Kick-up rudder design options

I think i just used that same link images to guess the 3d design, pictures can be used to recreate 3d objects and bungee cords are toxic synthetic while a well maintained spring can do and work forever

Yes make a 3d print and dont forget about using ropes too, metal parts sometimes are overrated

 

Okay, but even with ropes, I don't see a quick way of folding this design compact for transportation (at least, without having to undo a bunch of stopper knots). What exactly did you have in mind there?

 

There are plenty of knots and splicing and rope carabiners, i don't know, the only thing i know is bringing a screwdriver to remove old salty knots loll

 

Nice work on the original rudder, CAD, and animations.
I am getting acquainted with the Sunfish rudder systems, I have one boat that uses the old bronze 'mousetrap' and another that uses the aluminum cheek with springs.
I would remove the tiller and extension for travel rather than design to accommodate it.

 

Ok, so I scratched my head at this for a bit more, and worked out a geometry that allows full 180° motion without needing a cut-out in the front of the case:



(In fact it is possible to go even beyond 180°, but it's not needed here)

The issue with folding for transportation still remains.

I get it, but it seems to me that devil is in the details here. If the tiller is attached to the blade with a line instead of a bolt, the forces from the rudder will tend to split the Y-shaped part of the tiller apart. It would have to be made extra beefy to resist that. Bolt naturally prevents that because it keeps the forks of the tiller from spreading apart. Second thing is how to secure that line? It would have to be very taught to function properly (so the rudder is not loose), which probably means low-stretch rope, and probably a cam cleat on the side of the tiller. Attaching/detaching the tiller would require threading the rope through 3 holes, which would have to be sized pretty close to the rope diameter to avoid slack in the system. I don't know about this, it feels a bit sketchy. I will test this with a 3D print to see how it feels in reality. Maybe it's not as bad as I think.

Thank you! Yeah, I suppose it's a matter of preference, but having over-complicated my last boat, I want to go for maximum convenience this time, even if that means more time to build the boat. All these little things add up very quickly when launching and packing the boat, so I want to make it as "plug and play" as possible while staying relatively low-tech and without complicating things even further. Any suggestions on how to design the attachment between blade and the tiller so it can be attached/detached in seconds without any tools?

 

You are welcome. In the last animation (I really like how the cheek and tiller end come together), I would propose using a pin with a self-contained ball or lever to attach the tiller end to the upper rudder blade. I would leave the main pivot, blade to cheek, left in place (needs wrenches). I have such pins on my mast crutch and on the quick-release lever of my forestay (it's a 21' or 6.4m boat).

 

Thanks for the suggestion! But it seems to me that these pins are not designed for axial forces, only shear. In this use case, the tiller fork pieces that hug the blade would be spreading apart because of the twisting forces. If there was a bolt here, it would keep the fork ends of the tiller at a constant distance, preventing them from spreading, and greatly increase strength. Is there any kind of quick release pin/lever that is designed for axial forces, and can be made fast and rigid at a certain length, like bolt/nut combo?

EDIT: I refined the design a bit more to make it more compact and aesthetically pleasing, also started planning for the attachment points (grey eye-pads) for the bungee:



The bungee is supposed to serve two purposes - pull the blade into a fixed up/down position, but also to keep the tiller from sagging down when blade is up. However the angle is all wrong, as you can imagine it would do the opposite here. So my idea is to have an additional catcher hook that would catch the bungee when blade is semi-raised, causing the bungee to pull from entirely another angle when blade is up. It also has the benefit of equalizing the working length of the bungee in up/down positions. It is really difficult to explain in words (and to test the action in CAD), so I 3D printed the thing, glued on some toothpick ends to represent the eye-pads/hooks, and used a rubber band as a bungee.



For whatever reason doesn't show this gif, so if you can't see it above, here is the link to watch it: imgur.com https://i.imgur.com/9ljs8be.gif

As you can see the action is pretty good, and there seem to be several stability "islands" both for the blade and the tiller, which should be super convenient. For that middle bit that changes the angle of the bungee I can probably use something like this:



Alternatively, that middle point could be the attachment point for the bungee, rather than the one at the front edge of the case, although I suspect the change in bungee length might be too extreme while maintaining adequate tension. Difficult to say, I might probably have to fine-tune these details once I build this thing. But overall it seems to function very well. The only remaining detail is quick removal of the tiller from the blade while still having the pivot function as a bolt, holding the fork of the tiller at a fixed and rigid length.

 

As nice as the revised design is,I would recommend that you add some kind of system for retaining the rudder in the raised position.I have seen a few instances of similar designs being wheeled enthusiastically down a ramp and coming to an abrupt halt when the rudder swings down.In one case the damage to the transom was so severe that the boat was unusable for the weekend.A little thought about the leverage that a high aspect ratio rudder can impose and the weight of the boat plus trailer soon indicates why.

 

Good point, thanks for the warning. I will keep this in mind. I just updated my post above with a video of a physical test, check it out if you like.

 

Slick

 

For those who are interested, I further optimized the design. Decided to go with another eye-bolt instead of hook in the middle to simplify the setup, but keeping bungee longer to avoid stressing it too much.

Link to gif: imgur.com https://i.imgur.com/acZoxlC.gif (does anyone know why this forum sometimes allows posting image (from a link), but other times just shows "missing image" icon instead?)

I temporarily solved the issue of attaching/detaching rudder by encasing bolt and nut into large knurled handles to facilitate tightening/undoing nylon lock nuts by hand, without requiring tools. But it's still a hassle, and a poor solution overall because during gybes the mainsheet might get caught on these knurled handles. If anyone has any better ideas on what I can use there (something like a quick release pin, but one that can hold axial forces and keep the fork of the tiller at a fixed width), please do share. This is the only bit that I can't seem to solve, and then this design is good to go. I will gladly share CAD files on thingsverse or elsewhere

 

Here is a video on how to cast a rudder cheek from aluminum, demonstrating that it can be done using simple tools. I got the part when he was fininshed

Could the fork of the tiller be metal plates or a casting?

 

That is seriously impressive. I never thought that pieces with such complexity could be made with casting. Unfortunately I don't have the facilities for anything like it, but I will consider it for the future. As for the tiller fork, yes, it can be made from metal plates, but even with current method (carbon fiber layup) it can be made sufficiently strong. It's just that the load path is not ideal if the blade/tiller attachment point is allowed to spread. Sure, it can be brute-forced by making everything extra beefy, but I just can't help but wonder if there is a more elegant solution here

 

Laukejas, I think that you will need to move the pivot pin in the tiller before that last design will do what you intend. The pin in the tiller must be above the pivot pin in the rudder. Do a vector diagram to see whether my notion is correct.

 

I assume you mean this is required in order to make it possible to raise the rudder blade by pulling on the tiller? If so, then yes, indeed in the current design pulling does not work, because the tiller pivot pin is above the blade pivot pin, but that is intentional, so that pulling on the tiller during normal steering (there is always some pulling force) the blade wouldn't jump up accidentally. Instead, to raise the blade, you have to "kick" the tiller down in a fast motion. Doing this will cause the tiller to rest on the front of the rudder case, making it a lever, and that causes the other end to go up, raising the blade:



After the blade rises up to horizontal or thereabouts, the geometry becomes suitable for pulling on the tiller to raise it all the way up, although I suspect the bungee will do that automatically. Actually you can see this lever action in that video recording I made, here it is again: imgur.com https://imgur.com/9ljs8be. Notice how I don't pull on the tiller, but kick it down to send the blade flying up.

This might make me sound smarter than I actually am, because I discovered this by accident after I made that model. I though that raising the tiller would indeed be more difficult with this geometry, requiring to raise it very high to get an angle good enough to get enough leverage, but this kick-down is far more effective... And fun