Basics of Horizontal Sextant Angle - Chartwork - Chief Mates Phase 1

Master the fundamentals of Horizontal Sextant Angles (HSA) for coastal navigation and deck officer competency exams. ​While the sextant is traditionally associated with celestial navigation and vertical angles, measuring the horizontal angle between charted terrestrial landmarks provides one of the most reliable, non-electronic position fixing methods available on the bridge. In this video, we break down the geometric principles behind HSA, how to take accurate horizontal sights, and how to plot a Position Circle (Horizontal Danger Circle / Circle of Equal Position) on a nautical chart. ​What You’ll Learn: ​The Core Geometry: Understanding the circle of equal angle and why subtended angles define a position circle. ​Instrument Handling: How to hold and read the marine sextant horizontally without introducing parallax or tilt errors. ​Target Selection: Criteria for choosing prominent, charted shore marks (and why near-90° angles between marks give the best cut). ​Fixing by Two HSAs: Using three terrestrial objects to generate two position circles for an instantaneous, compass-independent fix. ​Horizontal Danger Angles: Using a pre-computed HSA to keep the vessel clear of hidden shoals and offshore hazards. ​Plotting Methods: Station pointer method vs. geometric construction on the chart. Don't forget to like, subscribe, and share with fellow mariners and cadets preparing for their competency exams! Drop your questions or tricky chartwork scenarios in the comments below. ​#MaritimeStudies #DeckOfficer #Sextant #CoastalNavigation #Chartwork #MerchantNavy #OOW #ChiefMate #NauticalScience #MarineNavigation