Running single on a twin to save fuel

[Icebreaker]

Here we go

Displacement hull 66 tons
Gross loaded tons 65
Net tons 33
Hull Speed 9.4

2 Volvo 225 HP diesel engines Model TMD100Ak
1 Gear Box SCG MF16-11c
1 Saffle adjustable Pitch Prop

Running both engines in calm seas with SOG of 8 knots uses 60 litres/hour

How many litres/hour with 1 engine ?? at say 7 kts in calm seas ??????

[powerabout]

I have done a few tests on displacement megayachts 40 to 50
metre and they all used way less fuel on one engine at less than full speed
I guess it depends on the power to move the hull versus the gph with the 3412 or 3508's running with very little load before they start to get much boost.
The problem is you can overload a single engine if you nail it and usually the gearbox is not designed to windmill unless supplied with prop side oil pump.
Was handy to know at what rpm you went to overload just in case you did need to run hard on one engine
Was also interesting to know that it was always at a different rpm ( by a few hundred) on each engine due to one gearbox going the other way.

[Icebreaker]

To Clarify:
The vessel has only ONE Gearbox, One Propeller

"
The Vessel
62.5 ft LOA
49ft LWL
Displacement hull 66 tons
Gross loaded tons 65
Net tons 33
Hull Speed 9.4

2 Volvo 225 HP diesel engines Model TMD100Ak
1 Gear Box SCG MF16-11c
1 Saffle adjustable Pitch Prop

Running both engines in calm seas with SOG of 8 knots uses 60 litres/hour
The Question :-
How many litres/hour with 1 engine ?? at say 7 kts in calm seas ????
"

[FAST FRED]

How many litres/hour with 1 engine ?? at say 7 kts in calm seas ????

If your displacement is correct at 66long tons , and the number is not the registered tonnage , which is volume not displacement .

2HP per ton , perhaps 2.5 should do the job, so the question becomes how efficiently does the single engine create 150-160HP ?

The simplest solution , that IS worth the bucks is to install a Flow Scan that hooks to both engines and the GPS.

This will give instant reading of MPG. www.floscan.com/

FF

[powerabout]

f you have the fuel flow you just need to spec sheets of the engine to work out how much load they are under at that speed.
If the BSFC goes down at a higher rev then you would be better off with one engine thats an easy one.
To work out anything else you would need the load curve ( some call that the prop curve) of the vessel