Seaway operators develop tool to integrate draft data to ensure under-keel clearances

The shipping industry and managers of the St. Lawrence Seaway have developed an onboard navigation system that integrates "real time" and predictive data about under-keel clearance to improve safety — and profitability — for maritime operators.

The Draught Information System (DIS) was tested last summer in a pilot project involving members of the Canadian Shipowners Association (CSA), St. Lawrence Seaway Management Corp. in Canada and the Saint Lawrence Seaway Development Corp. in the United States. The managers have issued a proposal for recommending DIS as a best practice for the industry.

DIS combines water-level measurements and bathymetry — the mapping of the bottom of the channel — with calculations of how a ship reduces clearance as it moves through the water. This effect, known as "squat," increases the ship's draft and varies with the type and speed of the vessel.

Squat equations have been developed for each type of ship using the seaway, taking into consideration each vessel's handling characteristics. The equations consider channels where the effect is mainly between a vessel and the bottom of the channel, and where there may be interaction with the sides of the waterway. The information on the projected under-keel clearance is integrated electronically with chart data, high-resolution bathymetry and other readings on a single unified display on the bridge.

The self-unloading bulk carrier CSL Laurentien transits the Poe Lock downbound at Sault Ste. Marie, Mich. St. Lawrence Seaway officials and vessel operators are developing a customizable system to predict draft clearance, allowing operators to be sure the water depth is safe for their load. (Photo courtesy CSL/Canadian Shipowners Association)

Robert Lewis-Manning, vice president of operations for the CSA, said the system increases the confidence of captains and reduces risk. The bottom line for operators is improved safety and efficiency.

"Industry led this initiative from the start, as the product of the initiative is the ability to carry increased loads safely," he said. "Fortunately it hasn't been driven by incidents at sea — it's been driven by commercial viability. Anything that provides both increased safety and the ability to carry more cargo is a good thing for the companies."

During the pilot project, ships were allowed to operate up to 3 inches deeper than the maximum seaway draft, which is determined by the level of the water. The draft limit applies from Montreal through the seven lower locks and the eight locks of the Welland Canal. Some oceangoing vessels go through the locks partially loaded to accommodate the limit, according to seaway officials.

The new information system was developed by CSA member companies Seaway Marine Transport and Canada Steamship Lines. Lewis-Manning said it allows ships to operate safely with the increased draft.

"Does 3 inches make a difference? Absolutely," he said. "The efficiencies are huge. I wish I could give you a dollar value, but you're talking about the magnitude of 15 percent more cargo. It depends on what they're carrying and what the water level is at the time — that's quite a variable. Late in the season when the waterway is quite low, that percentage decreases dramatically."

The cost of implementing DIS "is in line with new ECDIS and radar units," Lewis-Manning said. Training would include onboard instruction by the manufacturers after installation, he said. The equipment is incorporated into an operator's Bridge Resource Management practice.

"It's entirely up to the operators whether they participate," Lewis-Manning said. "I would suspect it might be cost-prohibitive for some of the smaller operators. But for the larger carriers in the Great Lakes basin, certainly it's very viable."

Lewis-Manning said last summer's trial showed that DIS works. He hopes seaway authorities will recommend the system as a best practice in the next couple of months.

By Professional Mariner Staff