Summary of Messages regarding Fuel Tank Measurement and Fuel Polishing

I also use a fuel log and fill the fuel tanks completely when I take on fuel.  I do this by removing the round fuel sender covers and monitoring the level of fuel I put into each tank...a bit of a nuisance and a bit of a risk if someone comes by and leaves a wake while I am filling my tanks.

I also log engine and generator hours and when I switch fuel tanks.  I reckon my fuel comsumption as 1.25 gallons per hour on my Ford Lehman 90 auxiliary and 0.5 gallons per hour on my Westerbeke 4 KW generator.  This is a high end estimate and I compensate with my dipstick to get a more accurate reading.  This labor intensive approach is the best I have been able to do and I appreciate that you do the same.

My fuel tanks are also equipped with a vent connection in the form of a "T" attached to the tank where the fuel return line arrives.  I'll have to try removing this plug to vent air during fueling and manually sounding the tank with a narrow dowel.  Since we both have the same configuration, I assume it's a factory installation.

I don;t have a fuel polishing and transfer system to transfer fuel from tank to tank and that's one of my next big projects.  When I do this, I'll also replace the old and brittle copper tubing with approved flexible fuel lines.  With luck that will be done by the end of the year.

Meanwhile, several folks have requested my dipstick "calibrations" so here they are:

Using the same dipstick for both port and starboard saddle tanks which measure a total of 27 inches from bottom to top where I take my readings, I remove the round fuel sender plate and slide it to one side while I dip a 36 inch dowel into the opening on my fuel tank, keeping the dowel as vertical as possible while letting it slide all the way to the bottom.


Reading from the bottom:


9 inches = 10 gallons

13 inches = 20 gallons

16 inches = 30 gallons

19 inches = 40 gallons

22 inches = 50 gallons

25 inches = 60 gallons

27 inches = 65 gallons


Unfortunately, I don't have measurements for the center fuel tank.  If anyone has this information, I would appreciate having it.  If not, I will be pressure testing my center fuel tank this year as part of my fuel system upgrade.  If the tank integrity is still sound, I will recommission it and start using it again.


Thanks again for your response, Jens.  It's reassuring to know someone else uses the same fuel level monitoring approach.  I'd be interested in learing about your fuel polishing and transfer system...especially if you designed and installed it...and any advice you may have before I take on my own installation.

 Joe, S/V Windreka III, Whitby 42 #309,Dataw Island Marina, SC

Sent: Tuesday, July 22, 2008 5:45 PM

Hi Joe,

That is a pretty deckfill setup in Defender.  I do notice however that it still uses the same resistive "swing-arm" senders that other tank level systems do.  My experience has been that it is usually a failure of the sender or an electrical wiring problem with the ground connection that causes these systems problems.  I still have the original tank level guage supplied with my Whitby and it works fine, however the tank level senders have been replaced many times over.  In an unsuccessful campaign to fix this problem I switched to capacitance senders (the NMEA 2000 Fuel Level Sender link on the Defender page you supplied is one).  The capacitive senders are attractive because there are no moving parts and in theory there is not much that can go wrong with them.  However they are difficult to calibrate and seem to interact with the strongly sloping metal sides of the Whitby wing tanks, so it is difficult, at least for me, to achieve a consistent and meaningful calibration over the entire depth of the tank.  The centerline fuel tank is also difficult due to bilge water sitting on top of the tank and interacting with the electrical sender.  So frankly after many years and many dollars spent, I have simply given up on reliable electrical fuel level on my Whitby.

We have a Hart system for water tanks which was on the boat when we bought it.  I have never been able to make it work, a situation shared with many other cruisers.  However I do know of several cruisers who use this system and love it.  I believe keeping the system airtight is key and those who have spent some quality time talking to the manufacturer, keep an inventory of spare parts onboard and have the patience to understand and maintain the system will likely get good to excellent results with it.  In the submarine service we used air, electrical and mechanical dipstick sounding systems.  Air and manual always worked fine.  The electrical was always problematic.

In practice for us sailing around the Pacific we simply use a fuel log. We always fill the tanks completely when we take on fuel and that is the only time we know exactly how much fuel is aboard.  We log engine and generator hours and when we switch fuel tanks.  It only takes a few cases of running a tank dry to sort out a good estimate of hourly fuel usage.  Use a high end estimate and you won't  go far wrong.  This is not hard to do and when you get it you will have a fuel gauge based on operating hours that is quite a bit more accurate than any system that relies on tank levels.

Our fuel tanks are equipped with a vent connection.  This vent consists of a "T" attached to the tank where the fuel return line arrives.  One leg of the "T" is vertical and has a pipe plug in it. We can remove this plug to vent air during fueling ops and we can also manually sound the tank by putting a narrow dowel down this hole.  These vents were installed on our Whitby when we bought it and I had always assumed it was a factory installation, but I don't know.

We also have a fuel polishing and transfer system on board which allows us to transfer fuel from tank to tank.  So sometimes when we have fuel in several tanks that are not completely full, we can pump all the fuel into a single tank and get a pretty good idea of how much fuel is on board.    This also allows us to collect the few remaining and precious drops of fuel in each tank and transfer into a single tank.  The transfer pump is less sensitive to sucking air from a tank in a seaway than the main engine is.  Also since we use a high estimate for hourly fuel usage this creates somewhat of a "reserve" in each tank which can then be collected into a single tank when the onboard fuel inventory is becoming alarmingly low.



I have considered the Hart system.  Did you install the system yourself?  Have you had any problems with accuracy or managing all the air tubes?

Also, there is a new fuel gauge on the market that uses the original fuel tank senders.  It's called the "Offshore Diesel Deck Fill Gauge" -|51|106370|316448|314211&id=1027065. I saw it at Defender recently.  It's basically a deck fuel filler with a digital readout indicating percentage of fill of the tank.  At around $300, it's a bit pricey, but the price may come down after the newness wears off.  The advantage of it is being able to accurately monitor fuel tank fullness right at the fuel filler.  There's also a NMEA-compatible version of it for a bit less cost.


Sent: Monday, July 21, 2008 12:45 PM

I use the HART tank tender system...It works just fine, and we monitor our water tanks as well.


"Lone Star"  #216

Sent: Monday, July 21, 2008 1:56 PM

Subject: [WhitbyBrewerSailboats] Re: Diesel tanks and Dipstick Story

No you can't use the filler fitting on the deck because they have an
elbow entering in the tank. You need to cut a hole in the inspection
plate or best on the top of the tank at the deepest end, thread it and
scew in a fitting that can be easily opened and closed. Make sure the
tank is emptied if you do that, and have it cleaned after, your
injectors will not like the metal debris. Personnally I don't see the
value of a manual gauge (dipstick) if the electrical ones work? One
thing is sure, the moment they indicate the fuel is low, it does go
down fast because of the shape of the tanks. Once you know that, you
can take appropriate action.

> Where do put the dip stick?Do you slide it down from the filler
> fitting on the deck. As at the moment the sender aren't work and the
> amount of diesel carried is based on a large amount of guess work with
> large safety Margins,