CHAPTER 16 A typical tidal river


Deep water Deep water


Shallows on inside of bends


Sand bar


Bars


Many rivers deposit debris and silt in the sea either at or immediately to seaward of their mouths. Be ready for shoaling and take special care approaching any river bar in strong onshore weather, especially when the tide is ebbing to windward.


Navigating an uncharted or marginally charted river


Generally speaking, rivers run deepest in the middle. Rounding bends, they tend to shoal on the inside of the corner as the current is thrown straight ahead by centrifugal force to scour away the outside. Given these basic premises, the rest is down to observation and common sense. Watch the bank carefully. A rocky cliff may indicate a steep-to foreshore. A gently shelving meadow probably continues in the same vein below the water, and so on. Watch out for bars off the mouths of tributaries, especially in areas where flash floods may be expected. Here, boulders and other rubbish may be carried down and deposited in the midstream area of the main river. If in doubt, favour the opposite bank.


Expect currents to be strongest in deep water. This effect is sometimes marked by noticeable wavelets where


the water is running faster and oily calm in the slack areas. Careful observation can reveal much. Echo-sounder alarms In rivers, one is often as keen to know how rapidly the water is shoaling as to be told the precise moment at which a predetermined depth is reached. Without forward-looking sonar, a depth alarm can only show the latter so, while it has its uses, relying on an alarm may be less beneficial than at first appears.


Power craft


No special considerations apply to sailing craft operating in rivers under engine. Power vessels with exposed propellers must take additional care to avoid grounding.


Sailing yachts COLREGS – Rule 9(b) of the Collision Regulations states “that a sailing vessel shall not impede the passage of any other vessel navigating within a narrow channel or fairway”. Subsection (a) of the same rule requires all vessels to keep to starboard as far as is safe and practicable. These provisions to some extent compromise the sailor’s rights of ‘power giving way to sail’, and a sailing boat making full use of the opportunities offered by a shifting wind will sometimes find herself on the ‘wrong’ side of the river. If no other boats are around, this presents no difficulties. Where traffic is dense, especially with power craft whose skippers may not have experienced sailing issues, you


MANUAL OF SEAMANSHIP | 141


River seamanship


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