|Left side shows layout lines;|
Right side is as built...
Rudder Post not shown.
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.
[NOTE: The angled aft edge of the lower rudder looks good to my eye, but in practice can induce heavy loading on the tiller. Consider rotating it forward (by trimming the upper edge of the 'hook') moves its CLR forward and increases balance, reducing tiller load. In practice, we usually end up with this edge nearly vertical.]
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.
At one point, a figure 8s chafed through at a point we couldn't inspect (rudder post hole). The lacing partially unravelled. We stopper knotted it, temporarily and got to shelter for repairs.
Sooo. Now we're using two pairs of a double, opposed lacings; upper and lower (a third, middle set is optional). Opposition prevents rotation around the post (the cause of the chafe), and multiple pairs reduce the likelyhood of a complete failure.
One pair of lacing starts with a stopper knot, passes across the post as an S (half an eight), leads up one hole, passes through and S back. Repeat as desired.
An opposed lacing starts stoppered opposite the first, and the pattern is repeated in mirror fashion. Opposing lacings are doubling through each post and rudder hole from opposite directions.
Lacing ends can be trucker hitched together for tightening as line stretches. A dedicated lift line takes rudder weight off the lacings, further reducing strain and presumably, chafe.
We're currently using 3/8in, braided nylon line.
I intend to update this post and video, shortly.
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: