By insideSail
Automated technical check · version 1 ·
The hull and the line drawn by the water
Hull, waterline, underwater body and topsides describe different parts of the same boat.
In this guide
Original schematic illustration. Read the explanation and limitations in the lesson.
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A boundary that can move
The hull forms the body of the boat. The normally submerged part is the underwater body; above-water parts are described as topsides. These terms may appear in an advert describing painting or hull work. They do not mean the boat is made of two independent pieces.
A design drawing can show a waterline for a stated condition. A photograph shows conditions at that moment. People, tanks, equipment and weight distribution can change immersion and attitude. A painted stripe on the hull should not automatically be treated as the actual waterline.
Connect the words to measurements
- LWL refers to waterline length under the source’s stated condition and definition.
- Draught describes immersion depth, including the relevant appendages.
- Displacement should identify its loading condition.
When comparing two models, start with definitions. A photograph helps you recognise shape; a measurement is comparable only when you know how it was obtained. These terms neither diagnose structural condition nor establish clearance beneath the keel.
Concepts in this lesson
Hull
The vessel’s body; the term alone does not identify its material or structural condition.
Waterline
The intersection of water surface and hull under a particular loading condition and attitude.
Sources and references
- NOAA field manual — nautical terminology ↗
NOAA · Historical field manual; terminology only · Table 15: bow, stern, port and starboard
Version: Historical field manual; terminology only. Jurisdiction: International.
Checked on - Cartografia — cartas náuticas ↗
Instituto Hidrográfico · Live institutional page · Chart information and vertical reference
Version: Live institutional page. Jurisdiction: Portugal.
Checked on
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