Proa steering

[SeaSpark]

I am working on the design of a proa for the Dutch inland waterways.

Focus is on portability (the reason why a choose a proa type) and ease of use. I am looking for a proa steering system that needs as less as possible user interaction when changing bows. Potential buyers may be scared of the proa concept so i want the steering system to be very easy to use.

Any suggestion is welcome.

[messabout]

Why not use a steering oar at each end of the boat? That is about the most practical method you could have. It is cheap, simple effective and easy to replace. Such an oar can also be used to scull the boat if the need arises. Figure a method for clipping the handle end of the forward oar down so as to keep the blade up. Unclip when the bow becomes the stern.

[SeaSpark]

Messabout, i like the solution you offer it is simple in design and very close to how rudders on traditional proa's work.

The helmsman however needs to move from one end of the proa to the other and the rudder needs to be pulled up and clipped. A steering oar is hard to control when the helmsman is sitting on the outrigger to balance the proa.

I have been looking into counter rotating rudders, these need a more complex construction but the helmsmen can stay in one place, near the outrigger. Pacific Proa has one design with rudders like this. http://www.wingo.com/proa/steering.html they use a drive shaft system but push/pull rods are also possible. A system with rods will be different from Pacific Proa for their rudders move more then 180deg to make the balancing part point in the sailing direction.

Picture from www.wingo.com :



Opinions on steering behaviour with counter rotating rudders are very welcome. I find it hard to imagine a well tracking boat with rudders like this.

[LP]

It's funny this thread should come up right now. A co-worker and I were bouncing ideas back (half jokingly) and forth about a bi-directional yacht that the windward and leaward sides never change. Just learned the term "shunting" from the thread. Anyway, dual-counter rotating rudders was decided as the best mechanism for steering since conventional rudders didn't make sense. I envisioned chain driven rudders with with sprockets mounted to the rudder shafts and at a central wheel steering station. Two separate drive chains would be employed due to the counter rotating feature plus it would provide system redundancy. Continuous chains would allow 360 degrees of rotation provide a method for keeping the rudders syncronized and would be necessary for continued shunting. When looking down on the craft from above with windward to the top of the page, the right-hand rudder will rotate clockwise and the left-hand rudder will rotate CCW with each shunt, regardless of shunt direction. Chain-driven rudders would also allow a person to select the sensitivity of the steering system by adjusting spocket ratios. A larger than standard rudder stock might be desired due to the possibility of a rudder position broadside to the freestream. Not necessarily a back thing. The rudders could double as speed brakes to slow the craft during course reversal. Possibly even provide a slight amount of impetus in the opposite direction, depending on how the rudder is balanced.

[SeaSpark]

We seem to be on the same direction

The rudder system you describe is very similar to the CBTF system and it tracks exceptionally well. It has another advantage, if you choose to set it up, and that is "collective" which allows the rudders to be turned the same direction when going upwind to virtually eliminate leeway.

[MalSmith]

For information on proas, try http://groups.yahoo.com/group/proa_file/
You will get plenty of opinions, if not any definitive solutions!

Mal Smith

[tspeer]

A big problem with proa rudders is the shift in hydrodynamic center when shunting. If you put the pivot axis at mid chord for symmetry, then it's over-balanced by 25% of the chord!

One solution is to use a conventional section and rotate the foils 180 degrees on the shunt, so the same edge is always the leading edge.

Another solution is to angle the foils aft so that the tip is behind the pivot axis. This allows you to get the right distribution of area about the axis for a stable rudder. The rake is then changed on the shunt to match the direction of motion. Experience has shown that there's invariably too much friction for the foils to do this on their own, however.

A third approach is to lock a foil in place to act as the centerboard and have the other foil with its pivot axis designed for a particular shunt. The problem here is you don't ever want to have the foil free to rotate with 3/4 of its area "ahead" of the pivot axis!

If you use the latter two approaches, you will need a bidirectional section. Ogival sections have sharp edges that make good trailing edges and poor leading edges. There are sections that have rounded edges and are specifically designed for use on proas.

[LP]

Good link Tom.

The cambered foil sections are intriging. Not for the rudder sections, but for the hull/keel sections. I think it would be useful to have a keel section that was maximized for lift in one direction since we are no longer encumbered with building an ambidextrous yacht. There's a joke for you. Would you like a left-handed or a right-handed yacht? I guess it would depend on which way you are circling the globe. Back to the matter at hand. We could employ Lorsail's mention of collective ruddering. Between the cambered keel sections and the use of a collective rudder system, we could build a yacht that actually "climbs" to windward (negative leaway). Any papers out there on such a craft?

[LL2]

I think I would like a right handed yacht please! Too funny!

[SeaSpark]

Tom,

Your conciderations and information again are highly appreciated.

[frosh]

Further from Tom's posting re turning the rudders 180 degrees after a shunt: From recently sailing on Rob Denney's Elementarry proa, the front rudder when down is nearly always superfluous and feels like it is causing considerable drag force judging by the visible turbulence. Also any sort of tiller control of the front rudder is a pain, and a considerable distraction for no net benefit. I think it best that if using two rudders that the front one is retracted fully. This turned out to be the best way in actual sailing. The other option is to design it so when partially retracted the front rudder is locked up so is acting only as a small lateral resistance foil. From my experience on Elementarry any attempt at steering at speed with the front rudder noticably slows the craft, so even if in theory it appears that we can design to climb to windward, the drag forces are far too high!

[tspeer]

Originally Posted by LP

...Between the cambered keel sections and the use of a collective rudder system, we could build a yacht that actually "climbs" to windward (negative leaway). Any papers out there on such a craft?

It doesn't work that way, for reasons that have been discussed at length in other threads. What really happens is collective rudder rotates the bow of the boat away from the wind. Which may be useful in its own right because of the effect on the rig. But by itself, it doesn't change the steady course through the water - that's determined by the lift/drag ratio of the hull & foils when producing just enough lift to opposed the side loads from the sails & topsides.

[sharpii2]

Why not just make a single outrigger. Then your only problem is supporting the mast. I would go with a bipod mast. After that, things get a lot simpler. No complex rudder system to break or jam up.

Like a proa, a single outrigger would have all of its accomodations in one hull. The other hull, which is much smaller in section (but not As much smaller as a proa) could carry bulk stores such as fuel and water.

Just a thought.

Bob

[LP]

Bob,

I must be missing the point. How does the outrigger provide steerage? Getting back to SeaSparks design, I think he is interested in simple operation, as opposed to simple design, which would be nice too.

Tom,

I guess I should have included smileys after my negative leaway statement.;) Thanks for the input though. The sailor's holy grail: sailing dead to windward.:cool: