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Anke and I are building our next boat, and writing about it at Access to the net comes and goes, so I'll be writing in fits and spurts.

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Dave and Anke
triloboats swirl gmail daughter com

Saturday, March 8, 2014

Kicking Up our Heels: A Simple Kick-Up Rudder

Left side shows layout lines;
Right side is as built
Rudder Post not shown.

He who loves practice without theory is like the sailor who boards ship without a rudder and compass and never knows where he may cast.
- Leonardo da Vinci

Kicking Up our Heels: A Simple Kick-Up Rudder

Kick-up rudders allow a very shoal boat to put down a deeper rudder without permanently increasing draft. This maintains positive steerage when "she's kicking up her heels", as they say, at the top of a wave. If it grazes bottom, it kicks back without help, maintaining steerage throughout. When not underway, the Blade can be pulled up and clear of the water, reducing wear, tear, noise and maintenance.

This style has a number of advantages:
  • Easy to Design - No fiddly bits or close tolerances. All the relationships can be adjusted to fit most any vessel and personal flair. For example, the straight, aft edge shown can be altered with a fairly free hand. The Rudder Post (not shown) might be angled forward (rudder flops outboard at rest), aft (swings to center) or plumb (neutral), each with pros and cons.
  • Easy to Build - Upper Rudder, Blade and Tiller are all solid pieces.
  • Easy to Maintain - Aft hung rudders are easy to get at, mount and dismount. This one breaks down into two, lighter components.
  • Hell-fer-Stout - Solid pieces (no housings) are at full strength, and no pockets for hidden rot.
  • Self-Sinking - The weight (zinc or lead), placed low and aft of the Blade Pivot Bolt forces the Blade down and forward (a bit more on this, later).
  • Balanced - Area forward of Turning Axis reduces stress on Tiller and helmsperson.
  • Roll Forward - As hull weight descends (ebb tide or grounding in waves), the lower curve rolls the boat forward, sparing the blade from breakage.
  • Effective when Horizontal - Fully kicked back, the shallow 'Hook' stays immersed, but clear of ground, protected by the hull, while steerage is maintained
  • Can Steer while Standing - The Tiller Bearing Plate allows positive steerage to a high angle. This allows standing high for a good view forward.


Upper Rudder - This piece (shown in blue and cyan) has a Tiller Bearing Plate at its head, and Blade Bearing Plate low. The radius of these plates can be adjusted as deemed fit. 

Consider that only their radius (half their diameter) is in play at any given time, and that leverages applied vary by whether the near or further half is active. Thus, they must be sized to withstand forces leveraged by that amount, in its high stress mode. Larger is stronger.

Note the Tiller Stop (forward and down from the Tiller Pivot Bolt)... it's top side supports the lower edge of the Tiller at its lowest position, while it's aft side supports the Tiller when raised up to over-balance backwards... this lets the tiller be stowed to clear the cockpit.

It can be cut from a plank or plywood. Simply draw pencil lines onto the Upper Rudder along the underside of the Tiller when held at these two, extreme positions. Cut the Stop to match (it's forward edge is free for art) and attach in position on those lines.

Tiller -  This can be simple or artsy, so long as it is plankish along the Tiller Bearing Plate, and strong enough to stand up to the large Blade. Consider, too, that when kicked near horizontal, Balance is lost and Blade leverage increases dramatically. Better too strong than not strong enough! Consider a spare with its own Pivot Bolt.

Its lowest position should be high enough to clear obstacles within its sweep. It's stowed position should be far enough back that there's no tendency to karate chop forward on ya.

It's Pivot Bolt is abetted by a lock-nut, and large, heavy washers at both ends. We prefer none in the middle, to keep play to a minimum.

Blade - This piece (shown in white and cyan) is rounded at its head to match the bearing plate, and extends downward, fore and aft of the Turning Axis. Greater area forward (up to about 25% of the total, immersed area) eases steering and adds lateral resistance. 

The immersed Blade can be tapered into a foil shape for more efficiency. We tend to do a little of this, but don't get too involved.

Its Pivot Bolt should be pretty heavy, with lock-nut and large, heavy washers. One or two between Bearing Plates keep friction down for easy raising. Or...

To keep things quiet, we've cut a 'washer' of camping pad foam - same radius as the Blade Bearing Plate, and a matching thickness washer of HMD (plastic cutting board) - about 4in radius. Cut a hole in the foam to match the HMD washer, and mount them between Upper Rudder and Blade. The small washer keeps the bolt from cutting through the foam.

Retrieval System - This is a line led low on the blade to haul it up for shoal sailing or stowage. We like to pass it through a strong fairlead (it has to resist a load at an 'unfair' angle when raised), and fix in a clam cleat (toothy cleat with no moving parts). A stopper knot at the end of the line keeps it from feeding through the fairlead, and provides a grip stop.

Attachment/Turning Hardware - We prefer figure-8 lacing or crossed straps a la Wharram designs (subject for another time). Alternatively, lifeboat hinges are sturdy and cheap. But gudgeons and pintles work, too.


I'll leave you with a video of some operations made on our rudder, made somewhere along our learning curve. The lacing had not been secured from lateral slippage (Wharram calls for epoxy; we're installing strapping)... it had chafed internal to the Rudder Post holes, and failed in an exciting manner during an autumn squall. Gives a good look at the disassembled Rudder:


  1. (Posting on behalf of JOHN:)

    Hello Dave,

    Does the rudder blade have some sort of stop to prevent it from rotating so far that it hits the hull?

    How tight does the bolt hold the rudder blade and the upper rudder together?

    When you lace the rudder to the transom, is the line one continuous piece, or do you tie off short sections?


    1. Hi John,

      RE Blade Stop - It can (and should) have a stop, primarily to keep the blade from popping too far forward when hard over... the hook loses contact with the bottom... blade swings forward and the hook up, jamming against the transom.

      Typically, we've never gotten around to installing one, and have to lean back and manually push it down to return to center. Very infrequent, though (see Tightening, below).

      As far as contact with the bottom, we mount a furniture coaster atop the hook, which slides easily across the (copper) bottom). Not sure what it would would do to paint, but my guess is the Stop would get installed quickly if we didn't have copper.

      You'll want the Stop set to allow only a narrow gap to discourage weed from working in between hook and bottom. It's easy to clear (by lifting the blade), but one more thing.

      RE Tightening the Blade Pivot Bolt - We tighten the bolt to the point that the Blade is snug against the foam 'washer'.

      We want enough friction to discourage kick back (due to water pressure at higher speeds) or forward (when hard over, as above), but little enough to allow easy raising.

      Various other gizmos (stop and preventer) can control the kicking behavior... the main thing we want is lack of play/noise.

      RE Lacing -- We've used one continuous piece. Less work (but also less fail-safe) than multiple lacings.

      In the next incarnation, I think we'll go with alternating straps (towing strap or fire hose work well). They have the advantages of redundancy, near zero chafe, not needing additional 'fixing' and fully accessible mountings. Downside is concern for rotty problems under the straps.

      Tough call, though... the lacing works well. If we break down and glue them into their holes, then - as in Wharrams - they should be good for more than a decade. Redrilling every 10-15 years is no big thang.

      Dave Z

  2. (Posted on behalf of JOHN:)

    Hello Dave,

    I'm attracted to the lacing approach of attaching a rudder to a hull. What type of line did you use, which eventually abraded and parted? Some of the newer synthetic materials (Spectra, Dyneema, etc) are suppose to have a great deal of abrasion resistance, though they can be difficult to knot.


    1. Hi John,

      We were using a laid nylon 1/4in line.

      We've tried low stretch lines, but they're very hard to draw tight. As it is, we trucker hitch the ends together (arranged for an upward pull) to really cinch down.

      Ideally, 1/4 or 5/16in braided nylon would be ideal... light enough to stretch manually, with very good surface area for less chafe, and accepts fasteners to fix its rotation (see below). Unfortunately, that's usually a special order item... not found in local hardware.

      The laid line actually worked very well, strength-wise, with no tendency to sag.

      Normally, we fix the line's position with woodscrews through a few of the lower wraps to keep them from working (sliding port and starboard with wave pressure). But that doesn't work well with laid line... that got installed 'temporarily'. Since its position wasn't fixed, it was able to work, and chafed inside the rudderpost holes (which may not be as smooth as we'd like), where we couldn't inspect.

      Sigh. Another temporary solution past its prime.


  3. Our Wharram tiki31 had those lacings and they worked extremely well. The line I'd used was braided polyester, and I had epoxied as indicated by Wharram. The epoxy kept the water out of the plywood rudders. It was hard work though putting the epoxy into the holes and not cover the whole of the lacings which ended having hard spots of glue on them, I think that would eventually have led the hardened lacings to fail. Just watched your video, lovely place to spend time in! The quiet must be marvellous!

    1. Hi Joel,

      Those hard spots were exactly why we were queasy about using epoxy to glue the lines in place. Especially since epoxy can produce such razory edges.

      One alternative to trial might be 3M5200 or the like... elastomeric and soft, but with a grip equivalent to epoxy. Maybe even thin it with a solvent (one that doesn't melt the line!) for penetration into the lacing.

      My best thought (so far untried) is to clamp several lacings with quarter round metal, bolted through the rudder post. This would allow easy, repeatable adjustment, inspection, replacement and dismounting.

      And yes, that is a beautiful spot... one of the most beautiful along the coast. Alas, endangered by Sitka's 'need' for power (population stable to decreasing; consumption skyrocketing)... a dam and road system are in the works.

      Dave Z

  4. Thanks, Dave! Now I have to rework part of the Tiller/Rudder on Kairos! :)

    (No, really. Thank you.)