Approval for Saint Lawrence Seaway Draft Information System
At the St. Lawrence Seaway is one of the most important transportation links in North America. To maximize the efficient use of the seaway, in 2001, the Seaway authorities started to a study which would determine the maximum load ships can carry while maintaining a safe Under-Keel Clearance (UKC). Over the years the maximum draft of vessels transiting the Seaway in the MLO Montreal to Lake Ontario and the Welland Canal has been gradually increased. At the opening of the Seaway in 1959, the maximum draft for ships was set at 6.85 meters (22.5 ft. ). This maximum draft is now set at (26.5 ft.). However, changes in water levels and a phenomenon called ship sinkage or "squat" made adjusting the maximum draft again more complicated.
Draft is measured prior to departure but a moving ship actually sits much lower in the water, particularly in shallow or constrained channels. How much a ship "squats" depends on factors such as the size and speed of the ship, shape of the channel, depth of the water, currents, wind, and even the presence of other ships.
Undertaken at the request of the St. Lawrence Seaway Management Corporation and industry partners that included the Canadian Ship owners Association and the Shipping Federation of Canada, the mentioned study resulted in standard squat models for the various types of vessels transiting the Seaway.
Over the past year and a half, the St. Lawrence Seaway authorities have developed a functionality description of a Draft Information System that incorporates the Seaway squat models, which was finally approved by all stake holders in March of this year and was then issued to the public.
In accordance with this specification, TRANSAS has developed a Draft Information System (DIS) based on the NS4000 ECDIS which allows the accurate display of the vessel’s position, real time water levels and data from highly detailed bathymetric charts.
An independent functionality verification and assessment was performed by Lloyds Register in June of this year after which the system was installed on board the M/V Algoma Spirit for final approval by the St. Lawrence Seaway authorities.
The Transas Draft Information System passed the performance tests without comments or open items. The DIS can run as a stand-alone system or in a network with the Transas NS4000 ECDIS providing a unique combination of precise navigation instruments, high definition chart data and real-time navigation information in both the DIS and the ECDIS. The Transas DIS is built on the same hardware platform as the Transas NS4000 ECDIS MFD providing for better redundancy and lower cost of maintenance.
The Draft Information System (DIS) is a program designed to calculate and display the under-keel clearance (UKC) on the basis of the following data:
• High Resolution Bathymetry data provided by the Canadian Hydrographic Service (CHS);
• Water levels; received automatically via Seaway AIS stations of a network of water level gauge stations or set manually by the user;
• Ship forward and after draft set manually by the user;
• Ship Squat based on Seaway Squat Models for the vessel and channel type.
(As published in the August 2012 edition of Maritime Reporter - www.marinelink.com)