Grounding


It has been said that if you never run aground, you aren’t trying hard enough. Whilst there may be some comfort in this, most shipwrecks result from a stranding of one sort or another, so running aground is obviously to be avoided. However, some groundings are worse than others. For a boat with no vulnerable under-water appendages, to slide gently onto soft mud on a quiet weather shore with the tide rising should be a cause of no concern whatever. For the same craft to strike a rocky shoal with the wind blowing onto it from the open sea would be very bad news indeed, even if the tide were making. For this to occur on a falling tide could prove catastrophic. A sailing yacht short- tacking up a muddy river on a flood tide might safely take some calculated risks with the weather shore. A power boat with vulnerable propellers navigating close to rocks in a big swell would be irresponsible to proceed without the utmost caution. In short, groundings must be considered in a seamanlike context, and the duty of care exercised to avoid them will vary in degree with circumstances.


The echo sounder


In conjunction with a chart and an awareness of the vessel’s position, the front-line guardian against grounding is the echo sounder. These instruments are generally highly reliable, but the readout is only as good as the skipper’s knowledge of how it has been calibrated, if indeed it has been at all. Depth below transducer Left to itself, an uncalibrated sounder reads depth below its own transducer. To know the depth, it is only necessary to be aware of how far this is below the boat’s waterline and add the two values together. Water depth Many sounders can be calibrated to read depth of water. The best way of verifying this readout is first to sound a depth with the backup leadline all vessels should carry, then calibrate the instrument to read the same. Anything else involves numbers and some degree of guesswork. This choice of calibration datum is a good one because it does away with any extra number-crunching when reducing to soundings. So long as the boat’s draught is in no doubt, you’ll know when she is about to run aground.


144 | MANUAL OF SEAMANSHIP


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