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Sailing reference

The YouSail sailing glossary

Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.

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COLREGs - Steering & Sailing Rules
Rule 13 - Overtaking
The boat coming up from behind must keep clear
Any vessel overtaking any other must keep out of the way of the vessel being overtaken, and this rule overrides the other steering and sailing rules, so a sailing vessel overtaking a power-driven vessel gives way. A vessel is overtaking when coming up from more than 22.5 degrees abaft the beam, that is from a position where at night only the sternlight and neither sidelight would be seen. Any subsequent change of bearing does not make her a crossing vessel.
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COLREGs - Steering & Sailing Rules
Rule 14 - Head-on Situation
Two power vessels meeting bow to bow both turn right
When two power-driven vessels meet on reciprocal or nearly reciprocal courses so as to involve risk of collision, each must alter course to starboard so they pass port to port. The situation exists when a vessel sees the other ahead or nearly ahead, at night seeing both sidelights and the masthead lights in line or nearly in line. If there is any doubt whether the situation exists, the vessel must assume it does and act accordingly.
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COLREGs - Steering & Sailing Rules

Rule 15 - Crossing Situation

Power vessel with another on its right gives way

When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side keeps out of the way and must, if the circumstances of the case admit, avoid crossing ahead of the other vessel. At night the give-way vessel typically sees the red sidelight of the stand-on vessel, giving rise to the mnemonic that seeing red means stop. The customary avoiding action is a bold alteration to starboard.

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COLREGs - Steering & Sailing Rules

Rule 16 - Action by Give-way Vessel

The giving-way boat must act early and decisively

Every vessel directed to keep out of the way of another must, so far as possible, take early and substantial action to keep well clear. Read with the action-to-avoid-collision rule, this means an alteration large enough to be obvious on the other vessel's radar and to the naked eye, taken while the range is still open. A last-minute nudge that passes the other vessel close aboard, even without contact, does not satisfy the requirement.

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COLREGs - Steering & Sailing Rules

Rule 17 - Action by Stand-on Vessel

The right-of-way boat holds course, then acts if needed

The stand-on vessel keeps her course and speed, but may take action to avoid collision by her manoeuvre alone as soon as it becomes apparent that the give-way vessel is not taking appropriate action. When collision cannot be avoided by the give-way vessel's action alone, the stand-on vessel must take such action as will best aid avoidance. A stand-on power-driven vessel taking early permissive action must not alter to port for a vessel on her own port side.

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COLREGs - Steering & Sailing Rules

Rule 18 - Responsibilities Between Vessels

The pecking order of who gives way to whom

Except where the narrow channel, traffic separation and overtaking rules require otherwise, a power-driven vessel keeps clear of a vessel not under command, one restricted in her ability to manoeuvre, one engaged in fishing, and a sailing vessel. A sailing vessel keeps clear of the first three. A vessel engaged in fishing keeps clear of the first two. A vessel constrained by her draught has its own qualified status, and seaplanes and WIG craft keep well clear generally.

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COLREGs - Steering & Sailing Rules

Rule 19 - Conduct in Restricted Visibility

Special rules when you cannot see the other vessel

This rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. There is no stand-on vessel. A vessel detecting another by radar alone must determine whether a close-quarters situation is developing and take avoiding action in ample time, avoiding an alteration to port for a vessel forward of the beam other than one being overtaken, and avoiding an alteration toward a vessel abeam or abaft the beam.

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COLREGs - Steering & Sailing Rules

Rule 2 - Responsibility

Nothing excuses poor seamanship, and rules may be broken to survive

Often called the general prudential rule. Paragraph (a) makes vessel, owner, master and crew responsible for the consequences of neglecting the rules or of any neglect of the ordinary practice of seamen. Paragraph (b) permits a departure from the rules where necessary to avoid immediate danger, taking due regard of all dangers of navigation and collision and any special circumstances, including the limitations of the vessels involved. It is a defence of last resort, not routine licence.

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COLREGs - Steering & Sailing Rules

Rule 3 - General Definitions

The official meanings of the words the rules use

Defines vessel, power-driven vessel, sailing vessel, vessel engaged in fishing, seaplane, vessel not under command, vessel restricted in ability to manoeuvre, vessel constrained by draught, underway, length and breadth, in sight of one another, and restricted visibility. Two definitions catch sailors out: a sailing vessel using her engine, even with sails set, is a power-driven vessel; and underway means not at anchor, made fast to the shore or aground, whether or not making way through the water.

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COLREGs - Steering & Sailing Rules

Rule 5 - Look-out

Duty to keep watch by every means at all times

Every vessel must at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate to the prevailing circumstances and conditions, so as to make a full appraisal of the situation and of the risk of collision. This explicitly includes radar and, in practice, AIS where fitted. Singlehanded and shorthanded sailing does not exempt a vessel; failure to keep a look-out is the most frequently cited breach in collision cases.

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COLREGs - Steering & Sailing Rules

Rule 6 - Safe Speed

Go slow enough to stop or avoid in time

Every vessel must proceed at a speed allowing proper and effective action to avoid collision and stopping within a distance appropriate to the circumstances. Factors listed include visibility, traffic density, manoeuvrability and stopping distance, background lights at night, wind, sea, current and draught relative to depth. Additional factors apply to vessels using radar, including its characteristics, limitations, scale in use, sea and weather clutter, and the possibility of small craft not being detected at adequate range.

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COLREGs - Steering & Sailing Rules

Rule 7 - Risk of Collision

How to decide whether a collision is actually developing

Every vessel must use all available means to determine if risk of collision exists, and if there is any doubt such risk is deemed to exist. Proper use must be made of operational radar, including long-range scanning and radar plotting or equivalent systematic observation. Risk is deemed to exist if the compass bearing of an approaching vessel does not appreciably change, and may exist even with an appreciable bearing change when approaching a very large vessel, a tow, or a close-range target.

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COLREGs - Steering & Sailing Rules

Rule 8 - Action to Avoid Collision

Make changes big, early and obvious to the other ship

Action must be positive, made in ample time and with due regard to good seamanship, and if circumstances permit large enough to be readily apparent to another vessel observing visually or by radar. A succession of small alterations should be avoided. An alteration of course alone may be the most effective action, provided it is made in good time, is substantial and does not result in another close-quarters situation. A vessel may slacken speed, stop or reverse.

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COLREGs - Steering & Sailing Rules

Rule 9 - Narrow Channels

Keep right and do not block big ships in tight water

A vessel proceeding along a narrow channel or fairway must keep as near to the outer limit on her starboard side as is safe and practicable. Vessels under 20 metres and sailing vessels must not impede a vessel that can navigate safely only within the channel; a vessel engaged in fishing must not impede any vessel navigating within it. Crossing is prohibited if it impedes such a vessel. Overtaking requires the Rule 34 sound signals and the agreement of the vessel ahead.

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Tidal Streams & Currents

Rule of Thirds (Fifty-Ninety Rule)

A quick way to estimate stream rate hour by hour

Assumes a sinusoidal rate profile over a six-hour half-cycle. In successive hours the stream runs at roughly one third, two thirds, three thirds, three thirds, two thirds and one third of maximum rate. The related fifty-ninety rule states that after one hour the stream has reached about 50 per cent of maximum and after two hours about 90 per cent. Both fail where the profile is distorted by shallow-water effects.

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Tidal Calculations

Rule of Twelfths

A quick mental method for estimating tide height between high and low

Divides the range into twelfths spread over six hours: one twelfth in the first hour, then two, three, three, two and one. With a 6.0 m range, the tide falls 0.5, 1.0, 1.5, 1.5, 1.0 and 0.5 m in successive hours. It assumes a sinusoidal curve of exactly six hours' duration, so it is unreliable at ports with double high waters, prolonged stands or markedly unequal flood and ebb durations.

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Points of Sail & Sailing Manoeuvres

Run

Sailing directly away from the wind, dead before it

On a dead run the true wind is close to 180 degrees off the bow, sheets are fully eased, and apparent wind equals true wind minus boat speed, so the deck feels deceptively calm. The mainsail blankets the headsail unless the sails are set on opposite sides, rolling is pronounced, and there is a constant risk of an unintended gybe, so a preventer is normally rigged.

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Coastal Piloting Techniques

Running Fix

A fix built from one object's bearing taken twice, with a run between

A bearing of a single object is taken, then after a measured run the same object is observed again. The first position line is advanced along the course steered for the distance run, allowing for tide and leeway, and its intersection with the second line gives the fix. Accuracy depends entirely on the quality of the run, so the interval should give a cut of at least about 30 degrees but not be so long that log and tidal errors dominate.

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Position Fixing

Running Fix (R Fix)

A position from one landmark, using two bearings taken some time apart

With only one object visible, take a bearing, note log and time, then take a second bearing later when the bearing has changed by at least 30 degrees. Transfer the first position line forward through the course and distance run in the interval, allowing for tidal set and leeway, and the transferred line cuts the second to give the fix. The transferred line is drawn with a double arrowhead and labelled with both times. Accuracy depends entirely on the quality of the run applied.

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Celestial Navigation Concepts

Running Fix from a Single Body (Sun-Run-Sun)

Combining a morning and a noon or afternoon sun sight into a fix

With only one body available, a morning position line is advanced along the course and distance run to the time of the second observation, where it crosses the later line. The classic sequence is a morning sun sight advanced to local apparent noon, giving a longitude line crossed with the noon latitude. Accuracy hinges on the accuracy of the run, so the log, course steered, leeway and any current must all be allowed for.

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Anchoring & Mooring

Running Moor

Laying two anchors while moving ahead to halve the swinging room

The vessel stems the stream, lets go the first anchor and continues ahead, veering roughly twice the intended final scope, then lets go the second anchor. She then drops back, heaving in on the first cable and veering the second until she lies midway between them with equal cable each side. Used in narrow tidal berths where a single anchor would allow too large a swinging circle.

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Sailing reference

The YouSail sailing glossary

Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.