SH Cap. 8 — Anchoring

1. Anchoring as a Basic Skill

Putting a ship to anchor is the master's most common shiphandling task: on almost every voyage a ship anchors for some reason, and no mariner is qualified for command until he can anchor safely, expediently, and with confidence under all conditions. Done well, the evolution is completed without fuss; done poorly, it becomes a complicated, dangerous mess with rust and mud flying and the chain jumping across the wildcat.

At first glance there seem to be many unrelated ways to anchor — one anchor or two, in line or spread, equal or unequal chain — but the task is basically the same every time: a ship approaches an anchorage, maneuvers as near as possible to the desired final heading, slows or stops, and drops the anchor to the bottom. There is no single technique "for all seasons," so the book covers only the most common situations, which a skilled handler then adapts.

1.1 Know Your Ship

An approach cannot be planned without knowing the ship's maneuvering characteristics — what she can and cannot do. Perform the master's trials from chapter 1 to gain a feel for her response to rudder and engine before having to anchor in a difficult spot. Knowing when not to anchor is probably more important than how: when the anchorage is crowded or the weather adverse, order a tug, or lay off and wait for conditions to improve.

Maneuvering characteristics are not static. A very light draft, greater than normal drag, or reduced underkeel clearance can significantly alter behavior; a loaded tanker is a different ship from one in ballast. Each anchoring is a new task — do not fall into the trap of doing the job the same way every time. The text assumes no bow thruster is available, since most ships have none and a thruster is only effective below about 2 knots.

1.2 Plan Ahead and Anchor in Steps

The same principles of successful shiphandling apply: plan the overall maneuver before arrival from charts, pilots, and local knowledge; reduce speed early; use existing forces to advantage; and think ahead of the ship, adjusting the plan as events develop. Treat anchoring as a seamanship phase (how the ship will be anchored, covered by any good seamanship book) and a shiphandling phase (how she must be handled to do it), which is what this chapter stresses.

Keep the shiphandling phase simple by viewing anchoring as four steps: approach, placement, laying out, and fetching up. Plan each as a series of small, basic tasks — reducing speed, backing and filling, stopping while controlling the head — most of which the mariner has already mastered. Broken down this way, even a complex anchoring becomes a string of simple jobs.

2. Planning the Anchorage

Every mariner studies the charts, sailing directions, predicted weather, and — as the ship closes the anchorage — the radar picture, looking for several kinds of information.

Mariners too often weigh these factors only to choose the anchoring spot, the amount of chain, and the number of anchors — forgetting that the same information must also plan the shiphandling phase, helping rather than hindering the work. It is as important to have an alternative "bail-out" plan as a primary one: usually leaving the anchorage until conditions improve, or — if it is too late to leave — putting down an anchor and riding to a short stay while sorting things out.

3. Wind and Current Effects

Wind and current set the preferred direction of approach, the final heading, and to some extent the ship's behavior while maneuvering. They make set and leeway grow and turn the ship's circle elliptical, the long axis lying in the direction of wind and current, and their effects increase dramatically as speed decreases. The mariner used to full sea speed must plan more carefully and make greater allowances at the reduced speeds of an anchorage.

Do not fight wind and current — plan to use them. Current can set a vessel toward other ships and shoals, but it can also carry her away from hazards; wind causes leeway, yet it can help turn a ship around short as she backs into it. Plan to pass downstream and to leeward of ships, buoys, and hazards, or allow plenty of searoom: the two or three degrees allowed for set and leeway at sea are not enough — think in fives and tens at slow speed.

3.1 The 100-Foot Rule in the Anchorage

How far is far enough to pass clear? At anchorage speeds it is usually farther than expected. The 100-foot rule from chapter 5 applies, using the ship's own length as the unit of distance. For example, a ship at 3 knots makes about 300 feet per minute, so a 600-foot ship needs two minutes to move one ship length ahead and clear a point — during which a 2-knot beam current sets her 400 feet, two-thirds of a ship length. The one ship length that looked sufficient leaves only about a 200-foot clearance, far too close for comfort.

3.2 Sail Area and Turning the Long Way Around

The term sail area gains new meaning with high-freeboard, light-draft ships in strong wind. Passenger ships, containerships, car and gas carriers present a large profile relative to their draft and make far more leeway, so it is even more important that they not pass close ahead, to windward, or upstream of others. Such ships may be hard to turn to windward when strong wind retards the bow's upwind movement.

When winds and currents are so strong that even an expert cannot maneuver to the final heading before letting go — the very conditions in which the master most wants that heading to minimize strain — put down one anchor and a shot or two of chain and turn on the anchor, or call a tug, or stand off until conditions moderate. Arrange these contingencies before arrival, not when the situation arises.

4. Depth of Water

Shallow water affects maneuverability: as depth decreases the ship's tactical diameter grows and she becomes more directionally stable, possibly needing twice the room for large course changes that she would in deep water. So approach a shallow anchorage at slow speed, ready to back and fill to help her turn, and remember she will twist somewhat more in shallow water while going astern.

5. Maneuvering Room and Briefing Officers

Ships at anchor, shoals, a lee shore, and other hazards limit maneuvering room, so the handler matches the ship's characteristics to the available space — adjusting the game plan to the size of the playing field. A reasonably skilled handler can usually turn and position the ship without a tug, but do not hesitate to maneuver on the anchor if there is not enough space to turn or back and fill unassisted. Sometimes there is simply no room to turn to the final heading before letting go, and the only option is to let go heading with or across the wind and current. If there really is not enough room, do not go — anchor elsewhere or stand off and wait.

Room matters as much when leaving as when arriving: other ships may anchor after yours, or your ship may swing to a new heading, leaving no room to turn and depart. The same techniques — backing and filling, using wind and current, heaving short and steaming around on the anchor, or turning with a tug — serve a departure too.

5.1 The Briefing

Discuss the plan with the mate on the bow, the mate on the bridge, and — if unusual maneuvering is involved — the engineer on watch, so no one is surprised. A neat maneuver is spoiled if the mate slacks too much chain when you mean to maneuver on the anchor, or holds the chain too soon so the anchor drags and the ship is set beyond the spot. Be sure the mate knows:

6. Navigate by Eye

Study the charts well before arrival and commit key information to memory; select prominent landmarks, aids, and ranges, and prepare a pocket course card with the leading marks and approximate courses. As the ship nears the anchorage, navigate by eye, conning her in on natural ranges and leading marks while the mate navigates as usual, as a backup, on charts with the courses laid down in advance.

Visual navigation is preferable going to anchor because the ship usually follows a circuitous route — backing, filling, and turning to round up into wind and current — rather than a straight track; without visible marks you must constantly break off the shiphandling to consult the chart. Accurate navigation matters, but it can be overdone: pilots routinely anchor by eye, placing the anchor at least as precisely as a team of navigators shouting bearings and distracting the handler. A few well-chosen marks plus an abeam reference are more than enough — quite simply, it is a matter of professionalism.

7. The Final Heading

The final heading is the direction in which a ship will lie at anchor, heading into the resultant of all external forces — chiefly wind and current on her superstructure and underwater hull — once the anchor has fetched up and she has swung into equilibrium. It is better to let go on this heading, and the advantages outweigh any extra time spent reaching it.

The more restricted or crowded the anchorage, or the stronger the wind or current, the more important this heading becomes. Sometimes it is essential: a large bulbous bow can be damaged by a chain leading under and around it with a heavy strain — and the chain itself may be damaged — while naval vessels often have sonar domes and other gear protruding from the bow that the chain can easily damage. Heavy winds, swell, and current make this worse as the chain surges against the wildcat and stem.

It is not always possible — nor always necessary — to reach this heading: a ship may anchor on any heading in light airs or slack water, and in a calm every ship probably lies differently anyway. A professional still tries for the approximate heading even in a light breeze, and usually succeeds; having wind and current a few degrees on one bow rather than dead ahead does not significantly strain the gear. The heading is found by eye — looking at boats already lying to wind and current, or estimating from the ship's draft, freeboard, and the strength of the forces — aided by the rule that a 1-knot current has about the same effect as a 30-knot wind over a given area. Vector analysis would work but is needlessly complicated for day-to-day work.

8. Anchoring Off the Final Heading

Sometimes the ship must anchor heading across or away from the resultant of wind and current. In a light breeze this is no problem — she turns to her final heading after fetching up. In stronger conditions it is best to let go an anchor and one to two shots of chain only — about twice the depth — while the ship moves slowly ahead. The chain is held while she makes a controlled turn on the anchor to the final heading, in the least space, the anchor alternately digging in and breaking free with little strain.

Come ahead with the rudder hard over in the turning direction, backing and filling as needed, as the ship swings on the slowly dragging anchor. Stop the engine on or near the final heading, then ease the brake and slack the chain to bring her to anchor as wind and current check her headway and move her astern. Do not open the brake wide as she falls back — ease it so the chain lays out slowly, or the forces will take charge and bring her up hard against the gear, damaging the ground tackle or pulling the anchor free. The technique is especially useful in a strong river current, as on the Mississippi, or in a strong wind or heavy swell.

9. Basic Anchoring and the Approach

Anchoring is almost always "plain vanilla": the ship enters the anchorage, turns as nearly as possible to the final heading, and backs down until she moves slowly astern over the bottom; one anchor is let go and the chain slacked to the desired amount; the engine is kicked ahead, if needed, until she loses nearly all sternway; then the brake is tightened and the anchor fetches up. Port after port the ship anchors in just this way.

On the approach the conning officer follows the planned track by eye, progressively reducing speed — less speed means more time to plan, respond, and stop. Detect movement over the bottom by the apparent motion of other ships and objects against more distant references: references ahead and astern reveal lateral motion, those abeam reveal headway or sternway. This works by day and night, long before traditional navigation shows any change.

9.1 When to Turn — the Turning Circle

The handler knows the ship's tactical diameter from the master's trials and estimates the point to start the turn. It is best to make large heading changes well before the anchoring spot, so only the final stopping remains. As a rule of thumb, a ship turning at constant engine speed in deep water (more than 1½ times her draft) will be about 3 to 3½ ship lengths ahead and 1½ ship lengths to the side after 90°, and about 1 ship length ahead and 3½ ship lengths to the side after 180°. An accelerating turn shrinks these; in water nearly as shallow as her draft the distances roughly double.

The handler knows from the trials how many lengths the ship advances after the engine goes astern, and thus when to back to be dead in the water at the spot. For safety, back down at least once before reaching that point to check the speed, using the location of the quickwater. When anchoring at night or in a crowded anchorage, put the engine astern well before the spot and back until the ship is dead in the water — then there is no doubt the speed is zero — come ahead slowly, move the last few lengths, and let go.

10. Placing the Anchor

The ship moves the last few hundred feet to the spot — on the final heading if possible — converting distance from yards or fractions of a mile into ship lengths or feet, the units the handler can use by eye. Crucially, the anchor drops from the bow, not the bridge: it is the bow's location that matters. Estimating from the bridge causes large errors on a bridge-aft VLCC whose stern may be a quarter mile from the anchor, or a bridge-forward car carrier 700 to 800 feet from her stern.

When placing the anchor, set up to back and keep control whenever the engine is astern. For a right-hand fixed propeller near the final heading, kick ahead with the rudder hard left to start the bow swinging to port, then go astern. Back until the quickwater reaches amidships, then keep backing: ideally the bow steadies up if the starboard anchor is to drop, or swings slowly to starboard if the port anchor is to be used. Masters too often stop the engine when the quickwater reaches amidships, fooled into thinking the ship moves astern when she is merely dead in the water — and the chain only piles up and stops running if the anchor is let go without sternway. Continue backing until the quickwater is forward of amidships, so she truly moves astern, then open the brake and let go.

11. Laying Out the Chain and Digging In

The brake is tightened and eased to control the chain as the ship moves slowly astern, laying it evenly over the bottom rather than in a pile that could foul the anchor, until it comes up tight with a heavy strain. The mate on the bow is the master's eyes, reporting the lead and weight on the chain and keeping a light strain so it lies clear of the stem and bulb, and notifying the bridge as soon as the ordered length is out so the engine can reduce sternway before the anchor fetches up hard.

What matters when letting go is movement over the bottom, not speed through the water. Against a 1-knot current from ahead, the ship has 1 knot of sternway over the bottom when the quickwater reaches amidships, and the chain lays out nicely. Once she moves astern, the apparent motion of ships against the background shoreline is the best indication of movement — the quickwater only tells you she has sternway, and the Doppler log becomes useless once the quickwater runs up under the hull.

When the required chain is out, tighten the brake; if the ship still has significant sternway, kick ahead one last time so the chain is not parted as the anchor fetches up — hard-over rudder may be used here to bring her closer to the final heading, but remember that the stopping effect of the engine is greatest with the rudder amidships. Use the engine only to reduce sternway, not stop the ship: she must keep a little sternway so the catenary of the chain absorbs most of the remaining force and the flukes dig well in. Back again if she stops too quickly, so the anchor is well dug in before the engines are rung off.

12. Swinging Room at Anchor

Masters prefer to anchor far enough off to swing clear on the present heading and any later one. But in a crowded anchorage, after days at sea, other ships always look closer than they are because of height of eye and the lack of references. Even experienced pilots, anchoring in seeming close quarters, are surprised from a launch near the water to find the ships quite far apart. You cannot reach a launch, but you can walk down to the main deck, where the true distance becomes apparent.

Radar, excellent in open anchorages, is less reliable for the absolute distance between closely anchored ships — it measures to an undefinable point on the other ship, to fractions of a mile, and stacks and gear create blind areas — but it is good at detecting changes in distance, as when a ship drags. Estimate distance by eye using your ship's length, measuring to your bow or stern, not to the bridge. Some pilots swear they judge distance better by bending over and looking between their legs; odd as it looks, it seems to work.

A ship in a crowded anchorage may have to maneuver on the anchor with engine, rudder, or thruster to swing clear as the tide or wind shifts. Calculate the changes, have the engine and thruster ready well before the change, and in a tight spot have a tug standing by — do not wait until other ships start swinging. The master may also put down two anchors to limit the swing, but this may not work if nearby ships ride to one anchor and swing in a wider circle; then use one anchor or be ready to heave up the second. Local practice matters, so that all ships swing together.

13. Mooring and Anchoring with Two Anchors

Seamanship books give the reasons for using two anchors; here only the shiphandling matters. The running moor puts down two anchors in line while the ship has headway: she comes to her final heading stemming the current, lets go the first anchor, slacks that chain as she moves slowly ahead to drop a second, then heaves the first while slacking the second so she drops back to ride between them — swinging within nearly her own length at each turn of the tide.

The standing moor (ordinary moor) is similar, except the ship comes to her heading, backs until she has sternway, drops the first anchor, and slacks the chain as she maneuvers astern to drop the second, then heaves the first while slacking the second to ride between them. The standing moor is more common for laying anchors in line with a current, since the handler has less control going astern; the running moor, with steerage and headway, is more often used to lay anchors perpendicular to wind and current.

Seamen avoid two anchors because of round turns — caused by the ship repeatedly swinging the same way, clockwise or counterclockwise, wrapping the chains so they cannot be hove home. Prevent them by turning the ship the opposite way at each turn of the tide or wind: put the rudder hard over and kick the engine ahead, or have a tug push the quarter, starting her swinging so wind or current pushes her around alternately clockwise and counterclockwise. The engine or a tug is usually more reliable than canting on the rudder alone for today's larger ships.

14. Stern Anchors

Stern anchors are most common on naval landing and assault vessels: they add control, prevent broaching from wind, swell, and current, and kedge a ship off a beach. A few merchant lines fitted them — Grace Line used them to hold ships at open roadsteads off South America, and El Paso LNG fitted nine LNG ships so they could anchor 950-foot vessels in the strong tides of Chesapeake Bay and the Savannah River, and keep control after a rudder or engine failure. Few merchant ships carry them now, so myths abound.

In an open roadstead both bow anchors and the stern anchor form a three-point "Y" moor. After planning the maneuver on the chart with three predetermined reference bearings, the ship approaches at minimum steerageway, bow to seaward, from the left of the moor to use her ability to back and fill to the right (fig. 8-9). She comes up to point "A" where the three bearings intersect, runs the reciprocal of bearing "B" to drop the port anchor with all headway off, backs and turns to bearing "D" to drop the starboard anchor, then backs to "A" and along bearing "C" to drop the stern anchor — again with all sternway off — and finally heaves the bow chains while slacking aft until she rides to all three.

To unmoor, slack the bow chains and heave astern on the stern anchor, paying the bow chains out slowly for control, and wait until the stern anchor clears the water and is in sight before moving ahead. The same sequence, performed stemming the current, anchors a stern-anchor ship in a river or restricted anchorage; one bow anchor may suffice, but the maneuver is essentially the same.

15. The Anchor as a Shiphandling Tool

The anchor is rarely used in handling and is wrongly thought of as a tool of last resort. Yet a ship can be maneuvered with an anchor in ways impossible with engine, rudder, and tugs alone — it is the "poor man's tugboat", often more effective than a tug. The mate sent to let it go must be well trained in handling ground tackle and putting out the correct amount of chain.

The pivoting moment becomes significant only if a large turn is deliberately initiated with engine and rudder after the anchor begins to drag, as the anchor's retarding force and the ship's momentum shift in opposite directions from the centerline. This delayed effect shrinks the turning circle — a desirable result — but it does not happen on its own, and its magnitude is the same for a turn to port or starboard regardless of which anchor is down.

15.1 Which Anchor — Inshore or Offshore

There is disagreement over which anchor to drop. Some favor the lee or inboard anchor, claiming it leads under the hull and holds better in a beam wind with less brake stress; others favor the windward or offshore anchor, which leads clear and needs more chain before it holds. The book recommends the offshore (windward) anchor.

A bulb alone is reason enough to avoid the inboard anchor. As for stopping the chain after letting go, this is no problem even on large ships: static friction is three times greater than dynamic friction on the brake band, so the brake holds three times as hard when the wildcat is stopped. The chain runs only until the anchor hits bottom and goes slack; the brake is then set up, and the anchor digs in, comes tight, and pulls free again before static friction is overcome — dragging as the flukes ball with mud.

16. Shiphandling with Anchors — How Much Chain?

Have the anchors manned and ready when maneuvering in restricted waters. Should the anchor be needed, let go only enough chain to let it grab, then break loose and drag — it must not dig in and hold. For greatest effect, put an amount of chain equal to about twice the depth well in the water and screw the brake up tight; if needed, the second anchor can be let go with a like amount. The ship slows and stops as one or both anchors drag.

The author recalls a deeply laden chemical tanker in the Panama Canal whose wheel was put the wrong way: she dove for the bank, anchors were let go, and shot after shot ran over the wildcat until she finally stopped — but only when hard against the bank at Contractor's Hill. A windlass brake simply cannot stop a loaded ship. The proper use of anchors is in danger of becoming a lost art; be sure every deck officer knows how much chain to slack before going forward.

17. Docking with an Anchor

Most dockings can be done with an anchor instead of a tug, though the tug is generally more convenient. Enough chain is put out to eliminate headway at dead slow or slow speed; how much can only be found by lengthening the chain a few links at a time until, with the engine coming ahead slowly, the ship is held in position both laterally and fore and aft. Drop the anchor well before the berth and drag it into position. Done right, the anchor takes nearly all headway off, and the ship makes no headway until revolutions are increased to at least slow ahead.

Because the ship slows and stops with her engine stopped as the anchor drags, no twisting occurs and she stays shaped up for the berth; the engine can be put astern if needed, though that is rarely necessary. The bow and stern are then moved separately as she is docked, with excellent control of forward and lateral motion.

The key is slacking enough chain that the ship holds at low revolutions but moves ahead as revolutions rise, the anchor either holding or dragging as the revolutions are adjusted.

18. Holding and Steering with the Anchor

Often a ship must proceed slowly with a strong beam wind, or hold position in a channel because of poor visibility or a late tug. The anchor greatly simplifies this, even for a ship a thousand feet long. When a blinding rain squall stops a ship in a narrow channel, an anchor and a shot of chain are put well in the water; the brake is set up and the engine used only to hold the heading as she slowly loses way; then, dead in the water, the engine goes slow or half ahead and she works against the anchor, more chain slacked until she just holds position while the quartermaster steers by compass. A ship that had been setting out of the channel and not answering her helm steadies up nicely with the anchor down.

If one anchor is not enough, put a second down the same way — best while the ship still has headway, so the chain lays out and the flukes fall flat and do not set against the hull. The chain needed depends on the ship's sail area, the bottom, and the wind: start with a shot and slack more until the anchor takes charge, using only the minimum until the ship has lost nearly all way, since the holding effect grows as speed is lost — you do not want so much out that the anchor fetches up.

18.1 Anchors to Assist Steering

When meeting a ship in a channel so narrow there is danger of sheering, when taking a turn smaller than the tactical diameter, or when steering is hard in a strong wind, use the anchor: it steadies the bow laterally and retards headway despite higher revolutions — or higher revolutions can increase the rudder's effect without adding headway. Use less chain so the ship keeps some headway as the anchor drags, and let go well before the critical point so the anchor has time to ball with mud. The pivot point shifts forward, so the turning diameter is much reduced; the stern initially swings wider, but steering becomes more precise from the restricted bow and the greater flow over the rudder for a given speed.

18.2 Anchors to Break a Sheer

Should the ship take a sheer, the anchor can regain control and prevent collision or grounding — but it must not dig in, so slack minimal chain. If it fetched up, the sheer would be accentuated as the pivot point shifts ahead to the hawsepipe and the suction of the quarter takes charge. Dragging properly, the anchor steadies the bow, the rudder becomes effective, the stern lifts off the bank, and the sheer is broken — the handler having also gone full ahead to force a maximum flow over the rudder.

19. Emergency Use of the Anchor

The anchor is most often used today for emergencies, and it is extremely effective for preventing groundings when the engine or steering is lost: the ship continues along her track, slowly losing headway, and can usually be brought to a controlled stop given enough searoom. Two anchors increase the stopping force, but neither must fetch up. A stern anchor, if fitted, is used with the bow anchors and is especially good at stopping a ship in a short distance while holding her heading — though it is no help if the heading must be changed while stopping.

Some steering control can be kept after a rudder loss by using the ship's natural behavior with the anchor: she turns right by backing (the twisting tendency), turns left using bank suction on the starboard quarter, turns into the wind with headway, and backs into the wind once sternway develops — after which an anchor lets her back nearly straight. Even with a total rudder loss, a ship can be backed off a lee shore this way.

If dragging anchors cannot stop the ship before grounding and the bottom is soft, slack more chain when one to two ship lengths from the shoal so the anchors are laid out and ready to pull her back off. When the engine is lost, steer and drift with the rudder until nearly dead in the water — do not get the anchors down too soon, since once an anchor takes charge much of the rudder's effect is lost; wait for a straight reach ahead. Hesitation to use the anchor comes from lack of confidence, which practice at the pilot station cures.

20. Lying Alongside a Bank and Going Astern with an Anchor

To anchor in a narrow channel and be sure the ship will not swing across it, she can be put alongside a steep, soft bank of mud or clay and held with the anchor regardless of wind and current. With the current from astern, bring her to the starboard side of the channel at bare steerageway, drop the outboard (port) anchor, and slack chain — but not so much that she stops before reaching the bank, or the current from astern will swing her crosswise. Ease ahead against the anchor and, nearing the bank, put the rudder to port and reduce or stop the engine so she lies easily at a slight angle: the stern rests against the bank and the anchor holds the bow off as the current strikes the port side.

Should the current reverse, come ahead a few revolutions with the rudder hard to starboard to lift the stern, let her fall back with the current, and kick ahead as needed to keep the stern off until she rides to her anchor; the eddy current between bank and hull then usually holds her a short distance off until the next change, when she is put alongside again as the tide floods.

20.1 Going Astern with an Anchor

A ship maneuvering astern for any distance can use an anchor underfoot to steady the bow and back almost directly astern — the anchor replacing a bow tug while the engine drives her aft. Skill is needed, since she still pivots somewhat going astern: the stern walks to port much more slowly than without the anchor, and when it does start to port, stop the engine and kick ahead with hard-over rudder to recover the heading before resuming. Use only the minimum chain to steady the bow — if the anchor fetches up so all astern motion is lost, the ship walks only to port.