... Even if your thruster never fails, knowing how your boat responds without it is vital. ...
My thruster had been broken for several months, and got by. Suppose that was for practice. How many twin-engine boaters operate for several months with only one working engine?
... I have admitted that I have done so (with only one of the twin engines operating?) for 2 complete cruising seasons, so yes, docking a twin on one engine is a skill that can be learned quickly. ...
I was brought up on single screw boats. Never had a thruster. No problem once you get the single screw's dance steps understood. Have only had twins in boats of my own. Dance steps with twins are a waltz. Never had a thruster with twins either.
Difference in the "docking" dance as compared to a single or twins = back in parking a heavy motorcycle compared to a golf cart.
Prop speed, running occasionally, and diver regularly checking and cleaning when they clean the rest of the hull. If you don't feel the need for a diver for the hull, I would still have one (or dive yourself in your case) dive periodically to check all through hulls, shafts, props, thruster, etc. I'd also double check for any stray electricity flow you might be experiencing on your own boat. If from other boats, not a lot you can do. Overall those blades looked bad and didn't get that way overnight. When was the last time they were checked?
Prop speed, running occasionally, and diver regularly checking and cleaning when they clean the rest of the hull. If you don't feel the need for a diver for the hull, I would still have one (or dive yourself in your case) dive periodically to check all through hulls, shafts, props, thruster, etc. I'd also double check for any stray electricity flow you might be experiencing on your own boat. If from other boats, not a lot you can do. Overall those blades looked bad and didn't get that way overnight. When was the last time they were checked?
For those purists who who are maybe a little derisive of thruster users: Would you disable the power steering pumps on your car to practice? Not use your cars air conditioner? Special order a car without power windows because they might fail? Keep your remote key fob in the spare parts locker just for emergencies? Use bias ply tires? We drove a lot of miles without these tools. The world is safer and more comfortable with them, and "because we've always done it that way" is not a good reason to resist change.
For those purists who who are maybe a little derisive of thruster users: Would you disable the power steering pumps on your car to practice? Not use your cars air conditioner? Special order a car without power windows because they might fail? Keep your remote key fob in the spare parts locker just for emergencies? Use bias ply tires? We drove a lot of miles without these tools. The world is safer and more comfortable with them, and "because we've always done it that way" is not a good reason to resist change.