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The Practical Mariner's Book of Knowledge
460 Sea-Tested Rules of Thumb for Almost Every Boating Situation
By John Vigor
The McGraw-Hill Companies, Inc.Copyright © 2013 John Vigor
All rights reserved.
Abandoning Ship The rule of thumb is never to abandon ship until you have to step up to your liferaft.
Unfortunately, this is much easier said than done. There is often great psychological pressure to escape from the responsibilities, physical labor, decision making, stress, and sense of failure that accompany a sinking situation in heavy weather. Many sailors suffering mental and physical exhaustion after a knock-down or a holing find the thought of drifting off in a rubber liferaft—and thereby abdicating all decision making and physical labor—immensely appealing. But, all too often, the partially waterlogged yacht is found still floating, months or even years later, while the liferaft and its occupants are never seen again.
Aground See: RUNNING AGROUND, FIRST ACTION TO TAKE
Air Pressure, on Sails and Rigging The force applied by wind to a boat's sails, or to its rigging and superstructure while at anchor, varies with the density of the air.
Cold air is denser than is warm air, so a sailboat heels more (with the same sail area and wind speed) in higher latitudes than in the tropics, or more in autumn than in summer.
The force of the wind also increases as a square of its speed, which means that if the wind speed doubles, its force increases four times.
See also: APPENDIX: HORSEPOWER GENERATED BY SAILS, APPROXIMATE; AND APPENDIX: WIND PRESSURE ACCORDING TO WIND SPEED
AIS as a Safety Aid The automatic identification system (AIS) is a modern digital, VHF-radio-based transponder system that broadcasts an electronic chart of your area marked with all ships of at least 300 tons gross, plus all passenger ships. The AIS automatically and continually shows these ships' present positions, speed, compass headings, and much more information.
Yachts and other vessels less than 300 tons are not required to carry full-function Class A AIS transceivers. Less expensive transceivers that consume less electricity and transmit at 2 watts, instead of 20, are available for pleasure vessels. In addition there are receive-only units specially designed for small craft. These receive-only units will not alert other ships to your presence but will provide information to you about their speeds and courses, which, like radar, could add greatly to your safety at night or in limited visibility, especially in crowded waters. For a free trial run showing vessels in real time in your own area, go to http://marinetraffic.com/ais.
See also: CARD, USES OF; PERSONAL SAFETY, SOME GUIDELINES; entries under RADAR; RESCUE AIDS, ELECTRONIC
Albatross, Superstition Concerning It was widely believed by European mariners that an albatross housed the soul of a dead sailor.
It was therefore very bad luck to kill one, as Samuel Taylor Coleridge tells us in The Rime of the Ancient Mariner.
Alternator, Power Absorbed by It's easy to regard the alternator as a source of free power, just spinning away as the engine runs. But, in fact, it takes a surprising amount of power—and therefore fuel, which could affect a boat's range—to turn over an alternator.
The rule of thumb is that the horsepower drain on the engine is twice the number of kilowatts produced. If, for example, a 100-amp alternator is charging a 12-volt system at full capacity, it's producing 1,200 watts or 1.2 kilowatts. So, it steals 2.4 h.p. from the engine's output.
Alternator, Sizing Rule Your alternator should have a recharging capacity in amps of between 25 and 40 percent of the total amp-hours in your battery bank.
This presupposes you are using a modern, multistep regulator that won't allow overcharging, particularly when the batteries become warm. If you don't have a multi-step regulator, the rule of thumb for long battery life is that you should limit the charging rate in amps to 10 percent of available amp-hours. But, because this takes so long, most boaters don't heed this rule, preferring to charge at about 20 to 25 percent and to buy new batteries more frequently as a consequence.
Anchor, Best Type to Use Once you understand the idiosyncrasies of your particular anchor, you can make it dig in and hold on almost any kind of bottom. However, these are the general characteristics of the more popular types of anchors:
Pivoting plow type (C.Q.R. and others): Good all-rounder, best in sand and mud. Poor on weed and hard rock. Cannot be fouled by its rode. Good at resetting itself when direction of pull is changed.
Fisherman type (Herreshoff, Luke, and others): Better than most on rocky and grassy bottoms, but needs to be heavier than most other anchors and can be fouled and dislodged by its own rode. Small fluke area drags easily through soft bottoms. Awkward to handle, but can be dismantled for stowage.
Lightweight type (Danforth, Fortress, Performance, and others): Sharp points on flukes are good at digging into hard sand and better than most at penetrating grass. Large fluke area is helpful in soft mud. Not good at resetting itself. Has great holding power.
Bruce type: Very strongly built, good all-rounder. A modified plow with no moving parts. Cannot foul itself. Stows conveniently in a bow roller and resets itself well. Good in sand, mud, rock, and coral.
Delta type: A sturdy, one-piece, non-pivoting plow. Weighted to land correctly, penetrate hard bottoms, and set itself quickly. Launches itself easily from bow roller and cannot foul its rode.
New types: Experimenting with new types of anchors never seems to cease. Of the recent new anchors, some of the most common are the Manson and the Rocna from New Zealand, the French Spade, and the Bulwagga from Florida. Some of them, such as the Manson and Rocna, have large roll bars to keep the anchor right-way up on the bottom, and their manufacturers claim advantages over conventional designs. But until these anchors have demonstrated their effectiveness over a long period of time, such claims are difficult to prove. No one anchor design has ever been the best for all bottom conditions. For many years, longdistance cruisers have favored proven designs such as the C.Q.R., Bruce (the genuine one), Danforth, and Delta, simply because they behave reasonably well most of the time.
Anchor, Direct Strain on Thomas Fleming Day, editor of The Rudder, declared in 1901: "The direct strain on anchors is of no consequence except in very high winds; it is the sea that causes them to leave their hold." He likened the anchor (an old-fashioned fisherman anchor, of course) to a workman's pick buried to the hilt in the earth. "When given sufficient scope, the anchor, like the pick, is resisting a pull at right angles, and stands fast, but the minute the sea begins to move the vessel up and down the handle of the anchor is worked up and down; the shorter the scope the more surely is this motion transmitted, and the more effective it is in breaking out the arm."
Anchor, Fisherman, Ideal Proportions of The fisherman-type anchor is not widely carried on modern pleasure boats because it's awkward to handle and stow, and because it's easily fouled by its own rode. Newer designs of anchor—such as the Bruce, the C.Q.R., the Danforth, the Delta, and others—have largely eliminated these faults, but the fisherman still has its uses, especially where the bottom is hard, rocky, or covered with grass.
Not all fisherman anchors are created equal, however. Claud Worth, the classic British sailor and author of Yacht Cruising, gave this advice for selection:
The arms and shank should be oval or flat in section. The flukes should be sharp and long to bite into hard ground. They should make an angle of about 40 degrees with the shank. The measurement from the crown to the hole for the stock should be not less than 11/2 times, nor more than 1 times, the length of the chord—the chord being the distance between the tips of the two flukes. The stock should be the same length as the shank.
Anchor, Proper Scope Under favorable weather conditions, the minimum scope of an anchor cable should be 5:1. Under average conditions, a scope of 7:1 is considered satisfactory. As much as 10:1 is needed in heavy weather.
Scope is measured as the ratio between the depth of the water and the length of the anchor cable veered out. Note that the depth of the water in this calculation also includes the extra length between water level and the bow chock. In other words, depth of water really means the distance from your bow roller straight down to the sea bed.
These amounts of scope allow a nylon rode with at least 8 feet of chain (preferably more) attached to the anchor to exert a low angle of pull against the anchor. Most anchors tend to break out if the angle of pull is more than 8 degrees from the horizontal.
The temptation to pay out less scope on an all-chain rode should be resisted. Although the catenary of the chain cushions shock loads from large waves, once the slack has been taken up, the snatching loads on your anchor and Samson post, or anchor winch, are much greater than they would be with a stretchy nylon rode.
Anchor, Safe Minimum Weight of Although it's their engineering design that makes them effective, anchors still need weight to dig into the bottom. It's generally agreed that no matter how small a yacht may be, it's not wise to use any anchor weighing less than 30 pounds for any purpose other than temporary halts during which the yacht is adequately manned and ready to sail at short notice.
A useful rule of thumb for plow anchors used on sailboats engaged in long cruises is to have 1 pound of anchor for every 1 foot of boat length, measured on deck. This ensures that the anchor will have sufficient weight to penetrate most "difficult" bottoms such as those of hard sand or those covered with weed or grass. Some modern lightweight anchors, while certainly possessing adequate holding power when properly dug in, may not be able to penetrate such bottoms.
See also: APPENDIX: ANCHORS, RECOMMENDED SIZES
Anchor, Size of Owners of cruising yachts should beware of generalized suggestions from anchor manufacturers about the size of anchors they need.
Seventy percent or more of many types of anchors are sold to inland fishermen for use with small open boats on lakes. Understandably, manufacturers' recommendations are tailored to this market, not the market constituting the 2 percent of their customers with offshore voyaging boats.
See also: APPENDIX: ANCHORS, RECOMMENDED SIZES
Anchor, Time Spent at, While Cruising While cruising in Mexico, the Caribbean, and the South Pacific, the average yacht spends 10 percent of the time at sea, 5 percent tied to docks, and 85 percent at anchor.
This rule of thumb, which originated with Lin and Larry Pardey, points to the importance of good ground tackle and an efficient dinghy.
Anchor, Weight One Person Can Handle The rule of thumb is that it's possible for a person of average strength and fitness to raise and bring aboard a 60-pound Danforth or C.Q.R. anchor without any special gear.
Nevertheless, it's heavy work, and in boats exceeding 5 or 6 tons of displacement, some mechanical assistance is generally considered necessary. A chain pawl attached at or near the bow roller is of great assistance. It also makes it feasible to do away with an anchor winch or windlass altogether when using a 35-pound anchor and 51/6 chain, particularly if an auxiliary engine can be used to ease the ship to windward while weighing.
Anchorage, Safe When seeking a safe anchorage, bear in mind these basic requirements:
Shelter from wind and waves
Room to swing around the anchor
Sufficient depth of water at low tide
Good holding ground for the anchor
Anchor Chain, Bitter End, Securing The inboard or bitter end of the anchor chain should be secured with about 3 fathoms of appropriately sized nylon line to the base of the Samson post, king post, or other heavy structural member in the chain locker.
The nylon line is easier to cast off, or cut and buoy, in the event of the cable having to be slipped quickly. The elasticity of the nylon also helps absorb the considerable shock of a runaway anchor chain coming up short against its bitter-end fastening. A chain shackled internally to a bolt through the bow might simply blast a hole through the hull when it reaches the end of its tether.
See also: CHAIN, STRENGTH OF
Anchor Chain, High-Tensile High-tensile chain is traditionally not recommended for anchor rodes. Although it has a high breaking load, it can fail without warning. Ordinary galvanized steel chain with short oval links is usually specified for pleasure-boat use because it gives visible signs of stretching before breaking.
Anchor Chain, Markings for If you have no other way to judge how much chain you're veering, paint a white mark at least a foot long on the cable every 5 fathoms (30 feet). All too often, in the absence of some method of measuring, insufficient scope is given, which is the gravest crime in the anchoring laws.
If you have trouble counting the marks as the line is paid out, you could try a system with fewer markings in different colors. That way, you can check at a glance the amount of cable veered.
Anchor Chain, Size of The American Boat and Yacht Council uses windage on the boat as a criterion for selecting chain. It recommends that the chain have a breaking strength to withstand at least five times the normal horizontal load.
To estimate the horizontal load, you need to know the frontal surface area on your boat exposed to the effect of windage. The rule of thumb is to multiply bow height by maximum beam. The result is in square feet. Add two-thirds of that figure to account for spars, rigging, and deck gear. Add the frontal area, in square feet, of anything else, such as a raised dodger. Then double the resulting figure to account for the effects of yawing. The pressure of wind on this square footage varies with its speed.
See also: CHAIN, STRENGTH OF; APPENDIX: CHAIN, RECOMMENDED SIZES FOR ANCHOR; AND APPENDIX: WIND PRESSURE ACCORDING TO WIND SPEED
Anchor Light, Required Size Vessels under 50 meters in length must show an all-round white light that is visible for 2 miles when anchored between dusk and dawn, except in designated "special anchorages."
The 2-mile range is normally reached by a 12-watt electric bulb or a half-inch wick in a kerosene lantern showing through clear glass.
See also: NAVIGATION LIGHTS, SPECIFICATIONS FOR
Anchor Rode, Minimum Length of The length of anchor rode that a vessel needs obviously depends on the depth of water in which she wants to anchor. However, unless she is too small to stow it, no boat should carry less than 30 fathoms (180 feet) of anchor rode. This is sufficient to keep her safe, in all but exceptional weather, in 25 feet of water.
However, it's vastly preferable in all cases to carry at least 50 fathoms (300 feet) to allow for anchoring in deeper water.
Incidentally, the term rode is generally taken to mean all the gear lying between a boat and her anchor—no matter whether it's rope or chain—although in New England and Eastern Canada it refers to a fishing boat's anchor rope.
Anchor Scope, Effect of It often happens that crowded anchorages limit your swinging room and, therefore, your scope. The more horizontal the rode on the sea bottom where it attaches to the anchor, the better. But if you are forced to lie to a shortened rode, here is how it will affect your anchor's holding power. Presuming that a scope of 10 to 1 offers 100 percent holding power, then, roughly speaking:
7 to 1 = 90 percent
6 to 1 = 85 percent
5 to 1 = 75 percent
4 to 1 = 65 percent
3 to 1 = 50 percent
2 to 1 = 35 percent or less (maybe much less)
Anchoring, Problems with Coral Heads When anchored in areas where coral heads are prevalent, a chain rode frequently wraps around one or more heads, dangerously shortening the scope. The general rule is to buoy the chain so that the main part of the rode cannot foul coral. Usually, several buoys are needed.
Some experienced cruisers prefer to anchor in depths of between 90 and 120 feet when possible, because coral heads are far less common in deeper water. But this requires more anchor line than many small cruisers can comfortably carry.
Anchoring, Problems with Snatching In shallow water and steep waves, any boat can snatch badly at her anchor rode. In such circumstances, it's easier on the gear to use a nylon anchor rode to absorb the snatching loads. Even with an all-chain rode, a 20-foot spring of three-strand nylon made fast with a rolling hitch to the chain near the bow is probably more effective than is a traveler weight in preventing destructive snubbing.
Excerpted from The Practical Mariner's Book of Knowledge by John Vigor. Copyright © 2013 by John Vigor. Excerpted by permission of The McGraw-Hill Companies, Inc..
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