Glossary

Wave & ocean

• FFT: Fast Fourier Transform, the math behind the GPU wave simulation. Generates a height field by combining many wave frequencies: the industry-standard approach for AAA water.
• Phillips spectrum: Simplest wind-driven wave model. Tunable but less physically accurate than PM / JONSWAP. Good default for prototyping.
• Pierson-Moskowitz (PM) spectrum: Model for fully-developed seas (wind has been blowing long enough that wave energy has saturated). Use for stable, “open ocean” conditions.
• JONSWAP spectrum: Joint North Sea Wave Project. A growing-sea model with sharper peak energy than PM. Good for storm fronts and coastal seas.
• Cascade: The plugin runs four wave simulations at different patch sizes and combines them. Each cascade (“layer”) covers a different wavelength band; that’s why WaveAmplitude, PatchLength, DomainSize, etc. are FVector4 (one entry per cascade).
• WPO (World Position Offset): Vertex displacement applied to the water plane to create the visible wave shape.
• Caustics: Light patterns projected onto underwater surfaces by the rippled water surface acting as a lens.

Hull & vessel

• Froude number (Fr): Dimensionless speed ratio: Fr = Speed / sqrt(g × HullLength). The fundamental scaling parameter for water-going vessels. Fr ≈ 0.4 is “hull speed” for displacement boats; Fr ≈ 1.0+ is the planing regime.
• Hull speed: Maximum efficient speed of a displacement hull, corresponding to Fr ≈ 0.4. Above hull speed, wave-making resistance grows steeply.
• Displacement: Hull movement state where buoyancy supports the entire vessel weight. Slow and efficient.
• Planing: Hull movement state where dynamic lift from forward motion lifts the hull partially out of the water. Fast and fuel-hungry.
• Foiling: Hull movement state where hydrofoils completely lift the hull out of the water, dramatically reducing drag.
• Block coefficient (Cb): Ratio of submerged hull volume to its bounding box. Range ~0.2 (sleek) to 0.95 (barge-like).
• Midship coefficient (Cm): Fullness of the midship cross-section relative to its bounding rectangle.
• Prismatic coefficient (Cp): How evenly volume is distributed along the hull length. Lower = ends taper more.
• Waterplane coefficient (Cwp): Ratio of waterline-plane area to its bounding rectangle.
• Deadrise angle: V-angle of the hull at the transom. 0° = flat-bottom, 25°+ = deep-V.
• Metacentric height (GM): Distance from center of gravity to metacenter. Larger GM = stiffer (resists heel) but rolls quickly; smaller GM = tender (rolls slowly but easier to capsize).
• Righting arm (GZ): Lever arm of the buoyancy force restoring a heeled hull to upright. The GZ curve maps heel angle to GZ; the integral up to the angle of vanishing stability is the energy required to capsize.

Buoyancy & hydrodynamics

• Heave / Surge / Sway: The three translational ship axes: heave (vertical), surge (forward / backward), sway (sideways).
• Roll / Pitch / Yaw: The three rotational ship axes.
• Added mass: Extra apparent inertia an object has when accelerating through water (because it has to push water aside). Lateral (sway) added mass is typically the largest for ship hulls.
• Slamming: Impact force when a hull re-enters the water surface at high vertical speed. Modeled as an impulsive drag spike, gated by bEnableSlamming.
• Subtractive shape: A collision shape on PhysicsBodyComponent that carves out volume rather than adding it. Used for cabin air pockets and other internal voids. Setting MaterialType = Air automatically marks a shape Subtractive.

Sailing & vessel control

• Trim tab: Small flap at the transom that adjusts bow attitude at speed. Used to optimize planing angle.
• Centerboard: Retractable lateral fin on small sailboats. Provides lateral resistance when down.
• Keel: Fixed lateral fin and ballast on larger sailboats. Both prevents sideways slip and lowers the center of gravity.
• Hydrofoil: Wing-shaped lifting surface that generates lift through forward motion. Once lift exceeds vessel weight, the hull rises (foiling).
• Bow thruster / Stern thruster: Lateral thrusters used for low-speed maneuvering.
• Main sheet: Line that controls the angle of the mainsail. Input range 0 (fully eased) to 1 (fully sheeted in).
• Jib sheet: Same, for the jib (forward sail).
• Spinnaker: Large lightweight downwind sail; deployment is essentially binary (0 = furled, 1 = full).

Engine & implementation

• GDF (Global Distance Field): Unreal’s cached signed-distance representation of scene geometry. The Pool boundary mask uses GDF to detect where pool walls are. Requires r.GenerateMeshDistanceFields = 1 in project settings.
• MPC (Material Parameter Collection): Unreal asset that lets C++ push parameters into materials. The plugin uses MPC_DRW for ocean visual params and MPC_Underwater for underwater post-process params.
• Fixed timestep: Physics calculation that runs at a constant rate (default 30 Hz here) independent of frame rate, with interpolation for rendering. Required for deterministic multiplayer.