Autopilot Reversing Pump Sizing

It is important to select the correct size pump as it directly influences the ability of the autopilot to steer the vessel.

An autopilot drive will need to give a compatible Hard Over to Hard Over time to suit the vessel type (Or as specified by the autopilot manufacturer).

The HO to HO may be faster on lightweight planing craft / yachts and slower on displacement power boats / long keel
or heavy yachts.

Note if the pump is too large, the vessel may over steer and will use more power, too small and the autopilot may struggle to maintain a course.

To use the table below you will need to know the volume of your steering cylinder. Select the HO to HO you require. Follow the column down until you approximately match your cylinder volume. Then select the pump on that row.

Note if your cylinder has a smaller volume, it will have a faster HO to HO. If it is larger, it will have a slower HO to HO. “ HO to HO” Is the time that the pump takes to drive the rudder from full port to full starboard. “Dock side” (no flow over the rudder).

If your existing ram is marked in Cubic Inches (cu in.), multiply this number by 16.39 to get the approximate cc volume.