Improving kayaks
Our test methods are well suited for improving kayaks. In order to systematically (and automatically) change parameters to seek for a better kayak, the hull must be described by a mathematical model. This is usually performed in 3 steps. We need data for a number of cross sections along the kayak.
First, the mathematical model is fitted for each cross section individually. When stability and resistance calculations are carried out at this stage, the kayak is interpolated longitudinally. At this step we get a rather precise evaluation of the original kayak. Second, the mathematical model is fitted to the cross section data using standard estimation techniques. This step is independent of the first step and results in a kayak that by accident may have better or poorer characteristics than the original kayak.
In the third step the design parameters are varied until we get the least resistance while preserving the stability from step one. We feel that preserving stability is achieved when the righting moment is not decreased either at 5 or 30 degrees of edging. The method finds improvemnt by small and rather subtle changes of the hull, not by radically changes in keel angle or other characteristics of the kayak. The improved kayak will look largely the same as the original kayak.
So far, we have performed this procedure on two existing kayaks.
Does it matter?
Does it matter to improve resistance by 1-2 N (1 N is about the weight of an apple) while retaining stability? No, it does not, not really. Sometimes it matters badly, should you turn up in Dalsland Kanot Maraton with ambitions, or give it a go for the Bue Ribbon along the Swedish coast. But touring the seascape, perhaps putting up a tent here and there, does the extra few per cent speed (or, equivalently, diminished effort) matter? Not much, what matters is connecting your body and mind to the sea, feeling tranquility and freedom.
But then there is the pleasure of feeling the response when you put some force to your paddle, and who says that half an hour saved during a long day does not come in handy?
Improving your drawings for a strip-built kayak or your professional design
Should you want us to improve on your strip-kayak drawings or are you a kayak designer that wants a final resistance-reducing polish of your design, please look here.
Improving Sibir Expedition
The picture below shows Per Tjelmeland paddling the Sibir Expedition.
Sibir Expedition is a touring kayak from Cobolt Kayaks. This firm has expired and the kayak is not made any more. It is fast for a touring kayak, and has a somewhat concave shape of the gunwale towards the ends, as seen from above. An interesting feature is the lack of backrest, which facilitates a backward lean during rolls.
The kayak was manually measured rather coarsely, so there is no guarantee that what here is taken as the original kayak in fact has exact the same resistance and stability as Sibir Expedition.
The result of the improvement process is a meagre 0.26 N at the test speed of 5 knots, using an 80 kg paddler and no cargo or ballast. At 6 knots, the improved kayak has about 1 N higher resistance, so not much seems to have been gained. This is a very fast hull for a touring kayak. It is a pity that the kayak is not made any more. Our test paddler, who has used the kayak extensively, reports the kayak to be quite stable. In fact, he would like to see somewhat less stability.
We might have made errors in measuring the kayak, as our measuring method is quite crude. Nevertheless, it could be interesting to make a new kayak with a basis in Sibir Expedition.
Improving Havsracer
Havsracer is a Bjørn Thomasson design for strip builders and is primarily designed for speed. It was modelled after published drawings on Thomasson's web site.
The picture below is taken from Bjørn Thomasson's web site.
The result of the improvement process is a decrease of resistance of 1.86 N at 6 knots for a paddler of 80 kg and no cargo or ballast. The skin friction of the improved kayak is somewhat larger, so the improvement stems from smaller wave resistance. Thus, the improvement gets larger at higher speeds and smaller at lower speeds.
The hull of the improved kayak is somewhat fuller at the ends, and the kayak is slighty wider.
Only the initial stability was limiting during the optimization process, so if one is willing to forsake some initial stability while keeping the secondary stability, the resistance could be decreased further.
A scaling and rotating enabled 3D comparison of the orignal and improved kayaks are shown here. The deck with hatch and cockpit openings is not the same as for Havsracer and is of no concern here, it is the hull shape beneath the waterline that is of importance.
The best kayak - for whom, for what?
The resistance of the kayak for a given stability is dependent on both the speed and on the weight of the paddler and cargo, i.e. it is dependent on the intended use of the kayak. Many strip builders could benefit from optimizing their kayaks in the direction of their intended use before they embark on building. Do you want as much speed as possible on a short afternoon training trip? Do you want to spend as little effort as possible carrying 50 kg of equipment and food on long overnight trips? What is your weight? What is your paddling strength? The optimized kayak depends on these factors, although there might be subtle and perhaps unnoticable diferences in hull shape. We may help evaluate the significance of these factors for your prospective kayak.
