Calculators & Checklists Hub

A checklist does not think.
A calculator does not doubt.
Both of those are the mariner’s job.

Introduction

This page exists for one reason: to put every Maritime Hub calculator and checklist in one place, with a single line explaining what each does.

It is a navigation page. Bookmark it. Return to it. The tools listed here will grow as the site grows. Some are live now. Others are flagged as forthcoming. All share a common design philosophy that is worth understanding before any of them are touched.

That philosophy is not complicated, but it is routinely ignored — aboard ships, in offices, and in the training centres that produce the people who end up in both. So it gets its own section below, before the index itself.

Contents

• 1. The Philosophy: Aids to Judgement
• 2. What a Calculator Cannot Do
• 3. What a Checklist Actually Prevents
• 4. Navigation & Passage Planning Tools
• 5. Collision Avoidance & Radar Tools
• 6. Weather, Stability & Cargo Tools
• 7. Checklists: Bridge Operations
• 8. Checklists: Emergency & Non-Routine
• 9. Closing Reality

1. The Philosophy: Aids to Judgement

Every tool on this page is an aid to judgement. Not a replacement for it. Not a shortcut around it. An aid.

The distinction matters because the modern bridge is saturated with systems that present answers — speed over ground, CPA, ETA, UKC — with an authority that discourages the user from questioning the inputs that produced them. A number on a screen looks like a fact. It is usually an opinion, calculated from assumptions the system never states and the operator rarely checks.

The calculators here are deliberately simple. They show their working. They require the user to provide the inputs consciously, which means the user must know what those inputs represent and where they came from. That is the point.

A tool that demands understanding from the operator is safer than one that hides the need for it.

Checklists operate on a different axis. They do not calculate. They interrupt. They force a pause in a sequence that has become so familiar it no longer receives conscious attention. The value of a checklist is not in what it contains. It is in the cognitive break it imposes — the moment where the operator stops executing and starts verifying.

Neither calculators nor checklists can compensate for a lack of competence. They assume competence. They exist to support a mariner who already knows what the right answer should look like and wants a structured way to confirm it.

2. What a Calculator Cannot Do

A calculator cannot detect a bad input.

Feed it the wrong height of tide, and it will return a UKC figure that looks perfectly credible. Feed it a compass error with the wrong sign, and it will produce a correction that doubles the deviation instead of removing it. The arithmetic will be flawless. The answer will be wrong. And it will be wrong with decimal-place precision, which makes it more convincing, not less.

This is not a theoretical risk. It is a routine cause of incidents. The operator trusts the output because the process of obtaining it felt rigorous. The act of entering numbers into a structured tool creates an illusion of diligence that can survive all the way to the grounding report.

Precision is not accuracy.

Every calculator on this site includes a note on what inputs it expects and where those inputs should be sourced. Read those notes. If the source of an input is uncertain, the output is uncertain. No formula changes that.

3. What a Checklist Actually Prevents

Checklists do not prevent incompetence. They prevent omission.

A competent officer who has completed a pre-arrival sequence two hundred times will, on the two hundred and first occasion, skip a step. Not from laziness. From fluency. The task has migrated from conscious processing to automatic execution, and automatic execution does not monitor itself.

The checklist exists for that moment. It is a physical interruption — a piece of paper, a screen, a read-and-respond exchange between two people — that forces the sequence back into conscious awareness long enough for the skipped step to become visible.

This only works if the checklist is actually used as a verification tool and not as a paperwork exercise completed after the fact. A checklist filled in retrospectively at the chart table is not a safety barrier. It is a piece of fiction with a signature on it.

The checklist that lives in a drawer protects nothing.

Used properly — read aloud, responded to, each item confirmed against the actual state of the equipment or procedure — a checklist is one of the most effective defences against normalised deviation that exists on a ship. It costs nothing. It requires no technology. It demands only the discipline to do it honestly every time.

4. Navigation & Passage Planning Tools

The following calculators support passage planning, position verification, and navigational mathematics. Each link leads to a standalone tool page with usage notes and input guidance.

• Speed, Distance & Time Calculator — Solves for any one variable given the other two. The foundation of all ETA and fuel-consumption estimates.
• CPA / TCPA Calculator — Manual CPA and TCPA derivation from plotted targets. For verifying ARPA output or working without it.
• Under-Keel Clearance Calculator — Computes static UKC from draught, charted depth, height of tide, and squat allowance. Does not account for dynamic factors unless manually entered.
• Compass Error & Deviation Calculator — Derives compass error from observed and charted bearings. Separates variation and deviation.
• Range of Lights & Visibility Calculator — Geographical and luminous range computation from height of eye and charted light characteristics.
• Meridian Passage & Amplitude Calculator — Forthcoming. Sun transit and amplitude for compass checks at sea.
• Great Circle & Rhumb Line Distance Calculator — Forthcoming. Comparison of GC and RL distances between two positions, with initial GC course.

Every navigation calculator assumes the user understands the limitations of the source data — particularly charted depths, which may be decades old, and tidal predictions, which are predictions.

5. Collision Avoidance & Radar Tools

These tools support manual radar plotting and the interpretation of collision-avoidance data. They do not replace systematic plotting. They provide the arithmetic once the plotting is done.

• Relative Motion Vector Calculator — Derives true course and speed of a target from own ship’s motion and the observed relative vector.
• Aspect Calculator — Estimates target aspect from relative bearing and target’s true course. Useful for confirming visual assessment against radar-derived data.
• Trial Manoeuvre Calculator — Forthcoming. Projects the effect of own-ship course or speed alteration on the CPA of a tracked target.

ARPA does all of this faster. That is not a reason to stop understanding how it is done.

When ARPA fails, degrades, or produces a track that does not match the visual picture, the officer who can work a plotting sheet manually still has situational awareness. The officer who cannot is now navigating on instinct in a traffic lane. The gap between those two states is the gap these tools are designed to keep open.

6. Weather, Stability & Cargo Tools

Operational calculators covering weather interpretation, stability estimation, and cargo-related computations.

• Roll Period & GM Estimator — Estimates metacentric height from observed roll period and ship’s beam. A screening tool, not a substitute for the stability computer, but valuable when the stability computer’s inputs are in question.
• Barometric Pressure Tendency Calculator — Converts observed pressure readings over time into a rate of change, with context for the expected synoptic pattern. Useful for validating weather routing forecasts against direct observation.
• Beaufort Scale & Sea State Reference — Quick-reference lookup correlating Beaufort number, wind speed, wave height, and sea-state descriptors.
• Draught Survey Calculator — Forthcoming. Cargo quantity estimation from fore, aft, and mid draughts with dock water correction.
• Cargo Ventilation Dew-Point Calculator — Forthcoming. Three-temperature method for ventilation decisions during carriage of hygroscopic cargoes.

Stability tools carry a particular caution. A GM figure derived from roll period observation is an estimate with significant margins. It is useful as a cross-check when the loading computer output feels wrong. It is not useful as the primary basis for a go/no-go decision.

If the only way to confirm the ship’s stability is to time her rolling, something has already gone wrong with the loading plan.

7. Checklists: Bridge Operations

Operational checklists for routine and recurring bridge evolutions. Each is presented as a printable, standalone document and as an interactive on-screen checklist.

• Pre-Departure Checklist — Bridge systems, communications, navigation equipment, steering gear, and propulsion confirmation before letting go.
• Master–Pilot Exchange Checklist — Structured MPX covering pilotage plan, contingencies, abort points, ship-handling characteristics, and communication protocols.
• Pre-Arrival Checklist — Anchoring or berthing preparation sequence including machinery status, deck readiness, and communication setup.
• Watch Handover Checklist — Outgoing-to-incoming OOW information transfer covering traffic, navigation status, standing orders, and machinery state.
• ECDIS Passage Plan Verification Checklist — Route check against paper backup or independent ECDIS, including safety contour settings, no-go areas, and alarm configurations.
• Navigation Audit Checklist — Forthcoming. Periodic self-assessment of bridge team navigation practices against actual operating standards, not just ISM paperwork.

A note on format. These checklists are deliberately concise. They list what must be confirmed, not how to do it. A checklist that tries to be a procedure manual becomes too long to use and too dense to read at the moment it matters. Procedure belongs in the procedure manual. The checklist belongs on the bridge wing console, stained with coffee and salt spray, actually being used.

8. Checklists: Emergency & Non-Routine

Emergency and non-routine checklists for situations where time pressure and stress degrade recall. These are not substitutes for drills. They are the structured memory aid that drills train the crew to reach for.

• Steering Failure Immediate Actions Checklist — First-response sequence for loss of steering, including emergency steering engagement and notification chain.
• Blackout Recovery Checklist (Bridge Actions) — Bridge-side actions during main power loss: navigation status assessment, communication on backup power, traffic management, and engine room liaison.
• Man Overboard Immediate Actions Checklist — Williamson / Anderson turn selection, MOB marker deployment, EPIRB/SART activation, and crew muster sequence.
• Collision / Grounding Immediate Actions Checklist — Forthcoming. Damage assessment, watertight integrity, communication, and crew-safety priorities in the first fifteen minutes.
• Fire on Board — Bridge Response Checklist — Forthcoming. Bridge team actions for fire alarm activation, including ventilation control, manoeuvring considerations, and SAR notification triggers.

Emergency checklists have a different design requirement than routine ones. They must be scannable in poor light, under stress, in seconds. They contain the minimum number of items needed to prevent the most critical omissions during the phase of an emergency where cognitive function is at its lowest. Supplementary detail — the kind that returns as adrenaline fades and the bridge team begins to think again — belongs in a separate extended procedure, not on the immediate-actions card.

The emergency checklist is for the first ninety seconds. Everything else is for after.

9. Closing Reality

This page is a directory. Its value is in being findable, current, and honest about what each tool does and does not do.

The calculators listed here will give correct outputs from correct inputs. They will also give precisely formatted nonsense from incorrect inputs. The difference is not something any tool can detect. That responsibility sits with the person using it — the same person who chose to go to sea, who holds the certificate, who has the watch.

The checklists listed here will prevent omissions if they are used before the evolution, not after it. Filled in honestly, they are a genuine safety barrier. Filled in retrospectively, they are evidence of a culture that has substituted paperwork for practice.

Every tool on this page assumes the user is competent, alert, and willing to question the answer when it does not match the picture outside the wheelhouse windows.

The tool is only as good as the judgement behind it. That has always been the case. Nothing on this page changes it.