Abeam describes a bearing directly to the side of a vessel — at roughly a right angle (090° or 270° relative) to the ship’s fore-and-aft line.
How It’s Used
“The lighthouse is abeam to port” means the lighthouse bears roughly 270° relative to the ship’s heading — directly out to the left side, neither ahead nor astern. It’s a quick, commonly understood way to communicate relative position without needing to state an exact bearing figure.
Abeam as a Reference Point for Other Terms
Abeam functions as the zero-point reference for related bearing terms:
- Forward of the beam — any bearing between dead ahead and abeam
- Abaft the beam — any bearing between abeam and dead astern
This makes “the beam” (the abeam line) a genuinely useful reference point that other directional terms are defined relative to, not just a standalone description.
Abeam and Navigation Light Arcs
COLREGs defines vessel navigation light visibility arcs using the beam as a reference point — sidelights, for example, are visible from dead ahead to abeam on their respective side, making correct understanding of “abeam” directly relevant to interpreting which lights should be visible at a given relative bearing.
Exam Relevance
Abeam and its use as a reference point for bearing descriptions and navigation light arcs are core Navigation and COLREGs topics in deck officer competency exams.