Fuel tank senders and gauges

[fallguy1000]

This Friday, I took passengers out for a ride. My fuel tanks read 15 gallons starboard and 12 gallons port. Ran about 15 miles downriver in heavy current and had lunch. Got back onboard and my port gauge read 0-2. I shut the engine off to make sure I did not run out. Got a mile from harbor and turned it on. When we got into the marina harbor; gauge went from 0-2 to 9-11? The other gauge also finally dropped to 13.

So, a couple of questions.

My system uses a yachtdevices analog to digital converter that takes the Moeller analog inputs and converts them for use in the nema2k systems.

Can I add analog gauges upstream of the nema device? If a converter fails, I don’t want to get lost at sea for running out of gas.

Does it seem wise to modify my senders to the donut or tower type?

All dialogue is welcome.

I would also like a discussion about fuel and vent hoses. Does anyone know where we can find permeation data? I think I need to tear out my floors and change the hoses, but I want to understand what I have versus what is best.

For the sake of all of us, maybe bbc can start to carry the right hose and the only hose worth using.

[Jaysen]

From an electrical perspective, the question becomes one of "buffering" the values. You know this but for clarity to those that don't...

In most of the analog systems a 12/24v source is supplied to the sender, the sender float is effectively a potentiameter that changes the voltage based on the amount of fuel in the tank. This new voltage is "sent" to the guage to turn into a visiable display of how much fuel is left in the tank. On super simple systems the guage MAY provide the source to the sender. This allows that guage to control the min/max voltages fed to the display circuits. (fallguys wouldn't be likely to use these, but we need ot keep this in mind).

the key to making this work for you is to "buffer" the sender output so that no one device is lowering the voltage to the point that other devices are getting a false reading (more on this in a minute). You A/D device should have a high impedence, internal buffer as they are normally used in line with gagues for conversions. My experiance is that if you use a quality analog gague with that unit it should work with no issues. I do recommend that you put the nema converter first in the chain though. The converter documents should show that.

My concern is that this is NOT a normal condition for these converters (fail then work). Have you tripple checked the connections at the sender and the A/D converter? This behavior is typical of high resistance on ground, intermentent connection on source or failure within the sender. I'm all for analog gauges, but with all the time you've spent getting it right, I'd hate to have you add one if it's just a bad connector.

[fallguy1000]

Well, the idea of a bad connection merits a check of the wiring.

I’m inclined to wonder moreso if the senders themselves are just crap and worse on last quarter tank. Here on the river, I run on quarter tanks often because the distances are low. On the ocean, I won’t. So another reason to add displacement to the aft hull sections.

My engines are too deep. Craig Watson visited and we went on a nice cruise, but in more of a sea trial phase on hard turns they were almost underwater. I digress.

My point is, suppose I have full tanks and head downriver next year. At some point I will be in the situation of quarter tanks and this nonsense cannot happen.

I will check my connections. Maybe I will buy a couple analog gauges and not mount them and see if they agree to the a/d . If they agree; the senders themselves are junk and I’ll need to upgrade them.

[Jaysen]

after I read your last post, I looked out my window, saw my "i love that POS car" and realized you may have a completely different problem.

My '75 MG fuel pickup only reads the bottom 1/2 tank accurately if the car perfectly level. the tank is sloped in such a way that the volume on the passenger side is much larger than the driver side, but the sender is on the driver side. If the car is slightly tilted to the passenger side (like my fat ass is in the passenger seat) the tank is suddenly empty even though there is a crap ton of fuel (pickup is in passenger side). Is there any chance the fuel was just "not there" for hte sender to read?

I know it sounds like I'm grasping, but it's normal on sailboats to "adjust readings for heal" when considering fule. Considering the changes to waterline (BB) and the motor weight you mentioned, it just kind of tickeled my single functional braincell...

You're going to love that boat in the gulg. My buddy in Orange Beach just bought a Glacier Bay 26. You will be the envy of everyone else down there with a boat that will eat the gulf chop. Not to mention you will have one of the best looking boats in the area.

[TomW1]

fallguy there may be another problem in your tanks if you are only keeping them 1/4 full. That is condensate contamination. Get some good fuel additives and use them to keep your fuel good for a year or more and fill those tanks up. i don't know if this would have prevented what you are going to have to do but chances are good. Good luck anyway.

Tom

[fallguy1000]

after I read your last post, I looked out my window, saw my "i love that POS car" and realized you may have a completely different problem.

My '75 MG fuel pickup only reads the bottom 1/2 tank accurately if the car perfectly level. the tank is sloped in such a way that the volume on the passenger side is much larger than the driver side, but the sender is on the driver side. If the car is slightly tilted to the passenger side (like my fat ass is in the passenger seat) the tank is suddenly empty even though there is a crap ton of fuel (pickup is in passenger side). Is there any chance the fuel was just "not there" for hte sender to read?

I know it sounds like I'm grasping, but it's normal on sailboats to "adjust readings for heal" when considering fule. Considering the changes to waterline (BB) and the motor weight you mentioned, it just kind of tickeled my single functional braincell...

You're going to love that boat in the gulg. My buddy in Orange Beach just bought a Glacier Bay 26. You will be the envy of everyone else down there with a boat that will eat the gulf chop. Not to mention you will have one of the best looking boats in the area.

My boat is 2” below dwl at no load. Add say 750 pounds of passengers in the cockpit and it is running maybe 4” below dwl. LwL is about 35 feet. So I am like 1% tilted aft. The tanks are 45” long, so 1% is 0.45” .. not enough to worry about. I wonder if they are sticking?

[Jaysen]

Yeah. It has to be something like that. The electronic systems are pretty solid. It’s nearly always a mechanical failure of some sort (connectors, float, etc). I’m sure you’ll figure it out just like you have all the other setbacks you e encountered with this monster build.