blackwater tank sensor

[2953]

Cheers, all. Seeking counsel on the selection and installation of a blackwater tank level sensor for a 04 SO 35 with stainless tank.  I see no posts on this subject, yet the tank is unmonitored, clumsy to access, and, to my experience, incapable of being "sounded" for level.  I would prefer not to install a mechanical/float type devise for obvious reasons.  Anyone with a solution?

[Charlie-Bravo]

Solution 1, leave the valve open except in a marina, and count the 'episodes' with a checklist beside the heads with a clipboard and a handy pen.
Solution 2, replace the tank with a plastic model so non internal monitoring can be purchased.
Solution 3, fit 2 hose couplings one low and one high and fit a clear tube for sight readings ( ug!)
Solution 4, a dip stick ........... actually that's a revolting suggestion , please ignore it.
Solution 5, ........ there is no solution 5 at this time mostly due to wine consumption.

Joking aside, it's a tricky one with a ss tank, a floater ( pun intended) switch is probably the answer, but slightly grim for maintanence as you say, the only other thing that I can think of is a thermal camera , not exactly an early warning system with alarms, but could see the level of sh**t with in, ( it is usual to be a few degrees warmer due to bacteria) and can be used for night time spotting of MoB etc at night.

Hope somebody else come along with a less wine ridden diagnosis and solution, this portuguese 'Porta 6' red is fantastic.

hic!
CB

[Don Reaves]

I know you have said you didn't want to use an in-tank monitor, but it may still be your best option. Practical Sailor did a review of internal monitors, which you can see by clicking this link. I have a simple system with just a 3/4 full indicator. It has proven to be accurate and adequate. It was installed when I had the tank replaced (the original was only 10 gallons!).

[rene460]

Hi, have you tried searching the topic on the forum, but not restricting your search to a particular model.  Everyone has to deal with this one, and I seem to recall there have been a number of relevant threads.  But no obvious totally satisfactory solution for black water that I remember.

I tried the Vetus ultrasonic sensors for both fresh water and black water.  They were not successful for different reasons in either case.

For the fresh water, I believe the problem is basically that the tank on our SO30i is too shallow.  Full is really full in the tank that is only about 14 inches deep, but the sensor seems to have a minimum air space requirement above the top level.  By the time the tank is low enough for the level to properly register, it is nearly empty.  Also, they can only read when the boat is still and level as the principle depends on the ultrasonic signal signal reflecting off the liquid surface directly back to the sensor, not via random reflections of the tank walls.

My next approach will be an internal float type.  I don’t think that is much of a problem with our drinking water tank.  The local dealer has one on display that looks good, and comes in appropriate ranges, sorry I can’t remember the brand, but the boat is four hours away and we are in lockdown, so no progress expected for a while.  It won’t be first on the list when we finally get the opportunity to go sailing again.

For the black water tank it is a different problem.  The space above the full level is probably close enough to adequate, but the tank top is very close under the deck, and I needed a low profile right angle drive to cut the mounting hole, and some wedges to get the sensor surface level, meaning parallel to the liquid surface, at least when the boat is level anyway.  The only practical location was too close the the vertical wall of the tank.  So the sensor is closer to the side wall than recommended, and I suspect it is reflections from that side wall that cause the signal to be erratic that the reading seems random, despite carefully following the calibration procedure several times.  Unless your tank top is a larger area and more accessible than mine, you can save your money on that one as well.

I was reluctant to make the hole in the tank, but reckoned that the top surface was just acceptable to me, but I am not interested in floats or other internal devices that require puncturing the walls.  Perhaps there is a capacitance type that only requires a clean smooth tube inserted from the top, perhaps using Arduino, but I don’t know how to design it.  I have also read somewhere about wave guides, but don’t really know what that would involve.

In the mean time, the top few inches of the tank below the full level but still above the boards that enclose the tank, is sort of translucent, and the level can be detected using a torch if it is in that region, we just keep an eye on it, and pump out often, “whether needed or not”.  As lake sailors, we always have to pump out, no other reasonable option.  At least regular routines and only the two of us, we have a fair idea of how often to pump out, much harder with visitors or children on board.

rene460

[windhond]

Hey, I realized a vary cost effective electronic warning solution for my synfast 26 tank.
It is a resistance based sensor whit a blink led. I used this kemo-m158 modul. www.conrad.nl/p/kemo-m158-watermelder-module-9-vdc-12-vdc-191317?WT.mc_id=affiliates:tradetracker:172347:191317&utm_source=tradetracker&utm_medium=affiliates&utm_content=kiesproduct&utm_campaign=172347
It was only 12 euro. It works on 12v. If the 2contacts touch the tank level de modul activate a led and relay. I connect it whit a led lamp. I put simply two metal M3 screws in the plastic fitting for the vent as sensing sticks. You can adjust the senor level by screwing in or put the M3 screws. It is nice that there are no moving or sticking parts.
Al work fine and is easy to install.

[reverie]

Hello all,

I installed a Gobius 3-sensor system on my aluminum holding tank 7 or 8 years ago. A fantastic solution. The new models now come with an app for your smartphone. Mine just had a small panel with indicator LEDs. Has been very accurate and reliable.

John
Reverie
2004 SO35

[saltymetals]

I agree w John. I self-installed a Gobius which comes w 3 sensors (25%, 50%, 80% full depending on how you position the sensors)) . After installation all you can see is a little visiting card sized , LED light panel, blue (empty), green (25%), amber(50%), and red(80%). very simple, no drilling required hence no leaks no smell, no floats to get gummed up. Good after sales service. Swedish. Works on SS and plastic. The Scandinavians think it is best thing since sliced bread.
Andrew
"Genial Bee"

[charlesriley]

I'm using the LevelPro Sentinel Remote tank level monitoring device for a long time without any trouble and also the support team is very helpful. You can also measure the level remotely. So you can check this device from Icon Process Controls website: iconprocon.com/product/sentinel-remote-tank-monitoring/