# LW33 motion laboratory — model R03 **Uncalibrated engineering preview. Not validated CFD, operating guidance, structural loading or a performance prediction.** ## CAD-derived buoyancy The previous symmetric proxy has been replaced by 648 volume columns sampled from `hull-fine-final-m.stl`, the watertight, consistently wound A13 simulation skin. SHA-256: `96a1430c84b328aef57315beb8d6fda5cd279252ce4e9546babc16881a172708`. Each column stores the actual bottom/top intersection pair and projected cell area; immersed lengths are integrated along the rotated body axis. No volume scale or displacement renormalisation is applied. The quadrature approximates surface inclination and wave variation within each cell. At 4,100 kg and density 1,025 kg/m³, this produces 4.00 m³ displacement at display-frame waterline -0.085434 m. Independent earlier clipped-surface integration gave -0.086141 m: a difference of 0.707 mm. Refining the sampling from 48 × 16 to 96 × 32 changes the column result by 0.364 mm. This demonstrates numerical consistency only. **Artificial closures remain unverified.** They start near A13 z=0.492 m, below the provisional loaded waterline. The A13-to-display registration is provisional and the two CAD revisions are not certified equivalent. Upper closure, flooding, deck wetting and re-entry pressure fields are not resolved. The shown water surface samples are not an exact hull/waterline intersection. CG is provisionally placed at the 4,100 kg zero-trim buoyancy centre, x=-1.02960 m in the display frame, with VCG assumed 0.8 m above the historical keel. Pitch/roll radii of gyration remain assumed at 2.5 / 0.9 m. The user's 2,750 mm estimate cannot be applied until its datum, direction and vertical coordinate are confirmed. Other masses use this same assumed CG and settle in pitch. ## Running attitude Optional dynamic pressure uses the **dynamic term** of the Savitsky correlation: CL0 = 0.012 × trim(degrees)^1.1 × sqrt(mean wetted length / beam); CLbeta = max(0, CL0 - 0.0065 × beta × CL0^0.6). Hydrostatic support is integrated separately, so the correlation's hydrostatic term is deliberately omitted. Reference implementation: [OpenPlaning](https://pypi.org/project/openplaning/), source distribution 0.4.9. Applying that term column by column using sampled longitudinal bottom slopes and a relative-flow incidence is our uncalibrated extension, not the complete Savitsky equilibrium method. We assume 2.7 m effective beam and 24° deadrise, infer wetted length from projected wet area, limit local incidence to 0–15°, and smoothly enable dynamic lift over beam Froude 0.5–1.5. The published prismatic-method trim range starts at 2°; low trim, non-prismatic geometry and transient seas are extrapolations. No trim-versus-speed curve is prescribed. Effective incidence in R03 is pitch + atan(longitudinal CAD bottom slope) − atan2(relative vertical contact velocity, forward speed), clipped to 0–15°. Relative velocity uses heave rate + pitch rate × longitudinal lever + roll rate × transverse lever − local water vertical velocity. This is a small-angle rotational-velocity approximation. It replaces the previous wave-surface-slope subtraction: water-surface angle is not the local flow-velocity angle. Horizontal wave orbital velocity, added mass and full unsteady lift remain omitted. Controlled calm-water tests found the previous velocity-independent lift oscillated at 25–30 kn. Including relative flow, with coefficients and geometry unchanged, settles the default 0–30 kn cases at both 1/240 and 1/480 s. See calm-water-check.md/json and preserved calm-water-check-r01.md/json. This isolates a missing velocity coupling in this implementation; it is not evidence that the full model is physically validated. The added tests also retain dry-hull ballistic motion and moderate-wave time-step checks. The user can switch to hydrostatic/contact forces only. Assumed thrust lever is editable from 0 to 0.8 m; horizontal thrust balances a friction proxy with coefficient 0.008. There is no verified drive installation, torque curve, propeller force model, engine power balance or solved forward acceleration. Speed is prescribed. H6/H8 suitability cannot be concluded. ## Motion, contact and stops Buoyancy is rho × g × immersed volume. Contact damping is -(1200 + 500 × abs(relative vertical velocity)) × immersed projected area × relative vertical velocity, faded over the first 0.12 m of immersion. Total column support cannot become tensile. Damping coefficients remain assumptions. Added mass, horizontal motion and full gyroscopic coupling are absent. Heave, pitch and roll integrate at 240 Hz with semi-implicit Euler. With all columns dry, water support and drive moment vanish; vertical acceleration is gravity. Pause preserves state. Reset restarts from mass-only, zero-trim flotation and resets the wave clock. Attitude beyond ±40° or heave beyond ±8 m stops the preview and marks its output as outside the model envelope. A stopped trace is never extended as a prediction. Cyan hull samples are wet, orange samples are dry; pale points show local water elevation. Yellow marks the instantaneous displaced-volume centre; white marks the assumed CG. Spray scales with sampled bow contact. Wake fades after loss of contact. A dissipating re-entry splash follows increasing contact while descending. These visual effects are not calculated spray trajectories or impact loads. ## Repeatable seas Regular waves use crest-to-trough height. Irregular waves use eight deterministic components with a Gaussian-shaped frequency weighting, seeded phases and ±12° direction spreading. **This is not JONSWAP or a measured sea spectrum.** Hm0 = sqrt(8 × sum(component amplitude²)); individual crests and waves can exceed the entered significant height. Crossing mode shifts three components to shorter periods and the chosen chop direction. All modes use linear deep-water dispersion and the same field in the force calculation, rendering and comparison. Waves fade in over 3 seconds with a cosine ramp, including its contribution to vertical surface motion. Initial response is a startup transient. The height-based minimum period is a conservative interface restriction, not a breaking-wave solver. A steep-component combination is flagged. Breaking waves, shallow water, flooding and capsize prediction are outside scope. ## Saved setups and comparison Scenarios are stored on this device, up to 40, with JSON import/export for sharing. They contain the explicit wave seed and model inputs. Device-storage failures are reported; observations in the existing shared sea-trial log are separate. A/B comparison starts both runs from the same mass-only reference, sea seed and phase, while changing prescribed speed. Different speeds naturally change encounter timing. Each run covers up to 30 seconds; first seconds are startup, not settled averages. The matched side views use the same native CAD image and scale. Pitch, heave, roll and water-contact traces are model output. CSV export includes time, speed, motion, contact, volume, stop status and validated=false. ## Still needed for reliable LW33 predictions - Verify real sealed CAD boundaries and display registration; confirm mass and bow/stern drafts. - Confirm CG datum/direction/height and inertia; verify drive and propeller installation. - Calibrate and validate steady running attitude at 20, 25 and 30 kn, then transient response and impacts. - Finish the mesh/flow checks and establish the independent calm-water CFD baseline. Numerical tests and agreement between two geometry integrations are not real-boat validation.