Diesel tank sender

Hi All,

My wife and I just got a Camano 31 Troll. Old but is in good shape.
Unfortunately, I am having issues with the fuel gauges. The tanks are 18 W x 44L x 14"H (external values). This equates to 48 USgal.
measuring with a wooden dowel rod I can measure the levels on both tanks. But the math (volumes based on stick readings) doesn't match with the gauges readings.
The port reading is stable but the starboard oscillates - sometime too much. One tech had mentioned the send might be bad and to replace is very crazy expensive - no access.
Noticed too that with engine running the levels on gauge are a bit higher.

Ex: stick reading 6.25" that would define a volume of 4950 in3 which is 0.446 ration of the full tank. But the gauge shows 1/4" ... maybe a bit above. Well 0.446 is almost 50% ... half tank!

Help here:
Options on fuel sender and metering?
How non accurate can the stick reading be?

Thank you all

Sticks can't be wrong any more than a tape measure can be wrong. They simply measure depth of liquid in the tank. If your tanks are cubes then no calibration is needed.

Unfortunately, this text can be wrong and some boats. It really depends on where the hole that you were dipping the stick into is located on the tank. A small amount a list one way or another will come up with a different reading all together. With my boat I found if the wind blew strongly from One Direction or if I had the boat loaded more forward or aft I could get different readings that with some times vary significantly. I ended up putting some fuel sender's in the tanks that I had to calibrate by slowly filling them.I don't know the name of it, but one mechanic told me that there are sensors you can put at the bottom of the tank that will literally sense the number of gallons due to the weight on top of the sensor. I might look into that.

Juliet 15 said:

I don't know the name of it, but one mechanic told me that there are sensors you can put at the bottom of the tank that will literally sense the number of gallons due to the weight on top of the sensor. I might look into that.

Click to expand...

I need to replace my senders. That is an interesting concept.

I too need to replace my failing electro / mechanical swing arm senders. Unlike OP's situation access to the tank tops is not too bad, not easy, but not to $$$ to get at.

Maretron has a pressure sensor system Maretron fluid pressure monitor but I don't have a Maretron network system installed with no plans to.

Hippocampus mentions in another thread he's happy with the Philippi tank monitoring system. Like Maretron it looks like a network is needed. Philippi's offers different kinds of sensors but it looks like all will require access to the top of the tank. No link posted because I have yet to find a vendor who sells all the bit n pieces needed to put it together.

I have yet to dig into the tech issues deeply enough to know if Maretron or Philippi require the use of proprietary networks or will run on non-proprietary NMEA200 or CanBus networks.

With access to the top of the tank Centroid or Kus products will work and they do not require a network. They are hard wired and use old style gauges. Both of these are designed to drop into the standard flange used on the old style swing arm sensors making fitting to the tank easy peasy. I'm leaning towards one of these two. It seems many of the problems encountered with the old systems are not just the swing arm mechanism but bad connections wires. If I go this route I'll pull new wires at the same time.

If the tanks are not metal you may be able to use SCAD

There's always the Tank Tender. Beautifully simple, no wires, no network. Just air pressure. But, access to the top of the tank is needed.

I've just started looking at ultrasonic systems. These too will require access to the top of the tank.

I've been thinking about this post. I think your mechanic is barking up the wrong tree. As your tank tips from listing or trim the fuel will be deeper at the low point, shallower at the high point. It doesn't matter what is used to read that level at that point it will read what it sees. This applies to old style electro / mechanical sensors, capacitance based sensors and air pressure systems. Or even what your mechanic recommends, liquid pressure. To envision this imagine you can tip the tank enough that at the sensor point there is no fuel, it will read empty. Now tip the tank enough that the fuel touches the top of the tank, it will read full. Don't be fooled by the promise the pressure sensor will read the tank volume regardless of list or trim. Pressure from a liquid is only for the height of the liquid above the sensor, not the volume. Fill a 1000 gallon tank to 12" and a pressure sensor will read 12" of pressure. Fill a 2" pipe to 12" and the pressure sensor will still read 12" even though the volume of the pipe is 0.1632 gallons!

You could eliminate errors due to list by putting the sensor point or dip stick hole in the center of the tank athwartships. The same with eliminating errors due to fore and aft trim. To eliminate both you'd need to put the sensor or dip stick hole in the center of the tank athwartships and fore / aft.

Your avatar shows a 58 ft boat. Unless the tanks are very low, wide and long I can't imagine the normal list or trim you encounter would greatly change the tank readings. The mechanic's recommendation to go to a pressure sensor system may well give you better readings. But not because it does a better job of dealing with list or trim. It will give better readings because there is something wrong with your present system.

Juliet 15 said:

Unfortunately, this text can be wrong and some boats. It really depends on where the hole that you were dipping the stick into is located on the tank. A small amount a list one way or another will come up with a different reading all together. With my boat I found if the wind blew strongly from One Direction or if I had the boat loaded more forward or aft I could get different readings that with some times vary significantly. I ended up putting some fuel sender's in the tanks that I had to calibrate by slowly filling them.I don't know the name of it, but one mechanic told me that there are sensors you can put at the bottom of the tank that will literally sense the number of gallons due to the weight on top of the sensor. I might look into that.

Click to expand...

Is the gauge stable when the boat is at rest?

The simple way to measure the tank is when filling it with a metered dispenser. Gauges working properly are very repeatable but not too accurate.

Get the fuel level down low then add fuel while recording the gauge readings. It will usually always read the same every time and you will know the amount of fuel added to get that reading.

Electric senders/gauges are notoriously inaccurate. Some are ok if quality and set up properly, but most the accuracy sucks.

If you can't easily remove the senders due to poor access, you are stuck with what you have.

Fortunately you can dip stick your tanks. After a while of use, you will figure out what the gauge readings mean relative to stick readings.

While the elec gauges are generally not accurate, they generally are repeatable.

So dip tanks at beginning of a trip, dip when shut down, dip when adding fuel. Eventually you will be see what gauge reading corresponds to stick readings.

On my ride I have no gauges. Stick only. 10gal/inch. I know exactly how much fuel I have before cranking up, and I have run the boat enough to know the burn rate, so it is easy peasy.

Seen way too many boats run out with gauge showing 1/4 tank.

You are fortunate that you can dip your tanks. Many boats can not.

I can't dip the tanks nor do I have any senders in the tanks. In actuality, I don't need either and have never even tried to add senders. Why? I know how much the engine/boat burns for fuel since I have always monitored engine hours and fuel fill-ups (always best to start w/full tanks). A little simple math - gallons to full / hours run - gives you the run-rate of fuel use. I have always been able to come within 10 gal if estimating a fill-up and since that's over 400 gallons of capacity it's a pretty good track record. As with most boat owners I never let the tanks get below about 1/4 capacity there's always plenty of wiggle room ... and in reality the fuel rarely gets below 1/2 capacity. I like to keep things simple, that's my ten cents.

Scrib said:

I can't dip the tanks nor do I have any senders in the tanks. In actuality, I don't need either and have never even tried to add senders. Why? I know how much the engine/boat burns for fuel since I have always monitored engine hours and fuel fill-ups (always best to start w/full tanks). A little simple math - gallons to full / hours run - gives you the run-rate of fuel use. I have always been able to come within 10 gal if estimating a fill-up and since that's over 400 gallons of capacity it's a pretty good track record. As with most boat owners I never let the tanks get below about 1/4 capacity there's always plenty of wiggle room ... and in reality the fuel rarely gets below 1/2 capacity. I like to keep things simple, that's my ten cents.

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+ 1 for this.
Fill the tank run for 10 hours and refill. Burn per hour.
Then all you have to do is keep track of engine hours.

Solly said:

+ 1 for this.
Fill the tank run for 10 hours and refill. Burn per hour.
Then all you have to do is keep track of engine hours.

Click to expand...

+2.
Started doing this with my first boat, a sailboat. The fuel gauge read "full" until the tank got fairly low, so was next to useless. Start with a full tank and then track engine hours. Next fill, calculate useage in gallons per hour (or some other volume like litres). Gallons added to refill divided by engine hours. After a few fill ups you will have a fairly accurate number.

On my Nordic Tug, I have a Tank Tender and tank sight tubes. My "manual method" is just as accurate as the TT and sight tubes. All 3 methods are usually within a couple of gallons of each other.

Your method is great in that it doesn't depend upon any hardware. To make it work you have to run at the same engine RPM all the time to get the level of accuracy you have achieved. I wish I could use your method but I need / want to vary engine speed from 1000, sometimes as low as 800 and up to 2000. The burn rate on my engines nearly doubles from lo to hi. I've tried working out burn for a day's run by tracking time at different RPMs. Not worth the effort.

Scrib said:

I can't dip the tanks nor do I have any senders in the tanks. In actuality, I don't need either and have never even tried to add senders. Why? I know how much the engine/boat burns for fuel since I have always monitored engine hours and fuel fill-ups (always best to start w/full tanks). A little simple math - gallons to full / hours run - gives you the run-rate of fuel use. I have always been able to come within 10 gal if estimating a fill-up and since that's over 400 gallons of capacity it's a pretty good track record. As with most boat owners I never let the tanks get below about 1/4 capacity there's always plenty of wiggle room ... and in reality the fuel rarely gets below 1/2 capacity. I like to keep things simple, that's my ten cents.

Click to expand...

Solly said:

+ 1 for this.
Fill the tank run for 10 hours and refill. Burn per hour.
Then all you have to do is keep track of engine hours.

Click to expand...

Same method I use. I refill based on hours as recorded in a log book. The number of gallons I take at the next fill-up is always what I expect.

To the OP, do you know what senders you have? I am guessing WMA/KUS. If you are depending on a mechanic to gain access for you, yes, bigger bucks, but if you can accurately locate the sender's location on the top of the tank, it is quite often possible to use a four-inch hole saw to cut through the deck or whatever flat surface is above it to gain access. Hopefully, you boat's configuration can accommodate this approach. A standard plastic deck plate fits nicely into the hole when you are done to give it a proper finished look.

My personal experience with the WEMA/KUS senders is that both only one was connected to the console gauge, and it was making the needle on the gauge act whacky like yours does. Eventually, the needle stopped moving off "E" altogether. I replaced the gauge which tested as faulty and then replaced both tank senders and connected them both so I can read either tank at the gauge. Now the gauge agrees well enough with the sight gauge which I use to confirm the console gauge, especially at low levels.

It was alluded to earlier, but are your tanks possibly wider at the tops like a lot of installations?

Ski:

IMO you are correct that gauges are inaccurate but they are usually very repeatable.

That is they will give the same reading with the same fuel level every time.
Just ignore the indicated levels and make your own calibration marks.

Gallons per hour sounds nice but since speed, engine, bottom, and sea conditions may vary from time to time calibrating your gauges is a good check.

Yes my Drifter has a very accessible and straight into the tanks which are XYZ boxes but no with way to access the top. I can see but I cannot even get there.

I like to thrust on instruments (sounder, compass, tach, etc) but it seems I will have to calibrate the gauges AND myself to deal with this differently. It will be okay.

Thank you

I have those Maretron fuel level sensors and also their fluid flow (fuel burn) sensors. They run on a NMEA 2000 backbone.

The Flow Scan style gauges will record fuel used , if you adjust them a few times you can get within 2 gal of fill required on a 100g tank.

The Tank Tender style of liquid measurement works for fuel, fresh water and black water.

tanktender.com

The original precision tank measuring system. One instrument measures from 1 to 10 tanks. It gauges the liquid level in water, diesel & holding tanks.

I can offer up some info on the various Maretron alternatives, just so they are fully understood. You might find one that is an easy adaptation to your boat. I have used all of these approaches.



Yes, they are NMEA 2000 (N2K) based, but that doesn't mean you have to build a big network. A sensor, display, power tap, and few fittings will give you a functional system. It won't be cheap, but it might be cheaper than cutting access holes and recovering with inspection plates.


Maretron has 4 different ways to measure tank levels. Two are based on pressure, just like a tanktender, one utilizes an existing (or added) conventional resistive float sensor, and one is an ultrasonic level sensor.


One of the pressure sensors is submersible, and gets lowered into the tank from the top, typically through the opening vacated by an old sender. The sensor lies on the tank bottom, and the cable runs through a cover plate and sealing gland through the tank top opening. The sensor then connects to a fluid pressure monitor (FPM100), and gets calibrated to report how many gallons or liters remain in the tank, based on the head of fluid above the sensor. One nice thing about this sensor is that the attached cable is flexible so the sensor can be lowered into the tank without much headroom over the tank opening. These sensors work very well, give very accurate level sensing, and best of all, they work equally well with gray and black water.



The other type of pressure sensor gets screwed into plumbing at or below the bottom of the tank. These can only be used if there is some sort of port or fuel draw from the bottom of the tank. It doesn't work if all fuel is drawn out from the top of the tank. The sensors have a 1/4" threaded end, and you need to tee into the existing plumbing somewhere. The location doesn't have to be right at the tank, but can also be further down the plumbing line. It just needs to be open to the tank, and at or below the tank bottom. These can be really easy to install if there is accessible plumbing that you can tee into. Like the other pressure sensor, this type connects to an FPM100. These are extremely accurate and reliable.



The next approach is a Tank Level Adapter, or TLA100. It gets wired to a conventional resistive sender. The advantage over a simple gauge display is that it can be calibrated to report fuel level in gallons or liters, and can accommodate irregularly shaped tanks. This approach is good if you want to use an existing float sensor, but accuracy is only as good as the float sensor, which generally isn't all that great.



The last approach is a replacement sender, but one that senses the fluid level ultrasonically rather than via a float. Calibration capabilities are the same as all the other approaches. I have only used these on black and gray water, and they worked very poorly. So poorly that I removed them. I know people first hand who have used them on clearer fluids like fresh water and fuel with much better success, though diesel foaming can be an issue under some circumstances. The bottom line is that I don't use these anymore. Sensing via pressure sensors works much better, and can be done from the top or the bottom of the tank, so there is just no reason to use an ultrasonic sensor when there are better alternatives.

I guess I've been lucky. @ boats both with swing arm gauges, both very accurate.
By that I mean that I could predict within about 10% how much fuel I could take on by reading the gauge.

twistedtree, thank you for the clear overview of Maretron's tank level sensors along with your experience. Great help to those of us trying to sort out what to install.


A question. Do we need to use Maretron's displays? Can the data be shown on a laptop or tablet? I'm using a laptop as a primary nav plotter and don't want to try to find space for another display.

Catam said:

Yes my Drifter has a very accessible and straight into the tanks which are XYZ boxes but no with way to access the top. I can see but I cannot even get there.

I like to thrust on instruments (sounder, compass, tach, etc) but it seems I will have to calibrate the gauges AND myself to deal with this differently. It will be okay.

Thank you

Click to expand...

I had those issues. Luckily the molded in bench seating over the tanks allowed enough room under them to allow for a 90-degree drill chuck and my 4" hole saw, AND the sensors were not so long that I could not get them in and out without bending them.

Portage_Bay said:

A question. Do we need to use Maretron's displays? Can the data be shown on a laptop or tablet? I'm using a laptop as a primary nav plotter and don't want to try to find space for another display.

Click to expand...

Yes, you should be able to display tank levels on other devices if they support the appropriate N2K data messages.


That said, you will need one of a few possible Maretron devices to get the stuff configured and calibrated initially. But once set up, you shouldn't have to mess with it.


Setup can be done though their displays. That's one option.


The other option is to use their free N2KAnalyze software. It can do the configuration, and is also a very hand diagnostic tool if you get very far into N2K.


But the "free" part has a catch; you need one of their N2K to computer interfaces to allow the computer to talk to the N2K bus. The choices are the USB100 which is USB connected to the computer, or the IPG100 which is ethernet connected to the computer.


The USB100 is the cheapest approach, but still order $200-$250 as I recall. The down side is that it only allows the one connected computer to access the bus.


The IPG100 is a good bit more expensive at about $500, but is also much more flexible and capable. Any number of devices on the ethernet can use it at the same time to access N2K. So you could have N2KView running, plus N2KAnalyze, plus a mobile device, all at the same time. Also, N2KView uses a USB license key, and that can be plugged into the IPG100 instead of into the computer running N2KView. That gets the license key USB stick out of your computer, and allows any computer to run N2KView, though only one at a time per the license terms. So if you plan to delve into N2K beyond the most basic system, I would highly recommend skipping over the USB100 and investing in the IPG100.


If you have no expectation of doing anything more with N2K beyond this one tank level sensor, then you could try to find a marine electronics person or friend who is familiar with Maretron gear and who has a USB100 or IPG100 who is willing to come hook up and configure your system, then leave with their gear. But if you are hiring a tech, I'll bet buying a USB100 is cheaper than what they would charge to come do the configuration. And if you ever had to call them back, you will be way ahead by buying the device and doing it yourself.

twistedtree, again, thank you. These two posts will help me get up to speed on Maretron much faster if I decide to go that route.

I do not have gauges for mine. Just nice teak dipping sticks for manual soundings. Fool-proof and know exactly how much is in there. Plus at 4gph, it only gets dipped a few times a year. These are new SS barrel-type long haul trucker tanks, so they have a provision for a sending unit at the top (or may already be installed), but never gave it a second thought until now.

Portage_Bay said:

I too need to replace my failing electro / mechanical swing arm senders. Unlike OP's situation access to the tank tops is not too bad, not easy, but not to $$$ to get at.

Maretron has a pressure sensor system Maretron fluid pressure monitor but I don't have a Maretron network system installed with no plans to.

Hippocampus mentions in another thread he's happy with the Philippi tank monitoring system. Like Maretron it looks like a network is needed. Philippi's offers different kinds of sensors but it looks like all will require access to the top of the tank. No link posted because I have yet to find a vendor who sells all the bit n pieces needed to put it together.

I have yet to dig into the tech issues deeply enough to know if Maretron or Philippi require the use of proprietary networks or will run on non-proprietary NMEA200 or CanBus networks.

With access to the top of the tank Centroid or Kus products will work and they do not require a network. They are hard wired and use old style gauges. Both of these are designed to drop into the standard flange used on the old style swing arm sensors making fitting to the tank easy peasy. I'm leaning towards one of these two. It seems many of the problems encountered with the old systems are not just the swing arm mechanism but bad connections wires. If I go this route I'll pull new wires at the same time.

If the tanks are not metal you may be able to use SCAD

There's always the Tank Tender. Beautifully simple, no wires, no network. Just air pressure. But, access to the top of the tank is needed.

I've just started looking at ultrasonic systems. These too will require access to the top of the tank.

Click to expand...

I loved the accuracy of my tank tender on a previous vessel. My current vessel has two tanks. One with a sender accessed from above, the other, and the reason for my response, is a Centroid that I had to replace. It was the only sensor I could find that installed at a 90 degree angel because there is no access to the top of the tank. It works well.

I closed on a 2000 Mainship390 this past July (two helms, two tanks, ONE fuel gauge sender, and a toggle switch at the lower helm determined which helm's fuel gauge would work). The tanks have a fuel line normally set to equalize between them.

Same problem: fuel gauge would bounce wildly at either helm/gauge indicator. It was almost worthless. You could tell if you had less than a half tank or more than a half tank... that's about it! The gauge was a 4" 4-in-1 VDO gauge, and fuel was only ONE of the 4 things being indicated (w/oil psi, voltage, coolant temp which all worked fine). I was able to find a VDO part number on the side of the gauge housing. Called VDO. VDO no longer makes this gauge, but the tech was able to tell me that the gauge's range is 240->33 Ohms. (240 Ohms=Empty, 33 Ohms=Full.) Searched online for a 2" gauge meeting that spec, found one (ISSPRO brand) and installed it at the upper helm where I operate 99% of the time. It is VERY smooth. It electronically "dampens" the signal, and moves up and down very slowly. Very nice! $49+2" hole saw drill bit. Good luck.

Group9 said:

I need to replace my senders. That is an interesting concept.

Click to expand...

I have the Maretron sensors aboard Rendezvous. I've used the standard ones with a float, the ultrasonic ones, and a few others in my testing. The pressure sensitive submerged sensors are hands down the most accurate I've ever used. They don't require cleaning, are hyper accurate as long as you calibrate them to the medium they are in, and have proven to be very reliable.

I have some in my fuel and water tanks, and can fill up to almost the max by using the sensor, down to 1-2 gallons. Highly recommend them.

I am going to try the oceanic 3271 sender. There is a guy on ebay selling some NOS so they aren't that expensive.

NMEA 2000 and seems very rugged.

https://www.navstore.com/oceanic-systems-fuel-sender-250-500mm-5-bolt-sae-3271-500.html