A Photo & Discussion Forum for Wharram Design Enthusiasts
The nice thing about a steering on a Wharram is that you can make the spindle any size you want, or you can do any custom mechanism that suits your fancy. Therefor, you can install whatever sized wheel you like. Even if you use the spindle size in the plans, a larger wheel will give better feel and a tighter response.
I think that the only reason to have a smaller wheel is if you are forced to drive with handcuffs on...
Whatever I can find closest to free that will readily take an off the shelf autopilot and control lines for self-steering. I try to touch the wheel as little as possible (they are like kitchen sponges: covered in cooties.)
Allen Bosely said:
Lol BB what size wheel you planning to use?
That is quite gracious of you Allen. I might just take you up on that.
Wheel diameter is an important factor in a steering system. Imagine driving a 40' boat at 22 knots. Would you prefer a 2' tiller or a 4' tiller. The short tiller would not work. With a wheel system it can be set up with any additional leverage you want via the hub cable drum. This can give you 2 turns lock to lock or 4 turns lock to lock or 17. The more turns lock to lock the more leverage (longer tiller). The down side is that the wheel has to turn twice as far (for the 2 vs 4 example) for an equal rudder response. This decreases the helm feel to the helmsman. Increasing wheel diameter from 2' to 4' doubles the effective tiller length as far as effort to the helmsman is concerned. This allows for better helm feel and a more responsive helm with the the same wheel load.
Wheel load is influenced by many factors. The Wharram rudders are of the barn door variety. They are aft hung non-counter balanced. Additionally the stock Wharram stern posts are at about a 23* angle. This means that about 1/4 of the energy inflicted by the rudders will be trying to push the sterns down into the water instead of turning the boat. At 5-6 knots this drag induces moderate rudder/tiller loads. At ten knots this load increases exponentially. Even more so at 20 knots.
On Brad's Ariki, Bazinga, the boat has been set-up with with a modern marconi full batten main sail with a fat roach, daggerboards, a carbon extendable bow sprit and a set of sails from Dave Calvert of warp drive Spectra material. Brad is a very experienced sailor and a boat that sails well was very high on the priority list. I expect Bazinga to exceed 20 knots commonly. This is fast for a cruising catamaran with a 41.5' LWL even by today's standards. But this is definitely not your grandpa's Wharram.
On the Ariki 48 I have changed the stern post angle to 5*.
The steering system on Bazinga is 6mm Dynex Dux that is heat treated and pre-stretched wrapped around a drum on the steering shaft at the helm and routed through the cockpit sole to the aft side of the rear beam where they cross the boat to the other side of the boat where the lash to the tiller bar. The tiller travels about 5 1/2' from lock to lock and we have 2 1/4 turns of the wheel. This would not be feasible with a 2' diameter wheel.
Also of concern when considering steering load on these boats is the autopilot steering system. I prefer an electric auto-pilot. These boats change apparent wind angle very quickly due to acceleration fluctuations. Again at low boat speeds this is minor but as the speed goes up the boat will tend to steer a snakey course. Many people are quite content with wind vanes.
The rudder loads of a barn door rudder at speed are disproportional to the boats weight and LOA which is how auto-pilots are generally sized. The auto-pilot on Bazinga is a Raymarine EV400 with a Type 2 rotary drive. This drive is rated for a 44,000 pound boat. The auto-pilot does not see any advantage from the larger wheel size. The auto-pilot leverage is determined with chain and sprockets on the steering shaft.
All of that aside a big wheel feels bitchin when you are in the groove jammin along,,, or not.
BB, I figure you will want to see what quality my work is first. Be a bummer to excited to get a wheel and when you see it think OMG! Not on my boat,I don't care if it was free! lol
Boatsmith, thanks for the wheel size info. Now I know it's OK to have a good size wheel on her. Now you got me thinking 48" wheel sounds pretty nice! :-) What diameter did you settle on for the Ariki that was in your video that had the mockup wheel & you weren't sure what diameter it was going to be at that point? I enjoy your videos BTW.
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