Updated Thursday, October 22, 2009 10:07 PM
Plans kayak - Sea racer, €100
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Inspiration for the sea racer was Martin Leonard III and his Arctic Cheetah and the reason was sea races and touring with a light load. It is very long and narrow (not quite as extreme as the Cheetah though - I wouldn´t fit): 598x42 and tweaked towards as small awetted surface as possible, a very high Cp (0,62) and considerable volume in the ends to handle difficult conditions in large waves.
It is configured for rudder - that long a kayak would be hard to handle otherwisw. The rudder may be an ordinary stern-hung rudder, an integrated rudder (a movable underwater section of the hull) or a newly competition-type of lifting rudder (not yet built). Construction is wood strip and the bottom covered in polished graphite - rendering a hard protective surface with very low friction.
The cockpit is drawn to my favorite size: 53x38 cm with a height difference between fore and aft deck to make entering quick and easy, and still offer rolling qualities on par with dedicated Greenland rolling kayaks. Thus the deck is very low compared to common competition kayaks - I use the knees against the underdeck to power my upper body rotation. But indicated on the plans is also a more "normal" deck height for those used to the vigorous competition style pumping of the knees. It is also very simple to build the kayaks longer or shorter or with another cockpit shape or size - these options are descibed on the plans.
The kayak is, according to the calculations slighly tippier than the Black Pearl - but with much less difference than I would have thought from the dimensions. It is in fact more stable than most multisport kayaks and surfskis in spite of being faster than all but the most extreme.
I have yet no real data from tests - but an indication was given when the first built Sea racer was tested against a couple of well known multisport kayaks and surfskis as a study for the new Fusion hybrid surfski from Nordic Kayaks. The test crew - competent racing paddlers - were surpriced to note that the Sea racer was the fastest of the group - and yet the most stable! On top of that it offered a drier run in choppy seas. This confirms one of my pet theories - speed and stability are not necessary excluding qualities.
Photos of the Sea Racer
More on the Sea racer
This project have been on the drawing board for a little over a year - resurfaced now and then for a little tweaking and trying out more or less far-fetched ideas. A huge amount of hydrodynamic calculating of speed and stability have been done for incremental improvements of speed without losing too much stability. I have turned every stone imaginable in search of clever ways to reduce overall friction and the wave resistance at relevant speed, and have reached lower levels than ever before. Primary stability is not far from that of Black Pearl now, while secondary is approx the same - surpricing for a kayak with 8 cm less waterline beam! Wetted surface is just below 2 sq meters - not bad for a 6 meter kayak.
Friction and wave building resistance. the dotted grey line is Njord for a comparison.
Here are a couple of speed curves. Data is imported to KAPER (the algorithm used by most magazines, fx Sea Kayaker) together with the data for some well known kayaks. That it is faster than Viviane and XP is not surpricing, but that it have lower resistance in all speeds than Nelo FW2000 was a real surprice! Can that be correct? Maybe not. Kaper is a experience based algorithm, created by John Winters and focussed on hull around 500x60 cm, give or take. For those kayaks the predictions are quite relevant, nut further from that norm they become more unreliable. I wouldn´t be surspriced if the shorter Nelo wins a flat water competition, but maybe not one in a seaway. The first indications seems to verify the predictions, but more is needed…
Diagram showing calculated stability - again Njord and Black Pearl for comparison. I find it interesting that it is possible to reduce beam from 49 to 43 cm without losing more! Length compensates to a degree.
The diagram shows the calculated stability curves with a static load and thus is not very relevant for a preal paddler. The curve close to zero indicates primary stability - the steeper the more stable. The curve left of the top indicates secondary stability - the higher and wider the better. The curve right of the top is hard to use - the slightest mistake and you are under water.
Lines - Sea Racer
prticulars - Sea racer
| Loa: | 598 cm * |
| Beam: | 43 cm |
| Draft: | 9 cm |
| Cockpit: | 53x38 cm* |
| Deck height: | fore/aft of the cockpit 25/14 cm* |
| Weight: | 14-19 kg** |
| Load capacity: | 115 kg |
| Speed: | 9,9 - 15,8 km/t*** |
| Cp: | 0,60 |
| Wetted surface: | 1,99 m² |
| Resistance: | (4 knop) 1,49 kp (5 knop) 2,56 kp |
| Stability: | (80 kg) very low - (max load) very low |
| Usage: | Competition, exercise, fast touring with a light load along the coast or at the open sea. |
* these dimensions can be easily:
** depending on choice of wood, equipment, building skills etc.
*** the speed data is cruising speed (what a reasonably skilled paddler can mantain for hours) and top speed. The figures are theoretical calculations (Crouch´s formula) and will be adjusted when real world data is available.
The plans
Three sheets covers the information needed to build the kayak. An online building manual is available here
Sea racer - the history
the Sea Racer is inspired by Martin Leonard III and his Arctic Cheetah and designed for competitions and fast touring with light load.
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