Perkins Fuel consumption

[BigAl.NZ]

I am trying to get a estimate of what our Perkins 4.108 burns per hour.
A bit of background, she is on a 3 bladed feather maxprop classic pushing a 38 foot 12 ton boat.

We idle her at 1500 RPM (for charging etc)
We motor sail at 2000 RPM
We motor at 2500 RPM at 5 knots.

I am guessing we use about 3.5 Liters per hour.

Please if you can add more to this let me know if its Imp or US Gal (if your answering in Gal).

Thanks

Al

[Mike OReilly]

My measurement is not refined, but my 4108 seems to burn about 3.5 l (~3/4 gallon) when motoring at about 1800-1900. I find if I keep it below 2000 my efficiency stays pretty good. But if I push to over 2000, fuel efficiency drops precipitously.

At this RPM we are moving at around 6 knots. I can get to full hull speed, which is about 7.2, with about 2300 RPM, but as I say, my fuel efficiency gets a lot worse; something like 7 l/hr.

I have a standard fixed 3-blade prop. My boat is more than twice your displacement (~15 tons). And it's a full keel, so lots of drag.

[Bermuda Forte]

< 3.5 l (3/4 US gal) @ 1900 rpm, 10 ton, 3 blade fixed prop.

[rbk]

3/4 gph @ 2000rpm 6.5 knts 3 blade fixed CSP LOA37 LWL31 22,500lbs dry

[donradcliffe]

Its not just RPM, its the load on the engine. That's a function of transmission ration, prop pitch and diameter, waterline, weight, bottom fouling, waves, and wind.

My best guess is that you would be burning about 3 liters per hour in flat water, mostly based on the 5 knot boat speed.

[Marathon1150]

I guessed 3.5l/h at 2500 RPM in the poll but I never run the engine that fast. Normally, we run at 1800 RPM when motoring or motor sailing and usually make between 5 and 6 knots, sometimes faster if motor sailing.

We have a 3 blade Campbell Sailor prop, the boat displaces about 12,000 pounds but we have a lot of stuff on it. So at 1800 RPM the boat normally burns about 2.4 l/h. The fuel tank is tiny - 117 litres - so I pay a lot of attention to fuel consumption. At 1500 RPM the engine burns 1.8 l/h. When calculating fuel needed I assume that we will burn about 2.2 l/h. These numbers are based on about 15 years of data.

Crossing the Pacific to Tahiti we had 10 x 20 litre jerry cans of diesel on board, just in case. But we only motored 19 hours during the 28 day crossing so we had a lot of fuel left when we reached Nuku Hiva.

[CSY Man]

The most efficient RPM seemed to 2100 on the 20,000 lbs CSY 33: 5.8 knots and 0.65 gallons per hour.. 2.5 liters, but easy to burn more if more power needed.
(3000 was max continues RPM but it would overheat at any RPM above 2500, heat exchangers was too small)

[BigAl.NZ]

Slightly off topic but hey I am the OP :-)

Where the hell is the oil sump plug?

[marcjsmith]

Over two seasons. We’ve averaged 3/4 gph on my 376.

[Marathon1150]

Originally Posted by BigAl.NZ

Slightly off topic but hey I am the OP :-)

Where the hell is the oil sump plug?

Good question! I have never looked for one and many Perkins 4.108 owners would say that it is not necessary because the crankcase oil finds its way out through a variety of means. We have been fortunate and ours doesn't leak much.

I previously used a handpump that seemed to be factory installed on the side of the engine to drain the crankcase. It however always leaves a bit of oil and right after a change, the oil on the dipstick is still quite black. I now use an electric pump with a fine diameter hose that goes down the dipstick tube. It works really well - faster, less messy and more effective than the old handpump.