NOAA Charts, Tides & Coast Pilot

Prerequisites

ASA 101 and ASA 103, or equivalent: you can read a basic chart and know latitude and longitude.
Familiarity with US buoyage (red right returning).
A calculator, or comfort with simple multiplication and division.

Learning Objectives

This lesson covers the US publications and tools behind the ASA 105 Coastal Navigation standard. By the end of it you will be able to:

Explain what replaced NOAA's paper charts and how to get a chart to print.
Use US Chart No. 1 to look up a chart symbol.
Explain what MLLW means for the depths on a US chart.
Read a NOAA tidal current prediction: maximum flood, maximum ebb and slack.
Say what the Coast Pilot, Light List and Local Notice to Mariners contain and where to find them now.
Convert between true, magnetic and compass courses.
Solve speed, time and distance problems.

The End of NOAA Paper Charts

For nearly two centuries, American sailors navigated on NOAA (and before that, Coast and Geodetic Survey) paper charts. That era is over. NOAA ran a programme called the "raster sunset", and it finished in December 2024 with the cancellation of the last of its 1,007 paper charts. NOAA now says plainly: it "no longer produces traditional paper nautical charts."

What exists now:

Electronic Navigational Charts (ENCs): NOAA's main chart product. They are vector data that your chartplotter, tablet app or OpenCPN can display. ENCs downloaded directly from NOAA Coast Survey are free.
NOAA Custom Chart (NCC): a free web tool that turns ENC data into a printable PDF chart. You choose the area, scale and paper size, and depths in feet, fathoms or metres. NCC charts are drawn on a Mercator projection referenced to WGS 84. They have no chart number, so Local Notices to Mariners are not issued against them. Re-create the chart when the ENC is updated.

Canceled charts do not meet carriage rules for regulated vessels and should not be used to navigate. The Coast Guard has allowed US commercial vessels to use ENCs instead of paper since 2016. For a recreational sailor, the practical lesson is to keep a recent printed NCC or commercial chart aboard as a backup to your electronics, and keep your ENCs up to date.

US Chart No. 1

Chart No. 1 is not a chart but a book: "The Symbol Legend for U.S. Nautical Chart Products", published by NOAA and the National Geospatial-Intelligence Agency. It shows every symbol and abbreviation used on paper-style charts (including NOAA Custom Charts) and on ENCs displayed electronically. It is free to download. The current edition is the 13th.

Some useful entries:

A single black anchor symbol is an anchorage of unspecified size that is not regulated.
Abbreviations on charted lights (such as Fl G 4s) and bottom types (S sand, M mud, Rk rock) are all explained.

When you meet a symbol on a chart you do not recognise, look it up. Guessing is how sailors anchor in a cable area.

Depths and the Chart Datum (MLLW)

Depths on US charts are measured from Mean Lower Low Water (MLLW). NOAA defines it as "the average of the lower low water height of each tidal day" over the National Tidal Datum Epoch (a 19-year period). Most US coasts have two low tides a day, usually of different heights. MLLW is the average of the lower of the two.

Because it is an average, the water can fall below MLLW. On some low tides, especially around a new or full moon or with strong offshore winds, the tide table shows a negative height, such as –0.8 ft. That means there is 0.8 ft less water than charted. If you are crossing a bar with little to spare, check for minus tides.

Note the difference from British practice: UK charts use Lowest Astronomical Tide, which is lower than MLLW, so charted depths there are rarely undercut.

Tidal Currents

NOAA Tides & Currents (tidesandcurrents.noaa.gov) publishes current predictions for every official current station. For each day they give the time and speed of maximum flood, maximum ebb and slack water.

Flood: the current flowing in towards the land, with the rising tide.
Ebb: the current flowing out to sea.
Maximum flood or ebb: the time of greatest speed in that direction.
Slack: the period when the current is weak while it turns. It is the best time to go through a narrow pass or dock in a strong-current marina.

Stations are either harmonic (full predictions) or subordinate, where predictions come from a nearby reference station with time and speed corrections applied.

A key point that surprises many sailors: slack water does not always come at high or low tide. In many US bays and rivers the times are hours apart. Some currents are driven by the difference in water height between two ends of a channel (NOAA calls these hydraulic currents). The current is strongest when the height difference is greatest. Always use the current predictions for current, not the tide tables.

The Coast Pilot

Charts cannot show everything. The United States Coast Pilot fills the gap. It is published in ten volumes covering US waters, with information "difficult to portray on a nautical chart": channel descriptions, anchorages, currents, local dangers, port facilities and Federal navigation regulations.

All volumes are free to download from NOAA. Updates are published weekly on NOAA's website only. They are no longer included in the Notices to Mariners. Read the relevant chapter before visiting a new harbour.

The Light List and Local Notice to Mariners

The US Coast Guard publishes two key resources through its Navigation Center (NAVCEN):

Light List: a description of every Coast Guard aid to navigation, with its position, light characteristic, height, range and structure. It is updated every 24 hours online, and a PDF is published once a year.
Local Notice to Mariners (LNM): changes to aids to navigation, new hazards, dredging, construction, marine events and other safety information for each Coast Guard district. The LNM used to be a weekly booklet. Since late 2024 it has been an online, map-based service refreshed every 15 minutes. You can select your area and print the notices.

Before a passage, check the LNM for your area. A buoy that has moved, a new bridge construction zone or a missing light is all listed there.

Compass Conversion: TVMDC

Courses on a chart are true (measured from true north). Your compass is affected by variation (the difference between true and magnetic north at that place, printed on the compass rose) and deviation (the error caused by the boat's own metal and electrics, from the deviation card). The ASA uses the mnemonic:

True Variation Magnetic Deviation Compass, remembered as "True Virtue Makes Dull Company" (some say "Can Dead Men Vote Twice", read the other way).

Going from true to compass, add westerly error and subtract easterly ("east is least, west is best" when going from compass to true).

Example: the chart gives a true course of 045°T. The compass rose shows variation 14° W. Deviation on this heading is 2° E.

True 045° + 14° W = 059° Magnetic.
Magnetic 059° – 2° E = 057° Compass.

Steer 057° by the compass.

Variation on a compass rose changes slowly each year, and the rose shows the annual change. Update it for the current year.

Speed, Time and Distance: 60 D Street

Dead reckoning relies on one formula: Distance = Speed × Time. With time in minutes, the ASA writes it as:

60 D = S T ("60 D Street")

D = distance in nautical miles
S = speed in knots
T = time in minutes

Rearranged:

D = S × T ÷ 60
S = 60 × D ÷ T
T = 60 × D ÷ S

Example: at 6 knots, how far do you go in 40 minutes? D = 6 × 40 ÷ 60 = 4 nautical miles. How long to cover 9 miles at 5 knots? T = 60 × 9 ÷ 5 = 108 minutes, or 1 hour 48 minutes.

Worked Example: Planning an Afternoon Entrance

You plan to enter a bay through a narrow inlet 12 miles away. You sail at 5 knots.

Time: T = 60 × 12 ÷ 5 = 144 minutes, so 2 h 24 min.
Current: the NOAA current prediction for the inlet shows maximum ebb of 2.8 knots at 14:10 and slack before flood at 16:50. Leaving at 14:00 would put you at the inlet at 16:24, still pushing a dying ebb. Leave at 14:30 to arrive near slack at 16:54.
Depth: the chart shows 8 ft in the channel at MLLW. The tide table shows a low of –0.5 ft today, so the least depth could be 7.5 ft. Your draft is 5 ft, which is fine.
Course: the chart course is 312°T. Variation is 11° W and deviation 3° W: 312 + 11 = 323°M, then 323 + 3 = 326°C.
Notices: the LNM shows the red "4" buoy at the inlet is off station. The Coast Pilot warns the bar breaks in strong onshore winds. Note both on your plan.

Common Mistakes

Assuming slack water happens at high or low tide.
Forgetting that a minus tide puts less water under you than the chart shows.
Mixing up the direction of the variation correction (adding easterly going true to compass).
Using an outdated or canceled chart without checking the LNM.
Using hours instead of minutes in 60 D = S T.
Using a variation figure that has not been updated for the year.

Summary

NOAA ended its paper charts in 2024. Use free ENCs, and print a NOAA Custom Chart as a backup.
Chart No. 1 explains every symbol. US depths are referred to MLLW, and minus tides do occur.
Use NOAA current predictions for maximum flood, ebb and slack, which can be hours from high and low water.
The Coast Pilot gives what charts cannot. The Light List and LNM keep aids to navigation current.
True to compass: T V M D C, add west, subtract east.
60 D = S T, with time in minutes.

Check Your Understanding

What is the datum for depths on US charts? Mean Lower Low Water (MLLW).
The chart shows 6 ft and the tide table gives –1.0 ft. What is the least depth? 5 ft.
Why use current predictions rather than tide times to plan a pass? Slack and maximum current can be hours away from high and low tide.
Course 090°T, variation 15° E, deviation 2° W. What compass course? 090 – 15 = 075°M; 075 + 2 = 077°C.
How far do you travel in 25 minutes at 7.2 knots? 7.2 × 25 ÷ 60 = 3 nautical miles.
Where do you find out that a buoy has been moved? The Coast Guard's Local Notice to Mariners.

Sources

https://nauticalcharts.noaa.gov/charts/farewell-to-traditional-nautical-charts.html
https://nauticalcharts.noaa.gov/publications/us-chart-1.html
https://nauticalcharts.noaa.gov/learn/faq.html
https://nauticalcharts.noaa.gov/publications/coast-pilot/
https://tidesandcurrents.noaa.gov/currents_info.html
https://tidesandcurrents.noaa.gov/glossary.html
https://www.navcen.uscg.gov/LNM-and-LL-app-frequently-asked-questions
https://americansailing.com/starpath/asa-105-coastal-navigation/