Team:
I've been following this discussion of tank sensors with interest. I've had several "rounds" in this fight:
1. When we built the second Koinonia (we call her "K2" for short), I knew I didn't want the WEMA float gauges that Jet Tern uses as "standard". Between mechanical "sticking" and the inaccuracies and unreliability of variable resistance gauges, I told them to not install those at all. Instead, we put in Headhunter's "Tank Sentry" system. It is based on a tiny air compressor/sensor module that sits on top of the tank and pumps a small amount of air down a dip tube. The pressure that appears in the dip tube is proportional to the tank level because it's having to push the fluid in that dip tube down to the bottom of the tube. The little sensor module is both the air compressor and the sensor. You can hook up these sensor modules to any number of their bar-graph displays. We have a nice bar graph display in the pilothouse for all 6 tanks (two fuel, two fresh water, gray water and black water). This system is also cool because some of the display modules also have a programmable relay that you can program to close or open at various tank levels. So, for example, I have the gray water tank display setup to automatically pump our gray water tank overboard when it reaches 70% (assuming I don't put the system in "hold" mode where it disables the automatic pumping). I use this capability for both my gray water and to control our Type 1 MSD (Groco "Thermopure") marine sanitation device (a.k.a affectionately known as "the turd burner").
This system has proven to be pretty reliable and it's nice that there's a simple bar graph display that you can repeat anywhere. We have the six bar graphs in the pilothouse and then a "repeater" in the master stateroom for the water/waste tanks.
The down-sides to this system are:
1. While the compressor/sensor modules have been pretty reliable, when they do fail (I've had one fail in 15 years), they are expensive to replace. The modules are close to 1 boat unit (i.e. $1,000). They've over doubled in price in 15 years.
2. The compressor/sensor module makes a little bit of noise when it's "charging". It makes a more significant noise when you first power it up and it's purging the dip tube. But then, every so often (depending on how much the tank level is changing), the little compressor makes a relatively low-level sound as it re-charges the dip tube.
3. There's no direct way to interface this system to N2K.
4. There's no way to calibrate this system for non-rectangular tanks. It just reads tank level. That's still a reasonably good indicator of level, but especially in the fuel tanks doesn't give you an accurate indicator of fuel remaining, since the bottom portion of the tank holds less than the top portion of the tank.
2. Several years ago, I put Maretron pressure sensors in the water, fuel, and gray water tanks. These pressure sensors all connect to one "Fluid Pressure Monitor" module (FPM100). One FPM can connect to up to 6 sensors---which is convenient given our number of tanks. Installing the pressure sensor in all but the black water tanks was relatively easy because all of the tanks have either a drain valve and/or a site gauge port at the bottom of the tank, so it's pretty easy to add one of these sensors to the bottom of the tanks. They are quite reliable and simple (with one exception I'll describe below). Advantages of this system are:
1. It's pretty easy to install on at least all the tanks except the black water/holding tank. It's tricky on the black water just because there's no drain or other port on the bottom of the tank in most cases. The pumpouts are typically dip-tubes through the top of the tank.
2. The sensors rely only on static pressure, so there's no air compressor or other plumbing required.
3. It's also nice that you can calibrate this system for non-rectangular tanks. Our fuel tanks, in particular, are "hull shaped" and so the level of fuel in the tank doesn't directly correspond to the amount of fuel in the tank, since they are narrower at the bottom than the top. The Maretron system will allow you to calibrate the level sensors so that they pretty accurately read the actual amount of fluid in the tank.....not just the fluid height.
4. This system puts the tank level information on NMEA 2000, so you can see it just about anywhere---including remotely.
5. With appropriate hardware/software, like N2KView, you can also setup similar programmable relay closures on tank levels if you want to control things or sound an alarm.
The one big issue I had with this system is monitoring the black water tank. YOu have to use a "submersible" pressure sensor that goes in from the top of the tank and hangs near the bottom of the tank. The first sensor I got from Maretron would fairly quickly plug up and become inaccurate/unresponsive. I complained about it and--to their credit--they replaced the sensor, even though it was no longer under warranty. They said that the sensor they were using had this problem of plugging up and that the newer design was more robust and less prone to that problem. We'll see. It's been reliable so far.
3. In the course of fiddling/fighting with the plugged-up submersible sensor, I also acquired one of Maretron's "ultrasonic" sensors that sounds fairly similar (but perhaps a different technology) than the one you've been describing from Safiery. The ultrasonic sensor does require a hole in the tank--it can't shoot through a fiberglass tank. It connects directly to NMEA 2000--it doesn't need to go through a FPM100 module. It's sitting on my shelf as a "backup" in the event that I have trouble with the newer submersible sensor.
So......with my long-winded explanation, I'm interested in that Safriery solution--if only because I'm always interested in new solutions. I noticed that in the manual there's a comparison to ultrasonic sensors (page 7 and 8). I'm completely satisfied with the Maretron pressure sensors for all the tanks except the Black Water tank--and I *may* be satisfied with the new black water sensor......time will tell.
I'll be curious to hear about your experience with battery life. I also don't have a Cerbo (I have a Color Control GX, and I guess there's an external module I could add that would support that tank sensor). I would have preferred that they offer a direct N2K connected version, like the Maretron one (and then you probably also wouldn't have to have a battery), but I do recognize that the Bluetooth/battery combination eliminates the wiring hassles.
Anyway......I just thought I'd throw in my experience with tank level sensing. It's been quite a road since we took delivery of our boat 15+ years ago.....
Mark Tilden
Selene 60 "Koinonia"