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Old 02-02-2010, 11:02   #1
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Autopilot Drive Setup

Looking for some feedback on my autopilot drive setup done last fall by a local boatyard. The yard installed a Raymarine Type 2 long linear drive in my 20,000 lb displacement sloop. For a couple of reasons they had to shorten tiller arm in installation to 10 1/2" instead of the 14" recommended. One reason was that I did not want to restrict my rudder to 35 degree turn as it turns 45 degrees. Without going into a lot of detail the tiller arm was shortened by 25 percent. My boat displaces 20,000 lbs unloaded and so adding 20 percent for load brings it up to 24,000 lbs. The Type 2 long linear drive may be used on boats up to 44,000 lb displacement when installed with 14 inch tiller arm. I calculated max rudder torque for my boat to be approx 8750 in/lbs. (Jorssel's formula). The drive according to literature has a max torque of 14,700 lbs. With the shortened tiller arm I assume that this torque is reduced by 25% to 11,000 lbs.My boat is an old CCA design that is pretty well balanced.Looks to me that the drive should handle the load. Has anybody here shortened the tiller arm on an oversized drive like this ? I wanted the extra torque but did not realize that angle of rudder turn would be an issue.
I asked Raymarine about it and their answer through Steven Cruz was "I will not be able to comment on how the drive is going to work with your custom setup.It seems your math is correct,but your set up was never tested for me to tell you it would function properly".
The autopilot/drive was installed late in the season and I didn't get a whole lot of opportunity to use it. Seemed to work well,but in a couple of blows the boat went off course with some wide course corrections..never really failed. I was pushing the boat hard and probably should have been reefed a bit more. The other thing is that response time of the autopilot might have to be adjusted.
Not looking to start another bash Raymarine thread. I think that most problems are caused by installation.Thanks.
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