I'm not sure what A/P unit your thinking of installing but the ram you are referring to will not have a bearing on what ever unit your going to install. That ram part# is the power steering actuator that makes up the M/C'r power steering system. I think you are probably looking at a straight hyd type system & they are asking what size hydraulic ram is already on the boat, whether it be a straight inboard or outboard with dedicated hydraulic steering, not an I/O, cable over hydraulic system that you have on your Penn Yan now.