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Efficient Fuel Consumption Whilst Cruising


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Ok I have done a few searches but couldn't find what I was looking for so apologies if this has been covered before.  On this trip, compared to the one over Christmas, we seem to have used far more fuel than normal yet we have hardly used  the Mukuni and we try to keep around the 2 mark on the rev counter. We have however, as previously posted, been using the Coventry Canal and had to stop at least 10 times to un snag the prop, everything from plastic bags and rope to a fully hoody complete with zip. Could this have affected consumption?  The RCR did a full engine check before we set off, no problems, oil & water & stern gland checked each day.  I read somewhere that 8 hours cruising = 10 litres of fuel.  Does anyone have any comments/suggestions/opinions?   Thanks

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By "2 mark" - do you mean 2,000 rpm? If so that seems very high to me.  My boat cruises around 1200 rpm on the canals - or less when passing long lines of boats...

If you have to run the engine that fast to make any progress, then either you've got something still attached to the prop, or the gearing is wrong or you'r digging a hole in the shallow canal....

 

 

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Most canal boats, irrespective of engine or length will use between 1.0 & 2.0 litres per hour run, depending on speed of boat and depth of water.

Make sure you aren't leaving large waves, or worse, a breaking wash behind you to maximise fuel consumption.

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Piece of string innit. Depends on engine and lots of variables. We have a Beta 43 and cruise at a 'fast tickover', about 12 - 1500 rpm, on bigger commercial canals and rivers we usually do 1600 rpm perhaps a bit more. 2000 rpm is reserved for panic and 'You haven't seen that huge ship have you' events. I doubt if we ever achieve 8 hours for 10 litres unless its a very relaxed drift along with the current with few locks or manoeuvres.

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I tend to cruise at around 1200 and use about 1.5l per hour.  A lot depends on water depth an the Coventry is fairly shallow.  When I first stated boating I noticed I seemed to be going slower than usual on the north Oxford and increased revs slowly until they were around 2000.  I didn't go any faster as the boat simply sat down at the back and was dragging the bottom.   

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10 minutes ago, Martin Megson said:

I tend to cruise at around 1200 and use about 1.5l per hour.  A lot depends on water depth an the Coventry is fairly shallow.  When I first stated boating I noticed I seemed to be going slower than usual on the north Oxford and increased revs slowly until they were around 2000.  I didn't go any faster as the boat simply sat down at the back and was dragging the bottom.   

That makes sense and is in common with my experience (Beta 43, 48ft boat) - 1150 to 1200 rev/min is plenty on a shallow canal.

I'd suggest the OP tries to correlate his speed over the ground (measured on a satnav) with the engine revs. There will be a critical engine speed above which the rate of progress is hardly increased at all -- if he exceeds those revs he is wasting fuel. 

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2 minutes ago, Machpoint005 said:

That makes sense and is in common with my experience (Beta 43, 48ft boat) - 1150 to 1200 rev/min is plenty on a shallow canal.

I'd suggest the OP tries to correlate his speed over the ground (measured on a satnav) with the engine revs. There will be a critical engine speed above which the rate of progress is hardly increased at all -- if he exceeds those revs he is wasting fuel. 

. . . and may actually decrease the speed as the extra engine power draws more water out from under the boat and hence decreases the clearance even more.

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Does anyone use the pre Rev counter back in the day method, when setting off or exiting a lock give the engine a bit of "wellie"& when the counter is sucked down or a reasonable forward motion is attained close the throttle by small amounts until the boat is still "getting on" at more or less the same speed but with less throttle hence more economical +not digging in as much.& possibly not creating a breaking wash, small adjustments of the throttle either  more/less revs to keep the speed required or possible.

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5 minutes ago, X Alan W said:

Does anyone use the pre Rev counter back in the day method, when setting off or exiting a lock give the engine a bit of "wellie"& when the counter is sucked down or a reasonable forward motion is attained close the throttle by small amounts until the boat is still "getting on" at more or less the same speed but with less throttle hence more economical +not digging in as much.& possibly not creating a breaking wash, small adjustments of the throttle either  more/less revs to keep the speed required or possible.

That was almost exactly what I used to do, it was a constant surprise to me to realise how few revs were actually needed. One also got very good at noticing when a canal got deeper by the way the boat moved and steered.

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2 minutes ago, Stilllearning said:

That was almost exactly what I used to do, it was a constant surprise to me to realise how few revs were actually needed. One also got very good at noticing when a canal got deeper by the way the boat moved and steered.

You Sir became a fully paid up member of the "Happy boaters association" or finesse triumphs over brute force.  :lol:

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In 2,298 hrs of engine running with very little just charging Theodora used an average of 1.21 litres/hr.

BMC 1.5

Normal canal cruising at 1,100rpm

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1 hour ago, Stilllearning said:

That was almost exactly what I used to do, it was a constant surprise to me to realise how few revs were actually needed. One also got very good at noticing when a canal got deeper by the way the boat moved and steered.

Absolutely!  Just been doing the summit level of the Leicester Section. It was deweeded and dredged a couple of years ago between Crick and Husbands Bosworth, I think.  As the canal shallowed it was obvious that I needed to reduce revs.

N

 

 

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Just to challenge the notion that all boats of all lengths with any engine use the same amount of fuel: My 35ft boat powered by a 500cc 2 pot Vetus uses slightly under 1 litre per hour whilst cruising. If I'm battery charging I get 2 1/2 hours from 1 litre of diesel. I guess the large difference is down to the fact that I need to rev it quite hard to get to 2 1/2 to 3 mph. I don't have a rev counter but I'd guess it's well over 2000 rpm.

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1 hour ago, Gareth E said:

Just to challenge the notion that all boats of all lengths with any engine use the same amount of fuel: My 35ft boat powered by a 500cc 2 pot Vetus uses slightly under 1 litre per hour whilst cruising. If I'm battery charging I get 2 1/2 hours from 1 litre of diesel. I guess the large difference is down to the fact that I need to rev it quite hard to get to 2 1/2 to 3 mph. I don't have a rev counter but I'd guess it's well over 2000 rpm.

Rather than challenging the notion that most boats, whatever their length, use between 1.0 and 2.0 litres of fuel per hour when cruising,  you have pretty much proved it, by stating that your small boat with a small engine uses slightly under 1 litre of diesel per hour

Obviously when battery charging only, the boat is stationary and running on a very light load, so will use much less fuel.

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It's 0.8 litres per hour, around 30% less than many other boats, non?

If most boats, moving through water using different sized engines use the same amount of fuel, why can't we say the same for cars moving along a road? For example; a small car with a small engine will use far less fuel than a bigger, heavier car, that has a bigger engine. Is there something about the physics of moving through water that is different from the physics of moving a lump of metal on wheels along tarmac?

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 A diesel Engine use some 0.2-0.22 liter per HP/h at a efficient Power, unless the load is very low, say 10% load it will be 0.3-0.33 litre per HP/h

and about 0.24-0.26 L/HP/h at 20% load.

 

If the Canal boat need say 4 hp to be cruising in a normal speed(s) it will use 0.23 L/HP/h if the Engine is a 10 HP Engine. (40%) = 0.92 l/h

if the Engine is a BIG 40 HP we use just 10% Power, and fuel burn is 1.32 L/h

To this comes some Electric charging, and the prop efficiency play in too.

 

Speed have a big inpact, (dept and width of canal too)

say we use 5 HP (of a 40 HP Engine) =1.5 L/h at 4 MPH, that will go down to 2,1 HP (but) 0,97 L/h (5% Power) at 3 MPH

Edited by Dalslandia
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9 minutes ago, Dalslandia said:

A diesel Engine use some 0.2-0.22 liter per HP/h at a efficient Power, unless the load is very low, say 10% load it will be 0.3-0.33 litre per HP/h

and about 0.24-0.26 L/HP/h at 20% load.

 

If the Canal boat need say 4 hp to be cruising in a normal speed(s) it will use 0.23 L/HP/h if the Engine is a 10 HP Engine. (40%) = 0.92 l/h

if the Engine is a BIG 40 HP we use just 10% Power, and fuel burn is 1.32 L/h

To this comes some Electric charging, and the prop efficiency play in too

I've been keeping records for about three years and we average just over 0.7 litres per hour.  Never run the engine just for charging and we don't hang about either.

This is with a Bukh DV24.  When we had an old BMC 1.8 it was at least twice as thirsty, in the same size boat.  

It doesn't tally with the above because the Bukh is about the most efficient engine you can put in a boat whereas the BMC is extremely inefficient.  Other variables have to be taken into account. 

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2 minutes ago, Neil2 said:

I've been keeping records for about three years and we average just over 0.7 litres per hour.  Never run the engine just for charging and we don't hang about either.

This is with a Bukh DV24.  When we had an old BMC 1.8 it was at least twice as thirsty, in the same size boat.  

It doesn't tally with the above because the Bukh is about the most efficient engine you can put in a boat whereas the BMC is extremely inefficient.  Other variables have to be taken into account. 

A modern common rail diesel is probably more efficient then a old pre chamber, and a long stroker will be better then a short stroke.

prop efficiency, a 50% bigger prop will be 30 % more efficient. like a 16" vs 24" say the propeller is 30-50% efficient from start a bigger prop will be 40-65% efficient (depending on speed)

if it takes one horse to drag the boat, a small prop need 3,33 HP but the big prop just need 2.5 HP from the shaft.

Hull shape ...

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7 minutes ago, Dalslandia said:

A modern common rail diesel is probably more efficient then a old pre chamber, and a long stroker will be better then a short stroke.

prop efficiency, a 50% bigger prop will be 30 % more efficient. like a 16" vs 24" say the propeller is 30-50% efficient from start a bigger prop will be 40-65% efficient (depending on speed)

if it takes one horse to drag the boat, a small prop need 3,33 HP but the big prop just need 2.5 HP from the shaft.

Hull shape ...

Ah, now if on our English narrowboats we could just pile all the accommodation up on top like on your nice Dutch cruiser we might just be able to have a decent underwater shape.  It's always seemed to me that air draught is a much more limiting factor on our canals that the narrow beam. 

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4 minutes ago, Neil2 said:

Ah, now if on our English narrowboats we could just pile all the accommodation up on top like on your nice Dutch cruiser we might just be able to have a decent underwater shape.  It's always seemed to me that air draught is a much more limiting factor on our canals that the narrow beam. 

Dalslandia, the passenger boat, have a horrible transom and "deadwood" keel, a lot could have been made better there.

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Nobody actually answered the OP, so, yes, having stuff regularly wrapped around the propeller will increase consumption if you maintain speed.  Or you will go more slowly for the same revs.  This is because the propeller is less efficient.

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The op has not been back to tell us what engine he has, but at them revs even with a modern engine he is either going very fast or is under propped, damaged prop or could have some fishing line or similar tightly bound between prop and stern tube.

Neil

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