DIY Under Stern Rudder, anyone?

Does anyone have links/instructions for building and fitting an understern rudder on a composite kayak? Already have an overstern rudder, looking to add an understern option to the same boat (ideally using the same lines).

Most interested in the mounting options. Links to a template for the blade itself would be useful too, though (e.g. the foilshaped shape itself - how wide/how soon to taper off, etc.)

I have a pretty good general idea of what’s involved, just want to see how others have done it …

No one? How about the tube?
The tube I suppose is needed to place thru the stern compartment to hold the rudder shaft. What would you use for the shaft and for the tube? How much does it need to be reinforced?

I thought I had seen some construction info on the topic but can’t seem to find the pages any more…

if youdo find something
please share.

For blade shape…
Pat at Onno paddle has an interesting foil.

As far as understern rudders go, all I can invision is problems. But I’m sure you’ve given it more thought than I have. Would it be retractable? Where and how? Would it fold up on snags/beaches?

Best of luck,


Not all problems -:wink:

– Last Updated: Sep-15-09 10:11 AM EST –

I typically do not beach the kayak I will be putting it on and where I use it is usually deep water. The problem with all overstern rudders is that they are often out of the water when needed most - trying to control the boat surfing down on a wave face on short/steep wind-generated waves. That's why there are no ocean racing surf skis with overstern rudders that I can think of.

It will be removable if needed and either the existing overstern or the new understern can be used with only a couple of minutes swap time.

P.S. There is a commercially available retractable skeg/understern rudder gadget in the UK (Kari-Tek) for a hair over 350 pounds if I recall (400+ USD?) but that is way too much money for what I want...

Found one!

– Last Updated: Sep-15-09 9:41 AM EST –

There is a lame attempt to translate automatically on the page left bottom:

There are hardly noticeable links within the text to other pages such as this one:

How I found it + discussion:;read=174331

Another DIY instruction:

You get what you pay for…
The Keri-Tek skeg/rudder system is hydraulically controlled with no mechanical linkage. When fully deployed, you set the rudder offset with the foot control bar & then put your feet back on the foot braces; the rudder stays in place until moved again. Sweet system - if you feel you need it. Not sure about using a rudder when surfing down the face of a wave; would rather edge the boat…

Good luck - sounds like your creativity will figure it out!

True, in some cases…

– Last Updated: Sep-15-09 12:58 PM EST –

To add some clarification.

"You get what you pay for: The Keri-Tek skeg/rudder system is hydraulically controlled with no mechanical linkage. When fully deployed, you set the rudder offset with the foot control bar & then put your feet back on the foot braces; the rudder stays in place until moved again. Sweet system - if you feel you need it."

Without being familiar with that system, your description seems to indicate that this device has similar effect as changing the trim of a regular skeg to maintain your heading as conditions change. Not what I want and on top of that - expensive.

"Not sure about using a rudder when surfing down the face of a wave; would rather edge the boat."

I'm thinking of putting it on my Valley Rapier 18 kayak, which is not meant to be paddled like a regular sea kayak with too much body control. Ever tried to edge a racing kayak or a surf ski to maintain direction? Edging pretty much does not work for this application. These boats do respond to edging but not in a way suficient for this purpuse, and edging robs you from forward paddling power, so they use full time rudders.

The reason these kinds of boats need rudders when surfing swells (not surf break) is that you want to jump from one wave face to another to link your runs. You are not trying to maintain a straight line but to actively steer where the best path is in your general direction.

Lightspeed Kayaks

Has anyone seen how these actually work?
What’s on the “inside”? These look interesting …

Only the MBA who wrote that those rudders generate lift would be able to explain the advanced hydrodynamics. My feeling - snake oil is somehow involved.

Do you think the rudder generated lift would be able to lift that kayak right out of water?


– Last Updated: Sep-15-09 6:22 PM EST –

Some snake oil is used on their foil -;) to make it as good as they portray it to be. But...

The foil shaped blade should be more hydrodynamic than the flat one they allude to. I'm not sure how much side-"lift" they can generate in turns but such shapes will create less turbulence during turning. Flat rudders also generate lift, just at the expense of more turbulence and more drag. So the more efficient shape allows them to have a smaller area compared to an equally turn/lift-generating thin flat rudder, thus going straight they may generate a little less drag too, due to the smaller size (though they are fatter so it negates this particular benefit somewhat).

I just finished installing a replacement foil-shaped smaller overstern rudder so I will report back soon if it the "foil" aspect really works better than the old large flat blade I had. I don't doubt it would work better (the old one had some deficiencies), just not sure how much better. And whether it would be better both in the straight line and in turning.

rudder shafts
my surfskis all use stainless steel tubes to run through the boat, and a stainless steel rod as the rudder shaft. If you look on the inside of the hull, you can see boxes (about 2"x1"x1" or so) that they expoxied in around the rudder tube to hold it and reinforce it where it connects to the deck and the hull bottom.

You have to figure out a way to attach the rod to the rudder obviously, and on my Fenn rudders you can see where the rod goes flat and bends backwards slightly inside of the actual rudder foil… that way it doesn’t rotate freely around the shaft or come loose. At the top, alot of people square off the top of the shaft, beveling it so it will fit in a T-bar with a square hole drilled in it. Epic is using a slightly different setup if I recall correctly… some sort of clamp.

I bought this from

1 piece @ $11.19/piece

Stainless T-316

Seamless Tube

0.375" x 0.028" x 0.319"

Cut to: 24"

and this from eBay:

.3125" Stainless Steel 316 Round Rod Bar 48"

it fits perfectly, with no play, but plenty of freedom to rotate smoothly. It is the identical stuff that came on my Fenn skis as far as I can tell.

Yes, Seen the Mechanism
Don’t know about lift, but the mechanics, as I recall, consist of a small pole which goes from the wheel you see on the deck down to the rudder. the cables attached to the wheel go to the footpegs. pushing on a footpeg spins the wheel, which rotates the pole, which turns the rudder. There are probably some gears along the way, but it’s not magic or rocket science. I think they patented it, so you might check with the company before trying to duplicate.

Great info - thanks!
One other detail I see that may be important is to build a small bulkhead area around the rudder shaft, pehaps a foot or so fore and aft or less, in case the shaft does leak due to damage - this way the rest of the kayak would not flood with water…

Well …
What you describe applies to any fixed rudder -:wink:

I was curious how they implemented the “retractable + steerable” properties together

Under Stern Rudder on Pintail

Installed just forward of the skeg box. Foot pedal steering with adjustable crossbar between the standard foot pegs. Crossbar allows foot pegs to be adjusted fore and aft. Stainless steel wire steering, routed through plastic tubes from CLC. The rudder tube is several layers of fiberglass wrapped around the shaft prepped with mold release. The bottom of the tube is glassed into the hull. The top of the tube is held in place by a cross bar which is glassed into the hull at the hull to deck joint. An O ring seals the top of the steer tube with the tiller plate. The rudder does not tip up - it is like under stern rudders on surfskis, and requires the paddler to enter and exit the boat in at least one foot deep water. I did this because the Pintail does not carve when leaned, and requires massive amounts of stern paddle rudder to steer when surfing. This cures that, and makes the boat a pleasure to surf.