Access channel design & Under Keel Clearance

Access Channel Design & UKC Services

Safe and reliable access to ports is essential to compete with the increasing size of ships that ports want to attract. However, capital and maintenance dredging are expensive and it can therefore be a considerable advantage to apply the latest technology in both designing and operating an access channel.

The factors that determine the required dredged depth include:

The volume of traffic expected and the split between ships of various types and draughts:
- Double lane and separation zones
- Manouvrability of (design) ships
The tidal range and currents
The wave conditions and their persistence
The type of seabed material
The (tidal cross-)currents and winds
The speed of the ship and turning manoeuvres
The level of sophistication of the admission policy

The nautical depth can be optimised by probabilisitcally accounting for the dynamic response behaviour of the fleet calling at the port and terminal. Each type of ship responds differently to the environmental conditions and a proper analysis can reduce the capital costs of maintenance and channel deepening.

We not only evaluate whether a ship can safely transit the channel (single transit criterion), but we also look at whether the channel is intrinsically safe for the the design life of the channel (long term criterion).

UKC Services

Aktis Hydraulics has tools for designing channel depth ranging from very simple approaches to sophisticated probabilistic design accounting for all the important factors. This is underpinned by in depth knowledge of:

Wind, waves, currents and tides;
The vertical movement of the ship in response to waves and the associated distributions;
Squat, trim and wind and turning induced heel;
The effect of winds and currents on the orientation of the ship.

The use of a sophisticated admission policy, allows ship access for a higher percentage of the time with a higher degree of safety than a simple system based on a limited number of simple criteria. A consequence of this is that the required dredging will be less when a sophisticated admission system is applied. An example of such a system is PROTIDE (see Bos, Koop & Bolt, PIANC 2011), as applied for the ports of Amsterdam, Rotterdam, Eemshaven, Zeeland (NL), Antwerp (BE), Emden (DE) and Port of Longbeach (USA).

The result of a typical study is typically a recommendation for the minimum dredged depth of an access channel for a particular safety level (e.g. the probability of any ship touching the seabed in a 25 year period is less than 10%).

Probabilistic approach

Especially in complex multiple wave systems, it is preferred to use more sophisticated techniques to account for the wave systems that simultaneously act on the vessel. Especially for large vessels underlying swell systems can significantly introduce large roll motions which may not be so apparent in common metocean Extreme Value Aanalysis (EVA).

The starting point of the response based analysis is generally that the probability of the a bottom contact event during the design lifetime of the approach channel as well as during a single transit will be acceptable. These can be computed by hindcasting the motion response of the ship as if it would have been present at the location of interest. Hereby, accurate statistical information is obtained from the simulations.

Example projects

Access channel design for Port of Lekki (Nigeria)
Cyprus – terminal berth pocket optimisation
Westerschelde (The Netherlands) – wind induced roll motion evaluation
Eems-Dollard approach (The Netherlands) – heel induced by vessel turning manoeuvres

Publications

Selected publications by our staff on access channel evaluation:

Bos, M., Koop, O.R. & BOLT, E., Safety Level of a Probabilistic Admittance Policy, Proc. of the ASME 2011 30th Int. Conf. on Ocean, Offshore and Arctic Engineering, OMAE, Rotterdam, The Netherlands, June 19-24, 2011.

Access Channel Design & UKC Services

UKC Services

Methodology

Probabilistic approach

Example projects

Publications

About Aktis

Core expertise

Contact