3-DOF (surge–sway–yaw), based on the standard MMG method (Yasukawa & Yoshimura 2015); state velocities are through-water, with current added to obtain speed over ground.
Low-speed regime: 20-section cross-flow drag integration; linear derivatives blend in at moderate speed.
Propeller: linear KT(J) approximation with 72% efficiency astern. CPP ships use an equivalent-rpm approach. Astern propeller walk is modelled for a single right-handed FPP.
Rudder: MMG normal-force model (FN, aH, tR); propeller race is added using momentum theory.
Wind: simplified Isherwood-type coefficients applied to AF/AL using apparent wind. Wind direction is entered as the direction it comes from; current set is entered as the direction it flows towards.
Thrusters lose effectiveness above approximately 5 kn and tugs above approximately 6 kn. Letting go a tug does not instantly reduce ROT to zero; angular inertia decays through hydrodynamic damping.
Bank effect uses the actual walls of berths 1–17 and the entrance and main north–south breakwater contours. In confined water, the nearest structures on both sides of the ship are evaluated together; the nearer side dominates, while distance attenuation and a smooth support envelope reduce the effect in the centre of the open basin.
Limitations: squat, ship-to-ship interaction and mooring-line dynamics are not modelled. Bank and shallow-water effects are bounded, deterministic manoeuvring layers, not detailed CFD or a full harbour/mooring model. Above 45 kn wind or 4 kn current, an “extreme conditions” warning appears: the model continues to run, but its accuracy envelope has been exceeded.
Pivot / ICR / NP
The pivot point is commonly used in practical shiphandling, but the angular acceleration caused by forces is calculated from moments about the CG. The instantaneous centre of rotation (ICR) is a kinematic result derived from motion, not the reference point for the force calculation. The neutral point (NP) is often the more useful reference for tug and thruster planning.
The ICR is drawn in Analysis mode only when |ROT| > 3°/min and it lies within ±0.75L. If it is outside the hull, a dashed “ICR*” marks it as the instantaneous mathematical centre. On a steady straight course, the panel reads “ICR remote / straight course”.
The NP is shown on the hull as an amber diamond in both modes; it moves towards the bow with headway and towards the stern with sternway.
Analysis mode also shows the CG mark, force vectors, moment arms, bow/midships/stern current samples, shear-induced yaw moment, bank Y/N contribution, and the surge/sway/yaw force-and-moment breakdown.
Prediction track
The dashed prediction track and ghost ships are not physics steps: they are a dead-reckoning projection that holds the current ground velocity and ROT constant. It does not resample the current field, bank/shallow-water effects or subsequent control inputs; in curved or spatially varying current it should be used only as an approximate trend indicator.
Docking view
The DOCKING button opens a close-quarters view on the right at one third of the screen width by default. Drag the divider between the views to resize it; double-click to restore the default width. The ⛶ button expands the Docking view within the application, and Escape returns to split view. On narrow portrait screens, the panels stack vertically.
The close-quarters view uses the same CARTO and OpenSeaMap layers as the main chart and keeps the ship centred. H-UP/N-UP and the bounded +/− zoom controls affect only the Docking view.
The bow, stern and resultant arrows show velocity over ground, including current; the SOG at each point is shown in knots at the arrow tip. All arrows use the same automatic gain, keeping cm/s-level speeds visible while preserving their relative magnitudes. Numeric heading, ROT, SOG, bow/stern distance and transverse speeds appear only once, in the normal instrument column on the right.
When prediction is enabled, the Docking view also shows a low-speed-sensitive dashed track and ghost ships at 30-second intervals, using the same constant-speed/constant-ROT assumption.
Berthing event system
Successful berthing requires contact speed < 15 cm/s, heading-to-berth alignment error < 8°, bow and stern transverse clearances < 3 m, SOG < 0.3 kn, and contact on a berthable line (any numbered berth face). When all conditions are met, the ship is secured alongside and “Berthing complete” is displayed.
Contacts that do not meet these conditions are logged with the reasons; > 20 cm/s counts as hard contact / failed berthing. Fender friction is applied during contact; there is no elastic rebound.
Depth model: training soundings and zones take priority, followed by the SHOD 1/2000 grid, DEPTH_OVERRIDES polygons and, outside their coverage, the GEBCO grid. Charted soundings come from DISPLAY_SOUNDINGS, TRAINING_SOUNDINGS and HAYDARPASA_SOUNDINGS; the 5/10 m shallow-water fills and contour lines come from TRAINING_CONTOURS and USER_CONTOURS. UKC ≤ 2 m is “near draft limit”, ≤ 1 m is “shallow-water risk”, and < 0 is “manoeuvre failed: entered shallow water”. Draft can be changed in the INITIAL POSITION section.
Scenarios
Berthing — initial position: pick a point on the water from the chart and select Apply (or use the default approach). Contact is evaluated against any berth face.
Unberthing — pick a point on or near a berth line (≤60 m) and select Apply to place the ship alongside.
Free Manoeuvre — pick a position from the chart and select Apply.
The simulator opens paused and starts with ▶. Reset and scenario changes pause it again.
Actuator delays (real-time response model)
Rudder: constant angular rate; hard-over to hard-over (70°) takes approximately 28 s for Capesize, 25 s for PCTC and 23 s for Handysize. Reference: SOLAS II-1/29.3.2 (35° to 30° on the opposite side in ≤ 28 s). On the arc indicator, amber is commanded and blue is actual.
Engine — CPP (PCTC): 1 s command dead time; full pitch travel (+100%→−100%) takes approximately 17 s; there is no dwell when reversing pitch (field range 12–20 s).
Engine — two-stroke FPP (Capesize): 2 s telegraph dead time; rpm rises at 4%/s in the manoeuvring range and 1.6%/s above 50% under the load-up programme (Stop→Dead Slow Ahead approximately 7 s, Stop→Full Manoeuvring Ahead approximately 45 s); fuel cut-off/rpm decay is 5.5%/s; crossing zero includes an 8 s dwell for braking air and air start astern. Handysize (medium-speed engine + clutch) uses shorter times (1.5 s dead time, 4 s dwell).
Bow/stern thruster: 0.8 s command dead time; thrust builds to full in approximately 4 s, and full port→full starboard takes approximately 8 s (tunnel-thruster field range: 3–10 s for full reversal). On the slider, left/red is Port and right/green is Starboard; the “RPM” value shows actual thrust.
Tug: power increases at 9%/s (Stop→Full approximately 11 s, representing engine loading and towline tension) and decreases at 30%/s. For direction changes > 30°, power first drops to ≤ 15%; azimuth turning rate is 12°/s unloaded (180° in approximately 15 s for an ASD tug) and 3°/s under load. A direction change > 120° (changing from pull to push) requires an additional 12 s for towline/position adjustment; the full pull→full push cycle takes approximately 30 s. The line below the card and the force vector on the chart show the actual delayed state.
Controls
The bottom icon bar toggles the tug / engine / rudder / thruster control groups; ⚠ opens the contact log and the gear icon opens Setup & Environment.
Tug panel: tap a point on the ship silhouette to make a tug fast and select it; drag the dial to set the force direction (amber: commanded, blue: actual); LET GO releases the towline.
On sliders, the blue triangle shows the actual delayed value; tapping the value commands STOP/MID.
Keyboard: in HAND mode, ← → changes rudder by ±5°; in AUTO mode it changes target heading by ±1° (±10° with Shift); ↑ ↓ changes engine command by ±10%, and Space pauses/starts the simulator.
View: N-UP / H-UP (heading up, with smoothed heading changes). The chart cannot be dragged in H-UP; use the +/− buttons to zoom and Follow mode for positioning. Follow mode has a dead band and recentres when the ship leaves the middle region of the screen.
Select HAND/AUTO on the rudder panel. When AUTO is engaged, the current heading becomes the target; change it with the ± buttons or the compass. Large changes use a limited ROT. The panel shows AP rudder command, actual rudder and low-speed rudder-authority warnings.
Drag the rudder control along the arc (amber: commanded, blue: actual); ROT is shown on an arc indicator. Engine levers are vertical (PITCH % on CPP ships). Colour code: rudder blue, engine amber, thrusters green, tug power yellow.
Berth labels (1–17): while “Edit berth labels” is active, drag the numbers to move them. Positions are stored in the browser; “Copy labels” provides JSON for the BERTH_LABELS array.
Tug force direction is ship-heading-relative (90° = resultant push/pull to starboard).
Select the initial position from the chart in the INITIAL POSITION section. In the Unberthing scenario, the selected point snaps the ship alongside the nearest berth line (≤60 m); in Berthing/Free Manoeuvre scenarios, any point on the water is valid (land and depths below the selected draft are rejected). Berth numbers (I–XVII) come from the harbour plan; positions are approximate and can be adjusted in the BERTH_LABELS array in the file.