Hard over time

B

BillH

New member
Hi, I’m putting together a AP system for my 40’ heavy displacement cutter. Around 30,000#, full keel with barn door rudder.
I had a naval architect calculate the hydraulic cylinder- 339 cc- +- 21cu/inch. He recommended a 2.0 liter pump which is around 10 sec / 70 degrees hard over. I emailed furuno support the verify this is appropriate and compatible with the 711c AP. The tech support recommended the 1.6l pump- around 12.7 seconds. I’m curious why the discrepancy?
Thanks, Bill
 
I suspect it will make no difference in practice which pump you choose. Many settings affect the autopilot response besides the nominal maximum time to hard over. The autopilot is generally making a large number of smaller course changes, not swinging from hard to port to hard to starboard. The difference in response time to make a 3 or 4 degree change in rudder angle would be fractions of a second between the two pump sizes and not enough to affect autopilot steering performance in all likelihood.

My guess is that the tech was trying to save you some money because the smaller 1.6l pump would be cheaper.
 
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