3.1 Vessel Nomenclature & Construction Terms
Key Takeaways
- Bow is forward, stern is aft; port is left and starboard is right when you face forward - port and left both have four letters.
- Draft is the vertical distance from the waterline to the lowest point of the keel and decides where you can safely float; freeboard is waterline to main deck and is your reserve buoyancy.
- Displacement is the weight of water the hull pushes aside, which equals the weight of the vessel and everything aboard.
- List is a static athwartships lean from uneven loading; heel is a temporary lean from wind or a turn; trim is the fore-and-aft difference in draft.
- Watertight bulkheads divide the hull into compartments so a single flooded space need not sink the vessel.
Why Nomenclature Comes First
Every command aboard a vessel - anchoring, docking, fighting a fire, recovering a person overboard - depends on shared words. The Deck General module opens with nomenclature because you cannot answer a rules or safety question if you do not know which end is the bow or which side is to starboard. Learn this vocabulary cold; it is the cheapest set of points on the exam and the foundation of everything that follows.
Directions Aboard
Stand facing the front of the boat and orient yourself:
- Bow - the forward (front) end. Stern - the after (back) end.
- Port - the left side when facing forward. Starboard - the right side.
- Amidships - the middle of the vessel. Forward and aft - toward the bow and toward the stern.
- Athwartships - across the vessel, side to side. Fore-and-aft - along the vessel's length.
- Inboard - toward the centerline. Outboard - toward the sides, away from centerline.
- Abeam - at right angles to the centerline. Ahead/astern - in front of or behind the vessel.
Two memory hooks make port and starboard permanent: "port" and "left" each have four letters, and a glass of port wine is red - which matches the red port sidelight. Starboard is therefore right, and its light is green. Because these never change with the direction you happen to be looking, a helm order to "come right to starboard" is unambiguous to every crew member.
Principal Dimensions
These measured quantities describe the size and shape of the hull:
- Length overall (LOA) - the extreme length from the foremost to the aftermost point. Related terms are waterline length (the length actually in the water) and length between perpendiculars.
- Beam - the width of the vessel at its widest point.
- Draft - the vertical distance from the waterline down to the lowest point of the keel. Draft decides where you can go: a boat drawing four feet cannot cross a three-foot bar. Always compare your draft to charted depth plus the height of tide.
- Freeboard - the vertical distance from the waterline up to the main deck edge. Freeboard is your reserve buoyancy; a low-freeboard, overloaded boat swamps easily in a following sea.
- Displacement - the weight of the water the hull pushes aside, which by Archimedes' principle equals the total weight of the vessel plus fuel, gear, passengers, and stores. Add weight and the boat settles deeper, increasing draft and reducing freeboard.
How the Boat Sits: Trim, List, and Heel
Three terms describe the vessel's attitude in the water, and the exam likes to separate them:
- Trim - the fore-and-aft difference between the draft at the bow and the draft at the stern. A boat down by the stern trims aft; down by the head trims forward.
- List - a static, athwartships lean caused by uneven weight distribution - fuel burned from one tank, cargo shifted to one side.
- Heel - a temporary, athwartships lean caused by an outside force such as wind pressure or the centrifugal effect of a hard turn. A boat heels into a turn's outside and away from the wind.
The distinction matters: a list signals a loading or flooding problem you must correct; a heel is a normal, momentary response to wind or maneuvering.
Hull Structure
The skeleton and skin of the boat carry their own names:
| Term | What it is |
|---|---|
| Keel | The backbone running fore-and-aft along the bottom centerline |
| Frames | The transverse ribs that give the hull its shape |
| Bulkhead | A vertical wall dividing the interior; a watertight bulkhead subdivides the hull for flooding control |
| Transom | The flat, athwartships surface at the stern |
| Stem | The leading edge of the bow |
| Gunwale (gunnel) | The upper edge of the vessel's side |
| Bilge | The lowest inside part of the hull where water collects |
| Chine | The line where the bottom meets the side |
| Scuppers | Deck drain openings that shed water overboard |
| Limber holes | Small openings in frames that let bilge water flow to the pump |
Watertight Integrity
A hull stays afloat only while water stays out. Watertight bulkheads divide the hull into separate compartments so that flooding in one space does not spread through the whole boat - the reason a single hull breach need not be fatal. Through-hull fittings (for engine cooling, sink drains, and heads) each carry a seacock or valve that can be shut to stop flooding. Reserve buoyancy - that band of hull between the waterline and the first opening that would let water down below (a downflooding point such as a low vent or hatch) - is what keeps the boat afloat as seas break aboard. Keeping seacocks serviced, hatches dogged, and freeboard adequate is the practical heart of watertight integrity.
Putting It Together
Picture a 38-foot charter boat: her LOA is 38 feet, her beam 13 feet, her draft 3.5 feet, and her freeboard at the stern just 2 feet. Load six passengers and full fuel and she settles deeper - displacement rises, draft increases toward 3.9 feet, and freeboard shrinks. If those passengers all crowd to the starboard rail to watch a whale, the boat takes on a list to starboard; when she leans into a hard port turn, that is heel. Knowing which is which tells you whether to redistribute weight (list) or simply ease the turn (heel).
What does a vessel's draft measure?
A boat leans to port because passengers and gear are unevenly stowed on the port side while the vessel sits still at the dock. This condition is best described as: