For many captains and crew, during our seminars, they tell us one of their biggest fears is bad weather. For them, bad weather can be a rough passage even with the sun shining. Wind blowing for hours can build steep and choppy seas, especially when the wind travels a considerable distance, pushing water as it goes. This distance is called fetch in the language of mariners.
I have learned the hard way about wind against current and the uncomfortable seas it can produce. Now I make it part of my planning for every long passage to calculate whether there is a wind against current condition that will produce large or uncomfortable seas.
(Photo (above): Courtesy of Jennifer and James Hamilton, M/V Dirona)
Safe and Comfortable Passage – Avoiding Wind Against Current
For help with your weather planning, print out our “Weather Checklist” from our Free Downloads page. Note up in the upper right corner, along with the date and time, look up the current in the area you will be cruising during the time frame of your passage. Is the current an ebb or a flood (with me or against me), and when does the current go to slack and turn.
I use our publication Ports and Passes – Tide and Current Guide to look up the currents, their projected speed, or the actual wind speed and sea state from buoy reports, and the forecasted time for slack when the current will turn from an ebb to a flood or vice a versus. I also note the phase of the moon. When the lunar cycle is at the point of a new moon or a full moon, I know the currents will be at their peak. During a half moon or within days of a half moon the currents will be diminished. I know that a tidal current cycle is approximately six hours to the next slack. With a semi-dinural tidal current, I can see whether I am transiting on the strongest current of the day, or the lesser.
Steps for Avoiding Wind and Current-Driven Seas and Uncomfortable Passages
- Look up the forecasted current and speed and the time of slack for the key areas you will be cruising through. Note a full moon or a new moon.
- Check the forecasted wind speed and direction. Better yet, check the buoy and lighthouse reports for the actual winds for a given area.
- If the wind has been blowing for hours at a speed of over 12-15 knots, over a long distance of two to four miles or more, there may be rough sea conditions. If a wind against current exists, consider delaying your departure until one hour or less before slack (currents will be 50% of the max value for that tidal cycle).
- If underway, consider a duck-in point to wait for the current to diminish. Even an hour may make a complete difference between rough seas and an acceptable passage.
Using the Weather Checklist
Next, gather weather information by noting the weather reporting stations for a route by consulting the map for this on page 56 in the 2018 Waggoner Guide.
Next, fill in the “Weather Checklist” form for the locations along your intended route. Then gather the weather data from the internet, via a phone call, or by listening to the weather on the WX VHF station for your area on the radio when you are aboard your boat.
For the best results, next, look up the current prediction and direction for the approximate times you will be passing through each area. Look for places where you will have a wind against current situation. Evaluate the wind speed and the fetch (distance the wind is traveling over the water). More than two miles and you will have a condition where a wind over 15-20 knots can create wind-driven waves amplified by the fetch. Then look at the forecast speed of the current. Even a small current flowing against the wind-driven waves can build to what is called square waves. There is no formula to determine the size of the waves, but you are now aware that there could be a problem.
Wind Against Current in Action
Last summer, I left Lagoon Cove, BC at sunrise to get an early start on a passage down Johnstone Strait with the intent of making it to Campbell River by the end of the day. After a quiet passage on Chatham and Havannah Channels, I broke out on to a calm Johnstone Strait for the most of the morning. Afternoon the typical winds started to pick up from the northwest funneling down Johnstone Strait. I was enjoying a flood tide current until it turned to an ebb, just north of Port Neville. Now the opposing current was slowing me down as I passed Fanny Island and the wind was against the current. The sea conditions quickly changed with green water coming over the bow. I knew it could only get worse in Race Passage.
This is all mapped out in Local Knowledge: A Skipper’s Reference, a valuable set of drawings and notes from our own Captain Kevin Monahan from his years of cruising this area as a commercial fisherman and Coast Guard officer. My ground speed slowed to about 3-4 knots through the water and winds were about 20 knots. What to do? I was going slow, it was rough and Kelsey Bay was the place to duck-in, dock the boat and take a walk. 90 minutes later you could see the waters were now calm and when I brought the boat out of Kelsey Bay, it was flat calm and the current had gone to slack and turning to a flood again. I missed the first slack at Seymour Narrows and decided to duck into Browns Bay when I arrived there for a 90-minute break. I took Seymour Narrows a little before slack and continued on to Campbell River after a long but comfortable day of cruising.
The rough sea conditions were not a surprise and I knew if I just sat it out in the comfort of Kelsey Bay, I could continue on a little later safely and comfortably. Earlier in my boating experience, I took green water over the bow on a rough passage not knowing that the conditions would change with the change in the tide and current.
This is not a unique condition for Johnstone Strait.
In the Puget Sound area, be aware of potential rough conditions when passing Deception Pass with the wind out of the west and an ebb current. Water is rushing out of Deception Pass and hitting the winds from the west causing steep choppy seas for up to 2-3 miles out from the Deception Pass Bridge.
Wind against the current is not a pleasant experience. With good planning, it will not be a surprise and with a few hours it will change and could even turn to flat seas.
For more information see Wind Against Current in Johnstone Strait by Jennifer and James Hamilton.
~ Mark Bunzel