So, which one do you trust your computer or fuel gauge?

K

ken35216

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C Dory Year
2017
C Dory Model
25 Cruiser
Vessel Name
Lady Onyx
I'm heading back from Pensacola Beach, FL to Blue Water Bay Marina about 50ish miles and I notice my fuel gauge showing empty. I added enough fuel to make it there and back, I thought. I'm still getting used to the boat.

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Fuel gauge shows empty but computer shows 32.9 gallons. The computer has been dead on when filling up so I trusted the computer. I didn't have to call SeaTow so I made the right decision.
 
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Here is the data for the last 260 miles. It shows 89.9 gallons used and that's about 2.89 miles per gallon. Which is about right for the last year. I added 20 gallons before the trip so the remaining fuel should be right BUT the fuel gauge showing empty was still a little disconcerting.
 
Ken yesterday my Garmin was showing that I was heading East while my compass pointed North, and neither one ever showed NorthEast. I followed the river so it didn't matter but that did bring up some trust issues with my instruments.
 
In my case, (a 05 22 Cruiser) my gas guages are the tanks themselves, poly, and able to see the fuel level inside the tank. In your case, if the computer has been right before, I woul tend to follow that. It could be that the fuel guage sensor and fuel pick-up are in the same place on the tank, and maybe not. Also the attitude, (for and aft or side to side tilt) of the boat could affect the guage reading. As you learn to know the boat you will become more comfortable with what it is telling you, and able to make better decisions as you go.

Harvey
SleepyC :moon
 
I have a Yamaha fuel meter and trust it and a fuel gauge over the fuel tank sender.
































y




















yI
 
With a newish boat--I would be checking the connections on the sender and gauge units...suspect if showing empty, with the amount of known fuel. (Or unless someone stole the fuel!!!--always a possibility!
 
We had a Navman fuel flow meter on our 25 - it was always within a gallon of what it took at the fuel pump. The fuel gauge... not as accurate. Over the years, I knew what we'd average for fuel burn, so I could hit it reasonably close from the hour meter, as well.
 
Ken,
disconnect and sand til bright the pink and black wires (and maybe blue) going into your analog fuel gauge and the pink wire on your fuel tank sender. Good call trusting the digital inputs instead.
Next time you're that close to our marina (Sherman Cove aboard NAS Pensacola) give us a holler. However, tonight we're aboard Ft Knox enroute to the Geogian Bay, 30,000 Islands/Trent Severn Waterway Adventure by car.

We asked to see the total bullion gold reserves for ourselves just to make sure it was really here, but They said No.
Maybe a Brat with higher Retired rank will have better luck than us.

Cheers!
John
 
The gas gauge on our boat is far from accurate, but it's still something better than guess-timating.
 
In the airlines, we had to "dipstick" the tanks if any of the fuel gauges were not working. (But all other gauges had to work. Ie, if the fuel gauge for that tank was out of order, then we had to have an operating totalizer gauge and fuel flow gauge. IOW, two of the three had to work, or the plane was grounded). That being said, like Hardee, my boat has a plastic tank so it's a simple matter of turning around and looking backwards to know my fuel level! :mrgreen: In your case, I'd still be a bit nervous with one gauge reading empty while another showed fuel.... unless you could "stick" the tank. Colby :P
 
colbysmith":3pvyv66z said:
In the airlines, we had to "dipstick" the tanks if any of the fuel gauges were not working. (But all other gauges had to work. Ie, if the fuel gauge for that tank was out of order, then we had to have an operating totalizer gauge and fuel flow gauge. IOW, two of the three had to work, or the plane was grounded). That being said, like Hardee, my boat has a plastic tank so it's a simple matter of turning around and looking backwards to know my fuel level! :mrgreen: In your case, I'd still be a bit nervous with one gauge reading empty while another showed fuel.... unless you could "stick" the tank. Colby :P
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The maritime industry is also a big fan of simple methods like this. I've been meaning to buy a wood dowel to notch and use for this purpose. My analog gauges work fine, but my honda digital display says full when full and shows empty after about an hour of running on a full tank.
 
BillE":hczxsd2r said:
Ken yesterday my Garmin was showing that I was heading East while my compass pointed North, and neither one ever showed NorthEast. I followed the river so it didn't matter but that did bring up some trust issues with my instruments.
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how fast were you moving?
 
PaulNBriannaLynn":1j35g69e said:
I love those clear tanks. Nothing to fail or misinterpret.
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Amen. :thup

"Sticking" a tank on a C-Dory would, I would think, be difficult due to the filler opening not directly over the tank and the up curve and vent in the line. Maybe the TomCat has better access to the tanks.

John, sounds like retirement is working out well for you. Travel safe.

Harvey
SleepyC :moon
 
gulfcoast john":39jka8pt said:
Ken,
disconnect and sand til bright the pink and black wires (and maybe blue) going into your analog fuel gauge and the pink wire on your fuel tank sender. Good call trusting the digital inputs instead.
Next time you're that close to our marina (Sherman Cove aboard NAS Pensacola) give us a holler. However, tonight we're aboard Ft Knox enroute to the Geogian Bay, 30,000 Islands/Trent Severn Waterway Adventure by car.

We asked to see the total bullion gold reserves for ourselves just to make sure it was really here, but They said No.
Maybe a Brat with higher Retired rank will have better luck than us.

Cheers!
John
Click to expand...

It was a working trip for me or I would have contacted you and Dr Bob. I was working a convention at the Hilton and rather then get a room I took my boat and stayed at Peg Legs/La Fitte Cove Marina. Cool place!!
 
The 27 has two 50 gallon tanks. Both have gauges on the tank themselves but not on the dash. On the dash I have a older flow gauge with a totalizator and current flow meters. Very often I will see what my current fuel burn is and then do the math on my phone and see what my MPG is. My system works for me and allows me to trim the boat out to the best setting for MPG. The interesting thing is that after 16 mph my mpg does not change very much all the way to 30 mph. In many cases slowing down in ruff water is leads to worse mpg. Its often better to lower the bow and up the RPM. Smoother ride and the MPG are the same or close enough to not matter.

One problem I do have with the older fuel flow meter is that it does not meter the kicker very well if at all at slow speeds. It does not meter the main ( 225 honda) very well if at all at idle. I spent hours trolling on the kicker and some times the main . This is some thing I have to watch out for but the gauges on the tank are always there. My honda is one year before it was able to plug in to the MFD as many do to day.

The fuel flow meter I saw at the boat show last year, )can not remember the name, it was a start up) was a far better meter and more accurate then my older flow scan. It metered ALL flows no mater how small. It also connected to wire devices like my phone. if i was to up grade I would go with some thing like this , but most likely I will have to re power before then and all the new motors have these functions built in to be displayed on the MFD. Which would not solve my kicker issue.

Sorry for the long reply but its a interesting multi facet issue. If you have a older system they just do not mesh with the newer tech and you end up with a cluster of systems.
 
I have a simliar but different issue. My two tanks are 30 gallons each. One showed as empty the other as 3/4 empty. Leaving me a quarter of 30 gallons basically. To fill both tanks was 35 gallons. Since new my gauges are way off. My guess would be with both showing empty I would still have 10 Gallons each. Maybe a just a buffer by design??
 
starcrafttom":2ezjic66 said:
The interesting thing is that after 16 mph my mpg does not change very much all the way to 30 mph. In many cases slowing down in ruff water is leads to worse mpg. Its often better to lower the bow and up the RPM. Smoother ride and the MPG are the same or close enough to not matter.
Click to expand...
On my 25 cruiser using a Yami 200, I have a very similar experience as you outline here.
 
smckean (Tosca)":2c1rjz2q said:
starcrafttom":2c1rjz2q said:
The interesting thing is that after 16 mph my mpg does not change very much all the way to 30 mph. In many cases slowing down in ruff water is leads to worse mpg. Its often better to lower the bow and up the RPM. Smoother ride and the MPG are the same or close enough to not matter.
Click to expand...
On my 25 cruiser using a Yami 200, I have a very similar experience as you outline here.
Click to expand...

Mine does pretty much the same thing. Once the boat is on a good plane, the MPG is pretty constant no matter the speed. I originally thought that a moderate speed was the sweet spot of MPG vs. time to get there. After installing a fuel meter I find that it doesn't make much difference once on the plane. Now we set the speed for the conditions (where we can travel at planing speeds). Generally it is about 20 MPH.
 
ssobol":3vetw86p said:
smckean (Tosca)":3vetw86p said:
starcrafttom":3vetw86p said:
Mine does pretty much the same thing. Once the boat is on a good plane, the MPG is pretty constant no matter the speed. I originally thought that a moderate speed was the sweet spot of MPG vs. time to get there. After installing a fuel meter I find that it doesn't make much difference once on the plane. Now we set the speed for the conditions (where we can travel at planing speeds). Generally it is about 20 MPH.
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Click to expand...
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Mine is the same thing. I usually go about 20 MPH but if the water is flat I'll kick it up to about 25 (4,100 RPM) and shocked that I'm still getting 3 MPG. I like it!!
 
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