Flagship Toolkit

Marine Navigation Calculators Toolkit

Use practical marine navigation calculators for CPA/TCPA, under-keel clearance, tide windows, route distance, set and drift, fuel range, ETA, anchoring, COLREGs encounter checks, and vessel turning estimates.

Who this toolkit is for

This toolkit is for sailors, yacht owners, maritime students, instructors, bridge teams, hobby navigators, and professional mariners who need quick planning calculations with visible assumptions. Use it to frame a passage plan, compare constraints, brief risks, and decide what must be checked against official charts, tide/current data, weather, local notices, pilotage guidance, vessel documentation, and bridge procedures.

Open the calculator that matches the current planning constraint, save the inputs with the result, and verify the decision against authoritative navigation sources before acting.

Open the marine formula reference

Recommended workflow

Start with the intended route: compare great-circle and rhumb-line distance, choose a planning speed, and note the assumptions behind the ETA.
Check water constraints: use tide-window and under-keel-clearance calculations before committing to a harbour entry, bar crossing, channel transit, or marina arrival.
Add environmental effects: estimate set, drift, wind/current ETA changes, and fuel reserve before treating the passage time or range as realistic.
Review traffic and manoeuvring risk: use CPA/TCPA, COLREGs encounter classification, and turning-circle estimates when close-quarters situations or restricted water matter.
Carry the result into the real navigation workflow: compare every consequential output with charts, tide tables, weather, notices, instruments, local rules, and bridge-team procedures.

Example scenario

Short coastal passage: a navigator plans a 42 nm leg to a harbour with a shallow entrance. They compare great-circle and rhumb-line distance, estimate set and drift for a two-hour tidal stream, check whether the tide window gives enough depth for a 2.4 m draft plus margin, calculate fuel range after reserve, and use CPA/TCPA to triage a crossing target near a traffic lane. The ToolPatch outputs form a planning brief, not the final authority.

Which calculator should I use?

Tool	What it helps with	When to use it
CPA/TCPA Risk Calculator	Compute closest point of approach and time to CPA with risk banding.	Use when another vessel's bearing, range, course, and speed may create a close-quarters situation and you need closest point of approach and time to CPA.
Under Keel Clearance Calculator	Assess UKC using depth, tide, squat, wave allowance, and safety margin.	Use when charted depth, tide height, vessel draft, squat, wave allowance, or safety margin controls whether a transit has enough water.
Tide Window Planner	Estimate passable tidal windows around high tide for draft-limited transits.	Use when depth, bar crossing, marina access, or shallow-channel timing depends on a safe tide window around high water.
Great Circle vs Rhumb Line Calculator	Compare great-circle and rhumb-line distance, bearing, and ETA.	Use when comparing route distance and bearing assumptions over longer passages.
Drift Estimator	Estimate set-and-drift impact on course over ground and offset.	Use when set and drift from current or leeway may move the vessel off the intended track over a short leg.
Turning Circle / Advance / Transfer Estimator	Estimate turning radius, tactical diameter, advance, and transfer.	Use when a bridge briefing needs first-pass advance, transfer, tactical diameter, and turn timing estimates.
Fuel Endurance + Reserve Calculator	Calculate endurance and range after applying reserve fuel policy.	Use before departure and when speed, sea state, or reserve policy changes.
ETA Current/Wind Compensation Calculator	Estimate ETA delay from current and wind speed penalties.	Use when current or wind affects speed made good and arrival time.
Anchor Scope & Holding Calculator	Check required scope and estimate holding confidence for anchoring setup.	Use when anchorage setup depends on depth, bow height, rode length, wind, and bottom assumptions.
COLREGs Encounter Classifier	Classify head-on, crossing, or overtaking geometry from bearing/course data.	Use for training or briefing when course and relative bearing suggest head-on, crossing, or overtaking geometry.

Marine navigation glossary

CPA

Closest point of approach; the predicted minimum distance between vessels if both maintain the entered course and speed.

TCPA

Time to closest point of approach; positive values indicate the closest approach is ahead in the prediction window.

UKC

Under-keel clearance; the water remaining between the vessel keel and seabed after draft and allowances are considered.

Charted depth

Depth printed or encoded on the chart, normally referenced to chart datum and subject to survey quality and updates.

Height of tide

Predicted or observed tide height above the chart datum used by the relevant chart or tide table.

Safety margin

Extra allowance reserved for uncertainty, policy, vessel motion, measurement error, or operational risk.

Squat

Reduction in under-keel clearance caused by a vessel moving through water, especially in shallow or confined channels.

Set

Direction toward which current or drift moves the vessel, expressed as a bearing.

Drift

Speed of current or leeway movement, commonly in knots.

Rhumb line

A route of constant bearing on a Mercator chart; simple to steer but not always the shortest distance.

Great circle

The shortest path on a spherical Earth approximation, with bearing that changes along the route.

Advance

Distance made in the original direction during a turn before reaching a reference heading change.

Transfer

Sideways displacement from the original track during a turn.

Common mistakes

Treating calculator output as a substitute for charts, local notices, weather, or watchkeeping.
Ignoring reserve fuel, sea state, current, or speed reduction when estimating range.
Using tide height without considering chart datum, squat, draft, and safety margin.
Relying on one CPA/TCPA snapshot when traffic and vessel intentions can change.
Mixing true/magnetic bearings, "wind from" and "set toward" conventions, or incompatible units.

FAQ

Can this toolkit be used for live navigation?

It is planning support only. Use official charts, instruments, weather, tide sources, bridge procedures, and applicable navigation rules for live decisions.

Why combine route, tide, fuel, and encounter tools?

Passage planning depends on several constraints at once; a route that looks fine by distance can fail on tide, clearance, reserve, or traffic risk.

What should I verify outside ToolPatch?

Verify chart data, tide and current predictions, weather, vessel performance, local notices, and regulatory requirements.

Which marine calculator should I start with?

Start with the constraint that can invalidate the passage first. Use route distance for timing, tide-window and UKC tools for draft-limited access, drift tools for current effects, fuel tools for range, and CPA/TCPA for traffic risk.

Navigation safety note

Educational and planning aids only. These tools do not replace official charts, bridge procedures, COLREGs, local notices, pilotage guidance, ECDIS, radar, AIS, tide tables, weather routing, vessel documentation, or professional judgement.

Related categories

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