CHAPTER 7 Choosing an anchorage
Strategic considerations Shelter Few things are as satisfying as a quiet night anchored free of charge in a peaceful bay or river. Little is so stress-mongering as a bad night hanging on in poor holding ground on a lee shore. An anchorage should always be selected with shelter in mind. Consider what the wind may do while you are anchored, then find a spot where you will lie in a good lee. Give thought to the sea state. Protection from the wind may ensure safety, but rolling around in a slop hooking into the berth from outside is a wretched business. Holding ground A chart of the appropriate scale will usually carry a symbol to indicate the nature of the bottom anywhere you are likely to anchor. It may even show an ‘anchor’ symbol enticing you to ‘let go here’. However, these are sometimes for the information of ships not boats, so treat them with caution.
Most anchors hold best in clay (‘cy’ on the chart) or firm mud (‘m’). Sand (‘s’) is surprisingly good also. Avoid areas where kelp and other weeds (‘wd’) are charted; only anchor in rocky ground if you have no other option because it is likely that your hook won’t hold at all. Even if it does, it may foul and be lost. The so-called ‘Chart
5011’ is really a booklet containing all the symbols used on UKHO charts. If in doubt about the letters relating to the sea bed, looking it up in ‘Chart 5011’ will resolve the question. Be especially aware of the dangers of ‘foul ground’. Often this will refer to old mooring chains and the like which can snag an anchor, making recovery difficult or impossible (see page 83).
Tactical considerations Crowded anchorages When the available space is well populated, try to deduce where the neighbours’ anchors may be lying before laying your own. If the other vessels are all wind-rode, it is generally safe to anchor so that you bring up three or four boats’ lengths away from the next yacht. Where wind and tide combine to create an ambiguous situation, the only sure policy is to assess likely swinging circles (are the neighbours on chain or rope?), and anchor so they cannot overlap. Swinging ashore It is always tempting to tuck in as close as you dare under the lee of the available shelter. Make certain that if the wind should change you are far enough to seaward to be able to swing through 180° and remain afloat.
Tidal height When anchoring on a rising tide, be sure to allow extra scope so that you don’t drift off at High Water after plucking the hook out. The penalty for miscalculating a falling tide fits the crime. A sailing boat ends up on her side, and a motorboat risks propeller damage amongst other hazards. Fortunately, the arithmetic to avoid this could not be simpler: • Calculate the height of tide when you intend to anchor (a).
• Note the height of Low Water (b). • Subtract the Low Water height from the present height to find how much the tide will fall.
• Add this to the depth you wish to lie in at Low Water, sound in until you reach this depth, then let go.
• Reading the chart to find the depth is not only a waste of time, it may be inaccurate, because the depths given are spot soundings and may not coincide with where you end up lying.
a
a Height of tide at arrival time b Height of tide at low water
a b
MANUAL OF SEAMANSHIP | 79
Anchoring
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