what is a boat kit
Boating Basics Glossary

Explore the language of professional boat designers and discover common boating terminology. Dive into our glossary to gain insights into the precise terms used in boat design and the broader boating community. Enhance your understanding of the nautical world with our comprehensive guide to professional terminology.

Abaft: Behind or toward the rear.

Abeam: Some point alongside a ship; used to define a position relative to the ship.

ABL: Abbreviation for above baseline.

Above baseline: Designated dimension above the baseline of the vessel.

ABYC: American Boat and Yacht Council. An organization that writes and maintains voluntary standards for small craft.

Arc radius: The radius used to draw an arc of a circle.

Back chipping: Removing unwanted weld metal between welding-bead passes. This is accomplished by a chisel or other mechanical means; a power saw is often used on aluminum welds.

Baseline: The common reference line for all elevations; parallel with the design waterline (DWL) and generally the lowest point of the keel.

Batten: A long, slender, straight-grained wood stick used to fair lines on the loft floor.

Batten holder: A cut piece of material, usually wood, used to hold a flexible batten in place during the pickup of loft-floor lines for template making.

Beam: Width of a vessel at a specific point; generally used to describe the maximum width of the vessel.

Bearding line: The line formed by the intersection of the inside face of the planking and the face or side of the keel.

BL: Common abbreviation for baseline.

BLKD: Abbreviation for bulkhead.

Body plan: Lines drawing view of stations at 90 degrees to the centerline; commonly located at the center of lines drawing with stations forward of midships on the starboard side and those aft of midships on the port side.

Boat kit: Boat kit typically refers to a package or set of materials and components provided to individuals or builders for the construction of a boat. Boat kits often include pre-cut aluminium or other material parts, and detailed construction plans. They are popular among DIY boat builders and enthusiasts who want to build their boats from scratch or customize existing designs. Discover our range of aluminium kit boats

Boot top: A narrow painted band at or slightly above the DWL to some distance (up to about 6 inches) above the DWL; a clearly defined parting between the bottom and topside paints.

Breakwater: A vertical bulkhead located forward on the main deck to deflect the force of water that may wash onto the deck.

Bulkhead: A solid vertical dividing structural member that may be watertight; nautical term for a wall.

Bulwark: A section of the hull side extending above the main deck.

Butt line: Short for buttock line.

Butt weld: Weld joining two pieces of plate edge to edge.

Buttock line: An edge-on view of a plane parallel with the vertical plane at the boat’s centerline. Buttock lines are straight lines in the plan and body plan views, normally equally spaced port and starboard of the centerline.

CAD: Computer-assisted design.

Camber: The arch of a surface, usually a deck; a 3-inch camber means the center of the deck is 3 inches higher than the edges at its maximum beam.

Ceiling: Longitudinal planking placed on the inboard face of the frames.

Centerline: An imaginary line running down the center of the vessel in the plan and body plan views.

CFR: Code of Federal Regulations.

Chine: The intersection of the bottom and side of a hull. A hard chine (normally associated with powerboats) has an abrupt change of direction; a soft chine displays a rounded transition from bottom to side plate.

Chord: The straight line used to join the end points of an arc.

CL: Abbreviation for centerline.

Collar: A filler at a bulkhead penetration around an angle or a T-bar that makes the bulkhead watertight or is used for structural purposes.

Compound curvature: Description of a surface that is curved in more than one axis, such as the surface of a ball.

Conical developed surface: A surface that consists of a section of a cone or sections of a number of cones; straight-line rulings will point to the apex of the instruction drawing.

Construction Drawing: Drawing prepared by the boatbuilder or naval architect to define details of construction.

Cumulative measurement: Laying out a series of dimensions by adding all dimensions together to obtain a total measurement, then laying out only one dimension.

Curve of areas (also curve of sectional areas): Developed by the naval architect for hydrostatic calculations; a curve plotted from a straight baseline representing the length of the ship, the ordinates of which represent the areas of the vessel’s immersed cross sections. Found on lines drawings (not used during the lofting process).

Cylindrical developed surface: Surface that consists of a portion of a cylinder; ruling lines are parallel on a cylindrical developed surface.

Deadrise: Change in elevation in relation to a horizontal plane, similar to slope. The difference in height between the keel of a boat and the chine is an example of deadrise. A boat’s cambered deck has a deadrise at centerline as compared to the deck edge.

Deck: Floor or walking surface; commonly parallel with the waterline, but decks may be sloped fore and aft and have camber.

Deck plan: Drawing looking down on the deck of a boat.

Declivity: Slope of a deck or vertical surface; used in conjunction with tumble-home found in a deck house side. Normally described in rise over run or in degrees.

Design waterline: The plane defined by the hull at the surface of the water; located by the naval architect during the design phase.

Developable surface: Any surface that can be constructed from a flat plate. Hull surfaces are defined as developable or undevelopable. A cylinder, which can be rolled from a flat sheet of material, is a developable surface; cones and flat planes are also developable. Surfaces such as spheres and ovoids are not developable; any attempt to construct these or other undevelopable surfaces from a flat sheet will result in wrinkles or stretching.

Diagonal: When used in lofting, a diagonal is similar to a waterline or buttock line but is located in a plane other than flat or vertical; commonly found in sailboat lines to assist in defining round-bilge geometry.

Directrix: A line or plane that guides the generatrix of a surface.

Displacement: Actual weight of a vessel; defined by the weight of water displaced by the vessel.

Doubler: See hull doubler.

Ductile: Easily bent or formed. Lead is more ductile than steel.

DWL: Abbreviation for design waterline.

Element: Term used to describe a specific location of the generatrix at any one position; in lofting, often called a ruling.

Elevation view: View on an engineering drawing looking from the side, or in elevation.

Engine bed: Girders, generally parallel with a boat’s centerline, upon which the main propulsion engines are attached.

Fair line: A continuous natural curve, free of bumps or kinks. Developed by spanning at least three reference points with a thin strip of straight-grained wood.

Fairing: Smoothing a curved line or surface; fairing a line is smoothing out the high and low points on a curve and averaging out the bumps – more art than science.

Faying surface: Mating surfaces of two adjoining materials.

FDN: Abbreviation for foundation.

Fillet weld: A weld joint where the edge of one piece of metal butts the flat surface of another piece of metal.

FL: Abbreviation for folding line.

Flair: Sloping outboard; opposite of tumblehome.

Flat-plate development: The process used to make a flat pattern of the surface of a three-dimensional object.

Floor: Horizontal part of a transverse frame connecting the keel to the frame. Often used as a deck support.

Folding line: A 90-degree change of direction of a line of sight as associated with views of drawings. Represents the folding line if a drawing of a boat were to be folded with a sharp crease, making the plan view 90 degrees to the profile view.

Foundation: Structure attached to the hull or house for mounting items or machinery, such as generators, stoves, life rafts, etc.

FR: Abbreviation for frame.

Frame: A structural member, usually in the same plane as a station; in some cases, longitudinal frames run fore and aft.

Freeboard: Height of the hull side above the DWL at midships or some other designated position.

Freeing port: A hull opening on a weather deck to allow deck water to escape overboard.

Generatrix: Line guided by the directrix to generate a surface. For a developable surface, the generatrix must be a straight line. Various locations of the generatrix are called elements.

Girth: The measurement around a curved surface or arc; used in expanding views into flat patterns.

Good boatbuilding practice: Standard of quality commonly accepted by boatbuilders and boatowners based on experience and tradition.

Grid: In boat lofting, the basic straight layout lines representing the baseline, waterlines, buttock lines, and station lines.

Gunwale (also gunnel): Where topside and deck meet; also called the shear.

Half-breadth: Horizontal measurement from centerline to some point port or starboard; half the distance from gunwale to gunwale is a half-breadth.

Hard corner: The theoretical corner between two surfaces that actually meet in a rounded corner.

Heights: Vertical measurements above the baseline.

House: A ship’s cabin or deckhouse.

Hull doubler: A plate welded to the surface of another plate to provide additional thickness in that area; often used to strengthen specific areas of a deck, such as attachment points for deck machinery.

Inboard profile: Elevation drawing showing the ship cut along the longitudinal axis, looking outboard.

Intercostal: An intermittent framing member abutting adjacent framing, as compared to a through-passing member.

Jig: Tooling used to hold parts in position during fabrication.

Keel: Backbone of the ship at the base of the hull; usually sits on the baseline. Also called the stem when located forward.

KNU: Abbreviation for knuckle.

Knuckle: A change in direction between two abutting surfaces.

Ladder: Nautical term for a stairway; often quite steep.

Ladder riser: Vertical portion of a ladder, compared with the step or rung, which is the horizontal portion.

Laying out: The act of measuring and locating a line or point.

Level: As used on large ships, a specific distance above the baseline; levels are commonly associated with decks, such as the 01 level on a large ship being the first deck above the main deck.

Lightening hole: A hole, commonly circular, where material has been removed to reduce weight.

Liber hole: Drainage hole cut through a structural member to allow fluid to drain by gravity.

Lines: Abbreviation for lines drawing.

Lines drawing: Drawing showing hull geometry of a ship or boat; normally includes plan, elevation (or profile), and body plan views defining the hull form by the use of waterlines, buttock lines, and stations.

LOA: Abbreviation for length overall.

Loft floor: The actual drawing surface where the lines are drawn full size.

Lofting: Drawing of the boat hull full size; drawing full-size bulkheads, frames, and girders, and the layout and construction of templates from the lofted lines.

Loftsman: Individual who draws boat lines full size and makes templates.

Long: Abbreviation for longitudinal.

Long ton: 2,240 pounds.

Longitudinal: In the fore-and-aft axis; used to describe a long structural member, such as a T-bar hull stiffener.

LVL: Abbreviation for level.

Margin plate: Strip of metal, typically about 10 inches wide, welded continuously to the inside edge of the shell plate and used as the attachment surface for a wood deck.

Midships: Toward the center of a ship in the fore-and-aft axis.

MIG: Standard abbreviation for Metal Inert Gas welding process, which uses a consumable electrode and an inert shielding gas.

Mold loft: The area where lines are laid down on the floor; usually a designated area of a shipyard.

Molded line: The line to which all layout dimensions are given. Used to determine which side of the surface to lay out, especially on metal boats. Notes on the molded line should be found on the construction drawings.

Molded surface: Similar to the molded line, but referring to a surface; normally the underside of decks, the inboard surface of longitudinal surfaces, and either the forward or aft face of bulkheads, as specified.

Mullion: Slender bar or post that separates windows.

Non-tight: Structural members not required to be watertight.

Offsets: Dimensions from centerline or above baseline.

Oilcan: Term used to describe distortion of plating, usually caused by excessive welding heat, as compared to a dented 5-gallon can.

Outboard profile: Elevation drawing showing the boat from the side view.

P: Abbreviation for port.

Pad eye: Any small metal plate with a hole in it attached to a structure and used as an attachment point for lifting or lashing; also a lifting eye welded to a base.

Panel breaker: Similar to a stiffener; commonly used to break up a vibration in a panel or to provide additional stiffness.

Passageway: A hallway or access route.

Plug welding: Process of welding two plates, one on top of the other, by welding through holes in one plate to fuse the two together in a number of spots.

Port: Left in nautical terminology; also a hull opening above the waterline.

Portlight: Nautical term for a window.

Profile: View from the side; elevation view.

Pulse-arc welding: A refinement of the MIG welding process involving rapid on and off of the welding current.

Rabbet: A longitudinal groove in a member used to receive another piece. Rabbet line is similar to the bearding line in metal boat construction.

Radial: One of a number of layout lines starting at a common point and radiating outward like the spokes of a wheel.

Rake: Forward or aft slope.

Rat hole: A cutout in a structural member for access to a welded seam.

Ray: A radial.

Ruled surface: A surface that may be generated by a straight line; a straightedge may be laid on the surface so that it will touch the surface for its entire length.

Ruling: An element of the generatrix.

Scale: Ratio of size in relation to actual size; a drawing showing a scale of ½ inch = 1 foot means ½ inch on the drawing equals 1 foot on the actual vessel.

Scantlings: Thickness of plates and sizes of structural members used to construct the hull.

Scribing in: Drawing a line using an adjacent surface as a guide; marking a cutting line to fit a surface.

Shaft horsepower: Output horsepower at the propeller shaft.

Sheer: A line in the profile view defined by the top of the ship’s side and the main-deck intersection.

Shell: A boat’s exterior skin or hull plate.

Shroud: A wire laterally supporting a mast.

STA: Abbreviation for station.

Stanchion: A vertical column or post used for structural support.

Starboard: Right in nautical terminology.

Station: A vertical plane perpendicular to the baseline in the profile view and to the centerline in the plan view; commonly the DWL is divided into 10 equal spaces separated by station lines.

STBD: Abbreviation for starboard.

Stem: Forward portion of keel; sometimes term used for the entire keel.

Stiffener: Structural member used to stiffen a specific panel.

Strake: An exterior hull stiffener running in the longitudinal axis; also one width of plate or planking running the length of the hull.

Stretch: Bundle of electrical wires transmitting current and electronic information between the power source and the weld feeder. An inert-gas supply tube is sometimes included.

Stretch-out: The dimension of a piece of material that is laid out flat (similar to flat pattern). Also used to define the flat-pattern layout distance around a circular shape.

Stringers: Longitudinal members, usually running through a number of frames, used to support sheet or plate members.

Strongback: A temporary structural member used to hold parts in alignment during fabrication; usually removed after welding on the part is complete.

Stuffing box: A packing gland used at the penetration of a shaft, wire, or other item through the hull or other watertight surface to keep it watertight; specifically the packing gland where the prop shaft penetrates the hull.

T: Abbreviation for transom.

Table of offsets: A table of numeric data included in the lines drawings that gives dimensions for heights and half-breadths; usually provided by the naval architect and scaled from the drawings. Dimensions commonly shown in feet, inches, and eighths.

Temper: Heat treatment to increase the mechanical characteristics of heat-treatable aluminum alloys; also the work-hardened condition of non-heat-treatable aluminum.

Template: A flat pattern defining the geometric shape of a frame or other part; usually “lifted” directly from the loft floor or the structure for fabricating parts. Previously called molds.

TIG process: Stands for Tungsten Inert Gas welding process, which uses a non-consumable electrode and an inert shielding gas.

Transom: Aft-most transverse member of the hull forming a watertight bulkhead.

Transverse: At 90 degrees to the centerline, running across the boat (port to starboard).

Triangulation: Method of layout using arcs of circles to locate the corner points of a triangle.

True length: A component shown on a drawing or loft floor in its actual length.

True size: A component shown on a drawing or loft floor in its actual size, such as a flat pattern for a curved surface.

Tumblehome: Slope of a surface in relation to a vertical surface; commonly used in conjunction with declivity.

Undevelopable surface: See developable surface.

Waterline: A plane parallel with the plane at which the vessel floats; waterline defines hull geometry at specific heights above the baseline.

Watertight: Describes any structure that will not allow water to pass under flooding conditions. All hull and deck shell plate should be watertight.

Weathertight: Describes any structure that can withstand a hose test without excessive leakage, such as a cabin door or window.

Wheel: The propeller.

Whip: Bundle of conduit, tubes, and electrical cables that provide filler wire, shielding gas, electric power, and electronic information to the welding gun from the welding-wire feeder.

WL: Abbreviation for waterline.

Glossary content – Boat building wtih aluminium // Stephen F. Pollard

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