Efficient Fuel Consumption Whilst Cruising

[mross]

King Edward's or Maris Piper?

[noddyboater]

Maris pipers I'd say. King Edwards are more JP3.

[ditchcrawler]

19 hours ago, Cheshire cat said:

I think you'll find that Oberon is no longer there. The owner of the caravan park has bought the dry dock and all the moorings that were part of Swanline. Two weeks ago there were very few of the "regulars" on the on-line moorings. I think they were all served notice. I don't remember seeing Oberon in her usual spot.

There's an overnight mooring fee to be paid to the cafe if you want to moor above The Swan. No one in their right mind would pay which begs the question as to what is going on?

Wasn't Oberon above the lock on the off side, maybe that bit is not included with all from the Swan to the Middle lock (if thats the right name)

[Cheshire cat]

You might be right Brian. We came up the Coventry and winded so we only walked up and down the T&M. It was noticeable that all the boats were gone from the lower pound but there were still a few higher up on the offside.

[cuthound]

On 2017-5-6 at 12:16, Grassman said:

 

We have a BMC 1.8 in a 62' Colecraft shell, PRM 150 2:1 ratio gearbox and need 1800 rpm to maintain 3-4mph in reasonable depth water.

The engine has done 10,500 hours and we've had it checked and it's in good condition.

It averages about 1.4 litres per hour fuel.

We had a larger prop fitted (from a 16x12 to an 18x12)  and it only made a difference at slower speeds, i.e less revs needed for say 2mph. At a cruising speed of 3-4mph the larger prop has made no difference.

Interesting. When I had my boat docked recently, I notice there is room for a larger prop. The main problem I have is stopping the boat within 2 boat lenghts, although fewer rpm when cruising would be an added benefit.

Boat is a 60 foot Alexander shell,  powered by a Beta 43, through a PRM150 2:1 gearbox, and a 17x11 prop. The boatyard  (the excellent Norton Canes Boatyard at Glascote) suggested either modifying the current prop,  to a 17 x 12, or replacing it with an 18 x 12.

What does the team think? 

18 hours ago, ditchcrawler said:

Wasn't Oberon above the lock on the off side, maybe that bit is not included with all from the Swan to the Middle lock (if thats the right name)

Yes, that's where she is moored. Hopefully (for my nostalgic reasons) she will remain there.

[IanD]

The Beta Marine website suggests 18"x12" as a generic choice for the Beta 43...

[cuthound]

Thanks IanD. 

Edited May 8, 2017 by cuthound
To unmangle the effects of autocorrect.

[Ex-Member]

thanks for all the comments guys, having cruised at an average of 1200 revs I am getting 50% more from my fuel,,,it takes me twice as long but sine we have no timetable who cares! 

[Sir Nibble]

On 04 May 2017 at 21:46, 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 ...

This interests me. Why should a long stroke be more efficient?

[Jess--]

7 hours ago, Sir Nibble said:

This interests me. Why should a long stroke be more efficient?

gut reaction says that it's due to a longer duration of the power stroke, think long push rather than quick prod

[Dave Payne]

This thread is getting weird!

[Tony Brooks]

7 hours ago, Sir Nibble said:

This interests me. Why should a long stroke be more efficient?

More torque for the same mean effective pressure? However a short stroke engine will often rev faster so both may have similar power ratings but one produces more torque to twist the prop for any given reduction ratio. More troque allows a larger prop to be spun and larger props tend t be more efficient than smaller one that make up for their size with pitch.

[Sir Nibble]

for the same swept volume at the same bmep torque will be independent of stroke. Also the rate of expansion will be the same. I have never found anything but disadvantages with a long stroke apart from a long defunct tax regime. That's why I ask.

[Boat&Bikes]

Hadn't taken any notice of fuel consumption but this thread got me curious. I have just refuelled with and have a reading of .9 litres per hour used. Barrus shire 45 with 18 X 12 prop. Seems good compared to most posted results. I do wonder though at the accuracy of mine and other boats gauges including the hours counter maybe? Ian. 

[mross]

IANALI, What revs or speed do you cruise at?

[IanD]

Long stroke engines tend to be more efficient because the combustion changer shape is better (lower surface area for same volume so lower heat losses) than a short stroke engine, though they also tend to have a lower rev limit and lower maximum power for the same capacity. This is why the most efficient (huge) ship diesels have stroke/bore >2 and run very slowly (~100rpm), every last little bit of fuel efficiency saves a lot of money...

[Lily Rose]

29 minutes ago, mross said:

IANALI, What revs or speed do you cruise at?

Can't speak for Ianali but I have a 35hp Barrus Shire (no idea of propellor size) and I tend to cruise at about 1300 revs except when passing moored boats.

I've been keeping records of engine hours and fuel since we bought the boat (with a full tank of fuel). The last time (the 4th) I filled up, before the winter, my records showed that in 280 hours we had averaged 0.83 litres per hour in a range from 0.77 to 0.95.

No idea about this year to date as I've yet to fill up.

[Boat&Bikes]

53 minutes ago, mross said:

IANALI, What revs or speed do you cruise at?

1300 on most canals, 1500 on rivers. Last 100 hours have been spent on the south Oxford, down Thames from Oxford then up K@A. 

[mross]

Keeping the revs down will certainly help the fuel consumption.

[Tony Brooks]

3 hours ago, Sir Nibble said:

for the same swept volume at the same bmep torque will be independent of stroke. Also the rate of expansion will be the same. I have never found anything but disadvantages with a long stroke apart from a long defunct tax regime. That's why I ask.

How can it be - torque = force x perpendicular distance. Long stroke means longer crank webs so if the force on the piston & piston area is the same a long stroke engine should deliver a greater torque. I accept long stroke engines tend to have smaller diameter pistons that screws the theory.

[Dalslandia]

11 hours ago, Sir Nibble said:

This interests me. Why should a long stroke be more efficient?

Good question, the most fuel efficient Engines is the big ship Engines, long stroke, low rev, like 100 rpm.

with a longer stroke the lever/crank get long.

[WotEver]

Speaking of big ship engines, did anyone watch that three-parter "Warship"? It was following the UK's only remaining warship as it wound its way through to the Middle East. In the first episode one then both engines developed a fault and the engineer said "Ooh, never seen that fault before!"  After trying a few things someone had the bright idea of switching them off and on again... it worked 

[Sir Nibble]

12 minutes ago, Tony Brooks said:

How can it be - torque = force x perpendicular distance. Long stroke means longer crank webs so if the force on the piston & piston area is the same a long stroke engine should deliver a greater torque. I accept long stroke engines tend to have smaller diameter pistons that screws the theory.

For the same swept volume doubling stroke means half the piston area which if bmep is the same means half the force on twice the lever equals the same torque.

[Dalslandia]

1 minute ago, WotEver said:

Speaking of big ship engines, did anyone watch that three-parter "Warship"? It was following the UK's only remaining warship as it wound its way through to the Middle East. In the first episode one then both engines developed a fault and the engineer said "Ooh, never seen that fault before!"  After trying a few things someone had the bright idea of switching them off and on again... it worked 

Called a Norwegean reset

[Scholar Gypsy]

11 minutes ago, WotEver said:

Speaking of big ship engines, did anyone watch that three-parter "Warship"? It was following the UK's only remaining warship as it wound its way through to the Middle East. In the first episode one then both engines developed a fault and the engineer said "Ooh, never seen that fault before!"  After trying a few things someone had the bright idea of switching them off and on again... it worked 

Yes - it was a little alarming. Then later they took a cylinder head off ...

Here we are passing HMS OCEAN at Greenwich, a few years ago.