Kick-up rudder design options

Hi guys, long time since I posted here. To a surprise of no one, I'm designing my 4th lightweight sailing dinghy for racing in open-class regattas. I'd like to consult you about kick-up rudder design for this new dinghy. I have the following requirements for it:

1. Raising and lowering the blade should be as quick and easy as possible, preferably done with one hand and not requiring me to let go of the tiller or walk to the transom.
2. I often have to launch from shallow water, so it would be great if rudder could be kept at partially lowered position for initial steering until I get into deep water.
3. Kick up automatically if grounded.
4. When raised, the blade should be as high as possible, preferably vertical (pic for reference of what I mean by "vertical").
5. Not absolutely necessary, but it would be great if it was compatible with semi-balanced blade design (where the blade protrudes forward from the case to reduce forces on the tiller).
6. Since I'll be transporting the boat a lot, the rudder should be as simple to set up and fold into as compact package as possible so I can stuff it into a bag and put in the trunk of my car. Hopefully without having to undo any screws or pins. Here is a pic from my earlier boat to illustrate what I mean by folding compact:



That's about it. Ok, so I've done my research, and I am considering 4 designs, but none of them fully satisfy the requirements above, and I'll explain why, so hopefully you can tell me if they can be improved or if there are any better alternatives. I'll show a quick GIF from my CAD designs to convey they idea of each. Please don't mind the different textures, etc., I just threw this comparison together from various projects.

#1 Traditional swivel rudder with 1 line to raise it, 1 to lower it, or 1 line + lead weight:



Pros: can be raised quite high, including full vertical with smart placement of the lines.
Cons: requires blocks/fairleads, messing around with lines and securing them, no automatic kick up (unless with lead weight or some smart bungee cord system).

#2 Open cassette style design, like on the Goat Island Skiff. I had this on my previous boat.



Pros: simple, reliable, quick to set up, compact to transport, very safe during grounding.
Cons: requires walking back to the transom of the boat to raise or lower. Also can't be used with a semi-balanced blade, as the blade has to be straight.

#3 Not sure what it's called, I copied this design from Dotan rudders - basically a kick up with a connecting rod/plate between the rudder blade and the tiller.



Pros: very convenient to use, can be held in either position with a bungee around the tiller, kicks up when grounding.
Cons: doesn't raise up vertically, doesn't pack well for transporting, more difficult to repair if it breaks. Also, it's a very tall system, I mean it literally takes up a lot of vertical space (compared to all other designs here).

#4 Also not sure of the name, I copied this from Grabner catamaran designs - tiller connects directly to the blade, and is pushed forward or back to raise and lower the blade.



Pros: simple, easy to use, also can be held in either position with bungee, kicks up automatically.
Cons: doesn't raise up vertically (at least I can't seem to make it do that), doesn't pack well for transporting (tiller can't rotate enough to become parallel with the blade). I also suspect it can be a bit prone to breaking in semi-raised position because of a small contact area between the tiller and the blade, essentially turning it into a single point of contact. Still, this one holds most promise, if I can figure out a geometry that allows raising to full vertical and compact folding for transportation.


So as you can see, I've done some preliminary work, but I can't seem to find a design that fits all the criteria I listed above. Can anyone offer any advice?

 

Good you should upload them to thingiverse and SketchUpwarehouse and grabcad

If you want to raise vertically you could just build a pulley mechanism with ballast attached to the tip of the blade so the falling weight lifts the blade when the rudder is released from position

You can modify the last system placing an external disc so the rope follows the disc and rotates the blade all the way up

 

Interesting idea! But if the blade is raised all the way to the vertical, that means the hole where the tiller is attached should end up 180° from where it currently is, so almost at the position of where you drew the red dot. Obviously that would interfere with the case. That is the issue I can't seem to solve, wherever I place that tiller/blade attachment point, it ends up 180° on the other side and interferes with something. This could be solved by having the tiller attached to only one side of the blade, and the rudder case would be a simple plate attached to the blade on the opposite side, but this would be very weak, as the steering forces would keep pulling the tiller away from the blade, with only 1 point holding them together, creating torque and easily breaking it.

 

I have used a range of rudder types over the years and unless I could be certain of never sailing in shallow water,I wouldn't go back to the cassette type.It is difficult to find a shear pin which is both secure and likely to yield before damage is sustained.Similarly,a weighted rudder on a pivot has no place on a performance boat,we should all know by now that weight in the ends of a boat is not helpful for performance.Since the mid 1990's I have used a pivoting rudder blade (several actually in different boats) and held it down with a non stretch line which is secured in a Clamcleat CL257.The force at which the cleat releases can be adjusted and I haven't been disappointed by the result.I'm happy to use a permanently attached tiller as the assembly lives inside the boat on it's trailer.If I needed a more compact solution I would tend to the direction of a tubular tiller,with an external packer that makes it a good fit in a tapered socket-a lot like the Laser/Kirby Torch / ILCA-and I would use the downhaul line in a similar manner to the line threaded through tent poles for keeping all parts linked.

Any design that depends on the over-centre principle can work but it is absolutely essential to get the geometry correct as you can't easily go back and make a small adjustment.Before typing this reply I did a quick search for ready made rudder stocks from the traditional UK makers and the selection is greatly reduced in these times.I confess to having thought of producing my next version from carbon and may yet do so as I will achieve precisely the piece that I desire that way with none of the compromises that a ready made stock would necessitate.

 

Thank you for your comment! For the cassette type, I never used a shear pin, I used a bungee, which also has the benefit of amortization when grounding, yet will still be the first thing to fail if grounding is hard enough.

Auto-release camcleat is a great thing, but in general, when you need 180° motion for the rudder blade, any design with ropes seems to become quite complicated, requiring fairleads/discs with grooves/something else to make these lines travel along the desired path and provide leverage. Perhaps it can be done without such complications, but I can't seem to find a way. Which is why the over-centre designs, as you called them, seem so enticing, they do away with all that complexity, especially #4 design that I showed. But yes, you are right, geometry has to be spot on. I have worked out manufacturing methods that can yield me parts with very tight tolerances, so that's not an issue, but designing one that can make the blade go 180° seems pretty darn difficult.

 

Just use a metal disc as back plate and will hold as a cassette

The drawing above was symbolic, the cord should be shorter route so the movement of the tiller to uplift position would be shorter too

You can use a metal spring with spares too

 

I don't really understand the need for 180 degrees of rudder rotation.I've always been happy enough to lift the rudder clear of the water while afloat and to remove it from the boat when ashore.Could you explain why it is a requirement please?

 

I'd lean towards #2 as it's closest to what what I'm familiar with. It's possible to raise/lower the rudder with up/down lines along the top of the tiller if you can live with a vertical staff (removeable for transport) for the up line. Cant the vertical axis of the rudder a few degrees forward and you will be semi balanced board down plus less chance of ventilation.

 

On the water it doesn't matter, true, but it's very convenient when temporarily parking the boat on the shore in a crowded regatta, when the wind is coming to the shore, so you need to put the transom on the grass. Having the blade go all the way vertical means the boat takes up a lot less space, less chance of someone tripping over it or damaging it. Also allows to attach the rudder away from shore and carry/troll the boat to the water, it doesn't get in the way. Sure, you can always remove the rudder completely if these things I mentioned are an issue, but having the blade go all the way up just makes it that much more convenient.

Yeah, I have considered a vertical staff idea, but it does seem very unsightly and complicates an otherwise very simple system... Still, worth thinking about, thank you. The axis angle is also a good idea.

 

maybe it should be smooth . Btw. why most of sailing vessels , use very risky fixed rudders .No kick up. Orcas like them .As well shallows.

 

Ok, I seem to have found a way to make the #4 design to allow raising the blade to fully vertical position.



The front cut-out looks a bit ugly when the blade is lowered, but I can probably find a way to blend it in better.

This design satisfies *almost* all requirements, except for compact folding for transportation without having to undo any bolts or anything. This is as compact as it gets, which is not compact at all:



Any suggestions?

 

Looks like thats decent solution, we should patent it and sell trillions and buy facebook, lol

You could share it on thingiverse, you can make it with plywood and some metal backplates to reinforce it

And don't forget in case of low tide and reefs surfacing, the other option allows you still using the rudder in 90 degree position if the cassette is underwater just following the hull depth

I didn't know how the #2 dotan system worked to be honest, i just uploaded the sunfish kickup rudder years ago to sketchup
3D Warehouse https://3dwarehouse.sketchup.com/model/1777082a-d719-47af-87ff-63fdee51bcc0/sunfish-kick-up-rudder

And also made a custom fixed kickup rudder


However for big boats rather this owen clarke kickup rudder looks fine

 

They say you can't get rich building boats, but no one said that about rudders

I think this design should also allow using the rudder in partially lowered position, it just wouldn't be fixed, so you'd have to mind the position of the tiller all the time. But I suppose that's okay. The bigger issue is folding for transportation that I mentioned, I can't seem to find a geometry that would allow the thing to fold compact. Perhaps it is not possible without sacrificing something else. Maybe there is some way that the tiller could be quickly detached from the blade without undoing any bolts or any high tech solutions. There is the traditional way of attaching tiller, like this:



(from the video on Nutshell Pram build)

Unfortunately, I can't think of a way to adapt something similar to my design because of the way rudder blade swivels, so that the tiller doesn't accidentally fall off when raising/lowering or during capsize recovery...

 

The simplest thing is using ropes instead bolts and also recovery rope tethered to the thing

 

Sorry, didn't see your post edit until now Oh, so you are the guy who designed that sunfish kickup rudder? The one from here? I kind of based my latest design on pictures from that link lol Thanks for sharing the link, it is even more clear than the pictures. The spring is a nice idea. Although I suspect it can also be done with a bungee as a low-tech solution? I thought about it some more, and realized that if I don't need fully vertical blade, sacrificing a little bit of angle (still good enough), then I basically arrive at what you designed there. Here's my latest revision:



As you can see I'm considering adding a pin to help transfer the loads between the rudder blade/tiller and the case. Although perhaps this is not needed, I'm not sure. I will 3D print some samples and try to bend/break them to try and get a feel of where the actual load paths and weak points are, my brain is having a difficult time braining after a recent party.