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Old 08-02-2017, 10:33 AM   #1
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Fuel Economy Monitoring?

Hello,

I'm new to these forums, but not to boats and electronics. I've been out of the marine electronics world for a while now, and am planning my Great Loop adventure to begin over the next couple of years.

As I have been reading, one of the most talked about topics is fuel efficiency.

I'm curious if there are specific fuel economy monitoring solutions on the market today, and if anyone is using something that provides a good indication of "real-time" gallons-per-hour and miles-per-gallon? It would also be good to have a profile for a boat that allows you to see the predicted trade-offs of speed and fuel efficiency.

Doing my research, it seems that if a good system had access to the fuel consumption rate (simple fuel-line flow sensor) and then your speed-through-water (SWT), and speed-over-ground (SOG), then you could easily collect the data required to create a boat profile, and offer suggestions on optimal fuel economy. Eventually, you could also create a throttle control integration that would allow you to set the throttle based on desired fuel efficiency, instead of RPMs, etc.

Overall, this would provide a very good idea of the characteristics of the engines and boat, and all anyone to understand the trade-offs of speed vs. fuel consumption.

I know that many people would ask "Why bother?" ... but this is what I do for a living, and I love technology and boats. :-)

Anyhow ... I was curious about inexpensive solutions that would do this, if any exist, and also to hear feedback from boaters who might have thoughts about this more.

Scott
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Old 08-02-2017, 10:41 AM   #2
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Yes, FloScan products have been out there for many years. Not really worth the money unless your boat is run on a plane or have small fuel tanks.
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Old 08-02-2017, 10:54 AM   #3
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I know that the Cummins electronic engines have real time and cumulative fuel burn.

With diesel engines, fuel consumption goes hand in hand with rpm. Most find that in a relatively short time they can determine a good approximation of fuel burn at various cruise rpms even without the real time data.

From then they just know, for example, that 1400rpm results in 1.5 gph fuel burn.
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Old 08-02-2017, 11:54 AM   #4
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Dave wrote this;
"With diesel engines, fuel consumption goes hand in hand with rpm."

RPM is related of course but it's really about load. Load is by far the dominant element of how much fuel is bruned. IMO

It's very possible to decrease prop pitch, gain rpm and burn less fuel at the same boat speed. Depending on all the many other variables. In the above example one would need to gain more from reducing the prop tip loss of more pitch to loosing less from more parasitic friction loss of the higher speed prop. But that's just one of the variables.
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Old 08-02-2017, 12:15 PM   #5
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As the PPs have noted, Flowscans and the newer Maretron meters for older non electronic engines give you exactly the data you are asking for. Newer electronic common rail engines have this feature built in and is usually available on the engine display.

Flowscans have been around a long time and although the electronics is pretty straightforward, the fuel flow sensors need to be very accurate and linear. This is because it takes two for a mechanical diesel- one for total flow and one for return flow so you can calculate the difference as net fuel to the engine.

Their output can be provided on a dedicated display or integrated into some chart plotter's displays.

But a simpler way is to look at your engines prop hp vs rpm curve and its fuel consumption vs rpm curve. This curve which is partially mathematically generated (the fuel consumption curve is derived from the hp curve which is mathematical but fuel is usually is based on real manufacturer test data) is a fairly accurate representation of actual fuel flow. In most cases the prop curve data is within 15% of reality and better in most cases particularly for full displacement hulls where extra hp required to climb over the hump for semi- displacement or planning hulls is not an issue.

These prop curves can be obtained for old and new engines. For new engines look to the manufacturer's website. For older engines they are available on boatdiesel's pdf library.

So, fuel measurement and display has been done before although just looking at the prop curve is a decent substitute.

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Old 08-02-2017, 12:53 PM   #6
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Most of today's larger engines, that would be used on planing boats or even semi-planing, have fuel scanning and recording as part of their electronics. Floscan and Maretron are also good systems. Whether worth it depends on how you use the boat. I've seen many people however believe they know their most economical speed and that really was in question. On a trawler, probably not a big deal. On faster boats, having a good performance curve through actual usage can be very valuable.
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Old 08-02-2017, 01:40 PM   #7
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Scott, I came into this world a couple of years ago with broadly similar background and curiosity. Modern CRD motors use a different more accurate method and the data is available in pretty much every standard install, but with a mechanical motor measuring fuel flow is trickier than it first appears because it requires two sensors, on for feed and one for return. And the return is likely to be at a higher temperature. So it's easy to get an approximation but difficult to get a really accurate net real time consumption. I'd suggest a +/- 5% tolerance would probably be a realistic goal for common installations. Vendors may claim better, but I remain dubious of claims of perfect accuracy across the entire range of operation.

Given that, it seems to me to be of low value on the sorts of boats typically chosen for looping, other than to establish a static curve showing speed vs fuel burn. If you have a common design like I do this information can be obtained from established sources and to a certain degree be refined through empirical observation. Safe to say that the slower the speed the better the MPG on any non-planing boat, it's just a question of what the curve looks like. The universal way to improve economy is to slow down.

Optimizing for current and/or varying wind/wave/load conditions is maybe interesting, but I'm not sure it's truly useful for most of us. I decided it wasn't of enough value to me to pursue. If I were regularly operating in strong current I might reconsider, but the majority of the loop is in relatively still waters, so the static graph can be used to guide operation. Bottom line: fun to have but pretty far down the list. There are no shortage of things to tinker with and spend $$ on as you can see elsewhere in the forum.

Hope this makes sense and helps. It's worth digging into the drivers of fuel consumption in advance to inform your boat buying decision and itinerary if fuel economy is important to you, but once underway I think it sort of fades away for most operators.
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Old 08-02-2017, 04:12 PM   #8
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For a displacement cruiser fuel burn optimization is mental masturbation.

So you burn 2.8 GPH and work out a way to be 10% more efficient.

The savings over a month wont buy a case of beer.
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Old 08-02-2017, 04:46 PM   #9
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For a displacement cruiser fuel burn optimization is mental masturbation.

So you burn 2.8 GPH and work out a way to be 10% more efficient.

The savings over a month wont buy a case of beer.
It may not be savings of money you're looking after, but making the destination. When you have 2000 miles to cover like Richard and others, then having a good feel for fuel consumption at various speeds becomes very important.
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Old 08-02-2017, 05:27 PM   #10
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It may not be savings of money you're looking after, but making the destination. When you have 2000 miles to cover like Richard and others, then having a good feel for fuel consumption at various speeds becomes very important.

Exactly. When you have a fixed distance to cover and fixed fuel to do it, it's much better to vary speed to maintain the requisite NMPG to arrive with the desired reserves. That takes care of all the variation due to weather, currents, etc.

Simply running to a target GPH consumption rate doesn't work as well since your distance covered is variable due to condition. With consistently unfavorable conditions, you could find yourself in trouble having burned the fuel but not covered the distance. That would be a big oops.

Typical compensation is to run at a slower than planned speed for the first 1/2 or more of the trip, then as you get closer and more confident that you have extra fuel, step it up a bit. But it's really only done that way because until modern diesels, there was no easy way to calculate NMPG. With that constraint removed, you can make better time, and with greater confidence in your fuel needs.
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Old 08-02-2017, 06:00 PM   #11
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Fuel economy monitoring is a very high tech affair on our vessel.
Totally unaffected by water and lightning strike - parts available anywhere
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Old 08-02-2017, 06:11 PM   #12
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I've mentioned and many others have that fuel burn is a fairly low part of the expenses of operating a pleasure trawler. Yet look at all the trouble and effort many use or employ to monitor and minimize it.

And it appears not many seem very concerned about it before they have the boat. It never seems to occur to people to get a smaller boat or a FD boat that would eliminate or greatly reduce the amount of posting here about monitoring and minimizing fuel burn.
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Old 08-02-2017, 07:00 PM   #13
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I've mentioned and many others have that fuel burn is a fairly low part of the expenses of operating a pleasure trawler. Yet look at all the trouble and effort many use or employ to monitor and minimize it.

And it appears not many seem very concerned about it before they have the boat. It never seems to occur to people to get a smaller boat or a FD boat that would eliminate or greatly reduce the amount of posting here about monitoring and minimizing fuel burn.
But that's true of all boat expenses in terms of when concern hits. Those who read TF go into boating at least having been enlightened, whether they comprehended or not. However, they are not typical. The typical purchaser of a boat is shocked at what it costs initially to get everything right, and then at the annual costs. Even in that though, fuel is normally a small part of their shock. However, it's the one they can control and so often leads to the boat sitting.
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Old 08-02-2017, 07:02 PM   #14
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Fuel consumption on my diesel boat is a logarithmic relationship with speed. Increasing a knot to hull speed increases consumption more than double.
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Old 08-03-2017, 12:56 AM   #15
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It never seems to occur to people to get a smaller boat or a FD boat that would eliminate or greatly reduce the amount of posting here about monitoring and minimizing fuel burn.
Maybe. But maybe the opposite is true. If you look at automotive forums the hybrid owners yack incessantly about fuel economy. The SUV and truck forums? Not so much. The discussions reflect the values of the vocal members. Those who had fuel economy as a major consideration in their purchase decision are likely going to want to talk about it.
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Old 08-03-2017, 02:19 AM   #16
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$200000 boat
Marina $8000 pa
Insurance $2000 pa
Hull clean and paint $2000 pa
Oil changes $500pa
Cleaning polishing $1000 pa
Owning a boat and all the other stuff + deprecation $10000 pa
Fuel $4000 pa Pffft who cares
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Old 08-03-2017, 02:39 AM   #17
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$200000 boat
Marina $8000 pa
Insurance $2000 pa
Hull clean and paint $2000 pa
Oil changes $500pa
Cleaning polishing $1000 pa
Owning a boat and all the other stuff + deprecation $10000 pa
Fuel $4000 pa Pffft who cares
$30,000 boat
Marina $800 (transient)
Insurance $500
Hull clean and paint $200
Oil changes $100
Cleaning and polishing $100
Winter hauling and storage $700

I care about fuel cost. Lots. And depreciation. They are my two biggest ownership costs. And I believe that it should not be absolutely necessary to have a six+ figure annual budget to participate in this game. I'm kind of old-fashioned that way. Plus I have three kids in university.

There are lots of different ownership models. Not suggesting that my model is well-suited to all, but forgive me if I get a bit prickly when fuel costs are so easily dismissed.
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Old 08-03-2017, 02:44 AM   #18
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$30,000 boat
Marina $800 (transient)
Insurance $500
Hull clean and paint $200
Oil changes $100
Cleaning and polishing $100
Winter hauling and storage $700

I care about fuel cost. Lots. And depreciation. They are my two biggest ownership costs. And I believe that it should not be absolutely necessary to have a six+ figure annual budget to participate in this game. I'm kind of old-fashioned that way. Plus I have three kids in university.

There are lots of different ownership models. Not suggesting that my model is well-suited to all, but forgive me if I get a bit prickly when fuel costs are so easily dismissed.

Whats your fuel costs ?
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Old 08-03-2017, 03:09 AM   #19
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Whats your fuel costs ?
Last year about $2400.
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Old 08-03-2017, 06:17 AM   #20
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"I care about fuel cost. Lots. And depreciation. They are my two biggest ownership costs"

The simplest way to have no depreciation cost is to purchase an older boat.

Condition, condition, condition create the value on a 20-50 year old boat.

To lower the fuel bill is easy , go slower.
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