Why Does Colregs Discourage Altering Course to Port

In theory, the rule of the road – or Colregs – is simple: vessels must keep to their starboard side when on the open sea. This prevents collisions by ensuring each vessel is aware of others around them, and gives everyone a clear path to avoid one another. So why then does Colregs discourage altering course to port?

The answer lies in the fact that while Colregs may be simple in theory, it’s not always so straightforward in practice. When two vessels are approaching one another head-on, both have an equal responsibility to take action to avoid a collision. The best way to do this is for each vessel to alter course slightly to starboard, giving them both some space and time to pass safely.

However, if one vessel alters course to port instead of starboard, they throw off the balance of responsibility and put themselves at risk. The other vessel now has no choice but to either also alter course to port (and risk running into shallower waters or hitting something else), or stay on their original course and risk a collision head-on. In either case, it’s far from ideal, which is why Colregs discourages altering course to port except as a last resort.

The Colregs are a set of international maritime rules that govern the behavior of vessels at sea. One of the key principles of the Colregs is that vessels should avoid altering course to port, unless absolutely necessary. The rationale behind this rule is that changing course to port can create a traffic hazard, since other vessels may be expecting you to maintain your original course.

Additionally, altering course to port can also interfere with the safe navigation of other vessels in the vicinity. For these reasons, it is generally best to avoid changing course to port unless it is absolutely necessary.

Why Does Colregs Discourage Altering Course to Port

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When Should You Alter Course to Port?

It is generally recommended that you alter course to port when the wind is blowing from behind you and toward your desired destination. This will help ensure that you make efficient progress toward your destination while also avoiding any potential hazards along the way. Additionally, it is important to consider the strength of the wind when making this decision, as stronger winds can make it more difficult to control your vessel.

Which Sound Means I am Altering My Course to Port?

If you are changing your course to port, you will need to sound the horn twice in quick succession. This is known as a ‘port signal’. You should only do this if it is safe to do so and you have the right of way.

What Rule is Alteration of Course Alone May Be the Most Effective Action to Avoid a Close Quarter Situation?

There is no definitive answer to this question as it depends on the specific situation in which you find yourself. However, if you feel that you are in a close quarter situation and altering your course is the best option, then do so. Remember to stay aware of your surroundings and be prepared to take evasive action if necessary.

Why Both Vessels Would Alter Its Course to Starboard?

When two vessels are on a collision course, both will alter their course to starboard (right) to avoid hitting each other. This is done so that each vessel has half of the other vessel to its right side, which is considered a safe passing distance.

COLREGs Rule 19 Restricted Visibility. Includes Situations


The Colregs, or the International Regulations for Preventing Collisions at Sea, are a set of rules that govern how ships should behave in order to avoid collisions. One of these rules is that ships should not alter course to port unless it is absolutely necessary. The reason for this rule is that altering course to port can often lead to collisions.

This is because when one ship alters course to port, it often ends up crossing the path of another ship. This can be especially dangerous if the other ship is larger or travelling faster than the one changing course. So, in short, the Colregs discourage altering course to port in order to avoid collisions.

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