Best engine for fuel economy and a kicker option

I'm shopping for a Ranger tug. I have concerns about fuel consumption, which engine would best fit me and a second kicker engine.

Fuel Consumption: Regarding a Ranger Tug 25 what would be best for fuel economy an out board gas or a in board diesel. What could I expect to get gallons per hour with the engine?

Can a kicker engine be connected to auto pilot?

Would it be worthwhile to have something like a 25 HP kicker engine to use as a cruising engine 7-8 knots to save fuel cost?

I'm a sail boat owner and am happy with 8 knots for extended trips. I'm leaning toward a Cummins diesel, but still wonder about a second engine for cruising and to help with fuel consumption and I'm too crazy about being out without a second option to move the boat. Even sail boats have the sails and a kicker engine.

I have a 2009 R-25 Classic with the 150 HP Yanmar diesel. You might want to check on dealer servicing availability in your area before deciding on either the Yanmar or Cummins power plant. Depending on where you live that could be an issue unless you plan on doing all maintenance and repair work yourself.
The R25 Classic has a 75 gallon fuel tank and I assume 70 gallon usable to be cautious. You can cruise slow at well under 2 GPH. You can go 7-8 knots at 3-4 GPH. Or you can go faster (12-13 knots) at up to 7 GPH.
Fuel is way, way down the list of expenses incurred when operating the boat. At 8 knots I get about 16 hours of run time before I start worrying about refueling. In the PNW there seem to be diesel fuel docks everywhere.
Can’t help you with a kicker - don’t fish.

I think if fuel economy is the main concern something with a smaller engine like the older nordic 26 might be a good option.
https://www.yachtworld.com/boats/1981/n ... 6-3668222/
This one has a 50 hp perkins for example. Purchase is cheaper too.

We have an R25 classic with the Mercruiser(aka Cummins) 150hp diesel. We cruise at 1500-1600 rpm and +- six knots 90 percent of the time. That costs just under one gallon per hour. You can run at slightly lower rpm and burn 25 percent less fuel with about 10 percent loss of speed but the turbo drops out and runs cool. I run it as indicated to keep the turbo engaged to minimize fouling. Plus the boat has so much windage that with even a slight headwind you end up kicking it up to 1600 anyway just to maintain hull speed.

Where we boat relying on a tow in case of emergency is not a good option. So we have a Yamaha 9.9 high thrust(aka sail drive) kicker. At half throttle it will move the boat at 4-4.5 knots on calm water and barely sip gas. With any sort of head wind you have to either run the kicker WOT or accept dropping to 3-3.5 knots. The kicker at WOT burns a gallon of gas per hour. So basically at hull speed the diesel burns about the same as an outboard.

It is possible to hook the kicker up to the steering system thereby making AP steering available when running with the kicker. There are as many way to accomplish that as there are opinions.

Al: And for you, what is it? Repairs?

FWTMD: We live about 550 miles from where we normally launch. Not a good diesel boat mechanic within 300 miles of our home. We have had several shops in WA north of Seattle work on the boat and my prior boat. Our Journey stays near Anacortes, WA on the trailer during the summer but still long drives (1,100 miles R/T) to drop boat at shop then another trip to P/U and put back in storage. We now have two Yanmar certified repair shops that we have settled on but they both have made significant boo-boos on their part over the past 5 years that required rework to get things right.
I do as much of the work on the boat as I can myself. But the impeller change, oil changes and major periodic engine maintenance work and a few other things I take the boat to a shop.
Having a repair shop you can trust is important - especially for us since we live so far away from them.