Fuel Gauge Accuracy

Blame this on MBevins. He kept bringing it up the cruzpro stuff.

The C18 engine computers are super accurate, just reset the trip and do it that way.......I'd also buy new senders. My guess is your senders are short because they couldn't wiggle the proper depth senders in their, given the ceiling height.

I understand that in some cases dipsticks are not an option, but I guess you must have a pipe connection at the bottom of all your tanks, don't you?
That's all you need to tee-in a sight tube, and then you can place it wherever more convenient for checking it out.
It's just a matter of marking it later, consistently with the actual fuel level.
Which is dead easy if the tank shape is regular, but also if it were larger/smaller along its heigth, since you have accurate engine displays, you could mark the tube consistently with them.
Takes a bit of time, but you only should do it once.

KUS make a Capacitive Level Sensor -CLS that is accurate to 1mm level changes. There are others as well.
You couple this with the CruzPro and you get the accuracy. After you "teach" it.
These have been around for over 15 years and for the life of me I don't know why more people don't use them.
As I said earlier, I can look at my gauge and it tells me I needs 256 gallons to fill the tank and the pump kicks off at 256 gal. It's that accurate. Providing you calibrate it right.

Agree (although I thought they're in New Zealand).

The "learning" mode is a bit fiddly. "Start with empty tanks..." isn't so easy to do with 500+ gallons of diesel on board... and smaller increments along the way gets old... but otherwise the FU60s worked very well. We mated ours with KUS/WEMA senders...

-Chris

On U.S. fuel tanks, it's fairly rare to have any pipe connections at the bottom of the tank. Generally American builders pull everything from the top of the tank, via fuel pick ups....... But in his situation with 3 tanks joined as 1, it would have to have hoses to each tank, but I'm guessing that they're too short to T a fitting off of for fuel level.

You might try using a pressure transducer at the bottom of the tank(s). This should be very reliable and accurate. You will be measuring the hydrostatic pressure of the fuel above the sensor which can be directly converted to fuel level. There are many types of transducers available. You can easily get ones which screw into a 1/4 npt fitting either in the fuel outlet line or perhaps in a small hole drilled into the tank side at the bottom. You can get virtually any type of signal output but probably 4-20 ma current loop would be best. Basically, you want a sensor with a range of 0-5 psig or 0-10 psig. I suspect your tank pressure would be less than 5 psi.

There are numerous types of display units available for 4-20 current loop.

This is a bit of a write upon the technique. Or you can just google "pressure transducer tank level". This should be the most accurate and reliable method. You will have to calibrate it to fuel quantity when you fill up.

https://www.te.com/usa-en/products/...nted-pressure-transducers-for-tank-level.html

I recall Raritan had a strip to attache to the sides of synthetic tanks that could give rather good tank levels.
Many years later, I wander if the technology has improved to measure thru metal (alloy) tanks.

Hatteras uses the ultrasonic stuff on their MYs.
It's fair at best. Requires cleaning from time to time.
They do have a good rythm programed in to it to eliminate wild reads when the fuel sloshes around.

Well, every day is a school day, as the old saying goes.
Thanks for enlightening me.

FUS/WEMA....had to replace a full set of gauges after a lengthy direct voyage where the power was left on to the gauges (versus a momentary switch). Sometimes they are a little sensitive and not reliable as well. Sort of an ongoing issue that continues to be studied and considered. With belly tanks, there is no path to sight tubes, but perhaps I can see my way to some sort of above-tank tube with a float inside that could relay the level to a visible cylinder, sealed on top for odor, but tall enough to display the level. It would likely stick, too, from time to time, but it perhaps could be accessible with a removable cap to jostle the visual float and verify the reading. Thoughts in progress on this...

...but another thought is to similarly install an audible alarm with a full-sensor for tank filling purposes. One could fill the tanks and be altered to full levels prior to overflow. More thoughts to ponder.

Generally speaking we keep solid hour and consumption/fill logs. We have a pretty good idea of what's going on in the tanks with or without gauge accuracy. Problem occurs when an event like a hose or prop fouling etc throws off your normal consumption understanding. You need the accurate backup.

gen fuel avg I read was 1g per 10kw

Probably accurate then of course the question is how much load are you actually using. That’s why I m ASSuming an average of 60% load

on some Exumas trips we use more fuel in the gensets than the mains which could make calculating fuel a bit of challenge but I ve been pretty close

Started working with tech at Centroid on Friday after learning BOTH new VDO fuel gauges were not correct. One read 1/4 with full tank even after removing its Centroid sender. The other gauge pinned to over full also when sender removed from tank and wires put back on. Replaced the fwd. tank with reed style from KUS but the sender for the aft tank goes into a long tube plumbed to bottom of the tank and tube lacking diameter for the KUS float so need other option. Never had any issues with Centroid senders but they were three wire models and these two problem children are two wire models. Centroid tech wrote VDO gauges work best with their 3 wire senders. Which ones caused your "never again" opinion ??

The company and products "Never Again".
The 3 wire capacitance sender is from the spawn of the devil.
When I dealt with them many years ago, the mother answered the phone, when the kid got a break at his job or came home, he would call me back.

Later model VDO gauges work both ways; Old style VDO and American standard or "Stewart Warner compatible".
What mode VDO gauges do you have and what do you need.

Is he supplying the matching gauges? Is the spec for a real VDO gauge in original VDO operation mode (bass ackwards from the SW norm).

VDO; a short on the two senders wires battery negative (or ground) and positive from the gauge makes the gauge go down or empty.
In SW mode, a short on these two wires and the gauge goes full.

Also, most auto parts store employees can not find there asp with either hand much less understand the difference between original VDO & SW gauges.
Bertram's and Vikings are not in their part look up computers.

Sorry I'm ranting, Let me sleep (it off) and ponder more on this in the morning.

Oh, Something I just remembered; any (ANY) water in the tank and all bets are off.
One trick was ordering the tube an extra inch (or 2) short than what you think you wanted.

Yeah they also double as detector of water and Friday their tech mentioned also algae, of which based on the Racor's I've got neither. What I do have is a 550 gal. aft tank under the cockpit deck with only a couple inches between them and no access from above. Rather then put any tank access from above like for a sender, Bertram plumbed a vertical tube along the forward wall of the tank behind the ladder stairs going down to the ER to place a sender. The level of fuel in the tube is equal to that in the tank. No idea what sender may have been OEM back in 95 but the 2 wire Centroid sender I've determined to be faulty has a date of 7/12 so obviously not original. As you earlier posted and the Amazon reviews support, the reed style KUS is a top sender and turned out the only one I was able to find 21" long to replace the also faulty fwd. tank's Centroid sender but it's donut style float will not fit in the tube at the aft tank. Tech support at Centroid mentioned their 3 wire senders work best with VDO gauges of which mine are the American Standard 240-33.5 ohm. Never had any problems after installing a 3 wire Centroid in my old 38 Bert or the 3 wire one placed in my Contender over a decade ago so sort of surprised to find 2 out of 2 faulty ones in this boat so I was thinking maybe the cause of them being faulty is that their only 2 wire models or perhaps during vessel's initial ownership an electric surge of some sort took place and ruined them.