Rudders

By John Winters

In Partnership With Swift Canoe & Kayak

2394 Highway 11 North RR#1Gravenhurst, Ontario Canada

P1P1R1

Scribd Online Database Series

January 2011

© 2010 Swift Canoe & Kayak/John Winters. This document is not to be printed, distributed, sold for profit, or used in any capacity outside the Scribd document database without the expressed written consent of Swift Canoe & Kayak and/or John Winters

Rudders – by John Winters

If the Inuit had possessed the materials and technology to make them, would they have used rudders on their kayaks? It is not an earth shaking question but interesting nonetheless given the debate over rudders among modern paddlers. On the one side, experts and traditionalists staunchly contend that paddling skills and proper boat design make rudders superfluous if not burdensome. On the other, modernists see no harm in making use of modern technology if it makes paddling more accessible to less skilled paddlers if not easier for everyone. Who is right?

Before discussing the merits or shortcomings of rudders we must understand how boats turn. Boats turn "around" their center of gravity. In other words, they rotate. The sweeping arc of the turn is a product of the boat's momentum working in combination with dynamic forces causing the rotation. When the boat travels straight ahead, all forces are balanced about the centerline and act to retard the boat's motion (called drag). Once a turn begins the forces become unbalanced with greater force acting at the bow on the outside of the turn. The Center of Gravity, obeying Newton's Laws of motion, resists any change in direction and the unbalanced force at the bow causes a rotation around the boat's CG. Anything that increases the force at the bow or moves it further forward relative to the center of gravity will increase the rate of turning while anything that reduces that force or resists it at the stern slows the turn. Any additional forces, whether through paddle action, rudder, wind, waves or alteration of the hull's shape through heeling or trim will affect the turn. How the boat responds to these forces influences its "controllability".

Naval architects consider this a serious business since a 400 meter long ship running amok in a harbor can be cause for expensive litigation and it should come as no surprise that the topic has been studied in depth and at great expense. Most of what they learned applies to kayaks despite the differences in scale.

For instance, lowering the Block Coefficient (This is the ratio of the volume of the boat divided by the volume of a block having the same length, beam, and draft as the boat) improves course stability (called tracking by paddlers) as does increasing the ratio of length to beam. Reducing deadwood aft reduces course stability and trimming down by the stern improves it. Increasing deadwood or draft forward resists initiating a turn but accelerates the turn once it begins. "U" shaped sections at either end increase maneuverability and "V" shapes decrease it. Moving the longitudinal center of buoyancy aft increases the rate of turn once initiated and moving it forward has the opposite effect. We can see that controllability depends upon many complex interactions between hull characteristics. The mix producing exactly the boat that you like is the "designer's art".

Of course, a boat can present an infinitely variable shape to the water with corresponding effects on handling. Heeling or changing the trim boat during a turn will shift the center of buoyancy and alter the shapes forward and aft with a corresponding effect on

maneuverability. Waves, of course, constantly alter the underwater shape having either positive or negative effects depending upon circumstances. Experienced paddlers can use all of these effects to make course corrections without ever altering their stroke. Novices, however, might find these techniques challenging.

Designers can design controllability into the hull shape making a rudder superfluous but not everyone will want to master the appropriate techniques. For them, a rudder makes good sense. A rudder (or a skeg) can provide subtle corrections to the unbalanced forces due to waves, wind and currents, and trim variations. In short, rudders provide added convenience. Sometimes a rudder can make a poor design perform acceptably but it does not follow that all kayaks with rudders are poor designs.

A common complaint about rudders has to do with the added resistance they cause. They do add resistance but they can also reduce wasted effort when paddling by allowing the paddler to concentrate on paddling straight ahead instead of using the paddle for control. This is why racing kayaks almost universally use rudders.

Typically novices make excessive use of their rudders but most soon learn that the paddle provides more effective control and the rudder graduates to the role of "trim tab" that, when properly set, permits relaxing straight ahead paddling even in extreme conditions. Perhaps the perceived problem with rudders stems from the name. "Rudder" does imply gross corrections but, as any sailor knows, most rudder function compensates for variations in wind and seas. Perhaps we should abandon the word "rudder" and adopt "trim tab" as being more descriptive for kayaks.

Not all is perfect with rudders. They have reduced effect on following wave crests where the water is flowing in the same direction as the boat travels. The added weight in the stern increases pitching and the blade increases drag. Concern for the rudder when beaching or launching from surf takes a bit of the fun out of those activities. Moreover, badly designed and made rudders function poorly and if not properly maintained can become even less effective. In this sense, they are a bit like people.

Even so, a rudder makes sense for some paddlers. We may all be created equal, but we are all created different.

The issue, then, is not whether rudders are good or bad but whether they contribute or detract from your personal paddling experience. Every paddler must find the right boat (with or without a rudder) and seek out what peace there is in a world of turmoil.

© 2010 Swift Canoe & Kayak/John Winters. This document is not to be printed, distributed, sold for profit, or used in any capacity outside the Scribd document database without the expressed written consent of Swift Canoe & Kayak and/or John Winters