Fuel consumption

[Dalslandia]

I would think you improve the fuel consumption to a higher number, good for those that sell fuel. :-)

 

Well is depends on the engine, but normally, as you say it will need the same HP, but the cylinder load will be higher at 1400, so burn the fuel more efficient, if it is possible to see the differens ?? you can do that in a modern car.

[Beaker]

is your bottom clean,

 

Try wet wipes, don't drop them in the pumpout though.

Edited February 1, 2014 by Beaker

[Paul's Nulife4-2]

Try wet wipes, don't drop them in the pumpout though.

:-) (I haven't got those smiley thingys).

[Naughty Cal]

We use somewhere between 3 litres and 30 litres an hour. Depends where we are!

Edited February 1, 2014 by Naughty Cal

[Alan de Enfield]

We use somewhere between 3 litres and 30 litres an hour. Depends where we are!

 

Been there. done that.

We had two x 6 cylinder Volvos and at full chat we were doing 28 knots (once touched 30 knots) and using 1 gallon (4.54 litres) in one and a quarter miles (about 100 litres per hour)

Needless to say we normally cruised at around 22 knts.

[Naughty Cal]

 

Been there. done that.

We had two x 6 cylinder Volvos and at full chat we were doing 28 knots (once touched 30 knots) and using 1 gallon (4.54 litres) in one and a quarter miles (about 100 litres per hour)

Needless to say we normally cruised at around 22 knts.

We have seen 36 knots from NC (with the tide) and at that she was flat out using 6 gallons an hour. Ouch!

 

For those that are not in the know it isn't usual to cruise flat out for long. Backing off a few hundred rpm gives a significant saving ....

Edited February 1, 2014 by Naughty Cal

[dmr]

We have seen 36 knots from NC (with the tide) and at that she was flat out using 6 gallons an hour. Ouch!

 

For those that are not in the know it isn't usual to cruise flat out for long. Backing off a few hundred rpm gives a significant saving ....

 

It reminds me of the old joke that sailors on the Solent always crack when they see a "gin palace" going past.....

What sound do the engines on a Gin Palace make?

One Gallon of Diesel,Two Gallons of Diesel, Three gallons of Diesel....

[Naughty Cal]

 

It reminds me of the old joke that sailors on the Solent always crack when they see a "gin palace" going past.....

What sound do the engines on a Gin Palace make?

One Gallon of Diesel,Two Gallons of Diesel, Three gallons of Diesel....

Tis very true!

 

Mind you the gin palace does get to the bar before it closes.

 

Then to the fuel berth as soon as it opens next day.........

[Alan de Enfield]

Fuel wasnt a problem at most of the commercial marina's / docks but on the Isle of Man we did have to get a road tanker to come down to the harbour and 'give us' 700 litres (the marina was used to sail boats who just took a few litres).

[nebulae]

I have an Isuzu 42hp in a 50ft narrow boat.Previously the boat had a Lister SR2(18hp?).The performance on narrow canals was about the same with both engines,as was the fuel consumption .Struggled on rivers a bit and the noise and vibration was doing my head in. H.P.I.,who marketed the Isuzu units also built pumps,generators etc from the base units in their factory in Gloucestershire.The same engine as I have in my boat could also be had in a generator,running at 3,000rpm and also rated at 42hp?As has been said,max power can only be obtained at a certain speed(I believe 3,000rpm with this engine)My engine is restricted to 2,000rpm.By the time power loss in the gearbox and 2 x70 amp alternators.have been taken out,Iwonder how many horses I am left with? Has anybody done a dynometer test on these engines?.Most major tractor dealers have dynometers nowadays to test P.T.O. output,so it should be possible!

[Naughty Cal]

I have an Isuzu 42hp in a 50ft narrow boat.Previously the boat had a Lister SR2(18hp?).The performance on narrow canals was about the same with both engines,as was the fuel consumption .Struggled on rivers a bit and the noise and vibration was doing my head in. H.P.I.,who marketed the Isuzu units also built pumps,generators etc from the base units in their factory in Gloucestershire.The same engine as I have in my boat could also be had in a generator,running at 3,000rpm and also rated at 42hp?As has been said,max power can only be obtained at a certain speed(I believe 3,000rpm with this engine)My engine is restricted to 2,000rpm.By the time power loss in the gearbox and 2 x70 amp alternators.have been taken out,Iwonder how many horses I am left with? Has anybody done a dynometer test on these engines?.Most major tractor dealers have dynometers nowadays to test P.T.O. output,so it should be possible!

We have often pondered that.

 

Ours is rated at 170hp at the props at 3800rpm so it's anyone's guess what the actual unit is developing!

[Dalslandia]

If you know how much fuel you are using, average or have a meter. you can back calculate the power.

0,22 liter per HP is close enough for a diesel.

If you mostly cruise at one speed/power setting you can calculate the top speed power needed.

For fishing and working boats you have some power rating system in UK, there is some hints of power calculation there.

 

If going in and out of locks, cruising on canals and rivers, it become harder to calculate the real power.

Grace and Favour's number show a formula of RPM^2,9

theory say ^3

I saw some boat makers/engine maker use ^2,8

The difference from theory is the engine and domestic power need beeing more or less constant

the fuel consumption don't start at zero at zero speed, but the difference is very small on larger engines

but on a 10-20 hp engine it is a large part of the usage.

Grace and Favour's number show a formula of RPM^2,9

theory say ^3

I saw some boat makers/engine maker use ^2,8

The difference from theory is the engine and domestic power need beeing more or less constant

the fuel consumption don't start at zero at zero speed, but the difference is very small on larger engines

but on a 10-20 hp engine it is a large part of the usage.

[Mukiwa]

I would think you improve the fuel consumption to a higher number, good for those that sell fuel. :-)

 

Well is depends on the engine, but normally, as you say it will need the same HP, but the cylinder load will be higher at 1400, so burn the fuel more efficient, if it is possible to see the differens ?? you can do that in a modern car.

Thank you for that informative answer. It is most helpful in making a decision about propeller size.

[RLWP]

Thank you for that informative answer. It is most helpful in making a decision about propeller size.

Another aspect. You might get a small improvement that you might be able to measure

 

On the other hand, you will definitely get an irritating increase in engine speed which you may find annoying when cruising

 

Lower engine speeds feel more relaxing

 

Richard

[Dalslandia]

If you are in the process of getting a new propeller, I wasn't aware.

But just think twise what you want and what you need.

 

In general terms:

if need good acceleration, for towing boats or water skiier, or for going in rough sea, you need to be little under propped in calm sea.

 

if you want best top speed, you go for max power rated rpm.

 

If you want good and economical speed, just a tad over propped

 

If you want ONLY good low speed economy, over propped is good.

 

I don't have photo, but you know the boat/propeller demand power curve beeing concave seen from top, the engine max throttle power curve is convex, where they meet is your top speed.

between the curves, slower then max, there is a distance between curves, thats what give acceleration.

 

An modern "big" engine that is over propped so it don't gan turn max rated rpm, will be limited in max power, so it will act more like a old timer with low rpm, when cruuising slowly with this one the load on the engine will be little higher then the propeller that give the rated rpm, so between the curves. this have two good effects the engine is more efficient, and the bigger propeller is more efficient.

 

The down side is that you can't or should race with the throttle bend over the stop for any longer periods. it is not good for the engine, that is setup for higher rpm.

[Keeping Up]

Too many people have a big engine which is propped for speed and power, so they cannot travel below about 2.5 mph. Deliberate under-propping allows you to travel slowly and to manoeuvre at slow speeds

[nicknorman]

Too many people have a big engine which is propped for speed and power, so they cannot travel below about 2.5 mph. Deliberate under-propping allows you to travel slowly and to manoeuvre at slow speeds

Whilst admitting that a min of 2.5mph is perhaps getting a bit fast, I don't see why there is a need to be propped for under 2mph - that is a reasonable moored boat passing speed. Whilst you see people manoeuvring too fast, I see people manoeuvring too slowly such that they get no response from the rudder.

 

Our boat (Beta 43 on 59' nb with big prop) does about 2 mph at tickover. I have never found it to be a problem. We are just slightly over-propped in deep water. The boat would probably be more economical if it were over propped a bit more, but allowance also has to be made for the 3 alternators which, if working hard, probably use 8hp.

[Dalslandia]

There is always two side of a coin.

 

The gear ratio whould also be looked at, so the biggest, practical, noise wise, propeller can be used.

Propellers move masses, a small prop that act like a egg beater don't improve stearing either, to much prop walk is also negative, sometimes.