This kayak needed a steering system. Most racing kayaks have rudders so that the paddler can concentrate on their forward stroke instead of making constant course corrections. All their energy can go into straight-line speed. They’re not essential.
This one was required though for a totally different reason: It was based on a surf ski.
The thing about surf skis, they’re designed to have a rudder. If you look at the boat in profile, the vertical area below the water line is biased toward the bow. There is more area up front than in the stern. The center of the lateral area is aft of the center of the boat. This makes a very loose stern that reacts quickly for surfing wave fronts. A large rudder balances the forces for stability. Björn has a very good explanation on the Spray’s design page. Being surk ski base, the Spray would be very hard to paddle in a straight line without a rudder.
OK, it needs a rudder. What kind? You basically have two kinds: the rudder is either hung off the back of the boat or it’s suspended off the bottom of the hull.
You see the bott0m-mounted ones on the top end racing K1s and K2s because they’re more hydrodynamically efficient. Most surf skis have them since in big waves they’ll stay in the water. Stern mounted ones may leave the water (not good for that lateral area control thing). A hole is drilled through the bottom of the hull and a tube is installed. The tube held by a brace. The rudder is installed up through the bottom and a simple yoke is attached to the stem. Often there is a watertight compartment sealed to the deck. A small hatch allows access to the stem.
Control lines then run to the cockpit and the footbrace. They’re really very simple. The major downside is since they are rigidly mounted to the hull, they are prone to damage. You really have to remember you have 8″+ of rudder sticking down beneath the lowest part of your hull. Hitting a submerged log or rock will do some serious damage. They also are weed collectors.
Second are the stern-mounted ones. They’re definitely the most common. You see these on most of the recreational kayaks and performance sea kayaks. They do have have more moving parts, are heavier and not as efficient. They’re biggest benefit is they usually kick-up if you hit something submerged.
Zack decided on going with the under-hull mounted rudder. He’s aware of the limitations but desired the increased performance.
With either rudder system the control lines lead to the cockpit. They’re controlled with your feet using either a tiller system (like on the last Wahoo) or with a foot brace with integrated pedals.
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For this kayak I again sourced my rudder and foot brace system from Stellar Kayaks. They’re New England based company that is fairly new (started in 2008) but makes beautiful kayaks and surf skis. I’ve been using their hardware for three years. Here we’re using their surf ski foot board and 8″ standard surf ski rudder. The foot brace and rudder are the same ones they install on their surf skis. They’re pressed carbon fiber for lightweight and strength. The foot brace system is especially nice. It rides on three rails, two black FRP ones and a center aluminum rail. It’s very easy to adjust for different paddlers. All three rails have quick release toggles. The lines also do not have to be adjusted when you slide the brace forward or back. The gas pedal steering pedals are comfortable and precise. It’s a very elegant system.
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I first formed a carbon fiber tray. It’ll support the top of the tube fore and aft and side to side. When bonded to the hull and deck it’ll also form a water tight hold. If any water seeps through the steering tube it won’t collect inthe main hold. I formed it on quick mold made from plywood with a release of Mylar film. Fitting it into the stern was the trickiest part. I couldn’t scribe it in place so I mocked up it’s location between the forms. I then scribed it off the forms. It worked quite well. It ended up being tricky to seal the top to the deck. Next time I would make it more like the hatch lips and have it bonded exclusively to the deck.
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Stellar doesn’t sell the down tube for the rudder so I had to make one. In the past I used the rudder shaft as a mandrel and wrapped it with carbon fiber. This time I tried something different. Carbon doesn’t wear well so instead I’ll use fiberglass. I used some polyethylene tubing, supported by a long Allen wrench, as the mandrel, and laid two thicknesses of fiberglass braid. On either side are a layer of stitched biaxial cloth and a mold made from sapele. The biaxial quickly builds material around the shaft and sapele compresses any extra resin out of the lamination.
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I decided to keep the sapele for looks and strength. After it the shaft had cured I turned it down on the lathe. At the top it’ll provide added bearing for the rudder yoke. On the bottom I turned down the shaft for a standard drill size.
The tray was trimmed to the scribe lines and a hole drilled to accept the tube.
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Time for a dry fit up before bonding everything in place. The rudder must be straight side to side and perpendicular to the hull. You don’t want the rudder to hit the hull.
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Now bond the tray and tube in place with fillets of thickened epoxy. The scrap wood strips help hold everything in alignment.
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Here’s a mock up of the foot board and the three rails. I used it to find the height of the top rails off the hull bottom.
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The rails are held off the sides of the hull on some strips of 4mm okoume plywood that are laminated on both sides with carbon fiber. The carbon does add some strength but is mostly for looks. Using the forms as a base I cut some plywood pieces to hold the rails in the correct alignment. The rails were scribed to the hull and bulkhead.
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The rails are then bonded in place with thickened epoxy. When cured the FRP rails were attached with stainless bolts. Their much easier to attach now than after the deck is attached. The aluminum rail was bonded to the hull with epoxy.
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The control tubes were then run from the cockpit into the rudder tray. They pass through the two stern bulkheads. They’re attached to the hull with some carbon fiber pad eyes and glue. At each bulkhead and tray penetration their attached with clear sealant.
After deck is attached and the exterior is complete I’ll run the control lines, install the foot brace and the rudder.