CLR and Canoeing
Some thoughts on the Centre of Lateral Resistance (CLR) and Canoeing
Some thoughts on the Centre of Lateral Resistance (CLR) and Canoeing
The Center of Lateral Resistance (CLR) is the point along the boat where adding a perpendicular force will move the boat directly sideways. The CLR can be equated to the pivot point (or perceived pivot point) of the canoe - this is a simplification since the pivot point will be somewhere between the gunwales but it suits my purpose. Adding a force in front, or back, of this point will cause the canoe to turn. Having an idea of the CLR is helpful in many paddling situations such as moving directly sideways, pivots, running side slips, and turns. Since a movement is relative to the water it will also help in moving water for ferrying, or generally dealing with current. It is an other illustration of why trim is important.
It is relatively easy to empirically identify the CLR by pushing (or pulling) the canoe directly sideways from a single point. Depending on how the canoe is weighted, and if the canoe is in motion, the CLR may be in various locations.
Things get a little more complicated when a canoe is in motion - in practise the CLR moves forward when a boat is in motion. Using an arm-waving explanation: The bow of a canoe in motion cuts into the bow wave. The bow is, in effect, deeper in the water (as if forward weighted) and held in place. This means the CLR will be closer to the bow. Think about the adjustment of trim in the stationary canoe in the first experiment below. This is not a strong effect so the change in the CLR for normal paddling speeds may only be 10-25cm (although I have found it can be as much as a meter for some combinations of boat and paddler). The effect is more pronounced in long narrow canoes with limited rocker, and becomes less accentuated in shorter flat bottom boats (e.g. WW play boat).
For a canoe in motion the new CLR location is sometimes called the perceived pivot point (PP). There is a nuanced difference when the boat is actually turning but I will leave that for another day...
I generally recommend intermediate and advanced paddlers determine the CLR of their own canoe from their normal paddling position, for both a stationary canoe and when in motion. This page relates to a solo paddler but understanding the CLR is also helpful for tandem paddlers. My preference is to have a person sitting in the boat so they get a feel for their own weight, weight distribution, and stance.
With the help of a friend, a door clip (for a car roof rack) that fits over the gunwale, and a light 4m piece of string or parachute cord tied to the clip.
Position the canoe perpendicular to a dock, about 3m out, with the paddler sitting or kneeling in their 'usual' location.
Hook the clip over the gunwale beside the paddler.
Have the friend, standing on the dock, pull the canoe with the string directly into the dock.
Do this several times moving the clip forward, and backward until you find a point where the canoe does not pivot when being pulled. Mark this point (I use coloured tape).
Repeat this procedure with the paddler sitting in other locations (trim), changes in heel, and position of equipment. Have fun, play around a bit...
You will find the CLR will be behind the paddler when the trim is toward the stern - typical of a Canadian Style paddler position. When the paddler is near the middle of the canoe (e.g. when paddling a more dedicated solo boat with central seating) the CLR may be right beside the paddling station. In the case of AFS when doing a high kneel or using other forward weighting techniques, the CLR will be in front of the paddler's location. Adding equipment to the canoe and changing the trim will move the CLR forward (or back).
You will need a somewhat longer dock, string, a door clip, and two friends for this experiment.
Position the canoe perpendicular to the dock, about 3m out, with the paddler sitting or kneeling in their 'usual' location.
Have your new friend push the canoe forward (from the stern). Do this several times until the canoe runs in a straight line the length of the dock at a moderate to quick walking speed. With shorter highly rockered boats any addition of torque will be magnified - WW play boats become almost impossible to push in a straight line.
Hook the clip over the gunwale beside the paddler, and give the other end of the string to the person on the dock.
Have the friend on the dock walk along beside the canoe, perpendicular to the clip location, and at the same speed. Pull the canoe sideways to the dock. When starting out the string should be loose, but not dragging in the water, to ensure no torque is added to the canoe.
Do this several times, moving the clip, until the canoe pulls directly sideways (as in a running side slip). This is the CLR of the canoe in motion. Assuming that the paddler is in the same location as the stationary test this point should be somewhat further forward. Mark this point (I use different coloured tape).
Repeat this procedure with the paddler in different locations (trim), changes in heel, and additional equipment. If you are an AFS practitioner mark these points when in a high kneel, transverse kneel, forward lunge, etc.... I might also suggest marking these points when the canoe is going backward.
Understanding the location of the pivot point will allow you to use box strokes, sweeps, or circle strokes to maximum effect. In some cases you will want to pivot around the paddling position, rather than the natural pivot point, and knowing the CLR will allow you to adjust appropriately with each stroke.
Using the CLR as a marker, and ensuring you draw (or pry) directly to that point will mean a nice straight side displacement without any yaw. By using a draw (or pry) ahead or behind the CLR you can complete a side displacement with a constant yaw. Putting pivots and side displacement together you can move the CLR along a line for doing line pivots.
One of the cool things about knowing the CLR is executing nice clean consistent running side slips. The key is to plant the blade so it is along a tangential line from the CLR. The blade is perpendicular to a radial line from the CLR. OK - the face of the blade looks directly at the CLR.
In practise this means a running draw is planted behind the CLR, and a running pry is planted forward of the CLR. My recommendation for running strokes is to plant them with a minimum of pitch, and a little further forward than required - especially with a running pry don't try to move the paddle forward.
Understanding the CLR will also help with ferrying in moving water for the same reason.
Planting a running draw or pry ahead of the CLR will cause the canoe to turn.