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> 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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