Tidal Basics for Paddling
When paddling on the ocean, there are several different environmental facts that need to be considered. One of these is the tides. How much the changing tide affects your paddling trip depends on whether you’re paddling relatively open water as opposed to a more enclosed area, such as a bay, harbor, or tidal estuary. It also depends on the phase of the moon, and to a lesser extend, where Earth is in its orbit around the sun. The complexities of tides can get fairly intricate, but we can aid our paddling a good deal just by carrying a broad set of information with us. What follows is intended as a broad stroke view of tides, and is intentionally simplified to be such. While there is an endless amount more to learn about coastal navigation and dealing with tides, this gives a good starting point for those just venturing into paddling in the ocean.
Tidal Timing
As the moon orbits the earth, it generates tidal forces resulting in, for most spots on Earth, two high tides and two low tides each day. There are roughly six hours between high and low tide. Since it is not exact, the timing of the tides advances forward a little under an hour each day. So, if high tide is at noon today, you might expect that tomorrow it will be somewhere around 12:52pm. .
Tidal Information Resources
In areas where the tide is constricted by land masses, there will be a tidal current, which will be strongest during the middle of the tide (about three hours after high or low tide, albeit with some variation).When planning a paddling trip where tides will be a significant factor, you can look at a nautical chart to get a general sense of where the currents will flow and in what direction, and then look at a tide chart/graph/app to know if the tide will be gaining strength or losing strength over the course of your paddle. You can find nautical charts online in several places, but NOAA is a good overall resource. For a tide app, we like Tide Graph Pro, but there are many to choose from.
Rough Rules for Gauging Tidal Current Strength
To help gain a sense of the strength of the tide, we use the 50-90 rule. At high tide and low tide, there is virtually no water moving. With the tide broken up into roughly six hours, and starting at either tide (but we'll take low as an example), then at the end of the first hour, the tide is moving at 50% of its max flow. At the end of the second hour, it's at 90% of its max flow, and at the end of three hours, which is also mid tide, it's at 100% of its max flow. At the end of the fourth, fifth, and sixth hours, the tide is at 90%, 50%, and 0% respectively.
Why is the Max Speed of the Tidal Current Different From Day to Day?
The max speed is largely dependent on the tidal exchange, which is the difference in height between high tide and low tide (as measured against mean low water, which is 0 ft. Note, low tide is sometimes above this average, which is called a plus tide, and sometimes below, which is called a minus tide.)
The bigger the exchange, the more water will flow during the same six hours, and so the tidal flow (often measured in knots-nautical miles per hour, or kts) will be faster at all parts of the tide than a day with less of a tidal exchange. These roughly correspond to the phases of the moon, with new moons and full moons causing bigger tidal exchanges (also called Spring Tides), and half moons generating smaller tidal exchanges (also called Neap Tides). Knowing the speed of the max flow is helpful because you can then calculate what the flow will be at each hour mark. If the max flow is 4 kts, then for the middle two hours it will be flowing at a minimum of 90% of that, which is 3.6 kts. If you can only paddle at 3 kts, that would not be a great time to be paddling against the tide. However, it is sometimes enough just to know that within the middle two hours of the tide, the current will be flowing between 90 and 100% of its max flow.
When Do I Most Need to Be Concerned With Tidal Currents?
When paddling on the open ocean, what most newer paddlers experience as a “current” is actually wind-driven movement of the water, as opposed to tidal current. However, as mentioned previously, anytime we are in an area where the water is constricted, we will experience some amount of tidal current, and this will vary based on the amount of constriction, and amount of flow. In particular, when paddling in harbors and bays, we must be aware of deeper channels, which have a tendency to funnel the incoming or outgoing tide, generating a faster tidal current. Because the change in depth is underwater, we often don’t notice these changes until we are in the flow and find ourselves moving in a direction other than what we anticipated.
However, these areas often coincide with the boat channels, so if you are knowledgeable of how to read navigational aids (those red and green buoys you see on the water), you can often anticipate these faster moving sections. Additionally, looking at a chart, and knowing the point of the tide cycle you’re in, can greatly help you navigate these waters with ease.
