The other day I heard reference to a stern thruster that lowers and swivels that can propel the boat forward, and can be used in case of an engine failure.
Anyone heard of such a thing?
If your still out there SeeVee.............YES. The Dickson Thruster is the way to go. However, it will take customization. It's the best solution for a Get-Me-Home scenario. However, you do need a hydraulic power source. Large gensets have a power take off feature (PTO) than can adapt a hydraulic pump. The Dickson Thruster will provide you 6hp each. You will need two thrusters to push your monster boat 4.5 - 5 knots. You can push the Dickson Thruster to 7.5 hp with increased pressure (4000 psi). As for a mechanism to lower the thruster and turn it 90 degrees, this will be a custom made tube in tube configuration. All in all, the set up will cost you $7500.00 when you're done. It will be the BEST investment you've ever made should you become dead in the water and currents or wind become you nemesis.
Here some basic calculations. Hydraulics are 80-85% efficient. Diesels can be loaded to 80%. Thus, you need 20 hp of PTO power to do the job. At 80%, you have 16hp of power to play with, then deduct 20% fluid power loss and you now have 13 hp to feed your Dickson Thruster. Your alternator and water pump on the genset will consume about 1 to 2 hp, so keep that in mind. The minimum genset to do the job is 20 kw.
I will be building the same for my boat. However, I will not utilize an AC style genset. Instead, I will utilize my Aux Diesel engine to push three components. The 1st is to drive a 30,000 btu clutch driven Sanden scroll compressor. This is found in mobile applications. The system will chill water to 38F, then be circulated to 3 evaporator coils designed for 50% humidity & 50% temperature. AKA Sensible / Latent heat ratio. With the AC running, I will also run a clutch driven 160 amp alternator. This will provide power to the evaporator fans that push 400 cfm's each (12 volt). The aux engine will be variable speed that correlates to water temperature. 50F water = full engine speed, usually 3200 rpm's. 40F water temperature or below equates to 1800 rpm's engine speed. If and when I need auxiliary power, the AC and alternator are turned off and the hydraulic pump engages to make fluid power to drive the Dickson Thrusters. If you have a 40 foot monster (or bigger) you'll really need 3 thrusters. Why? Because your boat is a kite and you need to overcome current and winds. Thus, you need to push your trawler 8 mph minimum. In all reality, a 40 footer really needs two thrusters just for docking maneuvers on windy days.
This set up is designed to not have anything AC electrical on the boat and to use your Aux engine as efficiently as possible. AC is stupid in my opinion, but this is how the industry is driven.
You are not out in left field with your idea. Hyd. driven Dickson thrusters made to drop 1 foot and rotate is the ultimate solution.
The absolute BEST engine for your needs is the Universal M25-XPB. It provides 26hp at 3000 rpms. This gives you 20 net hp to use up. Perfect to run 2 dickson thrusters at 4500 psi.
As for the Sanden compressor, the TRSE09 requires 6 hp (4.5 KW) to deliver 30,000 btu's (2.5 tons). The compressor would spin at 3500 rpm's, full load. You need to understand that this type of air conditioning is to run the boat (or flybridge) temperature below 70F on hot summer days in the south. This is what "she" requires. Not everybody needs their boat to be a blast freezer when it's 92F outside.
To run three evaporator blowers (fans), you'll consume 16 amps each (400 CFM), totaling 48 amps. A chilled water circulation pump will draw 6-10 amps.
This means the clutch driven secondary alternator will need to be in the 150 amp @ 3600 rpm's range (Balmar). Count on 4-5 hp off your engine to run your alternator.
Another thing to consider is the engine configuration. Toss the stupid transmission and go with a "bearing supported stub shaft". This provides you the means to side load off the shaft. Your side loads are your belts to run your stuff. You stuff engages and disengages by clutch pully. Hayes Manufacturing up there in Fife Michigan makes this kind of stuff. Here's a link:
https://www.hayescouplings.com/products/bearing-supports/
There you have it. Now get busy .
BTW, I am a test engineer with a refrigeration / air conditioning engineering background. I will build this set up in my warehouse before I install it on the boat. it will be built to be reliable and simple.
Also understand that the AC set up will be much like that used in your car, which is not the same as what is used in your house or office.
BTW.........your in St Pete, I'm in Largo Florida. If your still out there and care to elaborate, let me know. I know a ton of fabricators to do the thruster rotation rigging. I also know a really good machines named Joel Foster who has done some really good "one off" work for me over the years. Joel Foster is in Pinellas Park, FL.