Anybody in here mess with getting better FE out of Boats?
 

Boats are pretty thirsty an inefficient. I'm looking into ideas to get my 1538 1970s fisher water rover with a 1989 yamaha 30hp outboard to get better mpg. What ideas have you guys tried?

There are really only two areas you could look at.
 

The first is engine efficiency.

The second is your hydro-dynamic drag.

Both are complex.

I prefer sailboats but if you want to optimize on the water fuel economy, you have to design from the water up.

Foils that lift the hull out of the water reduce hydro-dynamic drag tremendously. Then, with reduced drag, you can outline an engine design that minimizes fuel use at that reduced drag.

If speeds get high enough, then you can start down the road of reducing your aerodynamic drag.

Water drag is much worse than aero drag and you have both with the boat. I assume with just 30hp it doesn't come up on a plane but I could be wrong. If it does plane you want to get it on a plane and then back off some to save gas but maintain the plane. If it isn't planing but the hull is designed to you need more power to make it happen or lighten things up and hope. Make sure its operating in the motors designed range as well, if it over revs you need more pitch on the prop and if it never revs all the way you need less pitch.

I took the Jetski out on a new-to-me lake last summer, got to the end, and turned around to head back. 5 minutes into the ride back, I had to switch over to reserve. Thinking I would conserve fuel I backed off to about half speed. 15 minutes later I was out. 3 hours later I had swam the boat back to dock.

Someone told me 2-stroke motors want to run at near full-throttle to get the most power out of the fuel. I'm not sure what is most efficient, and haven't seen a BSFC for 2-strokes.

All that said, I think reducing weight is probably most important if you can't change the hull shape.

Diesel engine?

Bingo!
 

Fuel efficiency in a hot pocket pouch.

https://newatlas.com/yanmar-dtorque-...utboard/51675/

Its great but $25,000+ for 50hp buys an endless supply of gas.

Some years back I found I intriguing a 30’ turbodiesel with Anderson drive prop a “high” mpg commuter. Hawaiian Islands, IIRC. Both of those were new enough (fir a small package).

One has to start from scratch. And optimize steady state cruise. It’s start and stop that kills boat FE.

Operating at the interface between air and water, you want a hull that optimizes for both.

https://www.brighthubengineering.com...ull-technolgy/

Apparently typical bsfc is on plane 5000rpm at throttle valve fully open (volumetric efficiency) with a mpg prop... big prop that wont let the motor rev up. So currently I run 100% throttle, 5000 rpm (max hp is 5500... max rpm is 6000 rpm). And.... I get a whopping 9 mpg lol. 15' flat bottom 25 mph. 90s yamaha 2s 30hp.