Our latest project looks similar to a lot of the previous ones: a long, narrow racing kayak. And it is. It just started life a little differently. As a surf ski…
This winter I was approached by Zack in Tennessee to build him a high performance sea kayak (HPK for ease of typing). He found the site via the increasingly popular Wahoo FSK design. He races surf skis during the summer months and a sea kayak in the winter.
Ok… Back up. I know what a kayak is. What in God’s Blue Sea is a surf ski?!?! Do you strap it to your feet? Don’t tell me it’s like one of those new-fangled stand-up paddle board thingies.
Surf skis are fast, open cockpit, speed demons propelled by a kayak paddle. These aren’t the sit-on-tops you see on the local pond. They are very light and usually have a highly elliptical hull for the max amount of speed. The sterns are designed to be loose and are paired with a big rudder so paddlers have the utmost control surfing down wave fronts. Compared to a kayak they are quite simple in terms of gear. If you fall out you just climb back in. They started in the warm waters of Hawaii, Australia and South Africa but are increasingly being seen in colder waters. While designed for big water they paddle very well on flat lakes and are blistering fast.
Zack wanted something that combined the best attributes of a surf skis and kayaks: the speed and maneuverability of a surf ski but with the cockpit of a kayak for rolling in colder waters.
We started by looking at the Wahoo. To get more speed out we looked at stretching if from 18′ to 19′-11″ while reducing the beam from 20″ down to 19″. It could have worked quite well.
Zack further looked at Björn Thomasson’s designs and first inquired about the Sea Racer. The Sea Racer was designed to compete against the surf skis and probably faster on flat water. He was quite hesitant about narrow beam (about 17″). Widening it to 19″ was a very attractive option.
While on Björn’s website he stumbled on the Spray and Spindrift surf skis. He was quite surprised to see that the calculated drag results of the Spray was lower than the Sea Racer (1.28/2.32 kp versus 1.47/2.67 kp at 4 and 5 knots) . More surprisingly it afforded higher stability (3 loaded/4 max load versus 1/2). There are no numbers for the Spindrift. Could I put a kayak deck on the Spray?!
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First we had to adjust the gross size of the Spray. The Spray is 560 cm (about 18 feet) long. A higher top speed could be achieved if we lengthen it to nearly 20′. That was easily done by adjusting the spacing of the forms. The beam was reduced from 20″ to 19″ by scaling the forms in one direction only.
Adding the kayak-styled deck proved to be more challenging. Without access to the original 3D file I had to modify the 2D plans the old-school way. I imported the plans into Illustrator and started playing.
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I first set the size of the opening of the new cockpit on the plan view and transferred the points to the profile. The height of the cockpit was set using Zack’s wishes and comfort from previous kayaks. I then shaped the deck to fit. Then it was a matter of adjusting the lines on the lines view for fair curves. To simplify my work I did not modify the hull hence the catch cutout in the sheer remains intact.
When I was happy with the results and had a build-able design, I had the plans printed full-size. I spray glued them to some 1/2″ fir plywood and they were cut out. Construction could commence!
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The popularity of surf skis is definitely influencing the design of kayaks as several kayak manufacturers are incorporating surf ski attributes into their high performance long distance models. Look at the Tiderace Pace series, Point 65N XP-18 and the Rockpool Taran. The heritage is clear.
We’ll be seeing more kayaks like these in the future. Björn has even hinted that he’s in the process developing his own. Stay tuned!