Replacing an old Robertson Autopilot with a new 711C for inboards w/ Pump. No numbers on the old cylinder, but it is 16" long, 1/2" ID and 1 1/2" OD. What pump would I use.
Pictures can often help, otherwise you may want to go see your local dealer and have them inspect it. In general, the method to size a pump often goes off of the size in cubic inches of your steering ram as well as the size of the vessel. For most small sport fisher yachts +/- 35' with a 7 - 12 cu. in. steering ram, the Octopus 10-12 is typically recommended.