Another fuel consumption question

[Glenn collins]

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...

[BogMonster]

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.

[two stroke mick]

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

[Searider]

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

[benc]

Originally Posted by Searider

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

[Searider]

Ben

That's ££££££ eek

[benc]

Originally Posted by Searider

Ben

That's ££££££ eek

Tell me about it! its very though

[BogMonster]

Originally Posted by Searider

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.

[C-NUMB]

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?

[martini]

Originally Posted by benc

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

[Pikey Dave]

I have my gauges set to show l/nm not l/h, personally I think that fuel/distance is more meaningful than fuel/time. So I'm not 100% sure of my consumption/hour, so....

@ 3800rpm i'm doing around 28kn & 0.65nm/l =comfortable cruising speed.

@ full chat 5750rpm I'm doing 45kn & 0.5nm/l =teeth rattling

The best I can get is 25kn@0.75nm/l on calm water, lightly loaded & fully trimmed up.= zzzzzzz!

So there is a 50% difference between best & worst, extrapolating the figures gives about
90l/h worst case & 33l/h best case, "Normal" cruising i'm doing around 43 l/h which I don't think is too bad with twins.

[Gdog]

Hi. I have a yam 80hp 4stroke. Worst case is 22lt an hour. If it was me I would be basing all my calculations on worst fuel consumption. That way you should always end up with fuel to spare upon your return.

Cheers

Gdog.

[willk]

In my real boat days I used a slightly different technique. I used my cruising average to make sure that I had a 50% surplus of fuel in my main tank to allow for overruns. Then I had an extra supply in deck tanks that gave me a known 30Nm range at modest speeds - enough to get me to port/fuel in a worst case scenario.

Nowadays I just keep an extra 2 liters of premixed gas in my pack - same thing!

[Searider]

Not wanting to hijack the thread but it would appear that Yam HPDI, Optimax and e-tech, 150hp variants, use the about same ammount of fuel.

[Searider]

Originally Posted by martini

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

But isn't petrol tax free in the CI?

[martini]

Originally Posted by Searider

But isn't petrol tax free in the CI?

Still 90 ppl though

[9D280]

I'll have two at that price!