Addicted to the fuel burn gauge

[Paul_S123]

I know what Bruce means . It's not as clear cut for some depends on how optimised the particular hull is
. Some will fair better @ D compared to P than others more so if the motors are on or near the "edge" power and thus burn rate when planing
My maths give a marginal saving but not really bothered as it depends on the conditions.
Only D of calm and flat . In a sea chop best to P
My favourite anchorage for a swim is 6 miles one way .
D at hull speed 8.3 @ 15 L/h or 9.3 @ 18 L/h
Plotter says 45 mins so 3/4 of the L/h 12 to 14 L used
On way each motor

P @ 27 knots plotter says 12 mins so 20 % of 1 h @ 90 L/H so 18 L burned in 11 /12 mins as opposed to 12/14 in 45 mins
X all by two
If it's rough and choppy then all done n dusted in 11/12 mins
And over time if D becomes more norm there's hours put on 11/12 mins compared to 45 - 4 x the hours
You can extrapolate up for longer passages . Sure there's a saving but is it that big to sacrifice 27 knots to 8 or 9 ?

I don't think so with my boat .

This is because they are only doing 1750rpm when WOT is 2150 .
Obviously at 2000rpm the burn rate is north of 200L /h
Real figure not internet btw .I don't need to push it as most other 14 M boats like the FL T47 and S/Ske Porto 46/57/48 have D9 or VP 74 at 575 hp or worse still 480 hp.
I have 700 hp motors which I can run at an economic rpm for a given speed
Those 575 boys above will be at a steep part of the consumption curve keeping up with me @27 knots .

So my maths makes it for the 6 miles you cruise to:

D at 8.3 knots at 30 litres per hour: 21.68 litres used
P at 27 knots at 180 litres per hour: 40 litres used

Probably insignificant on the 13 minute cruise like you do...but over a few hours it's a huge difference...even if you just take there and back it's saving about 37 litres on a tiny journey.

 

[Paul_S123]

WATCH THAT FUEL METER!
I can see your point clearly and it was also my natural assumption until I started playing Man Math. What's interesting here and whether it has relevance or not I dont know is the difference in speeds between the two boats D and P. For me the difference is nearer 4:1 and you are closer to 2:1. I suspect you are closer to SD bias where as I am pure planing and so our efficiencies will be markedly different. (question and questionable. I'm still hanging on to my belief structure. Be gentle)

LOL...I think you need to work with some real figures...taking your best D mpg and compare it to the best P mpg you can get from your boat..then factor in the additional cruising time and figure it out.

I can categorically state that I just completed a 75 mile trip past gib to Ceuta, then down to Morocco , then back to Sotogrande and used under 200 litres of fuel. I would get less than an hour with that fuel usage at 20 knots...so would have gone 8 or 9 miles up the coast, turned around and came back and burnt the same.

 

[BruceK]

Party-pooper. Trust me it's a helluva difference 5knts and a pinch under 9 knts. At 5 knts I have to suffer the crippling indignity of some WAFI in a sailboat overtaking me and asking if I need assistance. It's not the done thing!

 

[Paul_S123]

At 5 knts I have to suffer the crippling indignity of some WAFI in a sailboat overtaking me and asking if I need assistance. It's not the done thing!

Point taken

 

[Portofino]

So my maths makes it for the 6 miles you cruise to:

D at 8.3 knots at 30 litres per hour: 21.68 litres used
P at 27 knots at 180 litres per hour: 40 litres used

Probably insignificant on the 13 minute cruise like you do...but over a few hours it's a huge difference...even if you just take there and back it's saving about 37 litres on a tiny journey.

Yes on a long trip D pays off .
Say 100 miles at D @8.3 ish round to 10 hrs so 300 L , used out of a fill up of 2200 L
Or P gun it in @27 knots =3 hrs round up 180 x3 = 540 L used a difference of 240 L , a quarter of the fill up burnt .
But 10 hrs instead of 3 hrs is a big ask .Then again 240 x€1.58 = €379 buys the €80 / night berth and leaves €299 the man maths blow on a restaurant.
Or anchor off and cook in and bag the saving .
Yep my 6 mile swim trip is neither here or there in terms of D vs P running costs .
But a 100 mile trip out and another back with a bit of movement at the destination could easily = €1000 saving .

I think we all know deep down P boats are not on Greta Thunberg ,s wish list .
Wonder how much fuel would be used if she had P ,d to NY in something like Bransons “ Challenge “ boat ?
A lot !

 

[2hullsonemarinaberth]

Surprised that the large sophisticated plotters etc. aren't showing consumption per mile in real time as you wallow or bounce along accordingly. I thought that level of data would have been routinely available nowadays. I'm certainly looking for that sort of data if I re-engine my twin outboard boat with modern engines, or am I being naive?

 

[jrudge]

Surprised that the large sophisticated plotters etc. aren't showing consumption per mile in real time as you wallow or bounce along accordingly. I thought that level of data would have been routinely available nowadays. I'm certainly looking for that sort of data if I re-engine my twin outboard boat with modern engines, or am I being naive?

As long as you have fuel flow many do. I had new Garmin stuff that read litres per NM. My more elderly Raymarine just shows LPH but converting this in my head to lt per NM given the display shows speed and consumption is easy ( albeit I am surprised it does not do it for me)

 

[BruceK]

In my case large sophisticated plotters etc are largely useless when it comes to engine management of old analogue engines. Next argument. Would I want sophisticated and complex ECU driven engines? Probably, but I'd no longer be comfortable working on them and boy do they seem to throw a lot of issues judging from the forum queries. There is a lot to be said for the KISS approach inclusive of a blissfully ignorant belief structure. Is the engine hot? No. Cool, life's peachy.

 

[Elessar]

Lpm is what matters for me. Obviously you use less at d speed but often 20 knots uses less than 18 and definitely less than 14. A read out of lpm lets you trim the boat and make real time range decisions for diversions, weather changes etc.
My old engines don’t measure fuel flow.
On my last boat I fitted navman fuel flow meters and they were great.
They’ve stopped making them.
Where can I buy fuel flow meters other than floscan which are pricey and AFIK don’t do lpm.

 

[BruceK]

....... other than floscan which are pricey and AFIK don’t do lpm.

They do one have metric units but you are correct they are only lph http://www.floscan.com/html/blue/seriesdetail.php?sid=4&catid=2

You say pricey, I tried to find out more from their listed UK and European dealers. All links went to dead ends so apart from importing I dont know how you'd get your hands on one.

 

[Elessar]

They do one have metric units but you are correct they are only lph http://www.floscan.com/html/blue/seriesdetail.php?sid=4&catid=2

You say pricey, I tried to find out more from their listed UK and European dealers. All links went to dead ends so apart from importing I dont know how you'd get your hands on one.

I don’t care about the units as much as wanting a fuel / distance capability rather than fuel / time only which I think is a pointless measure unless you’re on a jet ski.

 

[gordmac]

Friends BT 35 with, I think, KAD 44s uses less than a l/m at displacement speed. About 3.5l/m low and high 20s and about 3.3l/m mid 20s. Engines don't come as standard with fuel consumption information but it is possible to access it.

 

[BruceK]

Friends BT 35 with, I think, KAD 44s uses less than a l/m at displacement speed. About 3.5l/m low and high 20s and about 3.3l/m mid 20s. Engines don't come as standard with fuel consumption information but it is possible to access it.

:encouragement: thanks

 

[EugeneR]

I don’t care about the units as much as wanting a fuel / distance capability rather than fuel / time only which I think is a pointless measure unless you’re on a jet ski.

Reason is that without speed or distance like your Navman had, you cannot calculate lpm.

 

[Elessar]

Reason is that without speed or distance like your Navman had, you cannot calculate lpm.

.

Of course. But tell me how to measure litres. Or gallons. Or quarts, buckets, handfuls or any unit of fuel burned. I’ll do the conversation in my head if I have to. But I’d prefer not to.
Seems I can’t even find a way to buy a fuel used per hour device any more. On any continent.
I must be wrong? Anyone?

 

[BruceK]

Aircraft? Electrical goods?

 

[LBRodders]

We have fuel consumption guage on our new Mercruiser with Smartcraft gauges.
What we find useful is not in particular the lph or miles to run specifically, but having the ability to see when the boat is trimmed correctly and running most efficiently at that speed.

Although all of this electrical gadgetry is great, our new engine currently wont start because the ECU 'says no'. So be careful for what you wish for. :encouragement:

 

[vas]

.

Of course. But tell me how to measure litres. Or gallons. Or quarts, buckets, handfuls or any unit of fuel burned. I’ll do the conversation in my head if I have to. But I’d prefer not to.
Seems I can’t even find a way to buy a fuel used per hour device any more. On any continent.
I must be wrong? Anyone?

I've gone down this search a few years ago.
Now have two truck derived kits one on each engine. They measure both in and return flows, do the calcs and show them on the NMEA2000 network.
Problem is that I'm still in contact with the builders to finetune the output but too busy during the summer, should work on that again and hopefully have a solution around xmas.

such systems are used extensively from companies running lots of trucks to keep track of consumption and avoid drivers overspending on fuel (or so I was told). Problem is that typically these are fitted with a log on the meter that the owner checks everynow and again (or when the truck is back in base...) and that's of no use to us, hence the NMEA2000 conversion.

V

 

[BruceK]

We have fuel consumption guage on our new Mercruiser with Smartcraft gauges.
What we find useful is not in particular the lph or miles to run specifically, but having the ability to see when the boat is trimmed correctly and running most efficiently at that speed.

Although all of this electrical gadgetry is great, our new engine currently wont start because the ECU 'says no'. So be careful for what you wish for. :encouragement:

A Port Dinorwic Pirate dead in the water? This is music to my ears. Hopefully your funbox will be fully stocked when I next pass by on a raiding sortie.

 

[LBRodders]

A Port Dinorwic Pirate dead in the water? This is music to my ears. Hopefully your funbox will be fully stocked when I next pass by on a raiding sortie.

Ha, I hope we'll have moved by the time you come through next. Even it is by tow - which is quite likely atm.

Anyway, the funbox is mostly stashed with the season's leftovers.. meagre pickings