Expected fuel consumption

[Dobieman]

I have a zodiac pro 420 with a mercury 40hp 4 stroke, I know it’s not an exact science but what kind of fuel consumption should I expect when doing some gentle cruising?
I’ve read a lot on here about bigger boats and outboards ( 6m and 115hp for example ) getting approx 0.8 litres per nm, could I expect to double that?

[jonp]

There's plenty of info out there that should give you close to the exact usage, remember a fully loaded boat will increase the use. This is very accurate Mercury 25 - 40 - 50 - 75 - 90 - 115 - 150 efi - Mercury Verado 150 - 175 - 200 - 225 - 250 - 350 hp SCi Outboard Fuel Consumption Chart GPH MPG Test & Specs | Portable 3.5 - 4 - 6 - 8 - 9.9 - 15 hp these figures are from correctly prppped outboards allowing them to reach the maximum rpm. The site will open on a 25hp, within that box click on next to get the 40hp.

[gpsguru]

Originally Posted by Dobieman

I have a zodiac pro 420 with a mercury 40hp 4 stroke, I know it’s not an exact science but what kind of fuel consumption should I expect when doing some gentle cruising?
I’ve read a lot on here about bigger boats and outboards ( 6m and 115hp for example ) getting approx 0.8 litres per nm, could I expect to double that?

I have a mercury ocean runner 420 and a Mercury 40hp EFI 4 stroke ........

On average I get about 2.25Nm per Litre ........... that figure is based on a season, so a mix of speeds.

Cruising (25knts) I get about 2.6Nm per litre ........... but that is on a flat sea.

Base your fuel load on 1/3 to get there, 1/3 to get back and a reserve of 1/3

[jonp]

Originally Posted by gpsguru

I have a mercury ocean runner 420 and a Mercury 40hp EFI 4 stroke ........

On average I get about 2.25Nm per Litre ........... that figure is based on a season, so a mix of speeds.

Cruising (25knts) I get about 2.6Nm per litre ........... but that is on a flat sea.

Base your fuel load on 1/3 to get there, 1/3 to get back and a reserve of 1/3

Those are amazingly good fuel figures, I thought my Yam f70 was good giving 2.5km per litre which is only half a nautical mile ( roughly ).

[Last Tango]

Originally Posted by jonp

Those are amazingly good fuel figures, I thought my Yam f70 was good giving 2.5km per litre which is only half a nautical mile ( roughly ).

2.5KM = 1/2 a nautical mile.....? er.. no. 1.3 nautical miles.

[jonp]

Originally Posted by Last Tango

2.5KM = 1/2 a nautical mile.....? er.. no. 1.3 nautical miles.

Haha yes you're right, I was thinking litres into gallons don't normally work in imperial so mxing the two isn't something I normally do. what's even more confusing is a US gallon is different to a U.K. gallon, litres and kilometres are so much easier.

[Aftica]

Originally Posted by jonp

Those are amazingly good fuel figures, I thought my Yam f70 was good giving 2.5km per litre which is only half a nautical mile ( roughly ).

1852m is 1 nautical mile, defined of 1mn latitude.
Regard

[Last Tango]

Originally Posted by Aftica

1852m is 1 nautical mile, defined of 1mn latitude.
Regard

Strictly speaking it's the arc on the surface of the Earth subtended by one minute of a degree of of latitude at the Earth's centre and, as the Earth is not absolutely spherical, it's radius varies with latitude so a "nautical mile" also varies with latitude.

Hence the reason we us the latitude scale level with our position for measuring distances........or...... we read it of the GPS and Google kilometers to nautical miles on google map's "measure" option

[jonp]

Yep there's a reason I use litres and km

Petrol stations sell the fuel by the litre, my fuel tank holds 100lt, my nmea to my sounder is set up in litres for fuel burn, range etc. I find it simple to measure between points on my navionics and can instantly work out how much fuel I need for the 80km offshore island hoping trips I do. The line I buy for my reels is in metres ( not fathoms ) even my Navy charts are metric.

All our cars work in km, my daughter's athletics, swims and triathlons are in km, the exits off motorways and all speeds are in km, so judging visual distances is far easier than going back to part imperial part metric. Things went metric in the UK while I was still at school many years ago, mixing the two together gets a little confusing especially when you live in a country that's moved away from it.

[Aftica]

Originally Posted by jonp

Yep there's a reason I use litres and km

Petrol stations sell the fuel by the litre, my fuel tank holds 100lt, my nmea to my sounder is set up in litres for fuel burn, range etc. I find it simple to measure between points on my navionics and can instantly work out how much fuel I need for the 80km offshore island hoping trips I do. The line I buy for my reels is in metres ( not fathoms ) even my Navy charts are metric.

All our cars work in km, my daughter's athletics, swims and triathlons are in km, the exits off motorways and all speeds are in km, so judging visual distances is far easier than going back to part imperial part metric. Things went metric in the UK while I was still at school many years ago, mixing the two together gets a little confusing especially when you live in a country that's moved away from it.

In my case, I use liter per hour, depending of the sea condition, the wind, the current and how I perform to trim my boat, I don't cover the same distance in one hour, but I always burn approximately the same amount of petrol.

[Poly]

Jonp - I’d agree with much of what you say, especially using MPG to describe vehicle fuel consumption is an odd quirk given nobody buys in gallons anymore (although iirc Europeans use a different convention of L per 100km which as the reciprocal to me is less useful). I do still think that Nautical Miles are the right unit for navigation at sea though - are the black grid lines on your chart not multiples of NM? Your plotter is easily configured to read NM and knots. Using NM also helps (me) translate GPS coordinates into something meaningful. Perhaps the world of plotter connected VHFs makes that redundant but to quickly hear a position and mentally know how far N/S (and roughly W/E) means that I have an idea if it is relevant to me and if I manually put in the coordinates to my plotter a little mental check in case I have typed wrong.

Either way it is more complex when people quote both L/NM and NM/L not to mention mixing in UK Gals, US Gals, statute miles etc.

[Poly]

Originally Posted by Aftica

In my case, I use liter per hour, depending of the sea condition, the wind, the current and how I perform to trim my boat, I don't cover the same distance in one hour, but I always burn approximately the same amount of petrol.

Likewise, especially the sea condition and load making a big diff to consumption. A crude rule of thumb is an old 2 stroke will use 3.8L (1 us gal) per hour at full throttle for each 10HP it produces. So a a 40HP will be using 4x3.8 L = 15L per hour at max throttle. In calm conditions it might well be doing 30 knots and delivering the 1NM/L figure people often suggest here. In horrible conditions the throttle might still be working hard to deliver 1/2 that speed.

Modern engines are supposedly more efficient but I’d be inclined to plan on the 2/ numbers until I had real data from real conditions.

[jonp]

To add to the confusion a US gallon is 3.8l, UK gallon 4.5l ( I thought they were the same) a mile is different to a nautical mile.

As far as how my charts appear on my plotter, I have no problem using metric, if I place my cursor on any offshore mark I instantly get the distance in metres which I can very quickly calculate the fuel needed. The same goes for plotting a course, each waypoint adds together in km which I find very easy to work out. I don't know of many people who talk in the old nautical terms here anymore, even on dive and fishing charters tourists want to know how far offshore they are heading in a measurement they know and grew up with over the last 45 years.

[Aftica]

Originally Posted by Poly

Likewise, especially the sea condition and load making a big diff to consumption. A crude rule of thumb is an old 2 stroke will use 3.8L (1 us gal) per hour at full throttle for each 10HP it produces. So a a 40HP will be using 4x3.8 L = 15L per hour at max throttle. In calm conditions it might well be doing 30 knots and delivering the 1NM/L figure people often suggest here. In horrible conditions the throttle might still be working hard to deliver 1/2 that speed.

Modern engines are supposedly more efficient but I’d be inclined to plan on the 2/ numbers until I had real data from real conditions.

If you want, you can fit a flow meter on your fuel line connected to your nmea2000, and you will have accuracy in reel time.
Regard

[Last Tango]

Originally Posted by jonp

To add to the confusion a US gallon is 3.8l, UK gallon 4.5l ( I thought they were the same) a mile is different to a nautical mile.

As far as how my charts appear on my plotter, I have no problem using metric, if I place my cursor on any offshore mark I instantly get the distance in metres which I can very quickly calculate the fuel needed. The same goes for plotting a course, each waypoint adds together in km which I find very easy to work out. I don't know of many people who talk in the old nautical terms here anymore, even on dive and fishing charters tourists want to know how far offshore they are heading in a measurement they know and grew up with over the last 45 years.

The upside of using nautical miles being you don't need a scale on a chart and if you hear a position quoted over the radio you can pretty much work out how far away they are in your head.