4 OTHER ASPECTS
4.3 Operational Rules and Environmental Limits
4.3.1 General
The maritime and environmental conditions for the various aspects of manoeuvring in a port or terminal have a direct impact on the design and operation of channels and other navigation areas. These conditions may be different for different types of vessels and for the particular conditions of every project. This section provides guidance on the limiting environmental conditions for vessel manoeuvring in channels and other areas of a port. If the specified limits are not confirmed by local experience, their suitability for the specific case must be carefully checked with maritime experts. The establishment of these limits has significant consequences for the operational downtime and profitability of the port or terminal. The finally adopted limits must be explicitly shown in the Operating Rules for the pilots, port or terminal.
Unless limiting operational conditions are already specified, the following general considerations may be applied:
For design, it is conservatively assumed that the different environmental limits act simultaneously. However, if it can be proven that this would be unrealistic, combinations of less extreme values could be used, taking each of the environmental variables at its maximum with the other variables at their associated maxima. Such combinations will lead to different design conditions
For operability, vessel manoeuvres will be suspended as soon as one of the environmental conditions reaches or exceeds its limits, independent of whether the remaining variables reach their limits. The possibility of operations under conditions where one limit is exceeded while the other limits are not exceeded is limited to cases where a detailed study has been carried out for the specific site.
4.3.2 Channels
The limits for navigation conditions in channels are recommended to be selected such that the drift angle β does not exceed the values specified in Table 4.2 and the vessel is sailing at the lowest permissible transit speed (see also Section 3.1.8). The channel conditions are distinguished for a range of relative depth ratios h/T, where h is the water depth and T is the vessel’s draught.
The drift angle β is calculated assuming that its sine is the sum of the sines of the drift angles for the different forces act separately, i.e.:
wind currents waves tugs
sin = (sin ) + (sin ) + (sin ) + (sin )
(4-1)This sum is algebraic and therefore each drift angle is considered with its pertinent plus or minus sign related to the direction of the specific action.
Channel Relative Depth Condition β (deg) Table 4.2: Drift angle β versus channel relative depth
If there are no specific criteria for the minimum vessel speed Vs, this can be taken as the smallest one of the values specified in Table 4.3:
Navigation Area
Piers and berthing approach
4 - 7.5 Table 4.3: Vessel speed range in navigation areas
4.3.3 Harbour Entrances
Vessel manoeuvrability for passing through a harbour entrance cannot be considered in isolation. The stretch of channel from the outer and inner limits must be considered. The following aspects have to be taken into consideration:
The outer stretch of the entrance is a channel with a completely defined alignment.
Although this stretch is recommended to be straight, it will often be necessary to include a curved leg. It may also be possible to navigate outside the harbour using different approach routes
The approach routes are pre-set and are not at all times aligned with the wind, waves or currents. Therefore, major cross-component forces and drift angles close to the maximum values admissible must be considered in the design. Environmental limits have to be determined as a function of the required service level. Unless specific measurements or model results are available, the following transverse or lateral environmental conditions are recommended (see also 3.1.8.2):
o Wind speed VW,1 min ≤ 15 m/s (29 knots) o Current speed VF,1 min ≤ 1.00 m/s (2 knots) o Wave height Hs ≤ 3.0 m
In small-craft ports of refuge (for fishing and pleasure boats), as well as in ports designed to operate under severe environmental conditions, approach routes may allow the ships/boats to arrive at the harbour with their stern into the storm or at a small angle with the channel (called sailing with the storm on a quarter), with angles of 15º to 20º between the route and the wave direction
The limiting in-line environmental conditions for these storm entry routes can be established by analysing the service levels required and, if criteria are not yet available, by the following operational limits:
o VW,1 min ≤ 16 m/s (32 knots)
o VF,1 min ≤ 2.00 m/s (4 knots)
o Hs ≤ 5.0 m
In this and subsequent paragraphs the following symbols are used:
o VW,1 min = Wind velocity at a height of 10 m above sea level, as a 1-minute average o VF,1 min = Current velocity at a depth of half the vessel’s draught, as a 1-minute
average
o Hs = Significant wave height.
4.3.4 Stopping Areas
The operational criteria for stopping areas are the same as for the adjacent (i.e.
connecting) channel area. If the stopping area will not be in line with the channel, the direction of the different actions on the ship will be different from those in the channel. In this case, the limiting operating conditions should conservatively be assumed as omnidirectional.
In some cases, the configuration of the port or manoeuvring area does not allow the vessel’s stopping manoeuvre to be carried out from beginning to end in a controlled manner. In such a case, the vessel’s stopping area has to be located outside the harbour or site under consideration, so that the vessel will come to a stop before entering the harbour or site area. The vessel can then proceed to perform this final turning or approaching manoeuvre to the quays with tug assistance. In this case, the limiting operational environmental conditions may have to be based on the limitations of the auxiliary vessels (pilot boat, tugs), which will guide the vessel towards its berth. Unless detailed model results for each area are available, the limiting operating environmental conditions may be set at the following values:
o VW,1 min ≤ 10 m/s (20 knots)
o VF,1 min ≤ 1.00 m/s (2 knots)
o Hs ≤ 2.0 m
Again, these conditions are assumed to be omnidirectional.
4.3.5 Turning Areas
The operational limits come from the resulting environmental forces on the ship and the drift angles due to these forces. In such cases the following operational limits are recommended:
Manoeuvres without tug assistance:
o VW,1 min ≤ 10 m/s (20 knots)
o VF,1 min ≤ 0.50 m/s (1 knot)
o Hs ≤ 2.0 m / 3.0 m (depending on the type of manoeuvre) Manoeuvres with tug assistance:
o VW,1 min ≤ 10 m/s (20 knots)
o VF,1 min ≤ 0.10 m/s (0.2 knots)
o Hs ≤ 1.5 m / 2.0 m (depending on the type of tugs)
When manoeuvring areas are located in zones with no geometrical restriction in one direction (e.g. in some river ports), the operational limits in the longitudinal direction (river) can be higher, in accordance with the particular conditions of the project.
4.3.6 Anchorage Areas
The environmental conditions for the operational limits in the anchorage area are listed below. They depend on the vessel, type of anchorage and the scheduled operation. Wind speed is determined for general-type vessels. Should they have relatively large exposure areas (methane carriers, container ships, car carriers, in-ballast oil tankers, etc.), the limiting operational wind speeds shall be 20 % less than those given in Table 4.4.
Activity VW,1 min VF,1 min Hs
Approach and mooring manoeuvres Vessel at anchorage
With one anchor ahead
With two anchors down (anchoring against ebb/flood with anchor ahead and astern)
Longitudinal forces
Transverse forces
Loading and unloading operations
17 m/s 24 m/s 30 m/s
24 m/s
2 m/s 2 m/s 2 m/s
2 m/s
2.5 m 3.5 m 4.5 m
3.5 m Anchorage not operative
Depend on (un)loading equipment Table 4.4: Limiting operational wind speeds
4.3.7 Moorings Areas and Buoy Systems
The environmental conditions recommended as operational limits for mooring areas and buoy systems are shown in Table 4.5. These depend on whether the vessel is able to freely rotate to an orientation with the minimum resistance or whether its orientation is fixed.
Activity
Mooring area with free orientation
Mooring area
1. Mooring to mini-single buoys or small buoys usually occurs with fishing and pleasure boats
2. Mooring area with fixed orientation usually means buoy systems, etc.
3. The first figure in this column is for longitudinal forces and the second for transverse forces on the vessel
Table 4.5: Operational limits for mooring areas and buoy systems
4.3.8 Basins and Quays
The limiting operational conditions for navigating and manoeuvring vessels (including stopping and turning) when performed inside basins and near quays are the same as those established for these manoeuvres in other harbour areas. This is irrespective of the fact that the more sheltered location of basins will usually cause a lower percentage of downtime.
Three conditions must be considered as specific quay conditions:
Vessels berthing
Loading and unloading operations
Vessels moored at quays and jetties
The limiting environmental conditions for these three conditions depend on other factors besides the vessel. Vessel berthing limits depend on the available tugs and the fender system at the quay. Stoppage of loading and unloading operations will mainly depend on the characteristics of the cargo and the (un)loading equipment used. Limits for vessels staying at quays and jetties depend on the design limits of the structure, on the availability of towing equipment to take the vessels off the berth under extreme conditions and on the capability of the vessel to navigate in a controlled manner to other quays, anchorages or outer navigating areas. Other considerations and factors may also play a role in some cases, such as the comfort limits for passengers on a cruise ship under wave action.
The limiting environmental operating conditions listed in Table 4.6 are likely maximum values for quays and jetties, but more site specific values may be used, e.g. the evaluation of downtime percentages resulting for different cases and associated investments necessary to guarantee operability under the limiting conditions.
Description VW,1 min VF,1 min Hs
1. Vessel berthing
Forces longitudinal to the quay 17.0 m/s 1.0 m/s 2.0 m
Forces transverse to the quay 10.0 m/s 0.1 m/s 1.5 m 2. Loading and unloading operation stoppage (conventional equipment)
Forces longitudinal to the quay – Oil tankers
< 30,000 DWT 22 m/s 1.5 m/s 1.5 m
30,000 DWT – 200,000 DWT 22 m/s 1.5 m/s 2.0 m
> 200,000 DWT 22 m/s 1.5 m/s 2.5 m
– Bulk carriers
Loading 22 m/s 1.5 m/s 1.5 m
Unloading 22 m/s 1.5 m/s 1.0 m
– Liquid Gas Carriers
< 60,000 m3 22 m/s 1.5 m/s 1.2 m
> 60,000 m3 22 m/s 1.5 m/s 1.5 m
– General cargo merchant ships, deep sea
fishing boats and refrigerated vessels 22 m/s 1.5 m/s 1.0 m
– Container ships, RoRo ships and ferries 22 m/s 1.5 m/s 0.5 m
– Liners and Cruise ships1 22 m/s 1.5 m/s 0.5 m
– Fishing boats 22 m/s 1.5 m/s 0.6 m
Forces transverse to the quay – Oil tankers
< 30,000 DWT 20 m/s 0.7 m/s 1.0 m
30,000 DWT – 200,000 DWT 20 m/s 0.7 m/s 1.2 m
> 200,000 DWT 20 m/s 0.7 m/s 1.5 m
– Bulk carriers
Loading 22 m/s 0.7 m/s 1.0 m
Unloading 22 m/s 0.7 m/s 0.8 m
– Liquid Gas Carriers
< 60,000 m3 16 m/s 0.5 m/s 0,8 m
> 60,000 m3 16 m/s 0.5 m/s 1.0 m
– General cargo merchant ships, deep sea
fishing boats and refrigerated vessels 22 m/s 0.7 m/s 0.8 m
– Container ships, RoRo ships and ferries 22 m/s 0.5 m/s 0.3 m
– Liners and Cruise ships1 22 m/s 0.7 m/s 0.3 m
– Fishing boats 22 m/s 0.7 m/s 0.4 m
3. Vessel at quay
Oil tankers and Liquid Gas Carriers
– Actions longitudinal to the quay 30 m/s 2.0 m/s 3.0 m
– Actions transverse to the quay 25 m/s 1.0 m/s 2.0 m
Liners and Cruise ships2
– Actions longitudinal to the quay 22 m/s 1.5 m/s 1.0 m
– Actions transverse to the quay 22 m/s 0.7 m/s 0.7 m
Recreational boats2 22 m/s 1.5 m/s 0.4 m
– Actions longitudinal to the quay 22 m/s 1.5 m/s 0.4 m
– Actions transverse to the quay 22 m/s 0.7 m/s 0.2 m
Other types of vessel Limitations imposed by the design loads
Notes: 1. Conditions relative to passengers embarking or disembarking.
2. Conditions relative to the limits for passenger’s comfort on board.
3. Longitudinal = wind, current or waves taken as acting longitudinally when their direction lies in the sector of ±45° relative to the vessel’s longitudinal axis.
4. Transverse = wind, current or waves taken as acting transversally when their direction lies in the sector of
±45° relative to the vessel’s transverse axis.
Table 4.6: Limiting environmental operating conditions at quays and jetties