Communication with other vessels is essential on the water. The use of day shapes is how you can ensure that you are able to communicate what you were doing to other boats. Likewise, they can communicate with you important information. Masthead light and running lights can only be seen at night, don’t forget.

What is a Day Shape?

Day shapes are geometric figures that relay something important about vessel navigation. Different shapes indicate different things about the vessel. Some can identify a fishing vessel, or a sailboat under power, and so on. Day shapes need to be shown from sunrise to sunset.

Unlike many flags or lights that vessels display the only color here is black. Black is highly visible during the day. It is important to understand what day shapes mean to remain safe on the water. When you can’t see navigation lights, day shapes let you know when to give way to other vessels. They also let you know when you need to avoid another vessel.

You can buy these shapes at most nautical supply stores. They are similar to flags and many are made of heavy-duty vinyl. They can be rolled or folded up for storage. When in use they should be hung where they are visible from all sides of your boat.

Basic Shapes

There are four basic shapes in use with day shapes. They can be combined together to create different meanings.

  1. Ball
  2. Cylinder
  3. Cone
  4. Diamond

The size of day shapes depends on the size of your boat. Navigation regulations lay out the minimum size.

  • A ball shall have a diameter of not less than 0.6 m
  • A cone shall have a base diameter of not less than 0.6 M and a height equal to its diameter
  • a cylinder shall have a diameter of at least 0.6 meters at a height twice its diameter
  • a diamond shape shall consist of two cones as defined above having a common base
  • the vertical distance between shapes she’ll be at least 1.5 m
  • If your vessel is less than 20 meters in length you can use shapes of a lesser size. They should be keeping with the size of the vessel.

Different Day Shapes

Day shapes are often displayed vertically in a straight line from the mast head. However, different day shapes can be displayed side-by-side. Understanding how these day shapes works will let you understand when you need to give way.

Boat not under command: The day shape for this is two balls. That’s one ball on top of another. One red light on top of another red light signals this at night.

Boat is restricted in ability to maneuver: The day shape to indicate this is a ball on top of a diamond on top of another ball. A white light between red lights signals this at night.

These two are important to understand. In both cases the boat is incapable of following rules. Not under command and restricted maneuverability mean give way. Don’t expect them to respect your signals. In fact, you cannot expect them to follow the rules of the road.

Boat constrained by draft: A black cylinder is the day shape that indicates this. A boat that is constrained by draft cannot move in shallow waters.

Fishing boat: When a boat is fishing or trawling it displays two black cones points together. Any kind of boat that is doing any kind of fishing needs to display this day shape.

Fishing with gear out over 150 meters: This is different from normal fishing. When your gear is out extended distance the day shape is a single black cone, point up.

Under sail and power: When a sailboat is using engine power it will display an inverted cone. That means points down. A sailing vessel not under power does not need to display this navigation signal.

Anchored: When your anchor is down, you need to display the anchor ball which is one single ball.

Aground: If you have run aground then the day shape to display is three balls on top of each other.

Towing over 200 meters astern: A diamond indicates your vessel is towing something.


In addition to the single line day shapes there are day shapes that can use several lines. Often these take the form of three lines of shapes. In these cases the center line will communicate information about the boat. The shapes on either side communicate what you should do in your boat.

If a boat is engaged in underwater operations it will display the following day shapes. Centerline will be the day shape indicating restricted ability to maneuver. That’s a ball on a diamond on a ball. On either side of those day shapes will be additional shapes. If there are two balls on the left and two diamonds on the right that indicates where you should pass. It also signals where the underwater work is being done on the ball side. You should pass on the diamond side.

Things to Remember

Vessels under 7 m in length are not required to display day shapes. You may see boats over this size not using them. In fact, for many everyday boaters day shapes are not used at all. If you head to your local marina and ask, you’re likely to find people who have no idea what day shapes are. That doesn’t mean they shouldn’t be used for pleasure boating.

One important thing to remember is face shapes are part of collision regulations. Colregs state that you must be displaying a ball shape when you’re at anchor, for instance. Imagine what would happen if you were a tanker but didn’t have the day shape displayed. If another boat were to hit your vessel, who would be at fault? And, how would that affect your insurance? If your insurance finds out that you were not displaying the anchor shape that could cost you money.

Finally, remember that at the end of the day common sense rules. Always err on the side of caution. If another boat isn’t to displaying day shapes, be wary. Likewise, if they don’t seem to be understanding yours, take caution. It’s always better to move out of the way then argue over who was right after an accident happens.