Thinking about get home setups is an entertaining mental exercise. But thinking about why you might need a get home setup and deal with those scenarios rather than install a full separate power and steering system that won't be used much and may not work when needed due to lack of use / maintenance is a better mental exercise.
It's been my experience listening to the radio and the few assistance tows I've done along with my own system failures the causes are in this order.
Perhaps Psneeld will log in with his extensive assistance towing background.
- Out of fuel. Simple fix, don't run out of fuel.
- Dirty fuel, plugged filters. Set up switchable dual filter system. Carry spare elements. Monitor the fuel system and if even the tiniest bit of water shows up deal with it before you put to sea again.
- Soft part failure. Impellers, hoses, belts etc. Proactively replace them, carry spares.
- Cooling water flow blockage. Install alarms, monitor sea strainers.
- Running gear fouled by pot lines. Watch where you're going, have your shaft fitted with spurs if you must frequently run in pot infested waters.
- Control system failure. Old mechanical, modern electronic or any of the less common systems. Learn the work arounds. If at sea beyond tow range disconnect the control from the input shaft, governor or transmission. Manually put it in gear at a decent RPM and fix the control shaft with anything handy and that position. Run until within towing range and call for a tow into the harbor.
- Drive saver or other soft part between transmission output and shaft failure. Replace them proactively. If you're really concerned carry a blank and bolts. Or better yet, don't use them.
- Total steering system failure on a single screw boat. Before you ever head to sea or into remote areas make sure you have emergency steering. Even a good idea for twins.
Now what's left?
Total failure of the main engine or transmission. Very unlikely if you've taken care of business. But it can happen. With a good gen set there are a number of ways the shaft can be turned to provide get home capability in the event of loss of main engine or transmission.
Loss of shaft or prop are the only things I can think of that will leave you completely stranded unable to help yourself. That's the only time a fully independent get home drive and steering system will be of use.
Failure of electronic engine controls. I don't mean throttle and shift, I mean the engine's systems. That's another can of worms all together and if you've got such a system needs serious thought and preparation. My total experience with electronic engines is 3 boats. Two have suffered failures at sea. Not a good track record.
The first was low voltage. The result of a failed battery isolator. A straight forward work around once the problem was identified.
The second was uncertain. Lots of time and money spent to solve the issue. Open, clean and close all connectors, new wiring harness, new ECU.