Diesel consuption

[chuzzlewit]

Can anyone remind me how hourly diesel consumption is related to
engine horse power?

 

[HenryB]

The rough guide is 1 gallon per hour per 20 HP being generated - i.e. a 40 HP engine running at half power will use about 1 gallon per hour.

 

[reeac]

Don't confuse half power with half engine speed. The so-called "prop. law" means that half power comes at about 80% of max. engine revs. if you have the correct sized prop. for engine/gearbox combination.

 

[fireball]

Sounds odd ... cos according to that we should be using just shy of 1/2 gallon (or about 2.2L) per hr (we run an 18hp at cruising revs of 2800) and we only use ~1L per hr ... really efficient or what!

 

[HenryB]

I've checked the performance curves of a couple of engines in the 20 to 30 HP range (Volvo and Yanmar) and my 20 HP might be a little on the low side, probably more like 23 HP per gallon per hour at the engine. Fireball - your motor probably only needs to generate 5 HP or so to push your boat at 2800 rpm if you only use 1 lt per hour. The engine manufacturers graphs usually show the maximum power and consumptions at each rpm. In the extreme case, say, if you run the engine out of gear at a given rpm then it will use a fraction of the fuel shown in the manufacturers graphs. To test the other extreme, try towing a drogue at 2800 rpm and see what that does to the fuel consumption.
All IMHO

 

[oldsaltoz]

We run twin 30 HP Volvo's via sail drives and stainless steel props on a 40+ foot cat and manage to burn just under 3 litres an hour.

The Port engine uses a little more as it has the 85 amp alternator fitted.

Avagoodweekend......

 

[PCUK]

2ohp per gallon naturally aspirated.
23hp per gallon turbo.

Generally accepted rough guide.

 

[andy_wilson]

I agree with this. My VP2002 18Hp uses 1.5 lit / hour over a season, same for the last 6 seasons, which equates to 5-6 hp.

That average consumption however covers everything to motoring flat out, cruising at 2800 rpm, motor sailing at 1500 to 2800 rpm, charging batts at 1400 rpm and running the Mikuni at 0 rpm!

 

[Yachtbornfree2]

Running a Perkins 36hp 4107 I use about 2 ltrs per hour at 1500 rpm

 

[Whitelighter]

I have never understood this equation. My volcos are 230hp each, so 460hp in total. Running at a cruise, 70% revs, I am getting about 2.5mpg, or about 44 litres/hour. By the equation reckoning I should be using 23 gallons/hour - which I aint. Is this because I am planeing/have outdrives or what?

 

[HenryB]

The bottom line reason is that at your cruising settings your engines are only NEEDING to produce around 200 - 230 HP. When you set the throttle on a marine diesel you are actually telling the governor to run at specific rpm. It will then control the fuel delivery in order to maintain those rpm. My guess is when you open the throttles from standstill the governor will arrange for the injectors to supply maximum fuel until the specific rpm is attained (so you use 23 gallons/hour for a short period, possibly some black smoke is visible), then, once the rpm is reached the fuel supply is cut back to maintain those revs, which with your boat means that the engines are then producing about 200 HP. You might well need close to 460 HP to get you up to your cruising speed, so don't change your engines!
All IMHO

 

[claymore]

Running a Leyland 48hp engine at 1400 revs uses around 0.5 gall per hour