Tank Tender, Hart Systems

Our Tank Tender from Hart Systems is 20 years old and one of the few pieces of original equipment left on Morgan’s Cloud.

For those of you not familiar with this unit, it relies on hand pumping air down a tube in the tank and then measuring the resultant pressure to determine fuel or water level. Our Tank Tender has helped us manage our fuel and water in some pretty remote places where it really mattered; like the east coast of Greenland where running out of fuel will result in a long and very chilly (we heat with diesel too) trip home. (We have carefully constructed a graph of liquid depth against volume of fuel or water remaining that is surprisingly accurate.)

At the end of our last cruise, the Tank Tender started to get a little flaky—still usable, but not its old reliable self. Even this failure was probably not the unit’s fault since it got drenched with salt water some years ago. We removed it, diagnosed a couple of bad valves and sent it back to Hart Systems.

Three weeks later it was returned (most of that time was for shipping) all cleaned up and in working order with a very reasonable invoice attached. Not only that, and without being asked, Hart included a new manual and a full set of tube ends just in case we had lost the manual (we had) or the tube ends had corroded (they hadn’t).

Sure, we could have replaced the unit with some fancy electronic system, but I wonder how many of those will still be working 20 years from now. Or, even more to the point, how many electronic systems of any type bought today will be obsolete, superseded, and not repairable just five years from now. My guess, based on bitter experience, is most of them. Makes you wonder if new, fancy and electronic is always, or even generally, a better way, doesn’t it?

Not only is the Tank Tender great gear, but Hart Systems are a pleasure to deal with: communicative, helpful and going the extra mile by providing the tube ends and manual without even being asked.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

10 comments… add one
  • Tobias Dec 13, 2015, 6:16 pm


    Just what I need! Mount on all fresh water tanks, the diesel tank and the waste tank.

    Saves my day.



  • Bill Attwood Dec 15, 2015, 8:49 am

    Hi Tobias.
    I have installed a TankTender on Kinsa and am delighted with it. A factor to bear in mind when installing it is that the capillary hoses which connect the Display unit (with the small pumps) with the tanks are very thin and need to be run in some sort of proctective sheathing. I used small diameter polyethylene hose.

  • Adam May 4, 2018, 11:34 am

    I read that the tank connection fittings are stainless steel. Any problem using w aluminium tanks? Is typ TefGel application used in potable water or diesel tanks, or do they provide a more mechanical isolation?

  • Dave Meindl Mar 22, 2020, 9:20 pm

    John (and anyone else using tank tender),

    One of our winter projects has been to research and install a tank monitoring system in our Beneteau 473. For 3 water tanks, 2 holding tanks, and 2 fuel tanks, we only have one (semi operable) fuel gauge for the port fuel tank. Definitely a much needed upgrade! Being that this article is a little older can you comment on if you are still using Tank Tender and if so, are you still happy with it? I really like the idea of a non-electronic tank monitoring system. Also, are there any other systems out there that people seem to be happy with from a reliability and longevity standpoint?
    Thanks for any info,

    • John Mar 23, 2020, 9:07 am

      Hi Dave,

      Yes, still use the tank tender and still love it. 33 years old and still going strong with just one factory rebuilt. Can’t argue with that.

  • Dave Meindl Mar 23, 2020, 8:17 am

    This is a follow up question … I’m getting mixed reviews (big surprise on the internet huh) about how well the Tank Tender does or does not work in holding tanks. It sounds like even with the purge valve option, the Tender can sometimes clog in a holding tank. Do you use the Tender in your holding tanks and how has it worked? Does anyone out there have experience with the SCAD brand holding tank monitor? It seems to have good reviews for holding tanks as it involves placing a strip on the outside of the tank which measures ohms. No fouling possible.

    • Bill Attwood Mar 23, 2020, 8:32 am

      Speculation – it depends on the mix of the “components” in your tank. I haven’t yet connected the 3rd line to the tank, just to water and diesel, for precisely this reason. Since the more solid components should be floating, the bottom layer should be easy enough to blow out of the capillary tube. Another possibility is pressure loss from the pump if the capillary tube has a long run.

    • John Mar 23, 2020, 9:18 am

      Hi Dave,

      No we don’t use the tank tender for holding and I would not recommend it. Seems to me that it would only be a matter of time before the tube blocked leaving one with an unpleasant, and probably frequent, job. We have one of the electronic holding tank measuring gauges that uses a set of sensors stuck to the outside of the tank to measure level. Seems to work well and we have had it for at least 15 years. Here’s a Practical Sailor article on this kind of sensor: https://www.practical-sailor.com/sails-rigging-deckgear/marine-holding-tank-sensors-how-do-you-know-when-the-black-water-level-is-at-red-alert

      Sorry, I don’t remember which one we have, but I will take a look next time I’m on the boat.

      • Dave Meindl Mar 23, 2020, 10:41 am

        Thanks John,
        Yes, if you could take a look next time you’re onboard, I would appreciate it. That was exactly what I was thinking with regard to the Tank Tender tube clogging (even with the purge valve option) and why I looked at the SCAD sensor. It’s exactly what you describe as far as sticking on the outside of the tank. If the brand you’re using has been working well for 15 years that’s the best endorsement possible. I look forward to hearing what you have on board.

        • John Mar 24, 2020, 8:15 am

          Hi Dave,

          Will do.

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