Kick up Rudder - downhull?

https://www.owenclarkedesign.com/Twin-rudder-lifting-kick-up-steering-system-design
I read somewhere that the effectiveness is questionable. Why?

I saw that Mumby's cat had rudders with some kind of brake fail-safe kick up.

 

I understand the philosophy and in some instances it can led to breakthroughs but there is also the probability that an amount of time will be lost while re-inventing several wheels on the way to the new idea that does work.

Those IMOCA rudders can be lifted to clear debris,they are normally locked in place and it is normal for the windward rudder to be allowed to lift as it will be well clear of the water.They are superbly engineered in every respect.Without any lead getting involved.

 

It also precludes learning from other people's mistakes, which I submit are the best mistakes to learn from. For instance something I have witnessed more than once is a ballasted rudder/tiller assembly being dropped overboard, sinking and being lost. There is something particularly infuriating about the forlorn snatch that just fails to grab the item as it disappears beneath the waves.

 

This reminds me of the time I lost my wedding ring in the beach of hawaii on my honeymoon, slipped from my freshly lotioned fingers from sunblock and i slowly watched if fall from my finger into the ocean floor about 50 feet from the shore....Long story short by the grace of God I found the gold reflecting in the sun and grabbed it while fighting the ocean waves.

Definitely don't want that feeling again and will work on a tension system using bungee cord as suggested.

 

This was an interesting thread. Sorry for re-introducing it.

My daysailer's rudder has the typical pull-down and kick-up lines listed in the various posts. Is anyone aware of a horizontal foil that has been used to provide downward trim to a kick-up rudder? I'm thinking that it would automatically rotate the rudder down/forward. It could be mid-height like an anti-cavitation plate, or at the very bottom like a keel foil. A foil at the tip may also eliminate a little bit of tip vortex.

Any experiences?

 

Piper I have some rudders in my future. My ideas have not gone past the mental flatulence stage yet, so no drawings, however I will attempt to describe.

I'm thinking of using dagger style rudders like in the animation below so that they can be raised vertically for shallows, trailing, beaching, and all that.

I would hinge the dagger case at the top forward edge to a vertical beam that hinges off the transom for steering; and use a strong magnet at the bottom encapsulated in epoxy, with a corresponding encapsulated steel plate. So instead of hingeing the dagger case off the transom, hinge a separate beam that the dagger case can flip up from under impact.

If the magnetic system is problematic a plastic or timber sacrificial shear pin could be used, or perhaps stainless tension springs.



Hopefully it makes sense, it is late here.

This is worth a look, and the animations are great.
Kick-up rudder design options https://www.boatdesign.net/threads/kick-up-rudder-design-options.69575/

 

I don't understand the description,could you post a sketch of what you have in mind?

 

This is what I got from horizontal foil on a rudder to provide downward trim like a 'keel foil' (wing keel?). Larger surface is the rudder, smaller is the downward trim bit. I imagine it'd be drawn out more curved and blended and such in a real application.

 

It is entirely feasible to make something like that but the only sort of rudder it will hold down would have to have neutral buoyancy and be installed in a daggerboard style rudder stock.The surface area is too small-as drawn-to create any significant downforce and you might just as well use a thin endplate to eliminate the tip vortices and avoid disturbing the trim of the boat should you consider making a larger version.Many years ago I posted a picture of my own rudder with a tip foil and you might be able to search the forum to find it.The intention was to have any force developed return the boat to a neutral state of trim and to lose the induced drag of the tip vortex.It worked up to a point but I had reduced the area to compensate for what I hoped would be the greater efficiency,only to find that as the boat heeled on the lee bilge too much rudder area lifted out of the water for the rudder to be effective.I have since made a larger specimen.

 

Thanks for the sketch, Tops! That is what I had in mind.

Yes, the hydrofoil shape will help to provide down force. But the other part of the feature is that as soon as the rudder tries to tip up behind, that little foil will act like a deflector and drive the rudder back down to its home position. No moving parts other than the tip-up rudder.

I was hoping to not have to invent this foil. I was expecting that some class of boat was already successfully applying something like this. Is anybody aware of a rudder with a deflector built in?

 

Unless you use the rudder blade in a daggerboard style,it won't stay down from the force generated by the foil.The drag component of the whole assembly will tend to make the entire immersed area tilt aft.If you plan to use a pivoting rudder blade it will still be necessary to use a downhaul line and it needs to be an ultra low stretch piece of cordage or the drag will mess up your carefully calculated angle of incidence.You might look for pictures of modern International 14's to see what they do with rudder foils.Their function is to change the trim of the boat and an adjustment mechanism is included.