Real Life Incident: Hydrodynamic Effects Create Challenges

A laden tanker drawing 12.75m was inbound in a restricted waterway. It was being conned near the centre of the main channel at a speed of about 7.5 knots. On the starboard side, outside the main channel, was a secondary channel used by smaller vessels such as tugs and barges.

The tanker’s bridge team had observed, by radar, a tug pushing a barge in the secondary channel about 6 nautical miles ahead and they were due to overtake the tug in the near future. An agreement was reached between the pilot of the tanker and the tug Master. The customary arrangement is that the tug and barge assume an angle (a) with the channel as the larger ship overtakes in order to reduce hydrodynamic effects and retain manoeuvrability, as shown in the diagram below.

large_vessel — Image Credits: nautinst.org

As the two vessels began to close, the tug and barge were seen to be at the limit between the secondary channel and the main channel (if not totally in the main channel), and the tug-barge combination had not taken the expected angle to reduce hydrodynamic effects. As the tanker approached, the tug Master reported difficulty steering. During the overtaking manoeuvre, the tug Master was unable to control his vessel and the barge. The units sheared to port and made contact with the stern of the tanker.

Lessons learned

Overtaking is a challenge in narrow channels; it requires proper planning well in advance, which should include contingency plans.
The intensity and effect of hydrodynamic forces cannot be accurately assessed due to the nature of the channels and confined waters.
In overtaking situations the difference in speed between the two vessels should be as great as safety and prudence will allow. This will reduce the time the hydrodynamic forces are acting on the vessels and negate the known ‘trapping effect’.

Press Release: nautinst.org

Disclaimer :
The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.

In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from loss of data or profits arising out of, or in connection with, the use of this website.

Do you have info to share with us ? Suggest a correction

About Author

Marine Insight News Network is a premier source for up-to-date, comprehensive, and insightful coverage of the maritime industry. Dedicated to offering the latest news, trends, and analyses in shipping, marine technology, regulations, and global maritime affairs, Marine Insight News Network prides itself on delivering accurate, engaging, and relevant information.