Fred, I’m assuming that the main issue is there is insufficient room above or below the hub of the radial to affix a tiller arm, correct?
Chuck From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Frederick G Street via CnC-List Sent: Tuesday, May 31, 2016 1:59 PM To: cnc-list@cnc-list.com Cc: Frederick G Street <f...@postaudio.net> Subject: Re: Stus-List Installing linear autohelm on LF38 Chuck — sorry for the bad nomenclature; I use “quadrant” interchangeably (and erroneously) to cover both quadrants and radial drives. The LF38 (mine, at least, and I expect most others) has an aluminum radial drive. — Fred Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- Bayfield, WI On May 31, 2016, at 12:42 PM, Chuck Gilchrest via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > wrote: Bob (and other LF 38 folks), As I don’t have immediate access to Edson’s steering parts data base, can you tell me if the Landfall 38 uses a radial drive wheel (full circle) or quadrant (like a slice of pizza) shaped rudder to cable attachment? Two somewhat different animals that basically do the same thing, however, Edson’s quadrants are bronze while the radial drive wheels are aluminum. In autopilot tiller arm installations that are “challenging” due to available space, there are a few nifty methods of reinforcing a quadrant (the bronze thing) using 2 transverse pieces of ¼”x 1” wide stainless that would set in the gap inside the triangular opening in the quadrant, one above and one below the bronze webbing that keeps the quadrant from twisting. The steel pieces would bolt to that webbing. The linear drive ram would attach to that piece of steel providing a contact point at around 8” or so from the rudder post as per Raymarine’s instructions. Radial drives are harder to properly re-inforce at a single contact point, partially due to the thin metal and also because the radial is dished and won’t be at 90 degrees to the angle of the rudderpost (and as such with the throw of the ram). They also have reinforcing ribs designed to bear the loads at the circumference. However, if a single point attachment on a radial drive is the LAST RESORT, you could cut two 2” “donuts” from aluminum that would sit above and below the radial (taking care to not foul the take up eyes and cables), and either weld the donuts in place (preferable) or bond them using epoxy to the radial prior to drilling the radial for the ram mounting bolt. In this manner, you’re spreading the load of the attachment pin where it passes through the radial, plus you are giving the radial a bit of lateral structure when the ram is fixed to a single post that sits up from its surface. The reason most tiller arm installations are best done with a tiller arm with a hollow channel that accepts the rose joint (ball joint) end of the ram INSIDE the tiller arm is to support the forces placed on the arm by a structure both above and below the ram. If torque is applied to an pin (or bolt) that sits 90 degrees from a horizontal platform (radial or otherwise), the entire load is being borne by the single attachment point below the joint. Perhaps the structure you’ve built to support the ram is sufficiently rigid and in line with your “quadrant” to prevent any twisting motion in a seaway, but I’ve seen plenty of bent or broken tiller arm pins (and even a few twisted tiller arms), where there was so much force applied by the ram to a single po.int attachment that the system failed or even worse, jammed. If enough force is applied, a bronze tiller arm (or quadrant) will initially bend and then tear. An aluminum radial drive will simply fracture and break. Neither is ideal but a broken radial drive wheel could render the boat unsteerable or at the very least, send you scrambling for the emergency tiller. And remember, this wouldn’t happen when the conditions are nice and smooth with 2’ seas and a mild breeze. It would happen when the winds were blowing 30+ and you’re getting green water over the foredeck… As much as I dislike wheel pilots, even if my boat was larger than the recommended size for the pilot, it would be safer to use a wheel pilot and have it disengage when the steering loads became too great than to simply bolt the ram to a radial drive wheel and risk the drive wheel cracking when the loads became more severe. At Edson, I never liked using the words “steering” and “failure” in the same sentence… Chuck Gilchrest S/V Half Magic 1983 LF 35 Padanaram, MA
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