2.1 Vessel Nomenclature & Construction Terms
Key Takeaways
- Keel is the longitudinal backbone; frames and floors run athwartships; bulkheads divide compartments and contribute to watertight integrity on COI vessels.
- Freeboard is freeboard deck to waterline; draft is keel to waterline; freeboard + draft ≈ depth of hull at that station.
- Sheer is longitudinal deck curve (higher at ends); camber is athwartships crown that sheds water; bilge is the turn of the hull and the internal sump area.
- Hawsepipe guides the anchor rode from deck/windlass to the water; a rose box (strum box) screens bilge-suction intakes from debris.
- Master 100 Q160 tests nomenclature as operational vocabulary: where water collects, what limits freeboard, and which openings protect small passenger vessels.
Why Nomenclature Matters on Q160
ONC06 Module Q160 Deck General is 50 questions at 70% (35 correct). A large share of those items is pure seamanship vocabulary: name the part, define freeboard versus draft, or identify where bilge water is drawn. On a Master Less Than 100 GRT ticket you command inspected small passenger vessels under a Certificate of Inspection (COI) as often as uninspected craft. When a surveyor, chief mate, or exam stem says "hawsepipe," "rose box," or "camber," there is no time to guess.
This section builds the structural map of a typical small commercial hull so later Deck General topics—anchoring, purchases, boat handling—attach to real places on the vessel.
Backbone: Keel, Frames, Floors, Stem, Stern
| Term | What it is |
|---|---|
| Keel | Longitudinal centerline structure; the backbone of the hull |
| Stem | Forward continuation of the keel / bow structure |
| Sternpost / stern structure | After structural termination (varies by design) |
| Frames | Athwartships members rising from the keel that give the hull its shape |
| Floors | Transverse members across the bottom connecting the frames ("floor timbers" on wood; plate floors on steel) |
| Keelson | Internal longitudinal member above the keel (common wood/older construction term) |
Think of the keel as the spine and the frames as ribs. Damage to the keel or multiple frames is a structural casualty; a dent in non-structural superstructure is a different class of problem.
Bulkheads, Decks, and Superstructure
A bulkhead is a vertical partition athwartships (or longitudinal bulkhead running fore-and-aft). On inspected passenger vessels, watertight and weathertight bulkheads and doors are not decoration—they limit flooding and support subdivision assumptions on the COI. Leaving a watertight door open "for convenience" during a harbor tour defeats the design the Coast Guard approved.
Decks are horizontal structural surfaces:
- Main deck / freeboard deck — primary continuous weather deck used as the reference for freeboard
- Weather deck — exposed to wind and sea
- Tween decks — intermediate levels on larger hulls (less common on tiny passenger boats, still exam vocabulary)
- Foredeck, afterdeck, side decks — location names used in line handling and passenger control
Superstructure is structure built above the main hull/weather deck: pilothouse, cabin, passenger canopy, upper deck seating. Superstructure adds windage, weight aloft, and passenger capacity—but it is not the same as the hull volume that drives gross tonnage measurement for your license limit.
Freeboard, Draft, Depth, Trim, and List
These four pairs show up constantly:
| Term | Definition |
|---|---|
| Draft | Vertical distance from the lowest point of the hull (keel) to the waterline |
| Freeboard | Vertical distance from the waterline up to the freeboard deck (or designated deck edge) |
| Depth (of hull) | Roughly keel to freeboard deck; freeboard + draft ≈ depth at that station |
| Trim | Difference between forward and after draft (down by the head / down by the stern) |
| List | Permanent or temporary heel to port or starboard (athwartships inclination) |
Worked picture: Draft 4 ft, freeboard 3 ft → hull depth about 7 ft at that station. Load 30 passengers aft and you may go down by the stern (trim change) without necessarily listing. Fuel burn from a centerline tank may change draft evenly; shifting deck cargo to one side creates list.
Masters of small passenger vessels watch freeboard for reserve buoyancy and boarding seas, and draft for under-keel clearance at the dock and in channels. Q160 often tests the definitions, not a stability calculation—save deep stability math for Deck Safety / stability sections, but never confuse freeboard with draft.
Sheer, Camber, Bilge, and Chine
- Sheer: the longitudinal curve of the deck line when viewed from the side—typically higher at bow and stern than amidships. Sheer helps keep water off the midships weather deck and improves reserve buoyancy at the ends.
- Camber: the athwartships crown of a deck—higher on centerline so water drains to the scuppers.
- Bilge (external): the curved turn of the bilge where bottom becomes side.
- Bilge (internal): the lowest internal spaces where water collects—bilge wells and sumps.
- Chine: a hard angle between bottom and side on many planing and semi-displacement small craft (hard-chine hulls).
Exam stems love: "The athwartships curvature of the deck is camber; the longitudinal rise of the deck toward the ends is sheer." Do not swap them.
Openings, Fittings, and Deck Gear Vocabulary
| Term | Function on a Master 100 platform |
|---|---|
| Hawsepipe | Tube/pipe through which the anchor chain or rode runs from the deck or windlass to the water |
| Hawsehole / hawse | Opening associated with that lead |
| Bitts / cleats / samson post | Strong points for making lines fast |
| Chock / fairlead | Guides a line and controls lead / chafe |
| Scupper | Drain opening that sheds deck water overboard |
| Limber holes | Openings in floors/frames allowing bilge water to flow to the suction |
| Rose box (strum box) | Strainer/screen on a bilge suction intake so debris does not clog the pump |
| Cofferdam | Void space separating tanks/compartments |
| Stringer | Longitudinal member along the side or under a deck |
| Gunwale (gunnel) | Upper edge of the side |
| Bulwark | Solid extension above deck at the side (with freeing ports) |
| Freeing ports | Openings in bulwarks that let shipped water escape |
A clogged rose box is a classic operational failure: the bilge pump runs but moves little water because the strainer is packed with rags, plastic, or scale. On passenger boats, keep bilges clean so the rose box can do its job.
Port, Starboard, Fore, Aft — Operational Orientation
Facing forward: port is left, starboard is right. Bow is forward end; stern is after end; amidships is middle. Inboard is toward centerline; outboard is toward the side. Athwartships means across the vessel; fore-and-aft means along its length. Q160 assumes this language without defining it every time.
Master 100 Context: Small Passenger Hull Reality
A 55-foot inspected whale-watch or dinner boat still has a keel, frames, bulkheads, freeboard deck, bilges, scuppers, and usually a windlass/hawse arrangement forward. Passengers stand on cambered decks with sheer you can see from the dock. Your job as master is not to design the ship—it is to name, inspect, and use these features correctly: watertight doors closed as required, bilge alarms understood, freeboard not eaten by overloading, and anchor gear clear to run through the hawsepipe.
High-yield definition pairs for exam day
- Freeboard ≠ draft
- Sheer (longitudinal) ≠ camber (athwartships)
- List (side) ≠ trim (fore-aft)
- Superstructure sits on the hull; it is not the keel
- Rose box protects bilge suction, not the fresh-water tank fill
- Hawsepipe is for ground tackle lead, not engine exhaust
Lock these pairs and Q160 nomenclature items become free points before you reach marlinespike and ground tackle.
On a small passenger vessel, freeboard is best defined as the vertical distance from the:
Which statement correctly distinguishes sheer from camber?
What is the primary purpose of a rose box (strum box) in the bilge system?