Loren,
You are right, and I was planning to use such a single-handle, and control it by the same wire I used to control the gearbox. In some of the pictures you can see this on my desk. The problem was that I needed to make the connection plate where four hydraulic pipes were connected to this control. If I choose to use flexible cables, the plate can be made without detailed adjustments, but if I should make it with only hard connections, fine measurements are needed. What I got now is only a solution, so I can get the boat out while waiting for the final solution. Also most of this single-handle units got internal holes that are less than ½ “, and for back and forth movement in the harbor that is fine, but for long distance drive, I want 1” pipes without too much frictions. So the plan is to have a combination of easy handling and good power. In the harbor I only use a small part of the power, so there the ½ “ pipes will be OK, and for most of my use this will be OK, but when I want to use the engine for longer periods, I plan to have the option to open the two large valves manually and get better performance. Also I hope the noise level will go down without the gearbox and the connection to the gearbox.