The Seven Mile Bridge in the Florida Keys connects the Middle Keys to the Lower Keys. Under the bridge, the water is shallow, and it seems like the 1,000 square miles of the Florida Bay flows through the opening on the tide generating up to 4 knot currents. In a kayak, the current is swift enough to push you out to sea on an ebb tide or into the bay on flood. The common practice in a situation such as this is to find a ferry angle that prevents you from drifting out to sea and this is also a common practice with preventing leeway in cross winds. This is commonly taught as the correct practice, but is it always the correct practice? Not according to John Winters, a naval architect and canoe and kayak designer, if efficiency is the goal.
I had an opportunity to experience the differences between two approaches to currents on a kayaking trip in the Keys.
You use a ferry angles to maintain a course when currents or winds would push you off that course. It is the angle between your course and your heading and is set so that you paddle into the wind or current at just the right angle to maintain your course while making headway. You can set a ferry angle by calculating the exact angle based on your paddling speed and the current’s speed. There’s a great explanation on how to do this in John Lull’s Sea Kayaking Safety & Rescue: From Mild to Wild Conditons, the Essential Guide for Beginners Through Experts or in David Burch’s Fundamentals of Kayak Navigation, 4th. Knowing how to calculate the ferry angle is helpful for when you can’t find a range, such as in the fog, in the dark, or on long crossings, but finding a range makes setting the ferry angle simpler.
To set a ferry angle with a range, just paddle at an angle and adjust that angle so that the two points in your range stay aligned. As long as the points are aligned, you maintain your course. As your angle increases, you’ll need to increase for forward speed to maintain a decent speed along the course. Ferry angles larger than 40 degrees are very inefficient and waste lots of energy for little progress towards your destination. Even at 40 degrees if you’re paddling at 4 knots, your speed made good towards your destination drops to around 3 knots.
Ignoring the Current or Wind
Instead of setting a ferry angle across the current or wind, you could just keep the bow of your kayak or canoe pointed towards your destination and adjust your heading to keep pointing at the destination as you paddle forward. You’ll experience leeway movement and your final course will look curved. According to John Winters,
From a pure efficiency standpoint … [this] method works best since you will constantly change course to adjust to conditions and maximize performance. This is good because conditions are always variable. The other positive aspect of paddling towards your destination is that you can ignore minor course variation and focus on the “big picture”. Most people steer too much believing that steering a straight course is best when the more efficient technique is to let the boat wander a bit to suit the vagaries of wind and waves. Few people do this instinctively.
He later adds,
The reason [that this method is more efficient] is that the boat is traveling more efficiently through the water. Because the boat is traveling faster it has greater course stability and you can more easily adjust for varying conditions. For example, you will need to correct your course less. The other nice thing is that it is a self correcting course and you need not calculate a proper drift angle which, if your crossing is long, could be wrong.
So, Which is the Best Way?
During my experience paddling past the Seven Mile Bridge, my friend Amy and I choose to use ferry angles and a little drift to make our way to an island we were planning to camp on. My friend Dave ignored the current and paddled directly towards the island adjusting his course as needed. All three of us typically paddle at approximately that same speed. The way it worked out was that Amy and I paddled in flat calm water, but Dave was pushed out of the shallows and into an area where the light chop was interacting with the current creating about a foot or so of white-capping chop. Despite the chop and the leeway, Dave beat us to the island. In this instance, his approach worked best for speed.
It’s not always going to be that way, particularly in current, but according to John Winters, the second approach “works best most of the time [in wind] due to the high leeway of shallow boats.”
So, why didn’t the kayaker cross the road? He couldn’t figure out the ferry angle.