Philiz
Well-Known Member
Probably but with all the gubbins SWMBO has put on board, the figures are probably out of the window!
I just thought it would be neat to have a guage to glance at rather than having to do rough calculations.
Fuel flow meter
- Thread starter Philiz
- Start date
Probably but with all the gubbins SWMBO has put on board, the figures are probably out of the window!
I just thought it would be neat to have a guage to glance at rather than having to do rough calculations.
MapisM
Well-Known Member
Good that you mention it's strange, because indeed it is.
The rule of thumb mentioned by hlb (either full displacement for the absolute higher MPG, or steady planning as a second best) is valid for most planing boats.
The only exceptions are VERY fast boats, with huge engines whose overhead at displacement speed, together with the hull form, makes D speed not as economic as it should be. My lake toy for instance achieves 2.1 MPG at 30 kts (most efficient cruising speed), and just 1.5 MPG at 5 kts. And for more extreme boats, the difference can be even higher, but as I said not for normal cruisers.
asteven221
Well-Known Member
I know that with Diesel fuel gets returned to the tank, making fuel consumption hard to calculate. So what about this thought?
Would there not be some value in a meter placed in the in the main fuel supply line before the fuel pump, which gave you a reading of the fuel flow. It does not need to be calibrated to any standard reference point as it is only being used as a reference for your own boat. What we are looking for is the speed that burns the least fuel, so by simply using the meter as a reference at different speeds, you can find the optimum fuel flow for your boat for a given speed. The rest takes care of itself.
Seems okay with my limited knowledge, so forgive me if I have missed something obvious.
Out of interest how do the forumites that state their boats most efficient speed get that information. Is there some scientific basis or is it just a guesstimate? Do people really fill-up, test the boat at a certain speed, for certain time/distance, go back fill up again, write down the fuel used, and do it all over again several times and so on....
Lastly does anyone know what speed is likely to give my Sealine F44 the best MPG, cause I have not got a clue. I am feafull that my toodling around at 8/9 knots is costing me more than flying along at my lowest planing speed - whatever that is. 15 knots maybe? It has a couple of TAMD63P pushing us along.
Would there not be some value in a meter placed in the in the main fuel supply line before the fuel pump, which gave you a reading of the fuel flow. It does not need to be calibrated to any standard reference point as it is only being used as a reference for your own boat. What we are looking for is the speed that burns the least fuel, so by simply using the meter as a reference at different speeds, you can find the optimum fuel flow for your boat for a given speed. The rest takes care of itself.
Seems okay with my limited knowledge, so forgive me if I have missed something obvious.
Out of interest how do the forumites that state their boats most efficient speed get that information. Is there some scientific basis or is it just a guesstimate? Do people really fill-up, test the boat at a certain speed, for certain time/distance, go back fill up again, write down the fuel used, and do it all over again several times and so on....
Lastly does anyone know what speed is likely to give my Sealine F44 the best MPG, cause I have not got a clue. I am feafull that my toodling around at 8/9 knots is costing me more than flying along at my lowest planing speed - whatever that is. 15 knots maybe? It has a couple of TAMD63P pushing us along.
gjgm
Well-Known Member
I was just suggesting that a fuel flow meter may not be as useful as you hope. OK, you can change your speed, but you cant change the sea conditions, or (probably) the amount of clobber on board once underway. And in the end, you will probably also adjust your speed to suit your mood/hurry/comfort. In essence then, the fuel burn is the outcome, not the input! Yes, its useful to be aware of the extremes in the consumption figures, or the humps.. but you probably instinctively know those bcz the boat is labouring.
So you are zooming along, enjoying the day, and it reads.. well whatever it reads. You might tweak it a bit and get a few less lph, but I wonder if those savings pay for the device?
Same as a car, really, where we all have those mpg outputs. Anyone actually drive according to those numbers? Prius onwers perhaps
Channel Ribs
Well-Known Member
With a 37ft resting waterline length you are likely to be at the bottom of the hump at about 6kn, the top of it at 12kn and planing nicely at 18kn. Probably 16kn would be your most economical in <F3 conditions, all guesses based on rules of thumb.
Channel Ribs
Well-Known Member
Every time I fill up I think back to the types of useage for that tankful, I then compare the miles covered with the literage and add that to what I already understand.
PaulGooch
Well-Known Member
To be anywhere near accurate, you'd h ave to meter the flow AND the return. At different engine speeds a different ratio of fuel will be returned to the tank, so the figures would be skewed if you only meter fuel flow to the pump. Later common rail engines have the high pressure pump fed by an electric pump that just delivers a constant flow of fuel, a low pressure, flowing circuit of fuel that the high pressure pump uses as required. So with that you pretty much get the same flow at idle as you would WOT, difference being in the amount of fuel returned to the tank.
Makes me wonder about the Garmin petrol system, not sure about the system details of the newer EFi engines, but in cars they too have a return. If the Garmin setup doesn't meter the return, it's basically useless.
Yup, exactly that. Record conditions, tidal data, engine speeds, distance travelled and fuel used each trip. After a few trips you know what you use.
When you're running at displacement speed, ease it up to say 10 knots or so (just a bit more than is obviously correct) and let it settle down. You'll notice that you can hear the props cavitating a bit, the stern will be digging a hole and you'll be running the engines at a disproportionately high RPM. Ease the throttle back a little and let it settle again, repeat the process and you find as the props stop churning you can ease some more RPM's off without really reducing speed. The props will quiet down and the water out the back won't look like the Hotpoint on a boil wash. That'll be your max sensible displacement speed and most likely the most economic toodling around speed.
When you're on the plane, ease back a little at a time and you'll find a spot where you can hear the engines labour a bit and you can just tell you're almost dropping off the plane, that's a bit too slow. You want to be going a bit faster then that, the engines will sound much less stressed and you'll gain some speed without too many more RPM, that'll be your min planing speed. I wouldn't expect much difference in MPG from there to somewhere around 200-400 RPM below WOT. Obviously there'll be a small difference in LPH, but you'll get a corresponding difference in SOG.
I'm not an expert on the subject, but those have been my own findings with my boats.
Philiz
Well-Known Member
So, the general consensus is a flow meter wolud not be as good as I may have thought.
Looks like HLB's rule of thumb is probably the best method, combined with a general feel for how hard the engine is working compared with the speed.
I can't be bothered with filling up and doing measured runs and refilling etc. etc. it's a bit of a pain getting to our fuel pump so I don't want to go in unless I'm taking on a good amount.
Thanks all, looks like you've saved me about £100 on a device, I'll fill the tank at the weekend now!
Looks like HLB's rule of thumb is probably the best method, combined with a general feel for how hard the engine is working compared with the speed.
I can't be bothered with filling up and doing measured runs and refilling etc. etc. it's a bit of a pain getting to our fuel pump so I don't want to go in unless I'm taking on a good amount.
Thanks all, looks like you've saved me about £100 on a device, I'll fill the tank at the weekend now!
MapisM
Well-Known Member
Hang on a minute!
Frinstance, the previously mentioned Floscan has an excellent reputation for accuracy and reliability, and their instruments are capable to read also the return line with a dedicated sensor. Besides, they can be connected to any speedo (typically GPS) to calculate MPG figures in real time.
These instruments are the only way to get reliable consumption curves with traditional engines. Doing that by tank refill for the whole rpm range would be an awfully time consuming job - and an approximate one at that, anyway.
Alternatively, if you have a modern electronically controlled engine, you just read the numbers on the display!
Nope, indeed there are accurate instruments, but they're not inexpensive (surely not in the £100 range, anyhow).
Frinstance, the previously mentioned Floscan has an excellent reputation for accuracy and reliability, and their instruments are capable to read also the return line with a dedicated sensor. Besides, they can be connected to any speedo (typically GPS) to calculate MPG figures in real time.
These instruments are the only way to get reliable consumption curves with traditional engines. Doing that by tank refill for the whole rpm range would be an awfully time consuming job - and an approximate one at that, anyway.
Alternatively, if you have a modern electronically controlled engine, you just read the numbers on the display!
polyanna
Well-Known Member
Hi Philiz - Fitted a petrol version to Pollyanna. Easy to fit and fairly cheap, linked in to the plotter. Thought I'd do the same with Seafisher until I saw the price of the diesel kit.
Philiz
Well-Known Member
Good to hear from you Bob! Mmm, it seemed a good idea at the time, but now decided it's not worth it having read all the views of the forum.
You, coming back to PD anytime soon?
hlb
RIP
Phil, I thort the kit might be a bit expencive, but kept quiet, cos I did not really know. It seems as expected, it is expencive.
Easy way is. Increase power till the bow starts to rise, if the bow is riseing, your uesing to much power and fuel is being wasted. Alternativly accelerate till the bow comes down again. This will happen around 12/14 knots. Dunno about your boat. Once the bow has come down again, this is very economic, except that, with a bit bigger wave, the boat will be slowed, causing the boat to yet again to climbe out of a trough again. So you maybe need to go to 16? knots . Tuther golden rule is. 200 REVS less than WAT, or less than max. In the Straits you might get away with 12 or so knots. There are no waves.
Bandit
Well-Known Member
I wanted a fuel flow meter for twin diesel engines.
Navman stopped making them about 3 years ago and only do petrol ones now.
I then looked at Floscan and from memory only about £800 each plus fitting and one per engine reccomended.
They give you litres/gallons per hour consumption and you can link in to your gps to get litres/nautical mile over the ground with strong tides around here that seems a bit daft?
I thought about getting one as a stand alone unit and working out my litres per mile through the water with a calculator which certainly would give you fuel burn figures per nm through the water.
Instead I did nothing except fit Hart fuel guages and calibrate them which are excellent at giving you an accurate fuel level and a fuel burn per leg, it can also show excessive fuel burn on one engine. this shows me the difference between a clean bottom and a weedy bottom.
A friend of mine fitted one on a single engine mitchel 31 with a 320hp diesel, he said it worked well although it took a while of fiddling about to calibrate it over several tanks of fuel.
I am still tempted to fit one.
Manufacturers claim that once calibrated they will show you what you have in the tank, what you burn per engine per nm and over the ground as well as highlighting injector problems, dirty fuel filters or prop damage on one engine?
I really want to know what my litres per nm is at different rpm,s then i can allow for clean or dirty bottom and it will give me a base mark but short of burning a tank of fuel at each 200rpm increment and drawing a graph ( a large ammount of fuel) I cant do that.
A manufacturers power curve will not show you that, because you need a prop curve as well so a manufacturers power curve can only be a rough guide.
Alternatively i could buy a new set of engines which come with fuel burn rate meters but this makes Floscan look cheap.
Navman stopped making them about 3 years ago and only do petrol ones now.
I then looked at Floscan and from memory only about £800 each plus fitting and one per engine reccomended.
They give you litres/gallons per hour consumption and you can link in to your gps to get litres/nautical mile over the ground with strong tides around here that seems a bit daft?
I thought about getting one as a stand alone unit and working out my litres per mile through the water with a calculator which certainly would give you fuel burn figures per nm through the water.
Instead I did nothing except fit Hart fuel guages and calibrate them which are excellent at giving you an accurate fuel level and a fuel burn per leg, it can also show excessive fuel burn on one engine. this shows me the difference between a clean bottom and a weedy bottom.
A friend of mine fitted one on a single engine mitchel 31 with a 320hp diesel, he said it worked well although it took a while of fiddling about to calibrate it over several tanks of fuel.
I am still tempted to fit one.
Manufacturers claim that once calibrated they will show you what you have in the tank, what you burn per engine per nm and over the ground as well as highlighting injector problems, dirty fuel filters or prop damage on one engine?
I really want to know what my litres per nm is at different rpm,s then i can allow for clean or dirty bottom and it will give me a base mark but short of burning a tank of fuel at each 200rpm increment and drawing a graph ( a large ammount of fuel) I cant do that.
A manufacturers power curve will not show you that, because you need a prop curve as well so a manufacturers power curve can only be a rough guide.
Alternatively i could buy a new set of engines which come with fuel burn rate meters but this makes Floscan look cheap.
MapisM
Well-Known Member
Nope. As I said in my post #29, Floscan can be connected to any speedo.
Indeed I also said "typically GPS", but if you have a transducer with the speed wheel connected to your sounder, and the sounder has a NMEA port, you can use that to feed the Floscan and get the consumption "over water", if that's what you're interested in.
I don't think the Floscan has a selectable double NMEA input, though (which would be nice, coming to think of it).
So, it's either SOW or SOG, not both. But that's your call.
polyanna
Well-Known Member
Hi Phil & Liz,
No plans to come back to PD at the moment. Still living on the boat during the week and only getting home at the weekends, so getting out at the weekend is a bit of a problem. Trying to persuade SWMBO to spend the bank holiday on the boat. Not quite there yet.
Spent the dark nights of winter re-wiring the boat. Removed the jumbled web of cables, clips, inlines fuses, dodgy connectors, etc, split the loom and wired into 2 switched fused panels. One for domestics and one for the nav kit on the helm. Had a little shake down cruise round Puffin and everything works. Only problem is I've got a neg and a pos wire left over and absolutely no idea what they are for ??
Hope you are all well - I have been having a sneaky look on the forum whilst in the office to keep up with the North Wales contingent.
No plans to come back to PD at the moment. Still living on the boat during the week and only getting home at the weekends, so getting out at the weekend is a bit of a problem. Trying to persuade SWMBO to spend the bank holiday on the boat. Not quite there yet.
Spent the dark nights of winter re-wiring the boat. Removed the jumbled web of cables, clips, inlines fuses, dodgy connectors, etc, split the loom and wired into 2 switched fused panels. One for domestics and one for the nav kit on the helm. Had a little shake down cruise round Puffin and everything works. Only problem is I've got a neg and a pos wire left over and absolutely no idea what they are for ??
Hope you are all well - I have been having a sneaky look on the forum whilst in the office to keep up with the North Wales contingent.
Kawasaki
Well-Known Member
Aha Bob, you may have cracked a problem.
Philiz has a switch like that too
I reckon its fer a Fuel Flow meter
Hey an no excuses Bob
Just nip in yer motor and come and see us some time
I,m sure its your Round