Looking for Kick-Up rudder idea/designs.

I'm working on a 26' double-ender design that I originally drew with a traditional "barndoor" type rudder hung on the sternpost. I've been convinced of the fact that a modern higher aspect ratio, kick-up rudder is the better alternative.

I'm considering switching to a rudder post type design where the blade can be raised above horizontal to keep it clear of hard objects while being trailered. A sternpost mounted rudder would certain make for a more easily removed rudder, but it would be nice the have a tidy little caboose on my vessel.

Many "kick-ups" are untidy and cumbersome in appearance and I would be curious to hear about or see if there are soon nice looking (and functioning)alternatives.

I'm also curious to find good methods for extending and retracting the blade. I was thinking of a heavier blade that self deploys (with some possible mechanical assistance) with a positive mechanical retraction mechanism. Another thread talks about a buoyant blade that will self-retract to horizontal and requires mechanical to extention. Do I have my wires crossed? Should I be looking at the buoyant type blade instead?

Also, I'm not sold on a rudder that isn't easily remove for road transport. Would it make sense to have a ruddershaft that separates inside the lazarette so the rudder can drop out?

 

Google "Gunning dory" to see a pivoting rudder blade on a double ender.

Alan

 

Greg, I have a patented kickup design that can be transom hung or under belly on a shaft. On most hulls it's minimum draft is the same or less then the hull, in the up position. It also doesn't have the blade captured between two "cheek" pieces, which is the typical approach, making for much less resistance at the top of the assembly. Drop me an email and I'll explain the benefits.

 

Thanks, Alan.

Is this the link?

http://www.woodenboat.com/forum/showthread.php?t=8120

Paul,

Eager to hear about your rudder.

Greg

 

Yes it is. That is to say you have a good photo of a lifting gunning dory rudder.
The cheeks are metal, probably bronze, and metal cheeks would be far better in terms of both attachment and water flow due to thinness.
If I were to design a pivoting rudder like the one shown, I would not use a mere bolt to join the two halves of the cheeks. I would instead join the two sides with a very large ring (say at least half of the rudder for-aft dimension), and that ring would be essentially a single piece with the two cheeks.
This large circular "bearing" would require a very large corresponding hole through the rudder.
The problem would seem to be how to assemble the unit. If the cheeks are one piece with the ring the rudder pivots around (probably stainless steel in any practical application due to cost, though bronze would be ideal), the rudder would have to be of at least two parts.
Yet the rudder should be a single piece also. How to build it?
I would probably construct the rudder from plywood laminations and afterwards apply two or three layers of glass/mat/epoxy.
If the rudder is in one piece, one side of the cheek assembly would be removable, assumedly with a series of flat head machine screws. The ring then would only be welded to one side.
Back to bronze, since stainless screw threads are subject to crevice corrosion. The ring bearing would have to be from (e.g. 6") thick-walled (1"?) bronze pipe in order to accomodate the (maybe 3/8") screws in your case.
Once assembled, the rudder should be very strong and streamlined, and it could be unassembled easily at any time to inspect or repair/replace the rudder.
Most all rudder cheek assemblies meant to allow the rudder to pivot are potentially weak due to the tiny connection point (pivot bolt). This goes for the small boat rudders made entirely of wood. The large bearing rudder assembly does require the plywood rudder to be robustly built since it has such a large hole through it.
However, I feel that the large-holed rudder could be reinforced with a bit of carbon fiber if warranted. Besides, the stiff cheek assembly would reinforce the weakest area.

Alan

 

Alan,

Lots of good ideas. I like your idea of the large pivot.

What do yo think of the pivot being made of something like HPE(?) plastic with some sort of a hefty through bolt? (countersunk or stremlined in some fashion of course)

Thx.

 

What plastics lack is stiffness and shape memory. Wood (in the form of plywood) is still the stiffest stable material that's affordable. White oak or similar hardwood is far stiffer (and twice as heavy) but the traditional method of bolting or drifting together several pieces is the only way to maintain flatness.
Nor can a hardwood rudder blade be epoxy-glassed or sealed.
Short of some exotic construction, I think plywood/glass/epoxy is far and away the only practical material for rudder construction for a boat like yours. It's not skin-dependant for strength, maintains shape for life, has the feature of custom-building directional strength to accomodate stresses from any direction (this is the amazing thing about plywood--- if you laminate a lot of thin ply layers, the direction in which they are stacked (grain orientation) can be calculated to bolster any directional strength at the cost another. Adding glass to this substrate, the glass also can be applied to favor tensile superiority in one direction over another.
Plastic (at least what is commercially available) has non-directional properties, and what properties there are are generally if not always inferior to plywood, including lightness.
In regard to the question of a larger bolt, realize the advantage of the large ring was to solidly and structurally connect the OUTER rim area of the cheeks, not to gain tensile strength of the cheek assembly in a horizontal (athwartship) dirction. what's wanted is rigidity to prevent spreading of the outer rim, especially at the trailing edge, which is necessarily open to allow the rudder blade to trail behind.

 

Alan,

Thanks for the clarification. I've read your posts at least 10 times now and I think I'm getting your intent now.

My current thoughts are towards a SS rudder shaft where the cheeks are welded to the rudder shaft at the forward edge of the cheeks. This would capture the blade laterally. Do you think that your SS ring could be slid in and captured with screws from both sides of the cheeks? This way would release both the ring and the blade for inspection. Also, the skeg would streamline to the rudder post.

What do you think?

 

Have you considered a rudder trunk similar to what is used on an International Canoe?
Makes for an efficient rudder tucked under the counter, maintains attractibe double ender stern detail and is still capable of being shipped for beacching or trailing.
SHC

 

Yes, the idea would work. In this case, a thick-walled ring of phenolic resin, drilled for through-bolts would work well. I don't see how that assembly could fail.

Like I said, stainless in (esp.) salt water should not have crevices if at all possible, and screw threads are crevices, so I would suggest flathead bronze machine screws passing entirely through the stainless into bronze nuts (there are ways to make the nuts nearly flush and streamlined).
Either that, or at least use some sort of barrier on the ss threads and inspect by removal annually. After all, bronze is ridiculously expensive now and you might go broke buying all those fasteners.
I think that using the bigger "ring bearing", the assembly is bullet-proof, and all you need to do is to make sure the rudder blade is strong enough.

Alan

 

Here is the Chris White-designed kickup rudder on the Hammerhead 34. This hull isn't quite double-ended, but it's not far off.

There is a cassette in a slot in the stern that pivots about a transverse axis forward of the stern post. The steering cables go through turning blocks that are located in line with that axis before going around the rudder quadrant (just visible to port; same starboard). This maintains tension in the steering cables as the rudder kicks up. The line loosely coiled on top of the rudder is the hold-down line - it goes from the eyestrap on the port side, over the rudder to the eyestrap on the starboard side, and up to be secured at the mooring cleat on deck.

The cassette/skeg extends to a distance below the transverse axis equal to the distance between the transverse axis and the stern. That allows the rudder to kick up when the rudder is turned, and ensures that the boat is still fully controllable when the rudder is partially kicked up.

 

Rudder design...

I played with a few designs, shaps, and compounds a few years ago.
The final unit was made using foam core...I made the core using a type A & B part of expanding foam in a simple mold made of 2x4s laid on plastic.
Then came the exciting part... I over-laid a templet of a fin of a grey whale and started cutting the foam with a grinder, cutting off everything that wasnt a fin... I then wrapped the fin in carbon fiber and faired the final unit.
With the addition of a couple pintals, we had a rudder that mimmicked a gray whale fin.. On a fixed keel 24 foot boat used for open ocean racing.
The keel had an overall height of 52 inches and the front to rear measurment was 10 inches at its longest part.
The boat performed fantastic with finger tip control...
The idea came from watching a program on whale migration.. I was amased at how well the whales would move around with little effort by the twisting of their fins.......
When loading it on a trailer, I would lift it off the mounts.........

 

Hey Everyone,

Thanks for all of the input.

Steve,
I wasn't able to track down a good example of what you are talking about. Do you have a JPG or link you can post?

Tom,
Very ingenuitive. Though it looks like all steering is lost if the rudder is kicked to horizontal.

Randyonr3,
No doubt, fins on water creatures have evolved to be very efficient. Sounds like your rudder worked out very well for you. I'm looking to try not to unship the thing for transit=One less item to rig or derig. With some imagination, my current rudder resembles a fin.

I feel like I'm trying to reinvent the wheel sometimes. I guess that happens when you step outside your comfort zone and realm of knowledge. I was originally going to have a good old fashioned barn door for a rudder. Nice, simple and easily built. After looking at internal rudders that are hinged to swing completely out of the way, I'm pretty sold on the concept. Not to mention a fairly sizable weight loss at the very end of the vessel.

Attached is a rather crude drawing of the geometry of my current thoughts. I just have to figure out the nuts and bolts of making it work.

 

Kick up rudder ideas

Probably not applicable to your boat LP, but others may see a kickup rudder thread and find it useful. Check out these rudders: http://www.dotan.com/

 

Not at all. The rudder is fully controllable as it kicks up.

The turning blocks leading the steering cable to the rudder quadrant are in line with the kick-up axis. That means they maintain their orientation relative to both the rudder and the bellcrank attached to the tiller, and there is no change in the tension in the steering cables.

The reason the upper part of the rudder is a fixed skeg is to avoid interference between the rudder and the hull as the rudder kicks up. When the rudder is at approximately 45 degrees from vertical, the top of the rudder is just past the edge of the transom. So the rudder does not become mechanically locked as it kicks up.

The only loss of effectiveness is due to the hydrodynamic effects of sweep, loss of depth, and the reduced wetted area of the rudder as part of it is above water. Which adds up to a considerable loss, but most of these effects would be true for nearly all retracting rudder concepts.