Skrivet av: Peter | februari 3, 2009

Surfski-hybrid for Nordic Kayaks

Taken from Björn Thomasson Design, http://www.thomassondesign.comnews090130-11

The last couple of months I have been tweaking the lines of a new surfski-multisport-hybrid for Nordic Kayaks. It started with a request for a little advice on the hydrodynamic development of a new kayak aimed at comfortable cold water paddling. There has been a little doubt on the suitability of surfskis and sit-on-tops up here on latitude 60 (actually the same latitude as southern Greenland and Alaska) and idea was to offer a working solution.

We quickly found out that we had some notions in common on this – ideas that I had built into a lot of kayak models but mostly in my Sea Racer.

To establish a common ground for discussions, Fredrik and Peter tried out the first launched Sea Racer, that happened to be in their part of Sweden. They were impressed with the stability of the craft – and even more that it in spite of this stability was faster than the comparison: a well known American surfski and a Swedish multisport kayak – and provided a softer drier ride in waves.

My basic idea is that hull speed alone is just a small part of the performance. Even more important is that the paddler is comfortable, feel in control and can make use of his or her full strength and technique.

Traditionally most manufacturers have focussed on hull speed – minimal wetted surface and high Cp. That means a rounded hull with significant flare, where the seat must be placed a couple of inches above the bottom to fit – forcing the sheer and deck up as well, and the necessity of flats in the deck to get the paddle close to the centerline. This severely compromises the initial stability with the result that many can never achieve real paddling efficiency in waves – it takes too much power and concentration just to keep from turning over.

The basic idea – tested on a lot of my kayak models – is to widen the bottom so the seat can be lowered and decrease the flare slightly. The result is that the center of gravity will be one or two inches lower, which is the single most important factor for stability. Then the sheer and deck can follow, for less windage and a more comfortable paddle catch. The stability increases to such an extent that some of it can be sacrificed for a decreased beam, giving a splendid loa/beam ratio (1: 14,5) and increased top speed. This kayak at 43 cm beam will have a initial stability comparable to a 5-6 cm wider traditional surfski.

news090130-22

The image shows the basic idea: the numbers a just to show the thinking and the potential, as the comparison is a fictive generic surfski/multisport hull.

Mention a lower seating position and the majority of competition paddlers dig in the heels. But since everything is lower – seat, sheer, deck – there will be no other difference than the hip angle changing from approx 86 deg to 88. In my experience this is a marginal change, and one that one gets used to very quickly.

I do not believe that the top elite paddlers will benefit noticeably from this kind of hull – at least not for short races. They can handle a far more tippy kayak in waves. But the others may use their strength, technique and stamina more efficiently in this kind of kayak hull.

I also believe that this kayak can be used for fast touring with light load. An accomplished paddler may be at ease in open sea conditions and achieve impressive daily runs at a high touring pace and with a reasonable effort.

There are also some new ideas for the cockpit arrangement – integral cockpit pod with minimal volume (surfski style), integrated rim/flange for a spraydeck, integrated bailer, ”soft” rudder pedals etc – but as my main task have been to develop the hull, I leave those to Fredrik and Peter at Nordic Kayaks to show.

If you want more information about the new Surfski hybrid from Nordic Kayaks,
click here


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