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The term Day Shapes refers to a series of black geometric shapes that identify vessels as having certain special characteristics.

I know what you’re thinking. What the hell does that mean Noel?!

Well, boats can need to have extra sea room and be given some extra space by other boats. This could be because they are fishing and have nets stretching out or they could be broken and unable to turn. Or there could be a number of other reasons. The way we can tell that other boats need some space is by these Day Shapes. There are shapes for fishing, shapes for unable to move, shapes for lots of things. The rules say that the “Day Shapes should be shown by day”. So that’s sunrise to sunset.

This guide to Day Shapes is easy to follow and you can have a FREE download at the end of this article so that you can learn, revise or refresh the knowledge I’m giving you here.

Firstly, I’ll show you the give way order of responsibility between different boats doing different things. Then I’ll explain to you what each one actually means.

In the IRPCS rules, or the Colregs as they are often known, Rule 18 details the give way order between different boats. This is shown by the infographic above. It lists the order you can see with the vessels at the top of the list being the ones that don’t have to move for the others.

Day Shapes for Not Under Command and Restricted in Ability to Manoeuvre

Vessels that are ‘not under command’ and vessels that are ‘restricted in their ability to manoeuvre’ are joint top of the list. It makes logical sense once you understand the full rule but there is often a little confusion among students about what these actually mean.

Vessels not under command are vessels that for some exceptional circumstance are not able to obey the rules as they should. These boats are broken in some way. This could be caused by something such as steering failure, engine failure or some other kind of problem. Because of this problem, they can’t move out of the way. Therefore top of the list.

When a boat is not under command the Day Shapes it shows are two black balls one above the other.

Vessels restricted in ability to manoeuvre are joint top of the list. Similar to not under command but these guys can’t move due to the nature of their work. This could be laying pipe or cable, or underwater works. These boats display a diamond between to balls. All of these are in a vertical line.

You can remember this because if someone has something sharp between their balls, they would be restricted in their ability to manoeuvre as well ?

A boat sometimes shows some extra Day Shapes if it is working underwater.

You can see the diamond between two balls to show this boat is restricted in ability to manoeuvre. The underwater gear is on the side with the two balls. It is safe to pass on the side with two diamonds.

Day Shape for Constrained by Draft

A vessel constrained by draft can only navigate in deep water. This one is next in the list. The draft is how much of the boat is sticking below the water. These guys display a black cylinder. You can remember this because draft Guinness comes in a black can ?

Day Shapes for Fishing and Trawling

The next boat in the list is a fishing boat. It doesn’t matter what kind of fishing they are doing. It could be trawling or purse seine fishing or any other type. Fishing boats are hampered by their gear and so need some space.

I don’t know how you can remember this one. Looks like a fish? It’s officially described as two cones apexes pointing towards each other. ?

Day Shape for a Sailing Vessel

The next boat that is the least manoeuvrable is a sailing vessel. This is because they need the wind to move. Also they can’t go directly to where the wind is coming from. However, if they are using their engine then they are considered a power driven vessel within the rules. Instead of a sailing vessel. There are different rules for power driven vessels and so there is no confusion, they display a cone as shown above.

Finally, in Rule 18, power driven vessels and seaplanes come last. However, there aren’t any specific day shapes for these.

Other Day Shapes

There are a few other Day Shapes that are detailed in the IRPCS rules. These are shown detailed on the Day Shapes cheat sheet that you can download by clicking on the button below:

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