I am going to install a linear drive for a back up autopilot system. The drive shaft attaches to the steering quadrant, the motor attaches to a bracket fixed to the inside of the hull. In the case of the Ocean 47 this would be located behind the aft cabin bulkhead. I can't access the boat for a while, its in Turkey so I need some helpful advice. The linear drive has 2 versions affecting shaft length. short and long. I don't know which one to go for Any suggestions?
I think you will find you already had the answer in your PBO question with the extract from the Raymarine document. The longer shaft is used for heavier boat (much heavier than yours, I think at greater than 15 tonnes. As the table clearly shows it provides a greater stroke, more torque but a slower hardover time.
Anyway, rather than guessing why not just call Raymarine for advice. Pretty sure they will know which is appropriate.
I have and they said its really down to the position for mounting the motor. I know only 2 other Ocean 47 owners (out of 23) and they can't help. I can't get to the boat to measure up but my guess is a longer shaft may give me more possibilities for positioning the motor. Any hardover maneuvers will be done at the helm with the pilot off. A bit more thrust capacity means less wear on the set up. I will ask some Agents who have had experience with installations and see what they suggest.
Long shaft means longer tiller arm (or bigger quadrant) to use the extra reach. Is there room for such a longer tiller arm? If not, the shaft length is dictated by the available space for the longest tiller arm you can fit.
After further thought I think to prefer the shorter shaft. Because the the quadrant is raised above the hull and the drive needs to be mounted with the shaft horizontal it looks like the motor will be mounted to the bulkhead/partition with the lazarette (to be reinforced). If the shaft can't reach the quadrant when extended I may need to cantilever the bracket for the motor. If space is too restricted and I have the long shaft version I would have to mount inside the lazarette and cut through the the plywood divider - not a preference!