best fuel economy

Some leisurely cruising today: 26.8 miles according to the GPS, 4.2 gallons of fuel used, according to the fuel flow meter. Trying for best economy, I kept RPMs at 1800 max, which resulted in speeds from 5.5 to 6.4 knots. That works out to 6.38 mpg... as long as you aren't on a schedule. I used the autopilot for a good portion of the day, idled around while we watched the dolphins for a while, tossed out the anchor and shut down for lunch, but mostly we just enjoyed the beautiful day and being out on the water.

While our landlubber friends would be appalled with 6.38 mpg, it seems pretty darn good for a boat. Of course, not the "hair blowing in the wind" (maybe that's where my hair went?), spray flying scenes you see in most boat advertisements, but what a nice day. :D
 
irlboater":ig9mipyg said:
I am just returning from a trip up the ICW from my home waters of the Indian River Lagoon to Savannah, Georgia and back via the St John's River to Lake Harney where I had a buddy pick me up with the trailer. I spent two weeks on board. I have a 2000 22' Cruiser with a 2000 carbureted Honda 90. Here are some of the statistics from that trip:
Total miles: 820 miles
Total fuel used: 189 gallons
Miles per gallon: 4.34 mpg
GPS total moving time (approximate): 60 hours
Average price for fuel: $4.37 per gallon
Total amount spent on gas: $826

On average it costs me $1.00 per mile to go on a trip in my C-Dory. This was all sheltered waters with only a few slow speed zones. I've gotten similar mpg numbers from my trip to The Bahamas last summer. Although the fuel cost more over there.
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That is about as good of fuel economy as can be expected with your setup. I have the same motor although newer but still it’s the same. Interesting to see how much difference weight plays into the equation. Best I have ever got is 3.6 MPG on any given weekend, but that’s fine with me. We are usually heavily loaded with tender, kicker, tender motor, large iced cooler, outdoor gear, fishing gear, shrimp pots, and usually 15 to 25 gallons of extra fuel.
Sometimes loaded out of port I can only make 20 mph at 90% throttle, returning with light fuel and water the same speed is achievable at 75% throttle.
These days I really don’t care much about fuel economy, life is too short.
 
Thought I'd reopen this thread, rather than starting a new one. I've been monitoring my fuel consumption, and after a year or so, here are my numbers.

I have a 2007 CD-22, with the Mercury 115hp 4 stroke EFI. I'm probably about as heavy as most other boats my size with the larger engine. I've been running a Permatrim on the outboard, and mostly run regular 97 octane gas. I've switched between 2 props. A 4 blade: Solas Rubex 4 Blade Aluminum 13.25" dia. X 13" pitch SR, and a 3 blade: : 14 x 13 Mercury Black Max Aluminum. Over the past year, these are the numbers I came up with.

4 Blade, running all speeds (average fuel use) came out to about 3.5 mpg. Running the Chicago River last year, where I was doing hull speed (5 mph) a little more than half the time, I got about 3.8 mpg.

This past March, I put the 3 blade on before going down to the St. John's River gathering. Running mostly hull speed (5 mph), I got about 4.7mpg. Then in Arkansas in April (both these times, relatively cooler weather), running mostly on plane (18-20mph), 3.9mpg. It appears that perhaps the 3 blade is just a tad bit more fuel efficient than the 4 blade. Also, unless running the entire time at hull speed, you don't gain much if you are still running on step half the time. Put this in Gallons per hour, and if I did my math right, it breaks down to 1.06 gph at hull speed and about 4.7 gph at planning speeds. While mpg is improved doing hull speed, it is also taking about 3-4 times longer to get somewhere. :mrgreen:

Colby
 
Colby with as many variables you had: different props, different rivers, current, wind, amount at hull speed (whoever that is--many C Brats seem to think it is 8 knots, yet is is really in the 5 or so knot category..) etc. I am not sure you can really come to any conclusions unless you do either fuel consumption tests with a calibrated container, or a calibrated fuel flow meter.

How about speed vs RPM graph to start with for each prop?

In the C Dory it seems to vary from different boats also. The C Dory 22's seem to be most efficient at a mid range speed. The 25's seem to be more efficient at higher speeds (from several C Brats own curves).
 
I have a FF sensor on my 22 with a BF90D, above 4000 rpm the mpg doesn't change much. Usually we travel in the range ~18-20 mph. If conditions allow we will go faster, but the usual speed range works best for the conditions we normally encounter. The usual mpg is 3.3-3.5.

I use the standard Honda 3 blade prop.
 
20dauntless":3prj8q53 said:
I don't have a fuel flow meter on board so I don't have precise figures, but this has been my experience based on 300 or so hours.
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Before I found a NOS Faria Fuel Management system (no longer made) for my boat, I bought one of these for fuel.

http://www.digisavant.com/PDF/DF0671L-34-Spec.PDF

The company makes many different variations, but I found a "micro flow fuel" version that is supposedly accurate to about .5 gallon per hour. It hooks up just like the Faria, but is powered by AA batteries and doesn't have a nautical looking gauge for the helm. It was about $50. By far the cheapest fuel monitoring gauge I found (because it isn't just for boats). It could be used to generate a table and then removed from the fuel line if you didn't want a permanent install.

I use mine some for economy but mostly for a really accurate fuel tank reading. I know to the liter how much to refill without a spill. It usually shows "zero gallons per hour" usage at slow hull speed. But after a few hours of that my total gas usage will have dropped a liter so I know that it is registering something even when it reads zero.

I have never had to use the Digiflow, but I'm now addicted to the Faria and would install it if the Faria goes out. The sending units look very similar, but the possibility of the Digiflow sender working with the Faria gauge isn't likely.

Mark
 
Bob, there are a lot of variables, and I think you realize the time and cost it would take to do an exacting test! :o However, I think over a length of time, one can get a pretty good feel for what their average fuel flow is. And in reality, isn't that really all that is important, since nobody is going to run in perfectly controlled conditions? The result of my earlier fuel monitoring is what I posted. I think I can safely use the figures of 3.5 or 4.7 when figuring out how far I can go between gas stations. If I'm hull speed the entire time, I'll use the 4.7. Or if I know I have to go 200 miles between gas pumps, I'd better carry another 5 gallons of gas, and plan on only doing 5 or 6 mph. OTOH, if I only need to go 140 miles between gas pumps, let er rip! :mrgreen: The 3 blade vs. 4 blade thing may not be as accurate, since the only data I have was the last two trips. Of course one of those was mostly at the hull speed of 5-6mph, so it might be nice if some time this summer I try using the 4 blade again at the slower speeds to see if it performs the same as the 3 blade.
Regarding River current, yes that is a factor, but again, averaging while going both up and down current, I think works ok. I think it gives a good representation of what I can expect in tidal waters of the same currents. I just need to realize that current will have an effect on my mileage!

Talking with others, and finding out what they are pumping into their tanks at the same time I am, seems like the 3.3-3.5 mpg range is about what our 22's get, when running faster than hull speed.

One other note, regarding fuel flow sensors in the fuel line. With an EFI outboard, they will not be accurate, except perhaps for an average over time. At least with my Merc, it has an internal fuel module that fills with fuel, then stops until it reaches a certain point, before filling again. So any inline fuel flow meter before that fuel module is going to read zero at times when it's not filling with fuel, and then what ever the max fuel lift pump input is when it needs fuel.:D Colby
 
Yes, Colby, the injected engines, have a minor challenge, but the average over a period of time works out quite accurately. I have had fuel flow meters on several injected engines, and the fuel flow gives you a lot of information--especially if you are going to AK! (Where there may be marginal runs between fuel stops, and unpredictable conditions).

The "average" you have fine works OK for reasonably smooth waters, and hopefully you have a way of knowing to some degree what the river currents are doing. But there are times when weather conditions will make a huge difference in your fuel consumption.

Here is a fuel flow compilation from the C Dory 25 Sea Weed, taken over several days up and down a mild current area with the boat loaded for cruising. The owner has a good idea what the consumption will be at various RPM. (Weather will still have some effect).

graph_data.jpg

The owner also made curves for RPM vs consumption and RPM vs speed.
 
colbysmith":j9a8s4wr said:
...

One other note, regarding fuel flow sensors in the fuel line. With an EFI outboard, they will not be accurate, except perhaps for an average over time. At least with my Merc, it has an internal fuel module that fills with fuel, then stops until it reaches a certain point, before filling again. So any inline fuel flow meter before that fuel module is going to read zero at times when it's not filling with fuel, and then what ever the max fuel lift pump input is when it needs fuel.:D Colby
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This only occurs at low engine speeds. My Honda engine does this. At idle the fuel flow will alternate between some value and zero as the low pressure pump cycles. Once the engine speed is above about 1000 rpm, the fuel flow out of the engine fuel accumulator needs to be constantly refilled and the FF reads whatever the fuel flow is (not the max pump lift). My FF meter seems to be pretty accurate.

The amount of fuel held in the engine is basically what is in the fuel filter and internal water separator and doesn't amount to a whole lot of fuel.
 
I like that chart Bob. Just don't have the time or equipment to be that accurate right now. Ideally I would like to hook my Merc up to the smart gauge capability on my Garmin GPSMAP chart plotter. However, I don't believe my outboard has the transmitter or "box" to currently do that. I started to look into it some a year or two ago, but didn't get far. Perhaps I need to delve into it again this year. Colby
 
Saxe Point":qafhx2mu said:
http://www.interactio.co/?gclid=EAIaIQobChMIiZHZq8DP2gIVE6vsCh1kGgg4EAAYBCAAEgKQ1vD_BwE

This is made and sold in Victoria, BC, just a short drive from my place. And cheaper for American buyers!

Does anyone have any experience with one?

Looks impressive in terms of the information it offers and the ease of installation.
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That looks like a great app--the fuel flow meter is about $300 US (shipping?). It can be done for less, if you have a system, such as Lowrance or Garmin which has the Transducers, which typically go for $150 to $200, but if you don't have the NMEA 2000 backbone, then it would bring it up to the $300 level. Nice to not have to run wires, and for older boats without a modern MFD which will show fuel flow and calculate the MPG etc. If I had a boat without a fuel flow system, I would certainly consider this one. Thanks.

Colby, I don't know what year Mercury integrated smart craft into the outboards. Suzuki did by 2007. But a Mercury manual from 2001 addresses the fuel use from the engine computer via Smart Craft Gauges--so your motor should just require the proper cable and adaptor from the computer and integration into the Garmin. Or for about $200 you can get the cable and a dash gauge which will show the information directly--for a little more you can get an android app. with wireless transmission..
 
-so your motor should just require the proper cable and adaptor from the computer and integration into the Garmin
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And that is where I got hung up on stuff. Trying to find that adaptor. Wasn't getting much information from the shops I was talking to back when... Perhaps I just need to get a hold of Merc and find out what's needed and the cost. I already have a network hooked up to the Garmin, which has the gauge page. (However, it's not the Garmin network, but rather the one RayMarine required for their autopilot. Another PITA regarding installing the lowcost RayMarine autopilot with everything else Garmin.) It would be nice to change all that stuff out and go strictly Garmin. But it's an added cost I'm not willing to pay! Colby
 
Something to keep in mind; Miles per gallon if you are on salt water is a variable. That is due to the ever moving tidal currents. If you are doing cross tide runs just for the numbers it is possible to get repeatable numbers, but for practical purposes miles per gallon on boats is going to have to be approximations. And hours per gallon (or more realistically gallons per hour) will be more useful for repeatability, not so much for fuel use planning.

Harvey
SleepyC :moon
 
Harvey,
Although there are always some tidal and current influences, many parts of the world in the oceans these are minimal--and can be from any direction. Some places they vary in speed, but usually consistent in direction--then occasionally they will change with no reason for a brief period of time.

That there are currents (not all tidal) is all the more reason to have a fuel flow device and know amount of fuel used, unless you have huge tankage. Many of the ocean crossing trawlers and large yachts have "day tanks" so there is a very accurate recording of fuel used, as well as the flow meters.
 
FWIW, I've kept records of every refuel, and every mile traveled over ground (via GPS) for the entire 18 years and 39,000 nautical miles I cruised with New Moon. 95% of this was on the Inside Passage, with tides and currents aplenty.

My mileage would vary considerably at first, when I spent some time at 18 knots and some at 6, with the proportion being pretty variable.

But after I settled down to traveling mostly at 6 knots, NMPG figures from tank to tank became remarkably consistent. I guess if I log a bunch of miles, the currents average out reasonably well.

For the last four years and more than 9,000 NM, averages by year were 3.84 NMPG, 4.18 NMPG, 4.27 NMPG, and 4.25 NMPG.

So I planned my fuel range based on 4 NMPG.

Remarkably enough, I get almost the same NMPG with the 37 Nordic Tug at 7 knots.
 
I kept our log book from our Monk designed cruiser. No gauges on the tanks, so we kept track of fuel usage primarily by engine hours. It was an odd feeling at first, but after a hundred hours of keeping track, it seemed fine to simply check the log book and calculate that we had plenty of fuel to go from Ballard to Friday Harbor and back.

I get a little nostalgic looking at the efficiency. Plus, diesel was 64 cents a gallon. I should have done more cruising. Words to live by.

Mark
 
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