Hi I have a long keel ketch with hydraulic steering to a pedestal wheel, I find it is quite stiff and judders when turning under power, Under sail it is not quite so bad. Someone said the oil may need bleeding. any ideas?
I have a large ketch with hydraulic steering as well . I installed a schrader valve [used on tire tubes] on the reservoir for the hydraulic system. I use a bike pump to keep the tank pressurized at 25 psi. The steering smoothed out for me and by monitoring the pressure with a guage, I can detect leaks in the system.
Sounds like air in the fluid. As said already, drain it and bleed it and then pour back the fluid, or renew the fluid if old or "off" looking. I use an aircraft landing gear hydraulic fluid called AT-4 as recommended by the hydraulic system manufacturer, Marol, but your mileage, etc.
I don't know that air in the system would cause it to be "stiff", generally it will feel kind of mushy, or skip a bit when you turn the wheel. You might be having problems with one of the check valves depending on the make and model of pump. I had a Wagner pump blow out on us not too long ago, it blew one of the threaded caps right out the side of the pump (and a LOT of fluid of course). Before it went it had started to feel "stuck" when trying to turn back from hard over.