaling causes the
wavelength to shorten which greatly exacerbates the pitching effects of a vessel. The relationship
between depth, speed and wave energy is very complex and the key aspects are summarised
below.
Pitch
8.32 The degree of pitching of a vessel as it transits the channel depends on the both the height and the
length of the wave (the period). As shown in Figure 12 the vessel is supported on a relatively long
wave period in the middle of the vessel. As the wave moves along the ship it will alternately support
and not support the vessel and the ship will pitch accordingly. A short wave alternatively will have
many waves along the length of the ship for support so the pitching effect will be much less. The
vessel’s resistance to pitching is much higher than its resistance to rolling due to its length being
greater than its beam. In this discussion, put simply, long period waves provide increased pitching
amplitudes whilst short period waves produce less pitching. Longer period waves also contain
more energy and are more affected by decreasing depth of water.
12
The length of water over which the wind blows to create waves.
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Figure 12: Long wave period on a vessel
8.33 Shorter period waves, with a slower speed than longer waves, are also more influenced by currents.
Under a southerly swell against an outgoing tide, waves in the harbour entrance in particular
shorten in length and become significantly steeper affecting the pitching behaviour of any vessel.
On the contrary when the tidal current is in the same direction as the wave is travelling there tends
to be a modulation of the wave height and pitching may be increased (but it all depends on the
vessel’s length versus the wave length).
8.34 The Waverider graphs in Figure 13 show the variability of the swell condition off the harbour
entrance with alternate periods of heavy swell and more moderate swell. The consistent swell
direction is from 200 degrees - directly into the harbour entrance and note how the period changes.
Figure 13: Waverider graphs of typical Swell condition off the port entrance
Maximum wave height in blue,
significant wave height in green
Wave period (time between peaks).
Note that there is no consistency
between wave heights and period
Direction swell is coming from - most frequent
from this direction (nearly south)
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13
8.35 With a swell directly ahead a vessel will pitch and in doing so increase her draught.
The degree of
pitching will be related to the ship’s length and the length and period of wave encounter as
illustrated above in Figure 13 above.
8.36 Waves/swell with a period of 7 seconds or less will have minimal effect on a vessel of the design
length, compared to swells of 10 seconds or longer.
8.37 Inward bound, with the swell directly astern the vessel is likely to roll, pitch, scend
14
and yaw as
period of encounter of the waves is longer. This was confirmed on the simulator during the
Optimisation exercise. In all cases these motions increase the vessel’s draught as can be seen in
the following diagram. Once at the Front Lead and north of Steeple Beacon the currents are
weaker and wave effects reduce. For example taking 6th February 2015 at the Waverider buoy the
15
significant wave height was about 4 metres, whereas at the Front Lead it was about 1 metre.
Outbound against southerly conditions the vessel will be steadier as the period of encounter with
the waves has increased.
Squat
8.38 Another key variable is squat. Squat is the bodily sinkage and change of trim of a vessel in the
water when making headway through the water as illustrated in Figure 14 below. This varies from
vessel to vessel and is dependent on hull volume/shape and speed through the water. The amount
of squat depends upon several factors but in certain conditions during the transit may be as much
as one metre.
16
Squat is reduced by reducing speed when this is possible but all vessels have a
minimum controllable speed which is influenced by the weather - in the region of 5 to 8 knots.
Figure 14: Effect of squat on a vessel
As the water accelerates to go under the vessel the pressure drops and the vessel sinks.
Heeling
8.39 Heeling can be caused by yawing (the swinging of the stern of the ship each side of course line) in
response to waves or sharp rudder movements or by wind pressure alone on the side of the vessel
as illustrated in Figure 15 below.
13
A 300m vessel pitching 0.5 of a degree (a difficult movement to determine) will increase her draught by 1.31 metres
A combination of roll, pitch and surge.
15
Significant wave height - mean wave height of the highest1/3rd of all waves - it is not the maximum height (which may be double
this).
16
Squat can be calculated by using Barass’ formula: Squat = (Block Co-efficient) v2 /100. Therefore for a container vessel at 8 knots
squat will be approx. 0.4m.
14
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Figure 15: Effect of heeling on a vessel.
8.40 As can be seen from the above illustration the vessel’s draught is increased on heeling.
17
UKC for Wellington harbour
8.41 The longstanding port static UKC used when calculating draughts and times of transit for the
entrance channel is 1.5m.
8.42 This 1.5m UKC is used to calculate the maximum draught of an existing vessel in the existing
channel at any time as set out in Table 4.
Table 4: Current maximum draught for Wellington
Depth available at Chart Datum
Height of tide (Spring)
Total available depth
Less required static UKC
Vessel’s draught not to exceed
11.3 metres
1.8
13.1
1.5
11.6 metres
8.43 Some ports use 10% draught of the vessel. However, although it may be a coarse measure, 1.5m
UKC works well for the relevant UKC factors listed above, and illustrated in Figure 10, for the transit
of a vessel through the Wellington harbour entrance. In situations of a significant southerly swell
where greater ship movement can be expected the UKC is sometimes increased to a greater
amount as determined from the Pilot’s own risk assessment.
Channel refinement - Optimisation Exercise on Ship Simulator
8.44 Channel characteristics and depth can be refined through modern tools such as a ship simulator.
CentrePort has used simulation to assess how various vessels, and in particular the model vessel
MSC Antalya, behaves from a movement point of view, when entering Wellington harbour in various
weather conditions. Such simulation is common and has been undertaken by other ports (for
example the Ports of Tauranga and Otago) when seeking channel deepening consents.
8.45 In June 2015 CentrePort senior marine and engineering staff undertook thirty eight separate
optimisation exercises on the Ship Simulator belonging to the Australian Maritime College in
17
Increase of draft due to heeling for a ship of 48m beam is determined by (0.5 beam x sine angle of heel). Therefore for 1 degree
heel the increase is 1.31m
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Launceston Tasmania to test MetOcean’s modelling. Figure 16 below shows the graphics from the
simulator of the model vessel.
Figure 16: Fully laden model ship passing through port entrance
8.46 CentrePort’s consultants, MetOcean, considered a variety of operability depth options for the
entrance to Wellington Harbour for the design vessel traveling at 10 knots, fully loaded. The
purpose of the simulator exercise was to test these options for the new proposed bathymetry.
Figures 17, 18 and 19 illustrate the simulator exercise. Entry and exit transits were conducted
within an historical 10-year period during which time the wave, current regime and tides along the
navigation channel were hindcast using numerical models.
8.47 The simulator enabled the behaviour of the model vessel in various environmental conditions to be
observed and underkeel clearances closely monitored until the vessel touched the harbour bottom
(or not). The transit was managed and controlled by a senior pilot who had the task of staying
exactly on track while the Port’s Engineer and Marine Manager viewed data in live time outside the
vessel’s bridge. Swell at the entrance was set at 6m in height and the vessel’s speed was 10 knots
throughout.
Figure 17: Birdseye view of vessel in dredged channel
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Figure 18: Fish eye view - watching vessel pitch in transit
Figure 19: Data - top line is swell and bottom lines is the vessel’s pitch either
end and resultant underkeel clearances
8.48 Centreport purchased a model of MSC Antalya (14.5m draught) which was hydrodynamically
correct and this model was used in varying sea/swell conditions to test model profile assumptions
18
and RAOs as provided by MetOcean.
8.49 The simulations also included checking for the best alignment, width of channel and underkeel
clearances. Transit speeds were undertaken at 10 knots, the manoeuvring speed of MSC Antalya
which gives good responses.
18
Response Amplitude Operators - see glossary
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8.50 In circumstances where the vessel touched the bottom during transit runs careful note was taken of
the circumstances and the positions and the model profiles were adjusted. It was found that:
(a)
after a minor depth modification to one small section of the chosen optimised profile, the
model ship could confidently and safely be navigated in and out of Wellington Harbour at a
speed of ten knots and into swells at the entrance measuring 6m in height;
(b)
that the wave encounter period between inward and outward transits changed ship motion
behaviour with inward transits requiring more management due to the extended period of
wave encounter;
(c)
the proposed width of the channel at the northern end could be reduced saving considerable
dredging effort (as a result of accuracy of navigation and fitting a sector light on Pencarrow
Lt); and
(d)
that by adjusting the direction of the northern leg (course) an existing light structure
(Pencarrow) could be used to fit a new sectored navigation aid.
What channel depth is required?
8.52 The required depth of the optimised channel varies according to its position measured from the
inner (harbour) end of the shipping channel. This is because of the changing vessel responses to
the increasing wave energy along the channel and the angle and period of encounter. Very low
vessel motion is predicted at the inner end of the channel due to much lower wave heights and
absence of swell. Modelling undertaken by MetOcean has shown that at the outer end of the
channel we can have, in a significant southerly wind condition, significant wave height in the order
19
of 6m or more.
8.53 In order to enable the design vessel at 14.5m draught to undertake a safe transit of the harbour
entrance at all tides and during a 6m swell height
20
it necessitates the seabed at the outer end of
the channel to be deepened further to approximately 17.2 metres - whereas it will only be 16.5m at
the inner end. This is similar to Ports Otago and Tauranga who arrived at the same conclusions
when undertaking their modelling and have deepened the outer ends of their channels to allow for
the more robust wave climates. Table 6 shows the depths needed for various draft options.
Depending on the timing of the arrival of the bigger vessels (and their size) CentrePort may wish to
stage the channel deepening programme. Table 6 shows the depths needed for the various
draught options. These are also shown in Figure 20.
Table 6: Channel depths for different draught options
Source of Profile
MSL optimised profile
Plus 0.5m overdredge
MSL optimised profile
adjusted to provide a min UKC
of 1.5m at all locations plus
0.5m overdredge
19
20
Draught
meters
12.0
12.5
13.5
14.5
12.0
12.5
13.5
14.5
Depth (m CD)
North
South
section
section
13.9
14.7
14.4
15.2
15.4
16.2
16.4
17.2
14.0
14.7
14.5
15.2
15.5
16.2
16.5
17.2
For the purposes of this paper we shall use 6m as being a worst case swell height for calculation purposes.
As explained in the commercial report this ensures access to CentrePort by the design vessel 98% of the time.
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8.54 Interpretation of the modelling suggests that a constant dredged depth would only accommodate
significant wave heights along the channel of about 1m (without any safety margin). This would
prove limiting as the harbour entrance is open to heavy seas and swells with considerable fetch (as
described above). Note that 30% of all significant wave heights at the entrance exceed 1.5m in
height with 8% being above 2.5m.
8.55 Figure 20 (over page), provided by MetOcean, shows the optimised depth profile of the dredged
channel for three ship draughts (these steps will be smoothed in reality).
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Figure 20: Required channel dredge depth profiles to accommodate a 14.5m draught vessel in all tides with a 6m swell
Shipping Channel Deepening Longitudinal Profiles
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9.
TCW - THORNDON CONTAINER BERTH
9.1
This is CentrePort’s main container berth. Once a vessel has navigated the channel it must be
berthed at a working berth which can also accommodate the vessel at all stages of the tide cycle.
Some ports accommodate this by dredging a defined and deeper ‘berth pocket’ for the ship to sit in
at LW.
9.2
As a vessel is in a static state when berthed the UKC is reduced to 0.6m as there are no dynamic
factors to be allowed for, only possible rare negative tidal factors.
9.3
Table 7 shows the static berth UKCs used by other NZ ports. They all vary according to their own
circumstances, berth shelter and risk assessments.
Table 7: New Zealand Port's Berth UKCs
Port
Comments
Wellington
0.6m
Napier
0.3m
Auckland
0.4m
vessels less than 28m beam
Auckland
0.5m
vessels 28m beam or greater
Taranaki
1.0m
vigorous environment
Otago
0.3m
Dunedin & Ravensbourne
Otago
0.5m
Container berths
Tauranga
0.8m
Revisiting this parameter down
Bluff
0.7m
Picton
0.3m
Waitohi Wharf
0.5m
Waimahara Wharf
Picton
Gisborne
Nelson
Marsden Pt
9.4
Berth UKC
1.0m min
Revised down from 0.9m in 2013
subject to forecasting
5% draught
0.3m
TCW presently has a depth between 11.3 to 11.9m at Chart Datum. This means that the present
maximum draught at LW is 11.1m to 11.7m (ie 11.3 + 0.4m - 0.6m). To enable bigger vessels the
berth must be able to be approached from both the north and the south to suit varying wind
conditions, particularly in strong winds, as well as stevedoring requirements resultant from the
stowage of cargo aboard the vessel. The approaches to TCW must be at the same depth as the
berth to ensure that the vessel can safely access and leave the wharf at all times (both to meet
shipping schedules and to enable the evacuation of the berth in an emergency).
9.5
Figure 21 shows the extent of deepening required for a larger vessel of the design draught to
access and berth at TCW. A ship’s typical approach line from the north is shown. The approach
line will be modified by the Pilot according to the wind direction and strength.
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Figure 21: Dredging plan for container berth
9.6
The present approach from the south is in water deep enough to safely accommodate the design
vessel's draught. However, the seabed shoals to the north to a depth that cannot accommodate the
design vessel's draught. This means that to be compatible with the designed channel depth both
the berth and the northern approach to the berth have to be deepened.
9.7
The required depth for the TCW access and berth to safely accommodate the design vessel's
draught is calculated as follows:
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(a)
Ship's draught of 14.5m.
(b)
Plus UKC of 0.6m.
(c)
Equals a required depth of 15.1m.
Draft for Public Consultation
(d)
Minus low water tide of 0.4m.
(e)
Equals a dredged depth of 14.7m chart datum (plus an over dredge allowance of 0.5m giving
a total depth of 15.2m).
9.8 This is shown graphically in Figure 22 below.
Figure 22: UKC calculation for the access to, and berth at TCW (plus 0.5 overdredge
means total dredge depth equals 15.2m)
10.
FITZROY BAY AND TCW DISPOSAL SITES
Fitzroy Bay
10.1 Although this area is near the charted Pilot boarding grounds there are no significant navigational
safety issues with the proposed Fitzroy Bay disposal site other than managing any dredger possibly
conflicting with an inward vessel embarking a pilot while the dredge is depositing the dredged
material. Any possible issue will be managed within the Operational Rules process which will be
developed nearer the time (see below).
TCW
10.2 There are no navigational safety issues with the proposed disposal off TCW1 site other than
managing any dredger possibly conflicting with a berthing or sailing vessel while the dredge is
depositing the dredged material. This will be managed within the Operational Rules process which
will be developed nearer the time (see below).
11.
DREDGING MANAGEMENT
11.1 All vessel activity associated with the dredging and disposal activities will be managed by
CentrePort and the Regional Harbourmaster and any changes to the current navigational
requirements and procedures will be less than minor, although temporary Operational Rules will be
developed. Ultimately the navigational environment will be improved as a new sector light will be
fitted on Pencarrow Lighthouse.
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11.2 The MetOcean Reports identify that the deeper and wider channel will result in changes to the
hydrodynamics of the harbour entrance, however they will not have any effect on vessel navigation.
11.3 As the port has a 24 hour Local Port Service station on Beacon Hill ("Beacon Hill Signal Station")
which overlooks the harbour entrance and the channel (see Figures 23 and 24 below),
management of the navigational aspects of dredging in the shipping channel will be readily
achieved. All shipping, including recreational harbour users, which transit through the harbour
entrance are managed or monitored through this Station. This station is owned by the Greater
Wellington Regional Council and managed by the Harbourmaster.
11.4 Beacon Hill Signal Station provides information on weather and shipping to all harbour users. They
maintain a 24 hour watch and, via remote monitoring, can track any vessel equipped with AIS and
radar tracks other vessels in other parts of the harbour not directly visible to them.
11.5 Following a Risk Assessment process, specific operating procedures will be developed once the
size and type of the dredger is known. However, in general, the contents of any Operational Rules
will cover:
(a)
consent requirements and conditions;
(b)
managing shipping conflicts during dredging and at the disposal sites;
(c)
weather limitations; and
(d)
navigational aspects other than that contained within the examination for a Pilotage
Exemption Certificate.
11.6 After completing an approved training programme, Dredger Masters (on a vessel over 500t gross)
will be issued with a Pilotage Exemption Certificate. This means that they will be able to operate
their vessel without a Pilot being aboard. As set out in the Commercial Report and the Dredging
Report there are two possible dredging alternatives - either a large or smaller suction hopper
dredger. In terms of navigational requirements there are few differences between them and either
option can be readily managed to ensure safe operation and use of the harbour by all other vessels
and recreational craft.
11.7 As described above there are very only minor navigational implications to the proposed deposition
areas off TCW and in Fitzroy Bay disposal area (near Pilot Station Bravo as shown in Figure 2
above) that can readily be managed by simple procedures.
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Figure 23: Operator on duty at Beacon Hill Signal Station
Figure 24: View from Signal Station over harbour entrance and disposal site
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