Glossary

Forward Perpendicular (FP)

FP — The vertical reference plane at the bow, station 0 on the drawing.

All station distances are measured in inches aft from FP unless noted otherwise.

Aft Perpendicular (AP)

AP — The vertical reference plane at the transom end of the hull length.

Used with FP to define overall length and reference lines on profile and plan views.

Longitudinal Center of Buoyancy (LCB)

LCB — The fore-aft location where the underwater volume acts as a single force.

Reported in inches from FP. Helps balance motor weight and predict trim.

Horizontal Center of Gravity (HCG)

HCG — The fore-aft location of the boat's weight acting on the hull.

Compare HCG to LCB to understand whether the boat will trim bow-down or stern-down.

Vertical Center of Gravity (VCG / KG)

VCG — The height of the boat's weight above the hull bottom (lowest keel), from named W/B loads.

KG is measured from the same hull-bottom plane as KB. That plane is the lowest drawn keel y, which may sit below Adory y = 0 when the keel is rockered. Height on each W/B weight is inches above this hull bottom, not the drawing origin. VCG/KG is incomplete until every weight in the case has a height; missing heights are not treated as zero. When every height is present, Hydrostatics and Sail calculate GM = KB + BM − KG at the floating waterline.

Gunwale

Gunwale — The upper edge of the boat's side; in Adory this is the GUN curve.

Also called gunnel. Not the same as sheer, which describes the profile curve of that upper edge. Adory labels this line Gunwale.

Chine

Chine — A sharp edge where two hull panels meet.

Adory tracks gunwale, mid chine, log chine, and keel chine curves for lofting and material length.

Station

Station — A cross-section of the hull at a fixed distance from FP.

Station spacing is controlled by S Stations. Offset tables list heights and half-breadths at each station.

Waterline

Waterline — The horizontal plane where the hull meets the water at a given load.

Design waterline height and angle drive displacement, freeboard, and hydrostatic calculations. For a W/B case Adory also solves the floating waterline (and trim) where displaced freshwater weight equals the case total.

Vertical Center of Buoyancy (KB)

KB — Height of the underwater volume's centroid above the hull bottom (lowest keel).

Computed from immersed station polygons at the floating waterline, then shifted from drawing y by subtracting the lowest keel y so KB and KG share one datum. For a wall-sided rectangular barge KB is half the draft.

Metacentric Radius (BM)

BM — I_T / ∇, the height from B to the small-angle metacenter.

Adory uses I_T = (2/3)∫ z³ dx over the waterplane, where z is the half-breadth of each section where it actually crosses the trimmed waterline, not the gunwale or the maximum section half-breadth. ∇ is displaced volume.

Metacentric Height (GM)

GM — KB + BM − KG, used for the small-angle righting arm GM × sin(heel).

Calculated per W/B case when every weight has a height and the hull can float the displacement. Sail uses that calculated GM by default and falls back to a typed value when heights are missing or the boat does not float within the hull. A manual override is available.

Gunwale Immersion Angle

DEI — Heel at which the leeward sheer first reaches the floating waterline.

Also called deck-edge immersion or a geometric downflooding angle for an open boat. Adory takes the minimum over hull stations of atan(freeboard / gunwale half-breadth), using the trimmed floating waterline from the selected W/B case and no extra sinkage. It is shop guidance, not an ISO 12217-2 or ABYC certification calculation.

Steady Heel

Steady heel — The heel where sail heeling moment equals small-angle righting moment.

Solved from HM = W × GM × sin(θ) with the calculated GM. The GM × sin(θ) arm is a small-angle model. Recreational sailing boats are often aimed at about 15–20° in the design wind, with a margin of 10° or more to gunwale immersion.