Passage planning
Ship passage planning
1. General
Investigations show that human error contributes to 80% of navigational accidents and that in many cases essential information that could have prevented the accident was available to but not used by those responsible for the navigation of the vessels concerned. Most accidents happen because of simple mistakes in use of navigational equipment and interpretation of the available information, rather than because of any deficiency in basic navigational skills or ability to use equipment.
Masters, skippers and watchkeepers should therefore adhere to the IMO Guidelines taking the following measures to ensure that they appreciate and reduce the risks to which they are exposed:
a) ensure that all the vessel’s navigation is planned in adequate detail with contingency plans where appropriate
b) ensure that there is a systematic bridge organisation that provides for:
(i) comprehensive briefing of all concerned with the navigation of the vessel;
(ii) close and continuous monitoring of the vessel’s position ensuring as far as possible that different methods of determining the position are used to check against error in any one system
(iii) cross-checking of individual human decisions so that errors can be detected and corrected as early as possible
(iv) information available from plots of other traffic is used carefully to ensure against over-confidence, bearing in mind that other vessels may alter course and/or speed
c) ensure that optimum and systematic use is made of all appropriate information that becomes available to the navigational staff;
d) ensuring that the intentions of a pilot are fully understood and acceptable to the vessel’s navigational staff
2. Responsibility for Voyage planning
In most deep-sea vessels the master delegates the initial responsibility for preparing the plan for a voyage to the officer responsible for navigational equipment and publications (hereafter referred to as the navigating officer.) On smaller vessels, including fishing vessels, the master or skipper may have the responsibility of the navigating officer for voyage planning purposes. Prior to departure the navigating officer will prepare the detailed voyage plan from berth to berth in accordance with the Guidelines and to the master’s requirements. If the port of destination is not known or is subsequently altered, the navigating officer must extend or amend the original plan as appropriate.
3. Principles of Voyage planning
The four stages of Appraisal, Planning, Execution and Monitoring logically follow each other. An appraisal of all information available must be made before detailed plans can be drawn up and a plan must be in existence before tactics for its execution can be decided upon. Once the plan and the manner in which it is to be executed have been decided, monitoring must be carried out to ensure that the plan is followed.
Appraisal is the process of gathering all information relevant to the proposed voyage, including ascertaining risks and assessing its critical areas. The Guidelines list the items that should be taken into account.
An overall assessment of the intended voyage should be made by the master, in consultation with the navigating officer and other deck officers who will be involved, after all relevant information has been gathered. This appraisal will provide the master and his bridge team with a clear and precise indication of all areas of danger, and delineate the areas in which it will be possible to navigate safely taking into account the calculated draught of the vessel and planned under-keel clearance. Bearing in mind the condition of the vessel, her equipment and any other circumstances, a balanced judgement of the margins of safety which must be allowed in the various sections of the intended voyage can now be made, agreed and understood by all concerned.
Once a full appraisal has been carried out the navigating officer carries out the Planning process, acting on the master’s instructions. The detailed plan should cover the whole voyage from berth to berth, and include all waters where a pilot will be on board. The plan should be completed and include all the relevant factors listed in the Guidelines.
The appropriate charts should be marked clearly showing all areas of danger and the intended track taking into account the margins of allowable error. Where appropriate, due regard should be paid to the need for advanced warning to be given on one chart of the existence of a navigational hazard immediately on transfer to the next. The planned track should be plotted to clear hazards at as safe a distance as circumstances allow. A longer route should always be accepted in preference to a shorter more hazardous route. The possibility of main engine or steering gear breakdown at a critical moment must not be overlooked.
Additional information which should be marked on the charts include:
- All radar-conspicuous objects and RACONs, which may be used in radar position fixing.
- Any transit marks, clearing bearings or clearing ranges (radar) which may be used to advantage. It is sometimes possible to use two conspicuous clearing marks where a line drawn through them runs clear of natural dangers with the appropriate margin of safety; if the vessel proceeds on the safe side of this transit she will be clear of the danger. If no clearing marks are available, a line or lines of bearing from a single object may be drawn at a desired safe distance from the danger; provided the vessel remains in the safe segment, it will be clear of the danger.
- Parallel index lines should also be drawn where appropriate.
If an electronic chart system is used to assist voyage planning the plan should also be drawn up on the paper charts. Where official (ENC) vector data is available an ECDIS provided with fully compliant ENC data for the vessel’s voyage may be used instead of paper charts. Raster Chart Display Systems (RCDS) using official and up to date Raster charts can be used in conjunction with paper charts to assist voyage planning and route monitoring. Hazards should be marked on the RCDS as well as on the paper chart. Systems that use unofficial chart data should not be used for voyage planning or navigation.
Depending on circumstances, the main details of the plan should be marked in appropriate and prominent places on the charts to be used during the voyage. They should also be programmed and stored electronically on an ECDIS or RCDS where fitted. The main details of the voyage plan should also be recorded in a bridge notebook used specially for this purpose to allow reference to details of the plan at the conning position without the need to consult the chart. Supporting information relative to the voyage, such as times of high and low water, or of sunrise or sunset, should also be recorded in this notebook.
It is unlikely that every detail of a voyage will have been anticipated, particularly in pilotage waters. Much of what will have been planned may have to be adjusted or changed after embarking the pilot. This in no way detracts from the real value of the plan, which is to mark out in advance, areas where the vessel must not go and the appropriate precautions which must be taken, and to give initial warning that the vessel is standing into danger.
Execution of the finalised the voyage plan should be carried out taking into account the factors listed in the Guidelines. The Master should take into account any special circumstances which may arise, such as changes in weather, which may require the plan to be reviewed or altered.
Monitoring of the vessel’s progress along the pre-planned track is a continuous process. The officer of the watch, whenever in any doubt as to the position of the vessel or the manner in which the voyage is proceeding, should immediately call the master and, if necessary, take appropriate action for the safety of the vessel.
The performance of navigational equipment should be checked prior to sailing, prior to entering restricted or hazardous waters and at regular and frequent intervals at other times throughout the voyage.
Advantage should be taken of all the navigational equipment with which the vessel is fitted for position monitoring, bearing in mind the following points:
(a) positions obtained by electronic positioning systems must be checked regularly by visual bearings and transits whenever available;
(b) visual fixes should, if possible, be based on at least three position lines;
(c) transit marks, clearing bearings and clearing ranges (radar) can be of great assistance;
(d) it is dangerous to rely solely on the output from a single positioning system;
(e) the echo sounder provides a valuable check of depth at the plotted position;
(f) buoys should not be used for position fixing but may be used for guidance when shore marks are difficult to distinguish visually; in these circumstances their positions should first be checked by other means;
(g) the charted positions of offshore installations should be checked against the most recent navigational notices;
(h) the functioning and correct reading of the instruments used should be checked;
(i) account must be taken of any system errors and the predicted accuracy of positions displayed by electronic position fixing systems; and
(j) the frequency at which the position is to be fixed should be determined for each section of the voyage.
Each time the vessel’s position is fixed and marked on the chart in use, the estimated position at a convenient interval of time in advance should be projected and plotted. With ECDIS or RCDS care should be taken to ensure that the display shows sufficient “look-ahead” distance and that the next chart can be readily accessed.
Radar can be used to advantage in monitoring the position of the vessel by the use of parallel indexing, which is a simple and most effective way of continuously monitoring that a vessel is maintaining its track in restricted coastal waters. Parallel indexing can be used in any situation where a radar-conspicuous navigation mark is available and it is practicable to monitor continuously the vessel’s position relative to such an object. It also serves as a valuable check on the vessel’s progress when using an electronic chart.
Pilot passage planning
The Plan covers the voyage from berth to berth and therefore includes the Pilotage stage. The IMO Guidelines do not give specific advice on this important stage therefore the following notes should be taken into consideration when planning and executing the pilotage stages.
Pilots make a significant contribution to the safety of navigation in the confined waters and port approaches of which they have up to date knowledge, but it must be stressed that the responsibilities of the vessel’s navigational team and the officer of the watch do not transfer to the pilot. After boarding the vessel, in addition to being advised by the master of the manoeuvring characteristics and basic details of the vessel for its present condition, the pilot should be clearly consulted on the voyage plan to be followed. The general aim of the master should be to ensure that the expertise of the pilot is fully supported by the vessel’s bridge team.
Attention is drawn to the following extract from IMO Resolution A.285 (VIII):
“Despite the duties and obligations of a pilot, his presence on board does not relieve the officer of the watch from his duties and obligation for the safety of the vessel. He should co-operate closely with the pilot and maintain an accurate check on the vessel’s position and movements. If he is in any doubt as to the pilot’s actions or intentions, he should seek clarification from the pilot and if doubt still exists he should notify the master immediately and take whatever action is necessary before the master arrives.”
Guidelines for voyage planning
GUIDELINES FOR VOYAGE PLANNING (IMO Resolution A.893(21)
Annex 25 of SOLAS V – GUIDELINES FOR VOYAGE PLANNING
1 Objectives
1.1 The development of a plan for voyage or passage, as well as the close and continuous monitoring of the vessel’s progress and position during the execution of such a plan, are of essential importance for safety of life at sea, safety and efficiency of navigation and protection of the marine environment.
1.2 The need for voyage and passage planning applies to all vessels. There are several factors that may impede the safe navigation of all vessels and additional factors that may impede the navigation of large vessels or vessels carrying hazardous cargoes. These factors will need to be taken into account in the preparation of the plan and in the subsequent monitoring of the execution of the plan.
1.3 Voyage and passage planning includes appraisal, i.e. gathering all information relevant to the contemplated voyage or passage; detailed planning of the whole voyage or passage from berth to berth, including those areas necessitating the presence of a pilot; execution of the plan; and the monitoring of the progress of the vessel in the implementation of the plan. These components of voyage/passage planning are analysed below.
2 Appraisal
2.1 All information relevant to the contemplated voyage or passage should be considered. The following items should be taken into account in voyage and passage planning:
.1 the condition and state of the vessel, its stability, and its equipment; any operational limitations; its permissible draught at sea in fairways and in ports; its manoeuvring data, including any restrictions;
.2 any special characteristics of the cargo (especially if hazardous), and its distribution, stowage and securing on board the vessel;
.3 the provision of a competent and well-rested crew to undertake the voyage or passage;
.4 requirements for up-to-date certificates and documents concerning the vessel, its equipment, crew, passengers or cargo;
.5 appropriate scale, accurate and up-to-date charts to be used for the intended voyage or passage, as well as any relevant permanent or temporary notices to mariners and existing radio navigational warnings;
.6 accurate and up-to-date sailing directions, lists of lights and lists of radio aids to navigation; and
.7 any relevant up-to-date additional information, including
- 1 mariners’ routeing guides and passage planning charts, published by competent authorities;
- 2 current and tidal atlases and tide tables;
- 3 climatological, hydrographical, and oceanographic data as well as other appropriate meteorological information;
- 4 availability of services for weather routeing (such as that contained in Volume D of the World Meteorological Organization’s Publication No. 9);
- 5 existing ships’ routeing and reporting systems, vessel traffic services, and marine environmental protection measures;
- 6 volume of traffic likely to be encountered throughout the voyage or passage;
- 7 if a pilot is to be used, information relating to pilotage and embarkation and disembarkation including the exchange of information between master and pilot;
- 8 available port information, including information pertaining to the availability of shore-based emergency response arrangements and equipment; and
- 9 any additional items pertinent to the type of the vessel or its cargo, the particular areas the vessel will traverse, and the type of voyage or passage to be undertaken.
2.2 On the basis of the above information, an overall appraisal of the intended voyage or passage should be made. This appraisal should provide a clear indication of all areas of danger; those areas where it will be possible to navigate safely, including any existing routeing or reporting systems and vessel traffic services; and any areas where marine environmental protection considerations apply.
3 Planning
3.1 On the basis of the fullest possible appraisal, a detailed voyage or passage plan should be prepared which should cover the entire voyage or passage from berth to berth, including those areas where the services of a pilot will be used.
3.2 The detailed voyage or passage plan should include the following factors:
.1 the plotting of the intended route or track of the voyage or passage on appropriate scale charts: the true direction of the planned route or track should be indicated, as well as all areas of danger, existing ships’ routeing and reporting systems, vessel traffic services, and any areas where marine environmental protection considerations apply;
.2 the main elements to ensure safety of life at sea, safety and efficiency of navigation, and protection of the marine environment during the intended voyage or passage; such elements should include, but not be limited to:
.1 safe speed, having regard to the proximity of navigational hazards along the intended route or track, the manoeuvring characteristics of the vessel and its draught in relation to the available water depth;
.2 necessary speed alterations en route, e.g., where there may be limitations because of night passage, tidal restrictions, or allowance for the increase of draught due to squat and heel effect when turning;
.3 minimum clearance required under the keel in critical areas with restricted water depth;
.4 positions where a change in machinery status is required;
.5 course alteration points, taking into account the vessel’s turning circle at the planned speed and any expected effect of tidal streams and currents;
.6 the method and frequency of position fixing, including primary and secondary options, and the indication of areas where accuracy of position fixing is critical and where maximum reliability must be obtained;
.7 use of ships’ routeing and reporting systems and vessel traffic services;
.8 considerations relating to the protection of the marine environment; and
.9 contingency plans for alternative action to place the vessel in deep water or proceed to a port of refuge or safe anchorage in the event of any emergency necessitating abandonment of the plan, taking into account existing shore-based emergency response arrangements and equipment and the nature of the cargo and of the emergency itself.
3.3 The details of the voyage or passage plan should be clearly marked and recorded, as appropriate, on charts and in a voyage plan notebook or computer disk.
3.4 Each voyage or passage plan as well as the details of the plan, should be approved by the ships’ master prior to the commencement of the voyage or passage.
4 Execution
4.1 Having finalized the voyage or passage plan, as soon as time of departure and estimated time of arrival can be determined with reasonable accuracy, the voyage or passage should be executed in accordance with the plan or any changes made thereto.
4.2 Factors which should be taken into account when executing the plan, or deciding on any departure therefrom include:
.1 the reliability and condition of the vessel’s navigational equipment;
.2 estimated times of arrival at critical points for tide heights and flow;
.3 meteorological conditions, (particularly in areas known to be affected by frequent periods of low visibility) as well as weather routeing information;
.4 daytime versus night-time passing of danger points, and any effect this may have on position fixing accuracy; and
.5 traffic conditions, especially at navigational focal points.
4.3 It is important for the master to consider whether any particular circumstance, such as the forecast of restricted visibility in an area where position fixing by visual means at a critical point is an essential feature of the voyage or passage plan, introduces an unacceptable hazard to the safe conduct of the passage; and thus whether that section of the passage should be attempted under the conditions prevailing or likely to prevail. The master should also consider at which specific points of the voyage or passage there may be a need to utilize additional deck or engine room personnel.
5 Monitoring
5.1 The plan should be available at all times on the bridge to allow officers of the navigational watch immediate access and reference to the details of the plan.
5.2 The progress of the vessel in accordance with the voyage and passage plan should be closely and continuously monitored. Any changes made to the plan should be made consistent with these Guidelines and clearly marked and recorded.
Portsmouth passage planning
The following information is for guidance only. Full use should be made of the appropriate charts and publications when planning a passage into Portsmouth. VHF Communication is mentioned throughout this text. For details please refer to the Admiralty List of Radio Signals Volume 6(1), and local NTM No.01/16.
Anchorages
Anchorages are available at “St. Helen’s Roads” and “Spithead”, (with permission from the Queen’s Harbour Master). There is an anchorage for deep draught vessels 5nm SW of the “Nab Tower”. Top of Page
Approaching Portsmouth from the Nab Tower
On approaching the “Nab tower”, caution should be exercised with regard to vessels arriving or departing from the deep water anchorage and for vessels embarking and disembarking a pilot in the vicinity of the tower.
Mariners should be aware that in the vicinity of the “Nab Tower”, the tidal stream runs generally ENE/WSW. It has a maximum ENE at HW – 4 with a spring rate of 1.8kn, and a maximum WSW at HW +2 with a spring rate of 1.6kn.
Vessels should report on passing the “Nab Tower” to “Southampton VTS” on VHF channel 12, giving distance East or West of the tower. A listening watch should then be maintained on this channel for traffic and other information. A report should also be made to The Queen’s Harbour Master ” QHM” on VHF channel 11 giving draught, intended berth and ETA at the “Saddle” Buoy.
There is a deep water channel for very deep draught vessels who can only use this channel because of their draught. It is marked at the entrance by the “Outer Nab No1” and “Outer Nab No2” buoys south of the Nab Tower. The deep water channel rejoins the main channel at the “Nab End” buoy. The main channel then runs until the “Warner” buoy.
In the vicinity of the “St. Helen’s” buoy, care should be exercised with regard to vessels entering or leaving the St. Helen’s anchorage and for vessels embarking or disembarking a pilot.
At the “Warner” buoy, vessels should call “QHM” on VHF channel 11 confirming position. From this point, a listening watch should also be maintained on channel 11 in addition to channel 12.
On passing between “Horse Sand Fort” and “No Mans Land Fort”, vessels should report and check out with “Southampton VTS” on VHF channel 12.
Mariners should be aware that numerous ferries may be encountered entering and leaving the Portsmouth Approach Channel, Vessels constrained by their draught transiting the area on route for Southampton, and also large numbers of recreational craft may at times be encountered.
On passing the “Saddle” buoy, permission to enter Portsmouth Approach Channel must be requested from “QHM” on VHF channel 11. Mariners are advised that QHM will operate traffic restrictions to facilitate the passage of Naval or any other vessel entering or leaving Portsmouth and vessels are not permitted to proceed past the “Saddle” buoy without QHM’s permission. Passage plans should therefore encompass possible delays in entering the Portsmouth Approach Channel.
In the vicinity of the “Outer Spit” buoy, the tidal stream runs generally East/West. It has a maximum Easterly direction at HW -4 with a spring rate of 1.4kn, and is a maximum Westerly direction at HW +1 with a spring rate of 1.8kn. Top of Page
Approaching Portsmouth from the west
In the vicinity of the “North Sturbridge” buoy, care should be exercised with regard to vessels embarking and disembarking pilots and for deep draught vessels shaping up to pass South of the Ryde Middle Shoal.
Mariners are also advised that there is an increased risk in the vicinity of the Swashway due to the presence of Ferries, yachts and other recreational craft. This is an important channel for shallow draught vessels approaching or leaving Portsmouth Harbour. In addition to car ferries, hovercraft and high speed ferries often transit the area at speeds in excess of 24 knots. Hovercraft, being non displacement craft, usually navigate outside the Swashway in areas where depths are shallow. The Spitbank area as a whole is often used for yacht racing and regattas. Caution should therefore be exercised and a thorough lookout maintained at all times.
On passing “Gilkicker Point”, vessels should report and check out with “Southampton VTS” on VHF Channel 12 and contact “QHM” on VHF channel 11 giving position, draught and intended berth. A listening watch should then be maintained on VHF channel 11.
Entrance to the Portsmouth Approach Channel may be gained via the Swashway for suitable vessels. The limiting depth on the Swashway is 2.1m. Permission must be requested from “QHM” on VHF channel 11 before entering the Swashway. Vessels using this route are advised to exercise caution as numerous ferries and recreational craft are likely to be encountered. Mariners are also reminded of the requirements of Rule 9 of the International Regulations for the Prevention of Collisions at Sea regarding Narrow Channels, particularly with regard to vessels that can safely navigate only within such channels or fairways.
Vessels should contact “QHM” on VHF channel 11 before the “Outer Spit” buoy and request permission to enter the Portsmouth Approach Channel. Vessels are not permitted to proceed past the “Outer Spit” buoy without permission.
Once a vessel has reached a position of within 0.5nm of the shore a speed limit of 10kn comes into force.
Vessels navigating in the Portsmouth Approach Channel should be aware of traffic entering and leaving the channel from/to the Swashway. In addition there is a Small Boat Channel which is obligatory for vessels under 20m in length, which runs from Number “4 Bar” buoy to the “Ballast” Pile inside the Harbour. Thus concentrations of small craft may be encountered on the Western side of the channel from this point. Those small craft fitted with engines are required to use these whilst navigating in the Small Boat Channel.
Vessels should further be aware that the Isle of Wight Car ferry departs from the Town Camber at half hourly intervals by day and hourly intervals by night. This ferry may be obscured visually until clear of the Town Camber docks and so care should be taken to listen for these ferries requesting permission to depart on VHF channel 11.
The Flood tide at the entrance reaches a maximum at HW -1.5 hours with a spring rate of 3.4kn. The Ebb tide reaches a maximum at HW +3 hours with a spring rate of 4.1kn. Eddies may be encountered near the Harbour entrance due to the strong rates of the tidal streams.
Once inside the Harbour, caution should be exercised with regard to small vessels crossing the harbour to join/or leave to Small Boat Channel, and for vessels entering or leaving the Gunwharf Quays and Harbour Railway Station.
Care should be exercised with regard to excessive speed when passing Naval vessels moored alongside the Naval berths in order to prevent surging damage caused by interaction. This is all the more important near periods of low water. Increasing the distance off when passing should also be considered.
The Dockyard Port of Portsmouth Order 2005 should be consulted for details concerning the use of anchors, mooring, and approaching naval vessels or berths, in conjunction with the latest “Notice’s to Mariners”.
Mariners are advised that due to Naval movements or movements to/from the Commercial Port of Portsmouth, vessels may be required to wait or pass other traffic in designated areas, and Passage plans should encompass this possibility with regard to manoeuvring.
Vessels bound to or from North Quay are advised that two tugs will be required for berthing and unberthing. This may be reduced to one tug with the prior agreement of the Commercial Port Harbour Master, if the vessel is fitted with an operational bow thrust.
Once alongside a berth vessels should report to “QHM” on VHF channel 11. Top of Page
Departing from Portsmouth
Prior to slipping from a berth permission must be sought from “QHM” on VHF channel 11. Vessels of 20 m LOA or more, are not permitted to slip a berth without permission.
Care should be exercised in the areas highlighted in the guidance for arrival above.
On approach to the “Naval War Memorial”, contact should be made with “Southampton VTS” on VHF channel 12 reporting the vessels position, and intended route either via the “Nab Tower” or the “North Sturbridge” buoy and requesting any relevant traffic information. A listening watch should be maintained on this channel from this point.
On passing the “Saddle” buoy vessels should report and check out with “QHM” on VHF channel 11. Caution must be exercised on departing the Portsmouth Approach Channel for vessels constrained by their draught proceeding through the area. Vessels proceeding out of Portsmouth are required not to embarrass these vessels or to present them with a crossing situation. Care should also be exercised with regard to vessels having recently disembarked a Southampton pilot at the “North Sturbridge” boarding area.
Vessels bound via the “Nab Tower”, on passing between “Horse Sand Fort” and “No Mans Land Fort”, should report to “Southampton VTS” on VHF Channel 12. A final report should be made to “Southampton VTS” when passing the “Nab Tower”.
Tidal regime: Nab Tower
Time | Direction | Spring rate |
---|---|---|
- 6 | 085 | 0.7 |
- 5 | 078 | 1.6 |
- 4 | 078 | 1.8 |
- 3 | 065 | 1.5 |
- 2 | 048 | 0.9 |
- 1 | 345 | 0.2 |
HW | 282 | 1.3 |
+ 1 | 265 | 1.5 |
+ 2 | 252 | 1.6 |
+ 3 | 236 | 1.2 |
+ 4 | 218 | 0.9 |
+ 5 | 193 | 0.4 |
+ 6 | 095 | 0.4 |
Tidal regime: Warner
Time | Direction | Spring rate |
---|---|---|
- 6 | 122 | 0.6 |
- 5 | 129 | 1.2 |
- 4 | 129 | 1.3 |
- 3 | 114 | 0.5 |
- 2 | 335 | 0.4 |
- 1 | 314 | 1.0 |
HW | 311 | 1.5 |
+ 1 | 311 | 1.7 |
+ 2 | 313 | 1.0 |
+ 3 | 168 | 0.2 |
+ 4 | 149 | 0.9 |
+ 5 | 141 | 0.7 |
+ 6 | 111 | 0.4 |
Tidal regime: Outer Spit buoy (7 cables SW)
Time | Direction | Spring rate |
---|---|---|
- 6 | 089 | 0.7 |
- 5 | 115 | 1.1 |
- 4 | 117 | 1.4 |
- 3 | 109 | 0.8 |
- 2 | 033 | 0.3 |
- 1 | 327 | 0.4 |
HW | 292 | 1.2 |
+ 1 | 293 | 1.8 |
+ 2 | 288 | 1.8 |
+ 3 | 231 | 0.4 |
+ 4 | 152 | 0.5 |
+ 5 | 131 | 0.4 |
+ 6 | 080 | 0.6 |
Tidal regime: Harbour entrance
The tidal flow at the Harbour Entrance can be considered as a 7 hour FLOOD and a 5 hour EBB.
At Spring tides the maximum FLOOD occurs 1.5 hours before High Water with a rate of 3.4 knots.
The maximum EBB occurs 3 hours after High water with a rate of 4.1 knots