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Sail Skills - ColRegs
Back Free Guide to ColRegs (the International Regulations for Preventing Collisions at Sea, the IRPCS or Collision Regs).  Guidance covers all aspects with animations, pictures and diagrams.  Aimed at small vessel users but suitable for professional mariners.  Especially recommended for RYA examination candidates.
Definitions
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© A Joy 2009-13
All Vessels Vessels in Sight Restricted Visibility
The wind is considered to be on the opposite side to which is carried the:

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mainsail, or
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largest fore-and-aft sail in a square-rigged vessel

Usually this is quite obvious.  These vessels have the wind on the starboard side:
Similar collision avoidance is used as in the first animation.  Note that:

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two vessels head-up to keep clear of leeward vessels.  This can:
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be the best action, depending on circumstances, but
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mean that the vessels are close to each other longer, as their courses are more nearly parallel
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one vessel keeps out of the way of a larger square-rigged vessel.  The ColRegs require her to do this because:
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they have the wind on the same side and
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she is the windward vessel
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small fore-and-aft rigged vessels:
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are more manoeuvrable than larger square-rigged vessels
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will usually take action as soon as the other is sighted to ensure that the larger vessel does not have to manoeuvre
 strictly however, any manoeuvre should be in accordance with the ColRegs - so a stand-on vessel should stand on!
Vessel With Wind on Port Side in Doubt About a Vessel to Windward

The pictures above showed that it’s not always easy to decide on which side a vessel has the wind

Therefore, a vessel with the wind on the port side:

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that sights a vessel to windward and
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cannot be sure on which side the windward vessel has the wind
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shall keep out of the way


The logic to this instruction is:

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except when one vessel is overtaking another
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a vessel with the wind on the port side has to keep out of the way of any vessel with the wind on the starboard side.  If the windward vessel:
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has the wind on the starboard side, she is the stand-on vessel and is required to maintain course and speed
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does in fact have the wind on her port side, then she should keep out of the way of the leeward vessel.  If she does:
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take action as required, all well and good
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not take action, then collision is avoided anyway
Note: Action to Avoid Collision
Sailing vessels with wind on different sides
Reminder

It’s worth restating that this rule applies only to vessels in sight of one another

Entirely different rules apply to vessels which are:

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not in sight of one another and navigating
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in or
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near
an area of restricted visibility
Wind on Different Sides

When two sailing vessels are approaching and each has the wind on different sides, the vessel which has the wind on the port side shall keep out of the way

In this animation, the vessel on the right has the wind on her starboard side.  She meets a number of vessels which have the wind on the port side.  They keep out of her way:
Note: Overtaking
Note: Vessels Under Sail
Sometimes it can be less obvious:
Vessels under sail - difficult to tell on which side they have the wind
Vessels under sail - difficult to tell on which side they have the wind
The vessel on the right actually had the wind just on her port side (on the quarter) - she was sailing “by the lee”


It can be particularly difficult to judge at night - when the sails cannot be seen.  Judging on which side a vessel has the wind is:

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a skill which comes with practice
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helped by an awareness of where the wind is in relation to your own vessel

The ColRegs provide for being unable to tell on which side a vessel has the wind by:

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allowing a stand-on vessel to take avoiding action in certain situations, or
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instructions for a vessel which has the wind on the port side and is in doubt about a vessel to windward
Rule 12 Sailing Vessels

The rules specify three situations where two sailing vessels are approaching one another.  These rules relate to when:

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they have the wind on different sides
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they have the wind on the same side
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a vessel which has the wind on the port side is in doubt about a vessel to windward (upwind) of her


Note that these rules do not apply when overtaking - which in the ColRegs is very specific.  Provided this is remembered, the rules are very simple
In the animation, most vessels avoid the stand-on vessel in the conventional ways.  They do this by:

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turning away (bearing away) from the direction from which the wind is coming, or
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turning through the direction (tacking) or
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turning into the direction (heading-up or hardening-up)

Most sources only discuss these.  However, two vessels avoid in a different way.  To allow the stand-on vessel to pass ahead, one:

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slows, by “easing” the sheets - that is, she reduces the power generated by the sail.  She maintains some speed in order to keep control
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stops the vessel by heaving-to (this is a very useful skill to practice - you may wish just to pop below to consult the chart, or to put the kettle on).  

These methods:

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should not be neglected
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are less common but can work well
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work better on some boats than others - for example, some vessels with narrow keels and small headsails may find heaving-to difficult without practice


Note that:

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it’s best to avoid passing close ahead of a stand-on vessel.  Only one vessel passes ahead but:
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she does so in good time
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makes more ground to windward than vessels which bore away
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turning away from a stand-on vessel does not make the stand-on vessel an “overtaking” vessel
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the vessel which hove-to did so the wind on her starboard side (the side opposite to which the mainsail is set).  This made her the stand-on vessel to the last vessel encountered - which had the wind on her port side.  If you are going to heave-to, always consider doing so with the wind on the starboard side for this reason
Wind on the Same Side

When two sailing vessels are approaching and each has the wind on the same side, the vessel which is to windward shall keep out of the way of the vessel which is to leeward (downwind)

In this animation, the windward vessels keep out of the way of the leeward vessels:
Sailing vessels with wind on  the same side
A sailing vessel overtaking a small power boat Diagram:  symbol stand-on vessel
Diagram:  symbol give-way vessel
Vessels:  retricted in ability to manoeuvre, sailing and engaged in fishing Two vessels under sail approaching
Two power-driven vessels approaching
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