What does a black cylinder mean on a ship?

Only a power-driven vessel can be constrained by draught. Other vessels (except those NUC or RAM) should avoid impeding her safe passage if circumstances allow (Rule 18(d)), so a yacht stays out of the deep-water channel she needs.

• At night she may show three all-round red lights in a vertical line, on top of normal power-driven lights.
• The signals are optional.
• In fog: one prolonged and two short blasts.
• This category exists in the International Rules but not the US Inland Rules.

Source: COLREGS Rule 3(h), Rule 18(d), Rule 28 and Rule 35(c).

Test yourself

More in the navigation lights quiz.

Read more

• Lights and shapes guide
• What shape and lights does a vessel at anchor show?
• When do you show a cone when motor sailing?
• What lights does a vessel restricted in her ability to manoeuvre show?
• What lights does a vessel not under command show?
• What lights does a fishing vessel show at night?