Sea Racer - 598x43 cm
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Plans, Sea Racer - 598x43 cm - 120 EUR
The 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 a wetted 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 otherwise. 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 described in the plans.
The kayak is, according to the calculations slightly 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 many multisport kayaks and surfskis in spite of being faster than all but the most extreme. The Sea Racer is generally good in waves, but a couple of builders have reported having troubles in the short steep sea, such as an estuary with tide and wind against the current. When the long hull lifts on two crests with the midbody and paddler hanging in between there is nothing but your acrobatic skills to save the day! So I guess the recommendation must be flat water or long non-breaking waves.
If used carefully the Sea Racer can be built very light. The best (as far as I know) is Matthias Jakubeks beautiful Sea Racer at 11.8 kg (see Photos below)!
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 hybrid surfski a couple of years ago. The test crew – competent racing paddlers - were surprised 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 (almost calm conditions with nothing but wakes from passing boats to test wave behavior in). This confirms one of my pet theories - speed and stability are not necessarily excluding qualities.
"I christened the boat Artemis II yesterday and took it for a spin, all I can say is wow, it is extremely efficient and flys with little effort. Having moved to this kayak from a 24 inch beam Granita design S&G I was concerned about stability but I stayed dry and found initial and secondary stability to be fantastic for such a narrow hull. According to my wife the craft leaves very little wake, a sign of the efficiency I was looking for. Drivers passing the lake stopped in the middle of the road to watch me paddle and were amazed by the lines of your beautiful design."
||598/588 cm (overall/WL)
||43/41 cm (overall/WL)
||25/14 cm (in front of/behind the cockpit)
||115 kg/263 litre
||1/2 (initial/secondary stability)
||Competition, exercise, fast touring with a light load along the coast or at the open sea.
¹ These dimensions can be adapted to suit personal needs or wishes.
² Depending on type of wood, equipment, care with epoxy usage, sanding etc. etc.
³ The speed numbers are based on mathematical standard formulas (175 lb paddler + 30 lb carco weight) and corrected from the kayaks actual performance om trials, on tours and in races.
⁴ Calculated resistance in 4 and 5 knots (at nominal load capacity).
⁵ Initial stability and secondary stability on a subjective scale, where 1 is very tippy and 5 is very stable.
⁶ Displacement is kayak + paddler + load. Count off the kayak weight to get the load capacity.
Three sheets covers the information needed to build the kayak. An online building manual is available here
The illustrated step-by-step building manual is in Swedish only, but it is available online in English: it covers all steps in detail and will guide first-time builders through the project.
Plans, Sea Racer - 598x43 cm - 120 EUR
Minimum window dimensions to get your kayak out from the workshop:
More on the Sea racer
This project has 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 - surprising 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 gray 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 surprising, but that it have lower resistance at all speeds than Nelo FW2000 was a real surprise! Can that be correct? Maybe not. Kaper is an experience-based algorithm, created by John Winters and focussed on hull around 500x60 cm. For those kayaks, the predictions are quite relevant, but further from that norm, they become more unreliable. I wouldn´t be surprised if the shorter Nelo wins a flat water competition, but maybe not one in a seaway. The first indications seem 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 real 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 to the right of the top is hard to use - the slightest mistake and you are upside down.
Sea racer - the history
The Sea Racer, designed in 2006, is inspired by Martin Leonard III and his Arctic Cheetah and designed for competitions and fast touring with a light load.