Tips From The Text “Tides and Currents”

Sailing Tips Come From Bareboat Cruising Made Easy, the Official Manual for the ASA Bareboat Cruising Course. (ASA 104)

This weekend while sailing out of Santa Monica Bay, I came close to running aground at low tide. In my defense, recent storms have drastically changed the depth of the north channel entrance in Marina Del Rey, California. This event did have me thinking about brushing up on tide tables.

Tides are the vertical movement of water caused by the gravitational fields of the sun and the moon acting on bodies of water. Tidal Currents are the result of water moving between high and low tides.

Depending on where you sail your experience with tides and currents will vary. Sailors in San Francisco Bay regularly sail with a fast-moving current that dictates even the most mundane of sail plans. Have you ever seen the tide in the Bay of Fundy?

While you most likely will not have to deal with such a dramatic tidal current as of the Bay of Fundy it is important that you understand tides and currents when planning your sailing itinerary. ASA 104 Bareboat Cruising explains tides and currents.

Tip:  Wind Blowing against tide (or any current) can create uncomfortable seas. To keep the fun factor high (and the decks dry) try to avoid encountering such situations by planning your passages carefully with regard to tides. 

Tidal data are predictions based on years of observations. On any particular day, weather or other phenomena can cause variations(sometimes significant ones) in water levels. For example, atmospheric pressure can affect water levels.

Terms:

• Tidal Range: The difference in height between the water level at low tide and high tide.

• Spring Tides: These tides occur when the full moon and new moon are in alignment with the sun and the earth. These combined gravitational forces produce the highest high tides and the lowest low tides in the lunar month.

• Neap Tides: These tides occur at half moon when the sun and moon are pulling at right angles and produce lower high tides and higher low tides.

• Tide Tables: These tables list the times of high and low tides and the height of each tide above a declared datum

Tidbits: 

Working With Tides

In some parts of the world, tidal ranges are so great that they dictate mariners’ comings and goings. In these regions, study the tide tables when planning departures and arrivals and also consult current charts to time passages as closely as possible to when currents are most favorable.  

Try to choose departure times so as well as having adequate depth, you sail with the current (or at least not directly against it.)

Non-Tidal Currents

Separate from the tidal cycle, currents are present in all of the world’s oceans. Driven by constant prevailing winds, constrained by continents and given rotation by the Coriolis force, they form gyres that circulate around the ocean basins.

One of the best-known currents is the gulf stream that flows (at speeds up to 4 knots) from the Gulf of Mexico, northeastward past the US East Coast to Cape Hatteras, and across the Atlantic to Europe. Together with the Equatorial Current that flows from Africa through the Eastern Caribbean, it is part of the North Atlantic Gyre.

All of these tips come from Bareboat Cruising Made Easy, the Official Manual for the ASA Basic Coastal Cruising Course.

Resource: NOAA

The National Oceanic and Atmospheric Administration (NOAA) has various tools and information on tides and tide predictions. You can create annual tide predictions for over 3000 locations around the United States. 

NOAA website: tidesandcurrents.noaa.gov/index.html

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ASA 104 – Bareboat Cruising

Able to skipper a sloop-rigged, auxiliary powered keelboat of approximately 30 to 45 feet in length during a multi-day cruise upon inland or coastal waters in moderate to heavy winds (up to 30 knots) and sea conditions. Knowledge of provisioning, galley operations, boat systems, auxiliary engine operation, routine maintenance procedures, advanced sail trim, coastal navigation including basic chart plotting and GPS operation, multiple-anchor mooring, docking, health & safety, emergency operations, weather interpretation, and dinghy/tender operation.