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Old 22 June 2011, 15:41   #1
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Another fuel consumption question

I don't know if anyone can help with this but...

I am aware that if I have a 60hp 2stroke at full open throttle it will use on average about 6 gallons per hour. At flat out with just me onboard I will cruise at about 26 knots.

Is there any rough calculations for guessing fuel consumption at anything other than full open? I'm looking to plan some trips out and remove some of the guess work. For instance, if I was going 20nm and cruising that distance at 14knts how much fuel will is use?

I know there wil be nothing certain but anything closer to a simple guess would be be grat if anyone knows of anything...
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Old 22 June 2011, 17:42   #2
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Your consumption at full moo is about 1.05L per mile then (27.2L to do 26nm).

I'd suggest use that as the basis for an absolute minimum amount for your calculations - at part throttle you'll be using less, and it's nice to have a reserve!

Not very exact either but probably ok as a rule of thumb? I'd also want a further reserve as well though.

I watch the fuel flow gauges on the E-TEC with some curiosity to try and find the sweet spot for best consumption (about 26-27kt on mine) and TBH you get significant variations due to sea conditions, load, and even trim. I probably get nearly a 5% difference just with the weight of full fuel (150L) against a tank that is close to empty, and in rough conditions you can use at least 10% more plugging into a head sea as you do skimming along when it's calm.
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Old 24 June 2011, 11:19   #3
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With My Etec 60 hp on a 4.9m rib it uses 13 lt/hr (avgerage) circa 1.3/ 1.4 nm / lt.
for the purposes of passage planning I use 1lt to 1 nm this tends to give me a reserve of 33 %

TSM
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Old 24 June 2011, 12:32   #4
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Agree with the above but would add:

If you slow down from your maximum RPM by about a quarter of your maximum RPM your fuel consumption may drop by as much as half whilst your speed drops by perhaps only a quarter.

In my case 5300rpm gives about 40 knots at 56 litres per hour. (Ithink it's 56 - I don't often go that fast££££)
3800rpm gives me about 30 knots for 28 litres per hour.

HTH
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Old 24 June 2011, 12:50   #5
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Quote:
Originally Posted by Searider View Post
Agree with the above but would add:

If you slow down from your maximum RPM by about a quarter of your maximum RPM your fuel consumption may drop by as much as half whilst your speed drops by perhaps only a quarter.

In my case 5300rpm gives about 40 knots at 56 litres per hour. (Ithink it's 56 - I don't often go that fast££££)
3800rpm gives me about 30 knots for 28 litres per hour.

HTH
If I am full chat, 5400 rpm, I am using around 120l/hour and get about 55.4 knots... if I pull back to about 4000 rpm I get 40 knots at 60l/h
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Old 24 June 2011, 17:24   #6
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Ben

That's ££££££ eek
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Old 24 June 2011, 17:44   #7
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Ben

That's ££££££ eek
Tell me about it! its very though
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Old 24 June 2011, 20:55   #8
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Quote:
Originally Posted by Searider View Post
If you slow down from your maximum RPM by about a quarter of your maximum RPM your fuel consumption may drop by as much as half whilst your speed drops by perhaps only a quarter.

In my case 5300rpm gives about 40 knots at 56 litres per hour. (Ithink it's 56 - I don't often go that fast££££)
3800rpm gives me about 30 knots for 28 litres per hour.

HTH
I'd go along with that logic - my Etec is about the same - have seen it touch 60L/hr at a little over 40kt but at 30 it's less than half that around 27-28lph.
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Old 26 June 2011, 04:10   #9
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My SR seams to use the same amount /NM regardless of the speed adjusted by throttle. Don't think much difference between 22 and 35 knots. Weather, load and trim(trimming down) seams to have a greater impact.

But as fuel is very expensive, would be nice to know the accurate consumption /h. Any reasonable priced gauges available?
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Old 26 June 2011, 04:34   #10
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Quote:
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If I am full chat, 5400 rpm, I am using around 120l/hour and get about 55.4 knots... if I pull back to about 4000 rpm I get 40 knots at 60l/h
Pah, that's nothing , at full chat I'm using 160 l/hr to do 40 kts, cruising at 4500rpm I get 30kts at 90 l/hr

Next one's going to be diesel
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