Karlis,
The rudder of the folkboats are plenty good for general use. Remember, at just over 2 tons displacement, they are just about ¼ or 1/5 of La Chica’s displacement, and tiller forces will thus be much lighter. Besides, the folkboats are both directionally stable and their tillers are long, so the actual force needed to hold them is light enough. However, the direct-drive windvane will have to work on a short tiller, 30 – 50cm long to get enough movement, and then the torque from the windvane may not be sufficient.

This is a very critical point with the direct-drive windvane: Gearing. Remember, an OGT MkI should not be regarded as a stronger helmsman than a 6-7years old kid, so tiller forces must be that light.

As I wrote yesterday, I would like to try fitting my windvane (Otto) to an auxiliary rudder, set about 50cm to the side of the main rudder. This would be a fairly hi-aspect-ratio rectangular rudder with a vertical shaft. I would make the balance adjustable such that I could fine-trim it for lightest possible tiller forces without the rudder starting to ‘snake’ when let to trail freely.

Now, different boats have different sterns. Fitting a vertical rudders to sloping sterns involves the same challenges as fitting outboard engines. Some sort of adapter is needed.

Recently I sketched a rudder for your boat. Generally I think that will improve your steering. If you want so light tiller forces that a windvane could drive it, you must be prepared for fine-adjusting the balance (trial and error). This can be done by having the pintles adjustable; you can add the balance horn area, or you can shave off the rudder along the trailing edge until the balance feels right.

Cheers,
Arne

PS: If that aux. rudder on my IF turns out as effective as I think it will, then I have effectively made one of two twin rudders. I could then remove the original rudder, move the outboard engine to the centreline (much better) and then build and fit the twin rudder. Since these rudders are working in free water, not in the thick boundary layer abaft the keel, they will give very powerful and precise steering. However, the main rudder is good enough for me, so I will not waste more time than necessary at the work bench.

PPS: If your boat is not directionally stable with the rudder set free, I would rather connect the windvane to a separate aux. rudder and keep the main rudder locked to add directional stability when sailing with the windvane.

Karlis Kalnins wrote:

Paul transformed La Chica's (LC) keel-mounted, unbalanced, forward-raked rudder into a vertical, naca foil, balanced rudder. Arne and any other full keelers, have you thought about a similar transformation on your rudders? How would you do it? LC rebuilt the keel so the rudder is still keel mounted; you could also extend the rudder shaft through the hull and have a spade rudder; or build up a lower mount for the rudder off the transom (like an autohelm servo mount) to create a transom hung rudder as well; or even cut away part of the keel to add some rudder balance ahead of the current transom/keel axis. Can a strong universal joint be used in a rudder shaft? 

What's the simplest way to achieve a balanced rudder on a boat like this? Is it worth the trouble? 

Just tacking on a new rudder may or may not give you what you want or it maybe only marginally better than what you already have. You need to study your problem and understand it before you can be sure that a new rudder will do what you want it to do. Then you need to do your homework on rudders.

Rudders are surprisingly complicated beasts for what is an apparently simple thing. You need to understand the speed range that your boat normally sails in and then pick a section that will work well in that speed range. The foil needs to be accurately made, every deviation from the correct section will cost you lift (the thing we want) so your workmanship needs to be up to creating accurate profiles and shapes in your chosen medium.

You also need to understand the various rudder shapes and types and the trade offs that they make between lift, drag and stall angles. Then you need to match the rudder to your hull type and the sort of sailing that you do. Unless you are a racer, you almost certainly do not want a true spade rudder, they are much too vulnerable.

This is not to scare anyone off but to make you aware that you do need to consider and understand the above. Changing your rudder can be as simple as just changing the shape of your current one to as big and complex a task as modifying the stern of your boat to accommodate a totally new type of rudder, one that the original designer never even imagined when they designed your boat. It's a doable project but the above caveats do apply.

I'm going to be writing an article on the design and building of LC's new rudder for the next issue of the magazine. I'll also make a separate PDF of that article and put it on the website as there has been a lot of interest in what I did. What I can assure you about is that I'm over the moon with LC's improved handling that the new rudder has made possible. It was a big job but it was also a very worth while job. No single change apart from the original conversion to junk rig has been such a significant improvement for the boat. A friend commented that LC is undoubtedly the fastest and best handling Tahiti ketch/Tahitianna in the world... and he may well be right. She's also probably one of the most modified, loved and sailed.

If you are looking at selfsteering wind vanes, take a look at the Hebridean windvane http://www.windvaneselfsteering.co.uk/ I'm busy building a modified one (modified to permit remote course setting which the stock design does not permit). I'll post on this in due course.

Arne is totally correct about weather helm. I should have said that the apparent weather helm on Footprints is much better, Footprints being a classic example of a low aspect junk rig which has a tendency to impose a lot of weather helm. The larger balance area on the rudder of course provides an amount of 'power steering' to lighten helm loads and the proper foil shape, especially on the lower portion of the rudder below the skeg will make the rudder blade more effective as it moves through the water resulting in smaller rudder angles required to achieve a turning force.

And getting back to wind vanes and self steering a more efficient rudder will make the boat a lot easier to steer via either a wind driven or electric self steering device. I have also learned by experimentation that with pendulum servo self steering if the servo blade has a proper foil shape as opposed to a flat blade then the whole gear works a lot more efficiently.

Arne Kverneland wrote:

 The last option is more attractive to me as it will let me experiment with rudder shapes and balance (inspired by Paul J Thompson’s La Chica). The rudders of both my Ingeborg and your Mariposa are big and un-balanced, so the direct drive self-steering will need a very big vane.

 

Having read the above I realised I had never reported back on the new Rudder for Footprints. Like Paul Thompson I have found that a new rudder has transformed the helming characteristics of the boat resulting in removal of most of the weather helm, in fact almost neutral helm in most situations. Footprints also tracks a lot straighter and requires much significantly smaller increments of helm to correct the course. This I am sure will make it a lot easier for a self steering gear to control the boat, just as soon as I build a new one.

Main features of the new rudder were to reduce the chord by 100mm, close up the open 70mm gap between the rudder and skeg by extending the rudder leading edge forward by 60mm under water and fairing the skeg around the rudder, and by doubling the balance area on the rudder below the skeg by making the leading edge vertical rather than swept back at 35 degrees, and of course by using a proper NACA foil (12%) for the rudder.

I wish I had done all of the above years ago but it took discovery of extensive rot in the timber of the rudder to stir me into action. 

Matt,
I made a Belcher type, direct drive windwane for my 1.4ton Malena, many years ago. It was an OGT MkII design (...named ‘Otto’...), about half as strong as the bigger OGT MkI. While Otto controlled the course of Malena quite well as long as she had a Bermuda rig, the introduction of a JR gave too much weather helm when broad-reaching and running. Besides, Malena now steered herself on the wind and was generally so easy to handle that I felt little need for a windvane for coastal cruising. Maybe Otto would have worked if I had been a bit more patient and experimented with additional bungees to balance out some of the weather helm.

Frankly I doubt if even the strong OGT Mk I will be powerful enough to control a junk-rigged Contessa 26 with direct drive. I hope to install Otto on my similar Marieholm IF, Ingeborg (just for fun), but I think I must either connect it to a trim tab on the original rudder, or to a perfectly balanced auxiliary rudder. The last option is more attractive to me as it will let me experiment with rudder shapes and balance (inspired by Paul J Thompson’s La Chica). The rudders of both my Ingeborg and your Mariposa are big and un-balanced, so the direct drive self-steering will need a very big vane.

Unless you are keen to set off on a long voyage at once, I suggest you focus on getting to know Mariposa and her rig first.

Anyway, good luck!

Arne

(PS: OGT= Ocean Going Tramway)