The International Regulations for Preventing Collisions at Sea, also know as ColRegs, are the laws that govern vessels at sea. The Basic rules for Power-driven vessels are the same as the rules we use on the highway.
Rule 11 states “Rules in this section apply to vessels in sight of one another” Therefore if you are operating in restricted visibility, the following Rules do not apply.
Rule 12 deals with sailing vessels and this rule will be covered in another post.
Rule 13 “Overtaking Any vessel overtaking any other shall keep out of the way of the vessel being overtaken.”
Notice the Rule says “any vessel”. The word “shall” means “must”.
A case that many people mis-understand is where we have a sailing vessel overtaking a power vessel that is moving slowly, perhaps they are fishing and trolling for salmon at 2 knots. Because the sailing vessel is overtaking the power driven vessel, the sailboat must keep clear. Many people have been taught that power always gives way to sail.
The question then becomes “When am I overtaking?” Rule 13 (b) states “A vessel shall be deemed to be overtaking when coming up with another vessel from a direction more that 22.5 degrees abaft her beam.” In simple terms if at night you would only see the white stern light and not the sidelights. In highway terms if you saw only the taillights of another vehicle, you are overtaking.
Rule 14 “Head-on Situation When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision each shall alter course to starboard so that each shall pass on the port side of the other. On the highway this would be the narrow road situation. When meeting another vehicle, everyone pulls over to the right.
Rule 15 “Crossing Situation 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 shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.” The highway version is two vehicles meeting at an uncontrolled intersection. The one on the right is right.
I have had two instances recently where Rule 15 has been broken. The first was while teaching aboard a 86′ Queenship motor yacht. We observed a Grand Banks 42 trawler approaching about 2 miles away off our port bow. The lady who was on the wheel observed that we had a potential risk of collision and that we were the stand-on vessel and therefore required to hold our course and speed. We discussed that the trawler should be altering course to cross our stern. 
As the minutes passed we could not detect any alteration of course so I suggested that we slow down. The other vessel kept proceeding and we then went to neutral on both engines. The trawler crossed our bow within 0.1 miles with the skipper waving his arm at us. I noted the vessel name on the stern and called him on Channel 16. When he responded I switched to Channel 9 and he told me we had a fender that was left down on our port side. When I thanked him I noted that we were the stand-on vessel and that we had to stop to avoid a collision, his reply was “Oh, sorry”.
In the diagram, I am aboard the black vessel.
The second instance was as we were returning to Tsehum Harbour in Sidney aboard a 38′
Meridian. There was a large 100’+ private motor yacht anchored near the Harbour entrance off our port bow. One of the local crab boats was approaching on our port side and heading for the gap between us and the anchored yacht. Despite me blowing the “I fail to understand the intentions or actions of the other signal,” 5 short blasts, the crab boat crossed our bow. In order to clear us safely, he had to alter course to port and cross the bow of the anchored yacht. In the diagram the crab boat is red and the anchored yacht is green.
The major point to remember is always keep checking that the give-way vessel is taking action to keep clear and if not, you must take action to avoid a collision. Never assume that the other boater knows the rules or will follow the rules correctly.
These rules form part of the required knowledge of the Canadian Yachting Association Basic Cruising Standard.