Average fuel burn?

[Capt. Johnson]

I know fuel burn can change a lot from area, weather, size of yacht, etc etc.... but can anyone give me a rough estimate of yachts average fuel burn. I don't own nothing yet so can not give example. But I am gonna be looking between 40-60 foot yacht. Most likely a trawler type. Plan to live aboard. Thanks in advance for any help. And sorry new to yachting and this community. But I am a licensed MMC Captain. But trust me my work vessels fuel burn is 20ish gallons per hour.

[donradcliffe]

Its all about how far you push the throttle forward. A 40 ft planing boat burns about 25 gph at 20 knots. A square sterned displacement boat like a Grand Banks will burn 3 gph at 7 knots, and 10 gph at 8.5 knots. A Monterey fishing boat with a round stern will burn as little as 2.5 gph at 7 knots.

[MicHughV]

Diesel fuel consumption in marine engines is pretty well documented.

I've always used the 20 hp/gal/hr rule, which seems to be relatively accurate for most people's needs..

ie, if you have a 60 hp engine, which operates at, say 2/3 throttle at cruise, in rough terms, producing about 40 hp at that rpm, fuel consumption will be about 40/20 or 2 gallons per hour at that rpm.

If you really want to delve into it, I can recommend reading the " The Propellor Handbook authored by Dave Gerr, who explains in great detail the ins and outs of it all.

You are likely to get many opinions on the matter.

[BlueH2Obound]

Our boat, displacement hull, 87,000lbs or thereabouts fully loaded, we went 3,100 miles last year over 87 days, including hydronic heat and about 45 hours of generator run, we averaged 7.5 kts, and just under 3.0 gallons/hour. We didn't refuel until we got back, so it was a pretty good test run/calculation. YM(literally)MV.

[Scubaseas]

Originally Posted by MicHughV

Diesel fuel consumption in marine engines is pretty well documented.

I've always used the 20 hp/gal/hr rule, which seems to be relatively accurate for most people's needs..

ie, if you have a 60 hp engine, which operates at, say 2/3 throttle at cruise, in rough terms, producing about 40 hp at that rpm, fuel consumption will be about 40/20 or 2 gallons per hour at that rpm.

If you really want to delve into it, I can recommend reading the " The Propellor Handbook authored by Dave Gerr, who explains in great detail the ins and outs of it all.

You are likely to get many opinions on the matter.

X2 on Gerr's book. His one on "Boat Strength" is worth reading also.

It depends as said up page, how far you push the throttle. And how clean your hull is and many other things. The 20hp/gal/hr is a good indicator.

[Bobby Lex]

Some good info above. I would only add that if you get a trawler you may be dealing with TWO engines not one, so double the fuel consumption. Also, most trawlers (and many sailboats as well) have a generator -- which also needs to be factored into the fuel consumption equation.

Bob

[StuM]

Originally Posted by MicHughV

Diesel fuel consumption in marine engines is pretty well documented.

I've always used the 20 hp/gal/hr rule, which seems to be relatively accurate for most people's needs..

ie, if you have a 60 hp engine, which operates at, say 2/3 throttle at cruise, in rough terms, producing about 40 hp at that rpm, fuel consumption will be about 40/20 or 2 gallons per hour at that rpm.

Just be aware that if "2/3 throttle" is taken to mean "2/3 max RPM", it is not 2/3 power, it's more like 1/3 power. i.e an engine which puts out 60HP at a max of 3000 RPM will only be putting out about 20 HP at 2000 RPM (and use about 1 gph).

[mvweebles]

Originally Posted by Capt. Johnson

I know fuel burn can change a lot from area, weather, size of yacht, etc etc.... but can anyone give me a rough estimate of yachts average fuel burn. I don't own nothing yet so can not give example. But I am gonna be looking between 40-60 foot yacht. Most likely a trawler type. Plan to live aboard. Thanks in advance for any help. And sorry new to yachting and this community. But I am a licensed MMC Captain. But trust me my work vessels fuel burn is 20ish gallons per hour.

Take a Grand Banks 42. They were available early with a single 120HP Ford Lehman; twin 120's; and later twin >300hp Cat 3208s (1980's); and finally, a more recent GB42 with twin 375hp Cummins B-Series (Tier 3/Common Rail - T/A) engines.

At 7.5 kts, I will guess the following as 'directionally correct' for continuous running in open water (+/- 0.3 gph):

• Single 120HP - 2.25 gph
• Twin 120HP - 2.75 gph
• Twin 3208's - 3.0 gph
• Twin Common Rail - 2.50 gph

As comparison, I was aboard a friend's Willard 40 with a John Deere 4045TA (Tier 2 at the time - 2001 build) from Long Beach to La Paz MX, about 1000nms at 7-1/4 kts and burned under 1-1/2gph in open ocean conditions - close to 5.5 nmpg (nautical mile per gallon)

Yesterday, I was aboard a newer 60k lbs 52-foot Power Cat with electronic control engines with full monitoring. We ran about 45nms out, and 45nms back. About 5nms of no-wake zone. On the way out we ran at 11-1/2 kts (huge wake) at 0.65 nmpg. On the way back, ran 8-1/2-kts and burned 6 gph - close to 1.5 nmpg. Cruise on this boat is around 17-18 kts, burn at cruise is 36 gph or 0.5 nmpg. Rough math, way out was 4-1/2 hours, way back was 5-1/2 hours. Burned about 45 additional gals of diesel on the way back, so coming up on an extra $200 in diesel to save an hour.

Speed is expensive. Just depends on whether you have more time than money, or vice-versa.

[Adelie]

Originally Posted by MicHughV

Diesel fuel consumption in marine engines is pretty well documented.

I've always used the 20 hp/gal/hr rule, which seems to be relatively accurate for most people's needs..

ie, if you have a 60 hp engine, which operates at, say 2/3 throttle at cruise, in rough terms, producing about 40 hp at that rpm, fuel consumption will be about 40/20 or 2 gallons per hour at that rpm.

If you really want to delve into it, I can recommend reading the " The Propellor Handbook authored by Dave Gerr, who explains in great detail the ins and outs of it all.

You are likely to get many opinions on the matter.

Only the very best diesel engines get 20hp-hr/gal, and then only those near 600hp peak output.

For engines near 60hp, peak efficiency will be 16-18hp-hr/gal.

For diesel engines pushing props, at 2/3 max rpm output will be 1/4-1/3 max HP. The engines are certainly capable of putting out considerably more power than this at that RPM but the props can’t absorb it.

However because fuel efficiency falls off considerably along a prop curve, assuming that fuel consumption per hour is proportional to rpm is close to observed reality. This is what MicHugh suggests above.

If you look at a fuel efficiency map you can see that fixed prop demand curve tend to run the mostly inefficient parts of the fuel map except need max output.

See attached graphic.

With a controllable pitch propellor (CPP) pitch and rpm can be adjusted to operate the engine more efficiently.

[ranger58sb]

Originally Posted by Capt. Johnson

I know fuel burn can change a lot from area, weather, size of yacht, etc etc.... but can anyone give me a rough estimate of yachts average fuel burn. I don't own nothing yet so can not give example. But I am gonna be looking between 40-60 foot yacht. Most likely a trawler type. Plan to live aboard.

You might find more useful info on trawlerforum.com (sister site).

Many posters there say fuel is not usually their largest expense item.

And fuel consumption with twin engines is often similar to fuel consumption with a single screw.

-Chris