Re: Stainless Steel FreeHand?
Posted by: Bil
Date: June 14, 2018 02:46AM
Category: Autopilots and windvanes
The Larry Pardey-designed Mike Anderson-built Freehand Steering System has much going for it. That includes light weight, relative mechanical simplicity, and lack of the need for strong components. Those three things of course go together - because you don't need much mechanical strength, the Freehand SS components can be simple and lightweight.
The major underwater component is the trim tab. That's just a servo rudder to the BCC rudder, sitting as it does in the water flow just aft of the rudder. So the trim tab does not need to be a sophisticated NACA foil. The forces needed to turn the rudder are not huge and the direct connection to the rudder means you don't need toothed gear wheels etc.
All that means that the foil of the trim tab can be a shaped plank of teak (we encapsulated Zygote's trim tab in GRP after a teredo worm in tropical water found that teak, even though antifouled, too attractive to avoid).
The attachments to the rudder, the pivot of the trim tab, and the worm drive on the rudder head - all of which allow (1) the minor adjustment of the angle of the attack of the trim tab to counter the transverse prop walk of the prop when motoring; and (2) provide attachment for a simple tiller pilot (Z carries an Autohelm 1000 to drive the trim tab, the deal being that the forces involved in turning the servo rudder are tiny compared to the forces needed to turn the tiller).
And those two benefits, probably important in reverse order to what I have given, are high enough to justify just having the underwater parts of a Freehand SS. A tiny tiller pilot does a better job of steering than me most days. And for any shorthander, an inexpensive tiller pilot is a little superior to lashing the tiller.
I see no reason why you could not get those parts (or at least the metal ones) fabricated in stainless steel. Plain ss bar, threaded ss rod, and ss plate are easy to buy and work (or have fabricated). The factor to watch is related to galvanic action and whether you want to add to more ss to whatever mix of metal you have below water.
On Z, the rudder pintle/gudgeon set and the prop are bronze (the prop passes for bronze, goodness knows what it really is!). The prop shaft is ss. I have sacrificial zinc anodes on the prop shaft (a fixed prop) and on the lower gudgeon set. I recently added a tiny shaft zinc on the trim tab axle (bronze and seemed to show a little metal loss at last haul-out).
I conclude that you could fabricate the same parts in ss and likely just add the same additional chunk or two of zinc.
BCC 116 Zygote,
Scarborough Marina, Moreton Bay, Queensland, Australia