Emergency Manoeuvring

Anderson Turn — MOB Recovery

Fastest single-rudder return-to-point manoeuvre · IMO emergency procedure

The Anderson Turn is the fastest of the three IMO-recommended man-overboard (MOB) recovery manoeuvres. The moment a casualty enters the water, the helm is put hard over toward the side the person fell from. The ship continues turning until the heading has changed by approximately 250°. The rudder is then centred and the ship coasts back toward the original line of travel, ideally re-acquiring the casualty within a few ship lengths of the MOB point.

Manoeuvre Sequence
$$ \delta_{cmd}(t) = \begin{cases} -35°, & \psi < 250° \quad \text{(Phase 1: hard rudder)} \\ 0°, & \psi \geq 250° \quad \text{(Phase 2: rudder centred)} \end{cases} $$

The 250° heading target — rather than 180° — compensates for forward drift during the turn and brings the ship onto a reciprocal track near the original course line.

Rudder Rate Limit

Real rudder machinery cannot snap instantaneously to ±35°. The model enforces a slew-rate limit (default 5°/s) on the commanded angle:

Slew-Rate Limited Servo
$$ \dot\delta = \mathrm{clip}\!\left(\delta_{cmd} - \delta,\; -\dot\delta_{max},\; +\dot\delta_{max}\right) $$

The plot view shows the commanded square pulse alongside the rate-limited actual rudder — the gap between them is the response lag that costs precious seconds in a real MOB.

Performance Metrics

Three numbers summarise an Anderson Turn run:

Recovery Quality Indices
$$ t_{end}, \quad \Delta y, \quad \Delta\psi $$

tend — time at which $\psi$ first reaches 250° (Phase 1 duration). Δy — final cross-track error: distance from the original line of travel at end of simulation. Δψ — heading error from the 250° target at simulation end.

Simulation Workflow

How the Visualiser Works

Single ship · live phase indicator · MOB beacon

Phase 1 Hard Rudder Turn

The ship enters with hard rudder (default 35°). Trajectory drawn in amber until heading change reaches 250°.

Phase 2 Rudder Centred

At ψ = 250° the rudder steps to zero and the ship glides back toward the MOB point. Trajectory drawn in teal.

MOB Beacon Casualty Marker

A red beacon at the origin marks where the person fell overboard. A dashed line at the end of the run shows the final cross-track error — the metric to minimise.

Replay 5-Second Loop

Whatever the real recovery time, playback is normalised to a 5-second loop so the full Anderson Turn signature is always visible.

Operating Guide

Simulation Guide

1

Set Ship & Conditions

Pre-loaded with Mariner-class defaults. Adjust hull mass, inertia, initial speed and the rudder slew-rate to investigate how mechanical lag affects recovery accuracy.

2

Run the Solver

Click Run Simulation. The integrator runs until ψ reaches 250° (phase change) and then continues to Tmax.

3

Inspect Results

The 3D view animates the full loop. Analytical Plots includes trajectory, heading-vs-time (with 250° target line), yaw rate, and the all-important commanded-vs-actual rudder signal.

Manoeuvring · MOB Recovery Trial

Anderson Turn Solver

Operational
Real machinery limit — slower rate ⇒ larger lag ⇒ worse MOB recovery
Hull Mass & Inertia
Added Mass ▾
Linear Damping ▾
Cross-Coupling ▾
Nonlinear Damping ▾
Rudder Coefficients ▾
Bias Terms ▾
Manoeuvre Constants
Hard rudder −35°
Heading target +250°
Anderson Turn convention — fixed by the manoeuvre definition.
Recovery Performance
Time to 250° (tend): — s
Cross-track Error |Δy|: — m
Cross-track in ship-lengths: —
Heading Error |Δψ|: — °
Recovery Quality: —
Samples: —
READY
U₀: — · Slew: —
Anim: 0.00 s · Phase: PHASE 1
MOB casualty (origin)
Phase 1 — hard rudder
Phase 2 — rudder centred
Phase change (ψ = 250°)
Final position