Kitchen rudder

Barry , thanks for the pictures. You have been running this for a while now so could you tell me if you have had trouble with the clams collecting weeds and such? I haven’t worked on my design much but every time this thread pops back up I start thinking again

Gary

 

Hi Barry - nice job !

I don't know if you're in a position to scan your drawings, but a copy would certainly be useful to have, but only if it's no hassle.
Question - when approaching this job - did you adopt a straightforward 'draw it and build it' approach, or did you undertake any experiments with the positioning between prop and clam-shells first ?

I'd be interested in learning how you find the device to operate in practice - is it's performance as good as you would like ? Are there any snags to be aware of ?

'best

Colin

 

When I designed my Kitchen Rudder, I first built a mock- up of the clam shells using a round card board form common in the construction industry. Some call these Sonotubes. I use a 12 inch diameter propeller so I selected a Sonotube of 14 inches diameter. The size was influenced by physical constraints of my vessel. This allowed me to visualize the physical arrangement before preparing a set of build drawings.

I did not conduct any tests, rather relied on Admiral Kitchen’s success, and the fact that many open vessels about 35 feet LOA were built for and used by the British Navy. These used Kitchen Rudders. Apparently all British vessels of Cruiser size and larger were fitted with these Gigs. Some of the British built open cutters that used Kitchen “Gear” were also used by the Canadian and Australian Navy.

This suggests the key feature of the Kitchen Rudder… exceptional maneuverability even better than twin screws… very fast stopping, right angle turning, very slow speed, reverse, stern thrust, etc…. all accomplished without changing engine RPM or engine load.

When I read Admiral Kitchen’s patent, I find reference only to the reversing feature whereas the great maneuverability provided by the device is reason for the British Navy use.

The mechanism used by the British navy to operate the Rudder clam shells was similar to the mechanism that I use, a screw that facilitates rapid opening and closing by turning a crank or hand wheel fitted at the end of the tiller. One very important feature of any operating mechanism is that it is self locking, that is the clam shells lock in any position regardless of the force of the water stream acting upon them. It is essential that the force applied by the coxswain to open or close the clam shells regardless of their position does nor change and is without effort.

Using this system, there is not the separated functions as is typical of traditional boat control; shifting gears from forward to reverse, changing engine speed, steering boat. Using the Kitchen rudder, engine speed and load is set and fixed, one hand usually the left grips the tiller and moves the tiller from side to side as needed for steering, the other hand usually the right is in close proximity with the left hand and rotates the hand wheel to control speed and direction. This is a harmonious relationship of mind and hand function, opposite to the discordant relationship typical of conventional boats. However it is not a natural process, rather it requires practice to be able to manipulate the rudder controls in a subjective manner without requiring an awareness of a specific action that will result in a specific result. This is very similar to the process of learning a new sport such as skiing, tennis, sailing. During the learning process individual actions are identified and practiced but it is only when these separate actions are accomplished as one natural mind/ body connection that a real level of competence is attained.

I am attaching images 12 and 13 that illustrate the relationship of clam shell and propeller. Note the propeller is positioned so that clam shells encircle the propeller during port starboard steering.

 

Many thanks for the information.

Ah - a misunderstanding. When I asked about experimentation, it was not in the sense of attempting to improve upon Kitchen's device (I wouldn't dream of being so presumptious) - but rather more in the sense of a method to determine whether or not the patent drawings were simply illustrations of the principle, or whether they could be relied upon as fascimiles of scaled-down engineering drawings, albeit non-dimensioned. You obviously didn't let such concerns prevent you from producing such a fine reproduction !

Well I must admit that it is the reversing function which first drew me to this device. My own requirement is for a simple and cost-effective method of producing reverse thrust for a sail-boat, when fitted with either an inboard or an outboard engine. It does seem a nonsense to me to install an expensive marine FNR gearbox (the leisure varities of which are not known to be exempt from failure in use) on a vessel which will spend the lion's share of it's time under sail, and even when under power, will only have a requirement for neutral and reverse when close manouvering - which probably represents much less than 1% of it's time under engine power.

In case anyone else is of like mind, since first researching this topic I've discovered the Doeffeur's (sp?) Rudder - which is a development of the principles of Kitchen's Rudder, as well as drop-down reversing cowls as commonly fitted to modern water-jet engines.

Colin

 

Saw something quite similar in concept to what shown on BCM thumbnails about 1999 in Fremantle Australia.Install onto a big tug boat under construction at that time at Austral shipyard if I'am not mistaken.

 

How a Kitchen rudder works

Am attaching a sketch that illustrates how a Kitchen rudder influences propeller stream.
If the image posts as a thumbnail, click on the thumbnail then click a second time on the image then click on the icon that appears at the bottom right corner. This should enlarge the image so it is easily viewed.

Barry

 

Nice illustration Barry that should clear up any mystification.

Gary

 

I agree, an excellent diagram. But - at the risk of raising an old chestnut - where does the water (the flow of which is being shown as arrows) come from ?

Of course it's being draw into the rudder from the other side of the propellor. This is where the fun and games start. If you draw in these flow arrows as well, then reversing isn't quite so simple.



As water is more-or-less incompressible, the propellor both pushes AND pulls. My logic says these forces should more-or-less cancel each other out, and a net reverse function shouldn't result. But it does.

Colin

 

A Kitchen rudder functions to provide reverse motion in a different way than a conventional transmission.

This is best understood by referring to Newton’s third law …for every action there is an equal and opposite reaction.

First consider forward motion. Using either a Kitchen rudder or conventional rudder. The propeller imparts energy to water that results in a backward force, the propeller stream. This is the “action”. The “reaction” is the same force in opposite direction that pushes the engine in a forward direction. Since the engine is connected to the vessel, forward motion results.

Using a conventional transmission, to move backwards, propeller direction is reversed, so the “action” is the propeller stream moving in a forward direction. However the force is less because the stream impinges on parts of the vessel hull. The equal “reaction” force pulls the engine backwards, and again since the engine is connected to the vessel, reverse motion results.

Now consider Newton’s third law when the Kitchen rudder clam shells are closed. Since the engine is rotating in a forward direction, the propeller stream strikes the closed clamshells. The shape of these reverses the stream outward and forward ( note the arrows). If the angle is 45 degrees then force component outward is the same as the force component forward. Again some of the forward force is interrupted by the hull so what remains is the “action”. The reaction is an equal force pushing on the closed clam shells that in turn pushes the vessel in a backward direction.

Another interesting and useful characteristic is effect of the outward force components when the clamshell are closed. When the rudder is midships the port and starboard outward forces are balanced and have no affect. However even a small tiller movement has large turning effect when moving in reverse so reverse control is very predictable. At 22 degrees of tiller movement, the vessel pivots rapidly.

When moving forward, rapid closing of the clamshell and at the same time turning the tiller about 22 degrees results in almost an instant and abrupt stop and 90 degree turn. I often do this maneuver during demonstations and then continue to hold the tiller at 22 degrees. This vessel continues to swivel rapidly without forward or reverse motion. Try this with a conventional rudder and transmission.

If there is enough interest, I will put together a description of the Kitchen rudder operation from the helmsperson’s perspective. Based on my hands on experience, I believe a Kitchen rudder provides maneuverability and control that is better than any conventional system . and it’s great fun to operate
(after understanding the application of Newton’s third law)


Barry

 

Please do. It still seems as though a lot of readers do not understand that it is the column of water leaving the propeller that imparts the movement to a boat - think waterjet; think waterjet reversing; think waterjet turning.

 

Indeed - your comment confirms to me that there is a focus only on the positive pressure side of the propellor, as if negative (pulling) pressure isn't doing anything. I found a particularly good description of what I am trying to convey at: http://www.boatbuilding.com/article.php/designofpropellers1 and I hope no-one will be offended if I quote from that web-page, as I could explain it no better than this:

So as I understand the issue, there are both positive and negative components to the thrust. Although the positive pressure side has a higher velocity, providing the water does not cavitate, an *equal* amount of water must always be moved on both sides of the propellor, as water is (for all intents and purposes) incompressible.

Now providing the negative and positive components 'complement' each other (i.e. their directions of flow are working to aid each other), the net result is forward motion.

Now if all the above theory is sound, then when the Kitchen Rudder (in reverse mode) deflects the positive pressure flow *forwards*, the 2 flow streams should cancel each other out, and there should be no net thrust, and thus no net movement through the water.

That the Kitchen Rudder works in practice, implies that something essential is missing in the model which is being used to explain how propellors work - either that or at least one person (me !) has a misunderstanding of something rather basic.

Ok - so this is clearly an academic issue - but, I hope interesting even so.

Colin

 

From the August/September Pro Boatbuilder online.
http://www.proboat-digital.com/proboat/200608/

Gary

 

I think you're missing the fact that the thrust is due to the whole flowfield, not just the local force on the propeller. The prop produces a narrow, high speed jet directed at the rudder clamshells. As it hits the clamshell, it slows, spreads and turns forward.

The attached picture of the potential flow into an inside corner, produced by the Ideal Flow Mapper applet, shows qualitatively what's happening. The jet from the prop forms a wall jet along the inside of the bucket formed by the clamshells. This wall jet has tremendously more surface area than the round jet at the prop, and it entrains outside flow with it.

This works like an ejector thrust augmentor, transfering some of the energy of the high-speed jet from the prop to a larger low-speed jet coming out (backwards) from the bucket. The large amount of low-speed flow directed backwards produces more thrust than the force acting on the prop itself.

Another way to think about it is the high pressure due to the low speed flow inside the colored arc in the attached picture means there's a high pressure region inside the bucket. The area of the bucket is larger than the area of the prop, so there's a net force backwards. Both the momentum and the pressure/force balance approaches are equivalent, of course - the difference is determining which one is more convenient based on what you know!

 

Am attaching a composite image to illustrate propeller thrust reversal when Kitchen rudder clamshells are closed. Note how a very slight tiller movement results in a significant imbalance of water flow. Thus reverse steering is very responsive to small tiller movement and helps to explain the maneuverability of a vessel equipped with a Kitchen rudder.

 

Thanks for the pics. I'm not sure if I've mentioned it in earlier postings to this thread, but a 26' steamboat in Texas is able to BACK 300+ feet out of a marina in a STRAIGHT line. I have this from several reliable sources. I've also heard "tales" of over enthusiastic coxswains in the Royal Navy who seriously damaged transoms on pinnaces by "backing down" too rapidly - know anything about that "walrus".