This report from a captain reinforces the need to be thoroughly familiar with the equipment on board your ship.
What the reporter told us:
During the handover prior to taking command, I noted the echo sounder manufacturer and the type of installation. This ship had two transducers, one forward and one aft. There was a single display and forward or aft transducer could be selected. After the handover I carried out a familiarisation meeting with the bridge team to make my requirements and standing orders known, and to answer any questions that the team might have. During the meeting I offered the following question, “On departure of the ship from port with forward draft 5 metres and aft draft 8 metres, we have to drift awaiting orders. After a while, the officer of the watch checks the depth under the keel which reads 3 metres. Is it safe or not?” All the watch officers replied that it was safe, and none pointed out that it depends upon which transducer was in use.
Proper familiarisation should be conducted by all the bridge team before they take responsibility as a watch officer. All officers were instructed to check which transducer was in use and the opportunity was taken to reinforce the company’s requirement for under keel clearance. Additional information was inserted in the watch officer’s handover information template.
The learning here is to ensure that bridge watch officers are familiar with all the bridge equipment fitted to their vessel. There are many different types of echo sounder; some have only a single transducer (normally forward) while others have two (commonly fore and aft) but normally and commonly are not good enough – bridge watchkeepers need to know exactly. Not all echo sounders equipped with two transducers readily indicate which transducer is in use. Equally the display may indicate the depth below the transducer or the total water depth depending on input settings and selection.
This report clearly demonstrates that assumptions can be dangerous and lead to an incident. The more familiar you are with equipment and the more you train with it, then the safer you and the ship will be.
It was also noted that whilst vessels may require a minimum aft draft to ensure propeller immersion the practice of good seamanship would suggest, where possible, to minimise sailing draft and trim in areas of shallow water. Additional ballast can always be added later once the vessel is clear of shoal waters.