MPGuino calibration on a boat
 

I'm looking at adding MPGuino to a ski boat. I know this is outside the common cause for this forum and a ski boats have very little to do with efficiency. However this seems to be the best place to find MPGuino experts. I've often wondered the optimal fuel efficiency point for my ski boat. It seems that near top speed (~35mph) would be the most efficient cruise speed since the amount of surface area on the water is lowest. However, its hard to believe that when the engine is turning 4200rpm. So I tend to cruise slower ~25mph. My gut says slower is more efficient, but logic says faster is. I'm also curious about the impact of weight balance, both Port vs Starboard and Stern vs Bow. Enter MPGuinio...

The boat I'm working with has a paddle wheel speed sensor that is accurate down to 1/5 of a mph. I'm quite certain it is a pulsed signal similar to VSS. This is a fuel injected V8 so injector signal is a matter of running a wire.

Where I'm not sure is calibrating the MPG. There is no odometer. From the research I've done, calibration appears to be a manual feedback function of miles traveled verses fuel added to the tank. I suppose I could use my Arduino Uno and build a program to replicate an odometer-(I think). I'm not looking for something super accurate, just a semi-accurate ratio of speed / fuel burn.

I appreciate any thoughts.

P.S. I tried searching the forums, but I picked up hundreds of results for "Metro Boat Tail" :)

your "MPG" figure doesn't have to be accurate to the mile or even to the gallon as long as it is consistent because you want to know if going twice as fast uses twice as much fuel so your figures could be in metric for all you care as long as you get a distance/fuel figure out of it, right?

Correct. It would be "nice to have" accuracy. But not required to accomplish goal -- 'improve fuel efficiency by use of speed/throttle position and weight balancing.'

I think this is one case where I would seriously consider a gps, perhaps connected to a duino to simulate a speed signal just for "simplicities sake". On a car it is a non-issue (unless you spin the tires constantly), but a boat is of course another matter.

There might be some other methods, i.e. I assume boat speed is largely a function of engine rpm plus some fudge for weight/acceleration. If you have a duino monitoring rpm, and you map out the slippage at different rpms and the slippage under various acceleration points, you could get a pretty accurate distance perhaps, and wish you spent the $60 on a gps module :)

edit, shoot gps modules are getting cheaper, this looks like $25
http://www.mouser.com/catalog/specsh...%20%282%29.pdf

and one of the values it spits out is speed.

I think the GPS is a good idea. To add a layer of complication is the 'ground speed' verses 'indicated speed' issue. Similar to aviation, 100mph indicated is equal to 90mph ground speed with a 10mph head wind.

The river I navigate has a current speed of 2-5mph. So if I avoided the paddle wheel for VSS and went straight to GPS, then I would have more accurate MPG readings (since fuel burn is greater and efficiency is reduced traveling upstream.) This would also allow for some interesting trip MPG --(motor up river, float back down to the boat launch.) Though, while pulling a skier indicated MPG would be slightly more useful since it would remain constant upriver vs down river.

Thanks for the input so far.

The paddle wheel speed sensor is of interest for establishing the most efficient speed over water. This would give you the best speed to use when there is no current and is probably the most useful bit of information.

For calibrating the MPGuino speed you just need to play with the pulse per mile value until the MPGuino speed reading matches the boats speedometer.

GPS data would of course give speed made good and would be useful for determining how much to speed up or slow down for best efficiency in the presence of a current.

A boat lends it's self well for steady sate cruising so it would be easy to collect data to generate a performance curve that relates fuel consumption to speed. From there it should be straight forward to calculate the most efficient speed for different currents. I think it will be a variation on the calculations for determining the best speed to fly gliders in a head wind.

Having both speed over water and GPS speed will allow you to map out the currents in the river so you can try to travel in the weaker currents heading upstream and stronger currents heading downstream.

Mike

the boat already has a speedometer? What sort of signal is it? That might be the simplest solution.

While of course you *could* compare indicated to made-good, nobody is asking for it :) and you would have to get programming to make sense out of it, for an individual user.

I think if there is a "digital" speed signal on the boat, see if we can use that, else gps up a speed signal is the pragmatic approach. gps would give a reading more in-tune with what us lubbers would consider mpg.

a speed through the water would be best to figure out the most efficient hull speed. Otherwise you are getting or loosing a little distance from the current. A calm lake early in the morning without much wind would be a good test for figureing out the most efficient speed. In my experience, the least throttle just after the boat breaks over on step is the most efficient. Just as you can feel it surge ahead.

If you know instantaneous fuel consumption, you can figure out MPG just by looking at your speedo. Get an E6B (whizwheel) to do the quick calculations.

Currents can be felt, and often change so mapping them out may not be a workable solution.

When flying I find that a decent technique is to throttle back with a tail wind, to take advantage of an airspeed with lower fuel consumption, then speed up with a head wind to limit the amount of time I am bucking the wind. On the river this would equate to minimum throttle to remain fully on step down river. Then some amount faster than that for the trip up.

I'm not so sure, I would use the water speed signal if it is already there just for convenience, but distance made good is distance made good.

Case and point, kill the engine and float back to the ramp and the whizweel will indicate 0mph and 0 mpg the whole way back, and the gps based speed signal will give you the actual infinity mpg and actual speed on the way back, just like EOC.

I mean who really cares how fast the current is going for efficiency? Your destination is still x actual miles away, and you still want to find the best way to get to that actual point with the least gas and it has to be in relation to actual miles, not water flow miles.

I don't see the fascination with water speed, at least not enough to buy a water speed sensor over a gps module, or why it is of any use except as an approximation of actual speed.

when you are running there will be a most efficient indicated speed. Some speed up or down from that depending on what the current is doing will yield the best MPG so some GPS information would be useful but a close enough approximation can be made just by knowing the current speed which can be learned by looking at it. Drifting down stream will be 999999999mpg but that is not useful information.

The OP already has a speed sensor. That will give a good deal of information if the signal is compatible, if not *shrug* the speedometer with knowing the GPH is nearly as good.

Increasing speed over that needed to be on plane is not likely to increase MPG. Yes there is less hull in the water but the force needed to lift the weight of the boat up on step is the same at 25 as at 50mph. The smaller contact area is doing the same lifting by hitting a smaller number of water molecules faster so the drag is about the same. Increasing speed will increase the amount of drag from the lower unit.

the second example, coasting back with the engine off, highlights a key point though. It is not instantaneous mpg that is important, but average. If you use a gallon of gas to go 5 miles up river and float back, the trip mpg with the whizwheel will be something between 5mpg and ??? (because it did not accurately detect the return trip and you spent time in different currents, maybe you were anchored for a while and it kept spinning), but with a gps the Actual mpg will be 10mpg. The drifting downstream at 999999 is terribly important for your trip averages.

If you drifted back down do you count it as a 10 mile trip or a 0 mile trip:p
If you are counting it as a 10 mile trip why could you not put 10 miles into the Whiz wheel and find the average for the whole trip? If you derived your distance from a map, you would have an accurate distance.


A GPS will continue to output speed when anchored. Due to how it calculates speed and the error every time it recalculates position, as well as when swinging on the rode.

I once averaged 3 knots while tied to a pier for a couple hours, some of that was stretching of the lines, most of it was position error.

A GPS coupled MPGuino would be very fine for tuning speed and knowing how much to increase speed to compensate for running against the current but with the equipment the OP already has a close approximation can be done from the speed of the boat through the water.

I would love to have a fuel totalizator coupled to a GPS in the plane it would let me know how much to increase airspeed to compensate for headwind. But a whiz wheel and fuel consumption information would do just as well.

Only boaters struggle with the concept I guess :) But if you go 5 miles, then you go another 5 miles, that would be 10 miles. Pretend you went to the convenient store 5 miles up river or something. You would NEVER say your commute is zero miles just because you wind up at home again. Just sell your vehicle and forget all this tracking business then ;)

My mistake, when I heard the term whizwheel, I envisioned a paddlewheel or impellor type speed sensor. I didn't realize an antiquated navigation device was being brought into the discussion.
E6B - Wikipedia, the free encyclopedia

While I encourage everyone to be able to use maps, I think a more automated solution is preferrable here.


Good to know. It also puts out grid coordinates too so that it *might* be compensated for (i.e. computer says your x or y haven't changed by more than .0002 for 7 minutes, I will just pretend you are sitting still then), as opposed to manually entering in current river speed or something. I don't know what a good absolute threshold is without experimenting.

Absolutely, I don't know anything about the onboard speed signal though (well I can guess).

If the gps were sorted then it would just be more convenient and perhaps accurate, and provide a basis to compare with land vehicles. Car miles are already made good :)


edit: more fun with gps inaccuracies (I never really looked before):
http://www.arduino.cc/cgi-bin/yabb2/...m=1295491451/3

This has been a great discussion, Thanks!

My course forward is to use the Paddle Wheel transducer since it is existing equipment. From there I can calibrate the MPGuino's speed against the existing Speedo & GPS in a lake. That leaves me with figuring out uS/Gallon.

With the MPGuino, is there a way to reveal the total injector micro-seconds for the most recent trip? If there is, then I can calibrate the uS/Gallon.

you just refill your tank (in a repeatable manner), reset the tank trip, drive a lot, then refill the tank again (in precisely the same manner) and see what percentage the guino is off on tank gallons and adjust accordingly

Mpguino calibration - EcoModder

I wish.

Hi, I'm new here (occasional past lurker) and I'm interested in this GPS/MPGuino concept. I've got a converted 1.0L Geo Metro engine powering an Experimental Light Sport Aircraft (ELSA). It's a 1990 model engine with factory ECU and throttle body fuel injection, so I think the injector feed should be easy to identify and connect, but in the ELSA application, I don't have speed data.

Would one of you knowledgeable folks know if a 'gps module' - like what's referenced here - is straightforward enough to use for 'speed' that an electronics novice (with decent soldering skills and aptitude) could make it work?

As a little additional background on this ELSA, I made some significant aerodynamic improvements to it a few years back with streamlined strut fairings, gap seals, vortex generators, and a few other subtle, but additive, improvements. I learned a lot in the process and increased the flight envelope by around 20 mph; approx 10 mph lower stall speed, and approx 10 mph faster straight and level flight.

Now I'd like to be able to collect some fuel efficiency data, as well as potentially increase awareness of fuel consumed and in reserve.

In anticipation of the question, I'm quite alright with the speed data being 'ground reference' rather than airspeed.

Thanks in advance for any advice. If I hear that GPS/MPGuino should be relatively straightforward, my next Internet stop will be to buy an MPGuino and other necessary parts.

Best Regards,
Dan Felix

current is everything in a boat.

how will you KNOW what your efficiency IS if you don't value the current into the equation? did you get better efficiency because you balanced it right? trimmed it right? or because you had a 3mph current pushing you along faster.

Remember in a car a head wind or tail wind will "move" you but with a boat the "ROAD" can move WITH OR AGAINST YOU since its "fluid"

you would need a way to factor in "ground and air" speed or in this case water speed and "actual" speed

I am not even sure how to do that? would paddle wheel be the equiv of air speed and GPS be your ground speed?

how would you calc that into a guino?

I have a feeling its going to be a VERY tough nut to crack and your going to go with Gallons per Hour for your fuel economy.

IE use time not distance to gauge your efficiency since water speed like air speed is a value NOT under your control.

Really it is only part of the picture. I think it is a legacy measurement (because they didn't have a better way to measure miles made good) that only complicates efficiency measurements.

It would be like saying headwinds and tailwinds are everything to a car, when measuring actual ground distance traveled is still the critical metric along with fuel used. Measuring windspeed might be a nice addition when rationalizing the currently displayed mpg number, but it is a tertiary bit of information when it comes to fuel used and distance traveled.

[quote]how will you KNOW what your efficiency IS if you don't value the current into the equation? did you get better efficiency because you balanced it right? trimmed it right? or because you had a 3mph current pushing you along faster.

[/quote

That is the problem with deriving MPG from GPS. If you don't know your effcincy through the water you may think you are ballanced well because of a boost from the current. If you are basing it on water speed you will know if your GPH is higher or lower than normal for a spacific speed through the water.

The effect of current is that your journy is effectivly longer or shorter up or down stream. Your goal is to run the thing through the water at as effcient a speed as posible.

The mpg from distance made good is interesting from a mathimatics and data point of view, but as practical for use when deciding how much throttle keeps you moving at the most effcient speed.

Having that information as well would deffinately allow one to fine tune speed for effcincy though.

You can still "fine tune" the throttle with good miles however, if available, and you can then make more accurate round trip comparisons to land vehicles, regardless of current or wind.

A level (or even a semi-circular canal) might be better for checking trim balance, and anything that floats (i.e. a loogie) can give you a snapshot of the current.