CHAPTER 17 Echo sounder variables


a b c


a = Depth of water b = Depth under transducer c = Depth under keel


Depth below the keel Many people calibrate the sounder to read depth below keel so that they can see at a glance how much shoaling is needed to ground the vessel. There is much to be said for this, but it must be done accurately. Some charter operators ‘add a bit for safety’, thus rendering any seamanlike depth calculation – in fog perhaps – null and void. It is in any case necessary to add the boat’s draught to the reading when such a depth is being used for navigation.


Action to be taken on grounding


‘Safe’ groundings If the grounding is in a non- threatening situation, perhaps with nothing more to do than wait for the tide to rise, a good skipper would invite the cook to put the kettle on as the crew settle down calmly to await re-floating. Dangerous groundings If a stranding seems even remotely likely to be serious, action must be taken as quickly as possible. As to the specifics, (see page 146), but in general the first concern must be the crew’s security. Their best chance may well lie in saving the ship, but if the likelihood of this seems in doubt, assistance should be called promptly. The SAR team can always be stood down later if the boat saves herself.


Checking for damage


If the boat has literally glided to a standstill on mud, harm is highly unlikely. On the other hand, when she has banged


to a sudden halt and is bouncing on rocks, her continued integrity will be in grave doubt. If she is making water faster than it can be pumped out, the best place for her – or at least her crew – may even be to stay where she is because at least she won’t sink any further. Bilge Lift the cabin sole and see if she is making water. If not, well and good for the moment. If she is, start pumping and monitor progress. So long as you are winning, move on to the next checks. If you aren’t, call for assistance, then see if you can improve things. Rudder It is common for a rudder to be damaged in a heavy grounding. Check to see if the tiller or wheel moves freely. If it does, either the rudder has gone or all is probably well. Most likely the latter. If it is heavy or jammed, be prepared for the additional challenge of steering problems when you come off. Keel bolts A sailing boat which grounds hard is likely to have strained her keel, which is evidenced by leaking around the keel bolts. If water is coming in fast, try to check these, because if this proves to be the source of the water you may have to look no further; there will be little that can be done about it in the short term without hauling out or beaching the boat. Propellers This is the nightmare scenario for the power boat. Propellers that stand proud, unprotected by skegs, are very vulnerable. If they touch the bottom it’s highly possible that the screw itself or its shaft and bearings may be injured. This can result in leaking, or an inability to power away once the boat has been re-floated. Be prepared.


MANUAL OF SEAMANSHIP | 145


Grounding


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