Turning Circle / Advance / Transfer Estimator gives first-pass ship turning-circle metrics from vessel speed, applied rudder angle, and vessel length when vessel-specific manoeuvring curves are unavailable. It estimates turning radius, tactical diameter, advance, transfer, and time to a 90-degree heading change for bridge-team briefings, pilot exchange preparation, simulator discussion, maritime training, and early manoeuvre planning. The method is intentionally approximate and cannot represent hull form, loading condition, shallow-water effects, propulsion configuration, windage, current, bank effect, tug assistance, or actual rudder response. Use it only as context until pilot-card, wheelhouse poster, sea-trial, simulator, or observed manoeuvring data is available.
Use this calculator as one part of a broader passage-planning workflow. The
Marine Navigation Calculators toolkit
explains how CPA/TCPA, UKC, tide windows, route distance, set and drift, fuel range, and manoeuvring checks fit together.
You can also browse the full
Marine & Navigation category.
Enter the vessel, route, tide, current, or clearance assumptions exactly as labelled, then verify the result against official data and onboard judgment.
How to use this tool
Enter vessel speed in knots, applied rudder angle in degrees, and vessel length overall in meters.
Run the estimator to compute turning radius, tactical diameter, advance, transfer, and estimated time to 90 degrees.
Compare each output against the vessel pilot card, wheelhouse poster, sea-trial data, simulator data, or recent observed maneuvers.
Use the result for briefing scale and margin discussion, not for final maneuver orders.
Turning Inputs
Result
Turning radius: 178.2 m
Tactical diameter: 356.4 m
Advance: 463.3 m
Transfer: 267.3 m
Estimated time to 90° turn: 45.3 s
Formula or method
The estimator scales turning radius by vessel length, rudder angle, and speed using a simple empirical approximation.
Tactical diameter is estimated as twice the turning radius, advance as 2.6 times radius, and transfer as 1.5 times radius.
Time to 90 degrees uses quarter-circle arc length divided by speed converted to meters per second.
Advance is distance made in the original direction during the turn; transfer is sideways displacement from the original track.
Tactical diameter and final diameter are vessel-specific manoeuvring characteristics; this tool provides an approximate tactical-diameter-style value only.
Worked example
Preparing a pilot-exchange manoeuvre brief
Speed: 12 kn
Rudder angle: 20 deg
Length overall: 110 m
Result: The estimator returns first-pass turning radius, tactical diameter, advance, transfer, and time to a 90-degree heading change.
Use the values to frame expected manoeuvre scale, then replace them with vessel-specific pilot-card, wheelhouse-poster, simulator, or sea-trial figures before relying on the plan.
How to interpret the result
Turning-circle estimates are useful for scale awareness, but actual vessel response can differ sharply from this simplified approximation.
Advance is the approximate distance made in the original direction before the vessel has turned through the reference heading.
Transfer is the approximate sideways displacement from the original track during the turn.
Tactical diameter helps compare whether available water, channel width, traffic, and abort margins are plausible.
Time to 90 degrees is a rough timing cue, not a helm order or guarantee of heading response.
If the estimate is close to a channel boundary or hazard, treat that as a reason to obtain vessel-specific data and add margin.
Common mistakes
Treating an empirical estimate as vessel-specific maneuvering data.
Ignoring shallow water, bank effect, wind, current, squat, loading, trim, propulsion mode, or tug assistance.
Comparing estimated transfer or advance with charted limits without adding operational safety margin.
Using speed over ground when the maneuvering reference needs speed through water, or vice versa.
Assumptions
Uses empirical approximation rather than vessel-specific hydrodynamic model.
Accuracy decreases outside moderate speeds/rudder angles or unusual hull forms.
Rudder angle is clamped to the tool's supported 5-35 degree range.
Review note and limitations
Method - empirical first-pass maneuvering approximation from length, rudder angle, and speed.
Does not model hydrodynamics, pivot point movement, stopping distance, tactical diameter asymmetry, shallow-water effects, or propulsion/rudder configuration.
Does not replace pilot-card data, wheelhouse poster data, simulator training, sea trials, or bridge-team procedures.
Navigation planning support only. Do not use this page as a substitute for vessel-specific maneuvering data, pilot guidance, bridge-team procedures, or qualified navigation judgment.
FAQ
Is this the same as a vessel's pilot-card turning data?
No. It is a rough approximation for context. Pilot-card, wheelhouse-poster, sea-trial, simulator, or observed vessel data should take priority.
What are advance and transfer?
Advance is distance made along the original course during the turn. Transfer is sideways displacement from the original track.
Does this estimate final diameter?
No. It estimates turning radius, tactical diameter, advance, transfer, and time to 90 degrees. Final diameter depends on vessel-specific manoeuvring behavior.
Why does shallow water matter?
Shallow water, bank effect, squat, and restricted channels can materially change turning behavior and required margins.
Related tools and workflows
Maneuvering estimates pair with drift, tide-window, under-keel-clearance, COLREGs encounter, CPA/TCPA, and fuel/endurance checks.