You definitely need to get someone on the boat who is familiar with these systems, if for no other reason than to sort out what you have. Is it manual hydraulic steering? Power assisted hydraulic steering. What other hydraulic systems are on board and is that completely separate from the steering? What equipment on board is still operations, or intended to be operational, and what has been abandoned over the years and is nothing but a Red Herring in this discussion.
Here's what I do know:
- I only know of one boat under 80' that has power assisted steering. All others a manual hydraulic steering. What I mean my "manual hydraulic steering" is that there is a pump at the steering wheel that is turned by you moving the wheel (the manual part). That pump movement then forces oil through lines to the steering rams/cylinders to turn the rudder. I would be very surprised if this isn't what you have. What I mean by "power assisted steering" is a fancier and more complex system with an engine driven pump (could be main engine, or electric motor) that does the work, and the steering wheel controls it and typically also provides some backup. This is like the power steering on a car. You can turn the wheel with a finger as long as the power assist is working. But if it fails, the steering is super heavy to turn, even heavier than manual steering.
- Boat steering on larger boats isn't finger-light, but it also isn't hard to turn. You should be able to turn it stop to stop with little trouble. You are likely to get sick of the 7 to 10 turns stop to stop long before you get sick of the effort to move the wheel. Unless you expectations are way off from what is normal boat steering effort, something is broken in your steering.
- Assuming something is broken with your current system, the solution is to find an fix the problem, not replace the system with power assisted steering.
- You have already narrowed down the problem by disconnected the rudder from the steering rams and verifying that you can move the rudder by hand and that the steering effort is still high. Unless there is a big judgement error if your perception of how each component should feel, the problem is in the hydraulic steering mechanism. Now you just need to figure out if it's cylinders (rams) that are binding up, if the pump is binding up, or if there are valves not working correctly.
To me, the next test would be to open the air bleed valves, using hoses to direct to fluid if needed, and see how the wheel feels. If it's still heavy, then the problem is in the helm pump. If it's now easy to turn, then the problem is in the rams/cylinders.