Fuel burn on one engine vs two

hottoddie

Well-Known Member
Jan 11, 2012
2,224
Boston/Cape Cod
Boat Info
1986 Sea Ray 390 EC
Garmin 4212 Chartplotter
Garmin 24 HD Radar
Garmin 546s Plotter
Engines
454 Crusaders
Sunday late afternoon I was returning to our slip in a no wake zone @ 8 mph/1300 rpm and I was curios how the boat would handle on one engine so I pulled back the port throttle to idle and shifted it into neutral. To my surprise the boat did not pull hard to port and only needed a minor wheel adjustment to starboard to keep a straight course. Also the boat also responded to the helm much better than I thought it would.

The interesting part was that as I was watching the Garmin GFS10 fuel flow info on my 4212. At 1300 rpm the boat was doing 8 knots @ 1.3 mpg. When I shut down the port engine the boat slowed to 6.4 mph and the fuel mileage went to 1.7 mpg. That's a pretty substantial increase. In today's world of $4 gas when more of us take our time and travel at hull speed to save fuel we are also putting more hours on our engines in order to get to our destinations. So if you can save even more fuel and reduce run time by running on one engine when it is safe to do so then maybe we should, I know I will.
 
Unfortunately, not all Sea Rays handle well on one engine. The 390EC is special in that she only draws 28" and has deep prop pockets. Other boats without the deep prop pockets and with a large distance between the shafts change a docile, great handling boat in to a big old narly monster that is danged near impossible to control when you run them on one. I know.....I've got one of them.
 
mine isnt aweful on one engine but bad enough that i keep them both spinning without worry
 
I can't give you fuel numbers, but mine handles nicely at low speeds on one engine. I've never put her to test running at speed on one.

After one shutting down on me last year I practice docking, and running on one engine but never over 1500rpm's
 
Last summer we were motoring along at 8 knots. There was a large tug pulling a log boom. I had plenty of time to cut in front of him. Figured would have 1/2 mile clearance. As I got near one engine went out. Later I found the fuel pump went. To maintain 8 knots I had to almost double the RPM. At that point there were no fuel savings. Planes that have 2 engines and can fly on one but do not. I have tried at 4 knots and it saves a bit but if you all of a sudden need power you do not have it.
 
My last boat, 1987 Wellcraft St Tropez with 5.7 V-Drives had fuel flow gauges so I could get an accurate comparison of this very subject. Now that boat didn't have prop pockets like mine, but cruising at 7mph with one engine vs two did save some fuel. IMHO it wasn't enough of a difference (maybe 5%) to make up for the additional work at the helm trying to keep the boat straight. Any savings would probably be taken by the extra zig-zag motion of the boat as it encountered wakes and wind variations. There may also be an issue with prop shaft dripless seals overheating or transmissions overheating while "free-wheeling".
 

Forum statistics

Threads
112,950
Messages
1,422,862
Members
60,932
Latest member
juliediane
Back
Top