Translate Tide Tables and Chart Datum Correctly

How do you translate a tide table correctly? Begin by preserving the prediction station, date, time zone, high-water and low-water times, heights, units and vertical reference datum. A tidal height reported above chart datum is not itself the depth of a harbour channel, and a prediction expressed relative to Lowest Astronomical Tide (LAT) is not automatically interchangeable with one referenced to Mean Lower Low Water (MLLW). Accurate multilingual translation of tide predictions and hydrographic tables requires the translator to keep the numeric value attached to the right datum, location and event.

Readers searching for tide table translation, chart datum explained, LAT versus MLLW, high tide and low tide times, secondary port corrections, predicted tide height versus charted depth, local time versus UTC, tidal range and tidal stream definitions need more than a bilingual glossary. They need a method for reading the original field, checking the issuing hydrographic authority and preserving how the number should be used. This guide focuses specifically on astronomical tide predictions and published tidal tables for coastal and maritime information. It is not a substitute for official charts, navigation planning, clearance calculations or current local maritime warnings.

Did you know that a perfectly translated number can lead to a completely different conclusion if the datum is wrong? An entry reading high water 2.6 m might mean 2.6 metres above a chart datum at a named station, not 2.6 metres of navigable water in every part of a port. Some hydrographic offices use LAT as the main tidal reference, while many US NOAA prediction products use MLLW. These datum labels, together with the station code and prediction time, form an indivisible part of the claim. Our fictional worked examples show how to preserve those facts without inventing a navigational clearance guarantee.

The one-minute answer

Translate every tide-table figure as a prediction with its exact station, date, time standard, tidal event, height unit and vertical datum. Leave LAT, MLLW, high water, low water, chart datum and tidal-stream speed distinct unless an official source explicitly defines an equivalence or approved transformation. A negative predicted height can simply mean water level below the selected datum, not negative water depth. Secondary-port corrections, chart-to-tide-datum offsets and weather-driven departures must not be silently ignored. For real navigation, consult the current official hydrographic publication, local notices and appropriately qualified professionals.

The visible problem: tide height is mistaken for water depth

Imagine a translated travel guide reporting that a port has 2.6 metres of water at 07:10 because the tide table lists high water at 2.6 m. Nothing in that single prediction establishes the total water depth at a berth. A tide table provides a water level relative to a particular reference, while the chart depicts soundings relative to a chart datum and the water at any actual place varies with seabed shape. Even a simplified combination of charted sounding and predicted height is only part of a navigator’s assessment, not a universal statement about safe passage.

The second trap is the datum. One publication labels its high and low values with LAT. Another lists MLLW. A translator may expand both abbreviations as ‘low-tide reference’ and delete the original acronyms to make the page look friendlier. The numbers now appear comparable, but they are not guaranteed to refer to the same vertical plane or epoch. When a user compares them without offsets, a difference in the reference plane can masquerade as a change in actual sea level.

The third trap is time. A tide table printed in standard time, a weather app presenting daylight-saving local time and a research spreadsheet stored in UTC may show the same high water with different clock labels. It is not enough to copy 06:40. The translator must identify the station’s convention, date and time zone, whether daylight time is applied, and whether a correction shifts the event across midnight. The correct translation keeps each source field recoverable.

First principles: learn the quantities before choosing the words

1. The datum is a vertical origin, not background punctuation

Chart datum is a reference surface against which charted depths and relevant water-level heights are stated. LAT is a defined astronomical low-water reference used by many hydrographic offices; MLLW is a different statistical tidal datum common in NOAA products. They should be translated as technical names, not paraphrased into one generic phrase. A datum offset requires station-specific official information. Copying the figures while dropping the datum can change the physical meaning.

2. A height of tide is not a sounding

A tide-table height describes predicted water level above or below its reference datum at a location and time. A sounding describes seabed depth relative to the chart’s reference. The translator should keep height and depth distinct even when both use metres. In some contexts a charted depth and appropriately datum-aligned water level are used together, but that is not a license to declare a real-time safe depth or under-keel clearance.

3. Prediction is not observation

Astronomical tide predictions are produced from methods based on periodic constituents and reference observations. Actual water levels can depart because of wind, atmospheric pressure, river discharge, surge and other factors. A table of predictions should not be translated as gauge readings already observed. Similarly, an observation dashboard cannot be converted into a future prediction merely because it has a tide-shaped graph.

4. The named station controls where the prediction applies

A harbour can have multiple prediction stations or designated standard and secondary ports. Water levels and timings vary along channels, bays and estuaries. A translation must retain station names, numbers and geographical context. A value associated with a standard port should not silently be presented as the exact tide at a nearby marina, especially when the hydrographic publication provides secondary-port corrections.

5. High water and low water are tidal events

High water and low water identify turning points or relevant highs and lows for a period, not simply daytime and nighttime. Many locations have two of each on a tidal day; others can have different patterns. Translate whether the publication is listing high/low events, hourly levels or a continuous curve. Avoid inventing events that do not appear in the source or assuming a strict six-hour interval everywhere.

6. Tidal range differs from tidal height

Range is the vertical difference between relevant high and low waters. Height is measured from a vertical reference datum. A high water of 3.4 m and a low of 0.7 m in the same compatible reference give an illustrative range of 2.7 m, not a water depth of 2.7 m. Keep the arithmetic and the reference labels clear so a translated educational example does not mix concepts.

7. Clock conventions can change the date

Standard time, local daylight time, UTC and fixed offset zones are not interchangeable labels. The same tide can occur at 23:50 on one clock and 00:50 the next day on another. The date belongs to the time standard. A translator must copy and explain the source convention, including whether a printed table is already corrected for daylight-saving time.

8. Secondary-port corrections follow a specified method

Hydrographic publications may use time differences and tidal-range relationships to infer high and low water at a secondary port from a standard port. The method can vary with predominantly diurnal or semidiurnal tidal regimes. Translators should not reduce this to ‘subtract 15 minutes and 0.2 metres’ unless that is exactly how the authority instructs the calculation. Preserve the table, sign convention and reference port.

9. Tidal streams are not tidal heights

Tidal streams describe horizontal movement with speeds and directions, often in knots and bearings. Water-level rise or fall does not uniquely determine the local current at a navigation point. A phrase such as ebb stream is not interchangeable with low tide. Keep stream direction, rate, reference position and time relative to the specified reference event in their own fields.

10. Spring and neap tides are not seasons

Spring tide refers to a tidal-range pattern associated with lunar and solar alignment, not necessarily to the spring season. Neap tides are associated with smaller typical ranges. Translating spring tides into ‘tides during springtime’ is a familiar but consequential error. Use a technical equivalent or short explanation that makes the periodic astronomical sense clear.

11. Vertical clearance and under-keel clearance use different inputs

A bridge chart may state an air-draft or vertical clearance referenced to a high-water datum, while a seabed sounding can use a low-water chart datum. Do not apply a tidal height from one vertical reference to every clearance without checking the reference and relevant correction. Translations should keep clearance information as sourced and never compute a supposedly safe passage window without the necessary chart, conditions and vessel-specific assessment.

12. Accuracy includes limitations and updates

Official tide tables are published for specific years and can be amended. Tide predictions may include local cautions on wind, pressure, river inflow or harbour conditions. A translation should retain publication year, edition, notice-of-correction references and warnings. A concise and cautious target text is more useful than a fluent summary that hides source currency or limitations.

The repeatable eleven-step translation workflow

Step 1: Locate the hydrographic source

Identify the issuing hydrographic office, official table or service, year, station identifier and publication edition. A copied image or spreadsheet extract may omit these essential details.

Practical quality gate: prepare a source-to-target ledger with six columns: field name, source value, original unit or datum, original time or station, translated label and verification note. Do not approve a sentence if its numeric component cannot be traced to the same labelled field in the source. If the publication has a technical correction that you do not understand, leave a translator query rather than guessing.

Step 2: Mark the reference datum

Record whether all heights are referred to LAT, MLLW, chart datum or another named plane. Check for a separate conversion or correction to a chart’s datum.

Step 3: Separate measurement categories

Create columns for event time, height, range, charted sounding, water-level observation and stream speed. Resist any temptation to treat two matching numerical values as synonyms.

Step 4: Record time conventions

Write the stated time zone and whether the table uses standard time, local daylight time or UTC. Check calendar boundaries after corrections or conversions.

Step 5: Verify physical units

Protect metres, feet, knots, degrees and interval units. Convert only when needed and label any supplementary calculation; do not blindly swap symbols.

Step 6: Establish standard or secondary station status

If the source references a standard port and secondary port, preserve their roles and link the correction rows to the correct reference station.

Step 7: Follow the authority’s correction workflow

Use official signs and formulas for timing, tidal range, height and datum differences. A generic ‘add the offset’ rule may not be correct across every product.

Step 8: Translate uncertainty and operational caveats

Preserve predicted, observed, approximate, modelled, weather affected and amended labels. Avoid turning predictions into guaranteed real water levels.

Step 9: Rebuild the table for reader retrieval

Keep date, time, event, height, datum and station visible next to the relevant number. If the page becomes narrow on mobile, repeat the full header rather than detaching figures from units.

Step 10: Conduct a numerical and semantic audit

Compare every digit, decimal point, negative sign, time, station code, datum and unit against the original; then read the target text for inadvertent safety promises.

Step 11: Give authoritative follow-up routes

Include official tide table links and notices to mariners for real decisions, while making clear that an educational translation is not a navigational instruction.

Twenty-nine worked translation cases

These mini-records and values are fictional educational examples, not real tide predictions, station advisories or instructions for operating any vessel. Each demonstrates how a datum, station, time, unit, event or qualification can change the meaning of otherwise identical numbers.

Worked case 1: LAT and MLLW are not automatic equivalents

Illustrative source: Source A lists a height relative to LAT; Source B lists a value relative to MLLW.

Unsafe translation: Unsafe: Both figures refer to exactly the same zero.

Safer translation: Faithful: Preserve the explicit LAT and MLLW labels and compare values only after an authoritative datum relationship has been established.

Lowest Astronomical Tide and Mean Lower Low Water arise from different definitions. Depending on location they may differ. A translation that suppresses these labels can create a false water-level discrepancy or an incorrect inference about clearance. The official station or chart metadata, not generic glossary intuition, controls any transformation.

Check the complete label before approving the text. In this example, identify the source station, vertical plane, physical quantity, relevant time and uncertainty. A reviewer should be able to reconstruct the original tabular row from the final target-language sentence. If the translation creates a promised clearance or a universal tide prediction that the source never made, narrow the claim and restore the missing field.

Worked case 2: Height of tide versus channel depth

Illustrative source: Source: High water 2.6 m above chart datum at Station A.

Unsafe translation: Unsafe: Every channel at this port has 2.6 m depth.

Safer translation: Faithful: Predicted high-water height at Station A is 2.6 m above the stated chart datum.

The figure is a level relative to a reference plane, not the depth to the bottom. Actual channel depth depends on soundings, local conditions and appropriate datum alignment. A high tide can raise water relative to the chart datum without making the tide-table height a statement about every berth.

Worked case 3: Negative low-water height

Illustrative source: Source: Low water −0.3 m relative to MLLW.

Unsafe translation: Unsafe: The sea has an impossible negative depth.

Safer translation: Faithful: Predicted low-water level is 0.3 m below the MLLW reference.

Negative heights are meaningful when a reference level is exceeded downward. A translator should retain the minus sign, units and datum without implying that the physical water depth itself is negative. The relevant water column is another quantity.

Worked case 4: Station code in a headline

Illustrative source: Source: NOAA station 9414525 with local prediction data.

Unsafe translation: Unsafe: Delete the code and call the forecast representative of all California.

Safer translation: Faithful: Retain the station identifier and its published location in the translated heading.

Station identifiers allow readers to reconnect a translation to the correct prediction and resolve nearby similarly named places. Removing an apparently unimportant numeric code can erase the only reliable path back to the issuing dataset.

Worked case 5: Secondary port and standard port

Illustrative source: Source: Secondary Port B uses designated Standard Port A plus official corrections.

Unsafe translation: Unsafe: The raw high water at Port A is the exact high water at Port B.

Safer translation: Faithful: Predictions for Port B are derived from the designated standard-port values using the supplied official correction method.

Standard-port records and secondary-port results are distinct despite their connection. Time, amplitude and reference-level effects may vary. The translator must retain the relationship rather than copying a convenient nearby value directly into the target port’s row.

Worked case 6: Negative timing difference

Illustrative source: Source: Secondary-port high water occurs 18 minutes earlier than standard-port high water.

Unsafe translation: Unsafe: Add 18 minutes to the standard-port time.

Safer translation: Faithful: Apply a minus-18-minute timing correction as specified by the table.

A negative time difference means earlier, not later, under the referenced convention. In a printed table, the minus sign may be small or detached from the unit; preserving it is essential. The date must also be checked if the shift crosses midnight.

Worked case 7: Tidal-height correction is not always a simple offset

Illustrative source: Source: A secondary-port calculation uses a tidal-range ratio and prescribed reference levels.

Unsafe translation: Unsafe: Simply subtract 0.2 m from every high and low water.

Safer translation: Faithful: Use the specific tidal-height procedure defined for the secondary port and its tidal regime.

Official methods can involve range ratios, mean levels or different diurnal characteristics. A casual additive correction that sounds intuitive can be wrong. A translator is responsible for preserving the procedure and its signs, not replacing it with a guessed arithmetic shortcut.

Worked case 8: Standard time versus daylight saving

Illustrative source: Source: AHO predictions shown in local standard time; a local notice uses daylight-saving clock time.

Unsafe translation: Unsafe: Both times must be displayed identically without labels.

Safer translation: Faithful: Preserve the source time convention and, if adding a daylight-saving conversion, label the converted clock time separately.

The time base is part of the data. Two documents can describe the same high water with clocks differing by an hour, and the date can shift around midnight. A target-language table should identify whether a conversion has been performed rather than silently substituting a contemporary local clock.

Worked case 9: UTC conversion crosses a day

Illustrative source: Source: Event 23:40 UTC on 12 June; local offset +02:00.

Unsafe translation: Unsafe: Local high water is 01:40 on 12 June.

Safer translation: Faithful: Under the stated offset, local time is 01:40 on 13 June.

Date and clock conversion must be handled together. Many translation errors occur when the hour is adjusted but the calendar day remains unchanged. The target time should be checked against the station’s specified time convention, especially around time-zone transitions.

Worked case 10: Metres and feet

Illustrative source: Source: Tidal height 1.5 m, datum unchanged.

Unsafe translation: Unsafe: Height is 1.5 feet.

Safer translation: Faithful: Height is 1.5 m; approximately 4.92 ft if a supplementary conversion is explicitly useful.

Unit swapping without arithmetic creates a factor-of-three error. In a translated table, keep the source value and unit prominent. If a target audience needs the other unit, provide a separately labelled rounded conversion and do not pretend the source used that value.

Worked case 11: Tidal range versus height

Illustrative source: Source: High water 3.5 m and low water 0.8 m above a common datum.

Unsafe translation: Unsafe: High tide depth is 2.7 m.

Safer translation: Faithful: The example tidal range between these levels is 2.7 m; high-water height remains 3.5 m above the datum.

Range is a difference, not an absolute height or a charted depth. Its numerical value may resemble an individual height in another table; the descriptive field controls the meaning. Do not drop the reference conditions when quoting the calculation.

Worked case 12: Slack water versus low water

Illustrative source: Source: Tidal-stream table indicates slack water at 09:30; tide-height table lists low water at 08:45.

Unsafe translation: Unsafe: Slack water and low water always happen at the same time.

Safer translation: Faithful: Slack water is a stream condition in the specified reference, distinct from the low-water level event.

Stream reversals and water-level turning points need not coincide at every location. Treat stream predictions as a separate product with a place, direction, reference time and method. The target language should not simplify both to a single ‘tide stops’ phrase.

Worked case 13: Ebb stream and ebbing water level

Illustrative source: Source: Ebb stream 2 knots to the southwest at the reference location.

Unsafe translation: Unsafe: Sea level falls at a rate of 2 metres per hour.

Safer translation: Faithful: The predicted ebb tidal stream is approximately 2 knots towards the stated direction.

Knots describe horizontal speed, not the vertical rate of water-level change. The word ebb may appear in both stream and level contexts, but the quantity and unit disambiguate its meaning. Preserve the direction convention specified by the source.

Worked case 14: Tidal-stream direction versus wind

Illustrative source: Source: Stream setting 210 degrees true, speed 1.8 knots.

Unsafe translation: Unsafe: Wind will blow from 210 degrees at 1.8 metres per second.

Safer translation: Faithful: Tidal-stream flow direction is 210 degrees true at the given reference and 1.8 knots.

A tidal stream and wind are different physical processes with different direction conventions. True and magnetic bearings may also differ. Do not replace a stream rose with a meteorological wind rose simply because both show arrows and numbers.

Worked case 15: Predicted versus observed level

Illustrative source: Source: Predicted 2.1 m; gauge observed 2.4 m at a comparable time and datum.

Unsafe translation: Unsafe: The prediction was 2.4 m.

Safer translation: Faithful: The prediction was 2.1 m; the reported observation was 2.4 m under the stated comparison conditions.

Weather and other factors can produce a difference between astronomical prediction and actual water level. The translator should keep predicted and observed in separate rows, confirm that their datums align, and avoid calling the difference a verified storm-surge height without source justification.

Worked case 16: Weather anomaly not included

Illustrative source: Source: Astronomical table excludes short-term wind and pressure effects.

Unsafe translation: Unsafe: The predicted level guarantees the exact water level.

Safer translation: Faithful: The prediction is astronomical and may differ from actual water level because of weather and local conditions.

A tide table is not a complete forecast of every forcing on the coast. Translators should preserve warnings on atmospheric pressure, strong winds and local fluctuations. A number becomes misleading when its limitations disappear from the target-language display.

Worked case 17: Different prediction years

Illustrative source: Source: Tables for 2025 and 2026 with different dates and hourly entries.

Unsafe translation: Unsafe: A valid time from the earlier year’s table can be reused this year.

Safer translation: Faithful: Each predicted event belongs to its specified calendar date and publication year.

Tide times change daily; they are not reusable timetables. The translation must keep date and source edition as structured data, particularly when a printed page is copied into an evergreen website. Encourage checking the current official issue.

Worked case 18: Chart sounding and height of tide

Illustrative source: Source: Charted depth 4.0 m and predicted height 1.2 m above matching chart datum.

Unsafe translation: Unsafe: This guarantees a safe 5.2 m clearance for every ship.

Safer translation: Faithful: A simplified datum-aligned arithmetic example gives a nominal water depth of 5.2 m before considering other clearance and environmental factors.

Even when datums align, actual safe passage requires location-specific soundings, draught, squat, under-keel clearance policy, water-level departures, survey uncertainty and other navigational conditions. A translation must not turn introductory arithmetic into operational clearance advice.

Worked case 19: Bridge vertical clearance

Illustrative source: Source: Bridge clearance marked relative to a high-water reference; nearby soundings use a low-water datum.

Unsafe translation: Unsafe: Add the low-water tide height directly to bridge clearance.

Safer translation: Faithful: The clearance and tide-height references differ and must be interpreted using the relevant chart and official vertical datum information.

Vertical clearance above the vessel and water depth below it have different measurement relations to water level. A translator should retain the bridge datum and avoid importing a formula for under-keel depth into the overhead clearance problem.

Worked case 20: High water with two daily peaks

Illustrative source: Source: 04:50 high 2.4 m; 17:20 high 2.1 m.

Unsafe translation: Unsafe: Each day’s single high tide is 2.4 m.

Safer translation: Faithful: The table predicts two separate high-water events at their stated times and heights.

Semidiurnal regimes can show two highs, often unequal. Dropping a row to simplify the table deletes information rather than improving readability. The mobile layout should retain both events and dates even if it takes more vertical space.

Worked case 21: Diurnal tide case

Illustrative source: Source: A location has one principal high and one low event in a tidal day.

Unsafe translation: Unsafe: Automatically invent a second high and low using a generic six-hour rule.

Safer translation: Faithful: Preserve the actual published event pattern for that station.

Some coasts show diurnal or mixed tidal regimes. A translator should avoid using a universal visual template that assumes identical timing and number of events worldwide. The original table’s event structure is evidence.

Worked case 22: Spring tide mistaken for spring season

Illustrative source: Source: Spring tidal range expected during a late-autumn period.

Unsafe translation: Unsafe: These are tides caused by the spring season.

Safer translation: Faithful: Spring tides here refers to the larger-range astronomical tidal cycle, not the season.

The familiar word spring is a false friend for general readers. A concise explanation can prevent misunderstanding while retaining the technical label. Neap tides likewise describe smaller typical tidal ranges, not a geographic or calendar name.

Worked case 23: HAT and LAT reversed

Illustrative source: Source: Highest Astronomical Tide (HAT) and Lowest Astronomical Tide (LAT) are defined levels.

Unsafe translation: Unsafe: HAT means highest tide forecast this week; LAT means last afternoon tide.

Safer translation: Faithful: Expand the formal astronomical reference terms while preserving their abbreviations.

HAT and LAT identify astronomical reference levels over a relevant analysis context, not informal summaries of a day’s highest or lowest prediction. Misexpanding an acronym is worse than leaving it unexplained, because it gives readers a confidently false definition.

Worked case 24: MLLW and MHW labels

Illustrative source: Source: NOAA lists MLLW, MHW and MHHW on a station datum table.

Unsafe translation: Unsafe: All three mean average low tide.

Safer translation: Faithful: Use the recognised terms Mean Lower Low Water, Mean High Water and Mean Higher High Water, each as a separate station datum.

The differences are meaningful for NOAA’s reference-level calculations. Retain official abbreviations and definitions rather than paraphrasing distinct datums into one low-water label. Translation may require a short explanation for non-specialists.

Worked case 25: Hour-by-hour interpolation

Illustrative source: Source: A table lists 06:00 and 07:00 heights; 06:30 height is not explicitly given.

Unsafe translation: Unsafe: The missing value is necessarily the simple average.

Safer translation: Faithful: The intermediate height is not supplied; derive it only using the authority’s recommended interpolation or prediction service.

Tidal curves are not generally linear between high and low waters. Invented halfway values can be wrong. A translator should not fill blanks with an intuitive average unless the source itself provides that value or official method.

Worked case 26: Station-specific local warning

Illustrative source: Source: Prediction sheet warns that atmospheric pressure can affect local water levels.

Unsafe translation: Unsafe: Delete the caution to keep the translation short.

Safer translation: Faithful: Keep the notice and state that actual levels may differ under local atmospheric and meteorological conditions.

A caution note may be the most important qualifier for a reader considering practical application. Removing it is not a harmless layout edit. The translated table should attach source warnings to the relevant station and period.

Worked case 27: Publication corrected by notice to mariners

Illustrative source: Source: An updated tide-table edition incorporates a formal correction.

Unsafe translation: Unsafe: Quote the superseded page as though no update exists.

Safer translation: Faithful: Use the corrected official edition and identify the updated publication context.

Hydrographic publications are maintained. The translator should check whether the table has been amended and avoid treating an old screenshot as the highest-authority version. When describing historical data, mark it historical instead of implying current validity.

Worked case 28: Rounding tidal heights

Illustrative source: Source: Predicted level 0.08 m below datum shown to two decimals.

Unsafe translation: Unsafe: Round to 0 m and declare no difference.

Safer translation: Faithful: Preserve the source precision and negative sign unless a specified display rule requires otherwise.

Rounding may erase a small but meaningful level difference or change the sign near the datum. A translator should retain the source’s precision and never invent a navigational tolerance from an editorial rounding decision.

Worked case 29: Tidal level from chart datum versus land datum

Illustrative source: Source: Coastal water level above chart datum; nearby ground elevation above a national geodetic datum.

Unsafe translation: Unsafe: Both elevations can be compared directly without transformation.

Safer translation: Faithful: Identify the separate chart and terrestrial vertical datums, with no direct comparison until the official relationship is confirmed.

The same word elevation can appear on sea charts and land survey maps, but their reference surfaces may be different. An unlabelled comparison can distort flood-risk statements and coastal engineering figures. Preserve each datum and coordinate framework.

Failure modes: why fluent tide translations fail

1. Omitting chart datum

A predicted level without its vertical reference cannot be reliably compared to charted soundings. Preserve the datum even if the number is familiar.

Repair the original field rather than hiding the problem in a more elegant sentence. Check that the numerical claim still names its place, reference, event, time and applicable caveat. When a datum conversion or operational consequence would require expert judgement, stop at a faithful translation and leave that decision to the appropriate source and user.

2. Assuming LAT and MLLW are identical

Different official definitions can produce different reference planes. Only an appropriate official offset supports transformation.

3. Calling height a depth

A tide table predicts a level relative to a datum, not the channel’s seabed depth. Keep height, sounding and clearance separate.

4. Removing a negative sign

A negative predicted height is possible below the reference plane. The sign is numerical evidence, not an error to repair.

5. Mixing station locations

Nearby harbours may have different timings, levels and correction methods. Retain station code and reference port.

6. Converting time without date

A time-zone change can shift the calendar day. Check the entire timestamp and any daylight-saving convention.

7. Using one correction formula everywhere

Secondary-port computations depend on official table methods. Do not substitute informal addition for the published procedure.

8. Treating a prediction as observed

Astronomical predictions can differ from gauges and local weather-driven water levels. Preserve the evidence status.

9. Combining tidal range with tide height

Range is a high-to-low difference, not the water level measured from chart datum.

10. Confusing tidal stream with tide level

A current speed in knots is not a water-level rate in metres per hour. Preserve the direction and reference.

11. Ignoring chart publication updates

Corrected editions and Notices to Mariners can change tables. Record source year and update status.

12. Inventing a safe depth

No educational chart-depth example guarantees clearance. Avoid operational promises and route practical decisions to qualified current sources.

13. Losing bridge-clearance datum

Overhead clearance can use a different vertical reference from seabed soundings. Retain the specific legend.

14. Simplifying spring tides into a season

Spring tides refer to an astronomical tidal pattern, not the time of year. Explain without mistranslating.

15. Over-rounding near zero

Small negative or positive levels and their precision can matter in interpreting the data. Preserve source precision.

Practice and transfer: test your understanding

Exercise 1

A predicted high water is 2.1 m above LAT. Is the water 2.1 m deep at every berth?

Model reasoning: No. The value is a water level relative to the stated reference. Seabed soundings and other conditions are separate. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 2

One table uses LAT and another uses MLLW. Are the raw height figures necessarily comparable?

Model reasoning: No. Confirm the official datum relationship and station before any comparison. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 3

A secondary-port time correction reads −20 minutes. What is the literal sign’s effect?

Model reasoning: Under the published convention it means twenty minutes earlier; check the date if the result crosses midnight. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 4

The table predicts low water −0.15 m above MLLW. Does the sign indicate an impossible observation?

Model reasoning: No. It represents a level below the datum; keep the sign and units. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 5

A tide event is 23:30 UTC and the local clock is UTC+2. What local date applies?

Model reasoning: The corresponding local time is 01:30 the following calendar day under that fixed offset. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 6

Can slack water be replaced with the phrase low tide?

Model reasoning: No. Tidal current and water-level turning points can occur at different times. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 7

A user asks you to turn a predicted height and charted sounding into guaranteed clearance. What should you do?

Model reasoning: Keep the source measurements and explain that an operational clearance requires a qualified, condition-specific assessment. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 8

A table labels 1.6 knots ebb. Can you call that 1.6 metres of outgoing water?

Model reasoning: No. Knots indicate current speed; ebb is the direction or phase descriptor in the tidal-stream context. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 9

An app lists actual gauge reading above prediction after strong winds. Does that mean the tide-table prediction itself was that higher value?

Model reasoning: No. Keep observed and predicted as separate series and verify common datum and time. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Exercise 10

The primary publication was corrected after printing. Which edition should readers consult?

Model reasoning: The current corrected authoritative publication for operational decisions; identify the source edition and correction in the translation. The transferable practice is to name the station, quantity, datum, unit and time before choosing a fluent phrase. Technical translation often fails because a common word such as height, depth or level is substituted before the source measurement has been properly identified.

Frequently asked questions

What is chart datum in a tide table?

It is the defined vertical reference against which charted depths and relevant water levels are expressed. Confirm its local definition and relationship to the published prediction datum.

Is Lowest Astronomical Tide the same as Mean Lower Low Water?

No. LAT and MLLW have different technical definitions. They may be related through a station-specific official datum transformation but should not be assumed equal.

What does a negative tide height mean?

A predicted water level below the selected reference datum. It does not literally mean the seawater has negative physical depth.

What is the difference between tide height and water depth?

Tide height is a water level relative to a datum; water depth also depends on the seabed elevation at the location and other conditions.

How do I translate a high-water time?

Keep the station, date, original clock convention, time zone or standard-time label and event classification together.

Why do secondary ports need corrections?

Local tides can differ from the standard reference port in time and amplitude. Apply only the official published calculation for that port.

Does a tide table include storm surge and wind effects?

Astronomical predictions generally do not fully predict weather-driven departures. Read the local authority’s cautions and compare to observations where appropriate.

Can tide tables be used to guarantee under-keel clearance?

No. Actual clearance requires multiple current, location-specific and vessel-specific factors; an educational translation is not an operational decision tool.

Is a spring tide something that happens in spring?

No. In tidal terminology a spring tide is a larger-range phase associated with astronomical alignments, not the season.

Are tidal streams the same as water levels?

No. Streams describe horizontal movement with speeds and directions, while tide-height tables describe vertical water level.

Why might NOAA show heights using MLLW?

MLLW is a common reference datum for NOAA tide prediction products. Preserve the source label and read station-specific documentation.

What if an official table uses feet but the translated audience uses metres?

Keep the source value and unit, and if useful add a separate correctly calculated and clearly labelled conversion.

Do high and low water happen at the same times every day?

No. Tidal patterns vary by place and date, and stations may have different numbers or timings of relevant events.

How should a translated table show corrections to port times?

Keep the standard station, secondary station, sign convention, applicable corrections and resulting date and time distinguishable.

Where can I learn which source is authoritative?

Begin with the national hydrographic office or official NOAA station listing as appropriate, then check current notices and official chart metadata.

Where to learn next

NAVTEX navigational warning translation — explore a related but distinct canonical reading task and return to this page when interpreting tide-table fields.

Oceanographic cruise logs and CTD records — explore a related but distinct canonical reading task and return to this page when interpreting tide-table fields.

Flood hazard maps, probability and elevations — explore a related but distinct canonical reading task and return to this page when interpreting tide-table fields.

Translate meaning rather than just words — explore a related but distinct canonical reading task and return to this page when interpreting tide-table fields.

Vocabulary Learning Hub — explore a related but distinct canonical reading task and return to this page when interpreting tide-table fields.

How English Works — explore a related but distinct canonical reading task and return to this page when interpreting tide-table fields.

Official references, editions and scope

Australian Hydrographic Office: Australian National Tide Tables (AHP11) — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

Australian Hydrographic Office: secondary-port tide calculation worksheet — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

Australian Hydrographic Office: tidal information and chart-datum support — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

NOAA Tides & Currents: station datums and their names — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

NOAA Tides & Currents: tide predictions and station/time conventions — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

Australian Hydrographic Office: notices to mariners and corrections — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

Google Search Central: Article structured data — consult the original documentation for station-specific definitions, sign conventions, updated editions and authoritative limits.

This world-facing educational article explains how to translate and read published tide-prediction terminology. It is not a live tide forecast, safe-navigation guide, vessel clearance assessment or replacement for current official charts, notices, pilotage rules or professional advice. All illustrative numbers and cases are fictional.

Top Ways to Translate Correctly | Translate Tide Tables, Chart Datum, LAT and MLLW Predictions Without Misstating Water Depth