Tides & Weather: What Boaters Need to Know

Tips for Navigating the Ocean’s Tides in Your Boat or Yacht

An essential part of safely cruising the ocean on your yacht or boat is knowing about the tide levels of the areas you’ll be cruising. Even if you’ve chartered the same passage countless times, it’s good to have access to tide tables and knowledge of what types of things affect tide levels.

The topic of tides is covered in safe boating courses, but if it’s been awhile, check out our brief overview of what all boaters need to know about tides.

Key Facts About Tides

Tides are one of the universe’s most fascinating forces – for boaters and non-boaters alike. Simply put, tides can be defined as the rising and falling of sea levels. Here are some more key facts about tides:

During a changing tide, the ocean’s waters are either being pulled towards the poles of the earth or pushed towards the equator. It’s all based on the position and gravitational pull of the moon, the sun, and the rotation of the earth.
Along most of the earth’s coasts, tides rise and fall (go from low to high and high to low) two times per day, meaning the tide changes 4 times per day – approximately every 6 hours. These are known as semidiurnal tides.
In just a few places around the world, the tide rises and falls only once per day. These are known as diurnal tides.
In some places, the first daily high tide is a lot higher than the day’s second high tide, and these are called mixed tides.
Depending on the position of the moon and the sun, there are two types of tides that can occur. A spring tide appears when the moon and the sun are aligned with the earth. A neap tide is formed when the moon is at a right angle to the line between the earth and the sun.
When the moon is closest to the earth, tides are higher than usual. When the moon is farthest away from the earth, tides are lower.
Tides are influenced by the geological differences in the shape of the ocean floor as well as the shape and dynamics of the coastline – they are not consistent across different areas.
A narrowing inlet may increase the speed of the tidal currents, while islands in the open ocean don’t usually experience significant tides.
Wind and other weather conditions can have an effect on tides. For example, high-pressure systems depress sea levels, while low-pressure systems produce tides higher than predicted.

Why Do Boaters Need to Care About the Tide?

Tides essentially affect the height of the water you’re cruising on, which is subject to change based on the tide. The changing tides can cause several feet of change in the water depth (sea level), so it’s important boaters are aware of the tide’s direction (is it coming or going?) and timing whenever they are boating. Even if it seems like a minuscule level of water depth change, tides can affect things like:

how much rope you need to tie onto a dock
how much clearance you have to sail underneath a bridge
whether or not your boat bottoms out on a shoal where just a few hours ago the water was deep enough to cruise across
your ability or desire to cruise into a harbour where you might be moored, anchored, or docked for several hours at a time
how long you can safely stay anchored somewhere. If you underestimate the tide, if the tide goes out, your yacht might just end up beached in place until the next tide rolls in. If the tide rolls in and your anchor isn’t fully dug into the seabed, your boat is likely going to drift.
when you’ll be able to pass narrow channels. For certain channels, boaters need to plan their passages around the direction of the tidal flow. In some locales, it may be impossible to travel against the current.

Get Familiar with Tide Tables

Always familiarize yourself with the seascape you’ll be navigating and try to have access to a tide chart whenever you’re out on the water. Tide charts or tables help boaters predict the sea levels of any coastal region at any time of day. Learn how to read them (consult your safe boating books for a refresher) and you’re far less likely to experience any of the issues as noted above.

In Canada, tide tables are published by the Canadian Hydrographic Service. Each tide table shows the predicted times and heights of the high and low waters that are associated with the vertical movement of the tide. They are available in three formats – table, graphic, and text – for more than 700 hundred stations in Canada.

Tide tables are also available on third-party websites like tide-forecast.com, as well as local newspapers, television news, and radio news outlets. No matter where you find your tide tables, look for three important details on one, including the time of high tide, the time of low tide, and the heights of each. For the times in between, you’ll need to use the Rule of Twelfths to best guestimate the sea level based on the stated low and high tides.

Rule of Twelfths

Using the rule of twelfths is a good way to approximate tidal levels if you don’t have access to a complete guide that lists tide levels by the hour. For boaters on the go, this formula is all you need. The basis behind the rule of twelfths is that it takes a period of about six-plus hours for tides to get from low to high tide and vice versa. (Lunar high tides occur every 12 hours and 25 minutes, which means that it takes 6 hours and 12.5 minutes to go from high tide to low tide or vice versa.)

Therefore, the difference between high tide and low tide (the range of tides) can be divided into 1/12th units. During the first hour after low tide, the water level rises by one-twelfth of the tidal range, in the second-hour two-twelfths, and so on. Using this calculation, in the third and fourth hour there is an abundance of tidal movement, but in the first and sixth hour, there is much less.

When You Don’t Have Access to a Tide Schedule

If you find yourself out on the water with no knowledge of the tide schedule for the day, all is not lost! Simply look to the water at the shoreline. The tidal current is actually visible – watch closely and you’ll soon see the sea either flowing towards or ebbing away from the land. You can also follow what other boaters appear to be doing, and tune in to your VHF radio for advice on tides.

Getting to know the tides isn’t difficult once you get the hang of reading tide charts and seeing the tide for yourself. Unlike the weather, and whether or not the fish are biting, tides are a relatively stable, predictable part about boating. They change slightly as the moon changes – and slightly more depending on the weather – but for the most part, tides are a constant, integral part of boating. Whenever you are out boating in unfamiliar locations, try and learn as much as possible about the area, which we believe is all part of the fun!

At Van Isle Marina – your go-to boat marina in the Pacific Northwest – we regularly post snapshots of Sidney, BC’s tide schedules on our Twitter page. Our staff love to help our fellow boaters learn about all the ins and outs of boating, including all about tides and weather patterns. Give us a call, come see our boats for sale, or pull up your boat to learn more about why so many people love to moor with us.