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Design & Illustration

Surfski for strip building...

Spindrift – surfski i trästrip

My wood strip surfski has been brewing for a very long time. It started with the Sea Racer. As the name implies, it was designed as a very fast sea racer with long distance touring capacity. I found the inspiration in Alaska and the plans were finalized during spring 2006.

Havsracer

I started building the prototype during the summer and had the hull and deck done when my calendar started to overflow with jobs and assignments and at the same time, requests for classes and talks (the Sea Racer parts was used for strip building demonstrations).

Other builders were more ambitious and Sea Racers got launched – almost 50 til now – and they seemed to deliver: tippy, super fast and quite able i rough seas – sometimes in unexpected contexts. Some examples: here, here, here and here.

I got requests for commercial designs, while the Sea Racer prototype collected dust in the workshop. First was Nordic kayaks. After a couple of successful multisport kayaks (Rocket and Rocket plus), they suggested a surfski for nordic waters. The Sea Racer prototype parts were redefined as test devices for surfski ideas. After some going back and forth between the drawing table and a newly built surfski prototype, the Fusion went into production.

Now requests for a strip version started coming in via mail and over the phone, and I confidently answered "Yes, working on it...". Which was true – a rough sketch was recently saved in the "bright ideas" folder in the computer.

Seabird Designs requested a line of surfskis, and the Wave line found its way to the kayaks stores.

Three new surfskis for Nordic Kayaks were next in turn, but by this time Fredrik Lindström were doing most of the actual design work. I helped in refining the software output into working drawings and worked on the visual design and decorating scheme.

...more and more questions about the coming strip surfski ;-)

Roar Berge got tired of waiting and built a surfski version of the Sea Racer.

Jan-Olof Karlsson offered to build a prototype of the surfski, from the not quite finished plans. So I adjusted the dimensions for Jan-Olof and he cleared the workshop and got started.

A new company contacted me with an idea that had been in my mind for a while: a shorter, less specialized surfski for "common" usage as a touring craft – with the best qualities from both sea kayaks and surfskis.

Then a week ago Alexandre Marcotte in Canada (he built a Black Pearl a couple of years ago) took the bold step of actually ordering and paying in advance for the surfski plans – and that, of course was the final kick. I had to clear the workspace from all urgent assignments and deadlines swishing by, and get those plans done!

So here it is, finally after six years, a strip surfski! It is of course a much much better surfski than the one I started drawing back then – I have learned a lot in those years, the surfski concept has evolved and the market has grown. It is designed as an intermediate ski – not an elite ski nor a beginner skis (even if it will be well within reach of the ambitious beginner as well). It can be built with an under-hull rudder for racing/excercise or an aft mounted rudder and hatches for touring. The dimensions are 608x48 cm and the length can be adjusted as usual during setup, with advice on the plans for hulls between 576 and 640 cm. The cockpit structure may seem complicated to build, but three suggested methods are indicated on the plans: strip, foam or carbon/fiberglass.

Spindrift 2 – surfski in wood

A shorter and wider version will be available later – in about six years... (just joking ;-)

I do not plan to include a top level elite ski. Very few amateur builders would be able to match a professionally built elite ski tipping the scale at approx 10-11 kg – and those who would, won't need my plans anyway. If you want to compete in the surfski top worldwide circus, I suggest you buy a Nordic Kayaks Nitro, or one of the other top skis.

Sea racer or surfski?

What is the real difference between the Sea Racer and the Spindrift? Or in general – what separates surfskis from sea kayaks or multisport kayaks?

Well, it turns out the only sure sign is the cockpit configuration. In everything else there are lots of crossover crafts floating around, defying categorization: sea kayaks with surfski maneuverability and surfski with the calm movements of sea kayaks and all kinds of hull configurations.

Surfskis were from the start developed to run off the wind on large swell reaching extreme speeds, and to surf the wave fronts in control. To keep the position and direction on those waves, extreme maneuverability was needed. To control the craft, precise steering and a large rudder was necessary. The stem was high to avoid diving in the gigantic waves of the native waters in Hawaii, South Africa, California, Australia – while the stern often became little more than a long tail with a rudder. The fore part was deep and narrow moving the lateral center forward to balance the large rudder, while the aft part was wide and shallow to prevent the stern from submerging in speeds close to or above hull speed. Surfskis became elite tools for tough oceans races. But eventually the market evolved to include also crafts more suited to "normal" paddlers with touring ambitions.

Sea kayaks on the other hand evolved towards strong tracking, rather than maneuverability. The designer sacrificed some maneuverablity for comfort on long passages – in automotive terms they have the soft somewhat imprecise steering with a healthy margin for errors of a family car, rather than the precise and attention-demanding direct steering of a race car. Of course some of the control is lost in the process. Have you tried to surf a steep wave diagonally in a sea kayak, you will know what I am talking about. But lately we have seen a lot of sea kayaks with almost surfski-like maneuverability and control.

A look at the lines of the Sea Racer and Spindrift reveals these differences. The Sea Racer hull is more symmetric, with LCB, LCF and CLA quite close to the center, indicating a hull that moves smoothly and predicably in the water (LCB = Longitudinal Center of Boyancy = the centroid of the underwater volume of the boat expressed as a longitudinal location. LCF = Longitudinal Center of Flotation = center of the waterplane, the "seesaw" pivot of the craft. CLA = the geometric center of the lateral plane). The seat is located slightly aft of the center, providing controllability without being overly dependant on the rudder (mildly understeering in automotive terms). The rocker is not very accentuated, which improves tracking. The kayak deck with cockpit rim/spraydeck keeps water out, allowing for a lower and less wind sensitive profile. For the same reason the freeboard midships can be lower, to allow a lower and less tiring paddle stroke on touring.

Sea Racer and Spindrift – lines

In the surfski the CLA is moved forward to balance the large rudder. The seat position slightly forward of the LCB is the key to the efficient and precise steering on wave fronts – in automotive terms the ski is slightly oversteered in low speeds, but becomes neutral in higher speeds since the longitudinal position of the hulls center of turning is related to speed.

Sea Racer and Spindrift – lines

The stations drawings show that the surfski is wider and higher than the Sea Racer. But the difference in volume and load capacity is not as large as it might seem – the higher Cp of the Sea Racer means that the volume is more evenly distributed along the hull, while the surfski has more volume concentrated midships. This suggests that the Sea Racer should be slightly faster on flat water, but the surfski should win in waves.

Sea Racer and Spindrift – stations

The shape of the sections look quite different. In the Sea Racer I wanted to optimize the intitial stability in what is a very narrow craft (43 cm), with the chines also enhancing steering control when the hull is leaned (a way to keep rudder turbulence to a minimum). For the wider surfski I chosed to minimize friction with elliptical sections below the waterline.

Software and the design process

The sectional shape is also to a degree influenced by different calculation algorithms. The Sea Racer was developed using Bearboat by Robert Livingstone for the hydrodynamic calculations. The main advantage of this is that the underbody defining vectors hang from the waterline and the keel, which makes it possible for the software to minimize the wetted surface for every set of design parameters chosen. It saves a lot of time finetuning the hull to low friction, but also means that the bottom and freeboard are two independent sets of curves, meeting at the waterline. On certain kinds of hulls this complicates getting a smooth natural curve from sheer to keel.

For the surfski I used Ross Leidy's KayakFoundry, forked from Bearboat, but with one important difference: the vectors hangs from the sheer and the keel. That means better overall control of the lines (including deck shape and stem and stern) compared to Bearboat, but the disadvantage that you have to work the wetted surface manually based on experience and through repeated iterations followed by checking the calculations. One further disadvantage is that KayakFoundry is just for Windows. I have to run it virtualized in Parallels on my iMac – it works, but a bit slower than real Mac applications.

Both softwares are easy to use and do an excellent job at their level, but the downside of the simplicity is the many limitations in what can be achieved (not a problem for the amateur builder, who would solve those issues in the construction phase rather than on the computer anyway). Therefore I use them for a quick zooming in on the hull shape I want, along with all the hydrodynamical data I need – getting within 95% of the final design in surpricingly short time and with adequate accuracy. From there I transfer the lines to Illustrator for the final manual finetuning, including both functional tweaking and the visual layout of lines and surfaces – which normally takes more time than the first 95% in the design software!

That may seem a tedious way to design a kayak, but the alternative – professional ship CAD design systems are very expensive and bloated with features of which I would use a small percentage (I do not need to know what happens to the ships stability when 600 tons of crude oil sloshes around in an half empty tank, nor at which parameters the risk of propeller cavitation becomes an issue ;-) and would take hundreds of hours training for me to master.

Spindrift

The surfski is named Spindrift – an apt name for a craft with an appetite for wind and waves.

Spindrift – logo

Comments

VERY exciting news! Paddlers have been looking for a commercially-designed surf ski for years. I'll be sure to add it on the next update to my webpage.

Thanks Dan. As I mentioned there have been requests ;-)

Vilken trevlig nyhet! :) Ser fram emot att se lite träskidor i surfskisverige!

Superkul! Jag är dock för otålig för att bygga själv. Är det ok att använda bilder från dig på bloggen? Jag länkar givetvis enligt dina önskemål. Ha det gott! Peter

Peter, som alltid är allt material på sajten fritt att använda: bilder, text, diagram etc – i utbyte mot länk och angivande av upphovsman.

900 Euros. Wow! Great design but is that correct?

Ooops! No, the figure was transferred automatically from the swedish text/currency. My mistake. € 108 is the correct figure. Thanks for pointing it out...

Impressive craft and an interesting explanation about its development.

Kayak Foundry may have been written for Windows, but it runs perfectly in Linux using WINE.

Then I guess it will run equally well on Mac OS – and in contrast to Parallels it is free.

But Parallels is not a very expensive application, and it is quite satisfactory with KayakFoundry – I believe the slower performance I referred to is not the application itself, but because my computer runs a backup frequently when I have Parallels, KayakFoundry, Illustrator and Photoshop up and running simultaneosly...

Hej Björn!

Först och främst måste jag berömma dig för otroligt envetet och bra arbete med både kajaker och denna sajt. Har länge tänkt bygga en egen men ännu inte hittat lämplig lokal.

Väntade också på en ny moderna form av kajak. Havsracern var en bra utgångspunkt. För ett år sedan upptäckte jag att det fanns något som kallas Surfski. Äntligen!

Och jag slog till och köpte en NK Breeze vilken jag är mycket nöjd med.

Vad skiljer din Spindrift med Breezen?

De ser rätt lika ut. Vore kul att höra dina ord.

Och sittbrunnen till Spindrift: finns formar att få tag på? Du skulle nog få många fler att bygga trälådor om just sittbrunnen fanns mer eller mindre färdig att få tag på. Jag t ex.

Tack Jacob. Det finns en del yttre skillnader som är lätta att se och märka: Breeze en större kajak: 455 liter totalvolym mot Spindrifts 381 och 120 kg deplacement mot Spindrifts 106. Vidare ligger flyt- och jämviktscentrum längre föröver i Breeze vilket ger lite mer attack i styrning och kontroll och mer typiskt "surfskibeteende" i vågor, medan Spindrift har en liten aning av havskajakers lugn i rörelserna. Volymfördelningskoefficienten (Pc eller Cp beroende på språk ;-) är aningen högre i Breeze (0,58 mot 0,55) vilket ger aningen högre toppfart, men den skillnaden äts upp av att Spindrift är lite smalare och har mindre våt yta (2,05 mot 2,15 kvadratmeter på konstruktionsvattenlinjen). Vidare är skillnaden i total- och vattenlinjebredd större hos Breeze, vilket ger mer racingegenskaper olastad och lugna långfärdegenskaper med last. Skillnaden lastad-olastad är mindre tydlig i Spindrift – vilket som är bäst är en smaksak.

Men sedan finns också mer svårfångade skillnader: Breeze är på sätt och vis mer en surfski med stort S. Fredrik på Nordic Kayaks som stått för merparten av skrovutvecklingen är duktig surfskipaddlare och har jobbat mycket med små subtila detaljer i prestandaprofilen – vilket innebär att Breeze i grunden är en elitsurfski som blivit lite bredare och kortare och därför passar även rätt ovana paddlare. Men klorna finns kvar! Spindrift är mer en ”standardsurfski” i mittfåran – bra på det mesta men utan att glänsa i någon speciell egenskap. Mindre topp och mer bredd. Jag räknar med att Spindrift kommer att kunna locka en del övertygade havskajakpaddlare att intressera sig för surfskikonceptet.

Det finns inga formar till sittbrunnen. Men det är inte omöjligt att till exempel Petrus i Tranås småningom tar fram en snygg sittbrunn i kolfiber till försäljning ;-)

Under tiden tycker jag den bästa metoden är att grovsåga fyra 10 cm markskivor i polyesterskum, limma ihop dem, och med hjälp av skålkniv och grovt sandpapper gräva fram en bekväm sittställning – och till sist med den som form laminera en lätt, snygg och bekväm sittbrunnsbalja i glasfiber/kolfiber. På det sättet behåller man samma fördel som kajakbygge generellt innebär – en individuellt anpassad sittställning med (förhoppningsvis) överlägsen komfort.

Uttömmande svar - som vanligt! Tack!

Vad tror du om vikten då vad det häller din i trä?

Jag väntar mig ett ganska stort spann: den som målmedvetet söker låg vikt bör kunna hamna neråt 13 kg (se Roar Berges surfski och och Roars kommentar till Jan-Olofs surfski), medan den som bygger "som vanligt" kan landa på 18-20 kg – eller mer om man är frikostig med utrustning och extraprylar.

Björn, this is indeed exciting news. Like Dan, I have been on the lookout for some time for professionally drawn plans for a surfski. Your Spindrift appears to have about the right attributes for my own, non-competitive use inshore on the south coast of Honshu, the Japanese big island. I have a couple of projects to get finished, but I'm looking forward to having a go at the Spindrift as soon as those are cleared.

Thanks Rick, I'll be happy to ship a set of plans when you get those other projects done...

Björn, I can't now find the comment you made about it, but I seem to remember reading just last night, 29 May, your mention of thinking about designing for wood strip construction a shorter, beamier beginner's surfski, a configuration that it seems might work well also in surf or rough water for recreational paddling. Your final quip about our having to wait maybe three years, with a smiley punctuation, is the clue I remember and cannot find now.

A length of about 4.3 to just under 5 meters with concomitant beam increase sounds about right to me. Might make a good surf play-boat if given harder bilges midships so it could cut and hold on a wave face. I should think harder bilges would also aid initial stability for a beginner.

That I can't find your comment now makes me worry that you may have dropped the idea. I note in another of your news items that you've worked out a design for a Chinese-made beginner's ski for a Norwegian outfit.

I'll be watching keenly for a similar boat for wood strip construction. I have been considering another designer's stitch and glue plywood "play" kayak design, and a similar one for SOF construction, but I'd be more interested in an open cockpit model.

No, it is still there, just under the rendering of Spindrift: "A shorter and wider version will be available later – in about six years... (just joking ;-)". The post about Axis kayaks and surfskis is also still there (as are all other 1382 archived posts). I never remove any such things...

But what I am contemplating is something of approx 5.5 m, with a little more beam than the longer ski above and with a round surfski bottom. No chines this time – they would interfere with the active and direct steering and make the ski less predictable in confused waters of large waves. That would have been another kind of craft, not on my list for now...

Stability will be achieved with beam, not with chines (that actually does very little for initial stability – and what little you gain there, ist lost on secondary).

Sorry, Björn; obviously when I went back to look for it I somehow repeatedly overlooked that line of text. I actually skimmed through the article several times, looking for that sentence, before asking. I can only guess that I assumed that it was a cutline for the illustration above it.

If somehow I offended you, I sincerely apologize for that as well. That certainly was not intended, as I like what I see in your work.

The shorter, beamier, round bottomed boat you describe would be of interest, when you get to it.

...for the same reason that it is very hard to proofread your own text – you miss something the first time and then you repeat ;-)

And I am not at all offended – on the contrary, quite flattered by the interest you take in what I have to say.

When I am skimming large chunks of text in search of something I know is there, I often use the browsers page-search (cmd-F in Chrome). One remembered word is enough, the search finds all instances, saving a lot of time...

It's command-f in Safari too. Afraid I've neglected that powerful attribute of a browser for so long that I had quite forgotten about it. Thank you for reminding me.

By the way, the orange and "anthracite" color scheme you chose, and the pattern, is striking and beautiful, and it's functional in that it increases the visibility of the craft on the water. We, my wife and I, live in an area of heavy coasting and commercial fishing traffic, so visibility in a small boat is always a concern. But mostly that color scheme just looks right on those boats.

Thank you! What a clever cat I have!

Ooops" That post is in Swedish only – but I think the last photo indicates the mening.

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