Sunday, October 15, 2017

Installing a Tank Monitor

Need to Know

As mentioned in a recent post, our holding tank was unexpectedly full and we had to visit a pump out station rather than leave 25Gallons of Poop in the tank till our next trip. If we had a Tank Level Monitor we would have realized that we were heading (no pun intended) for a problem. 

Researching online for Tank Level monitors, I found a great article on Practical Sailor that identified several units and their recommendation was the SensaTank Marine 100 and I found one on Amazon for $174. It has 3 sensors, so we could use it to monitor the Holding tank, and the two fresh water tanks. Ordered on Tuesday, arrived on Thursday - thanks Prime.






The kit has 4 components.
  • Display Panel
  • Interface Module
  • 3 x 15' Wire Harness each with 4 Sensors
  • Cat 5e Cable that connects the Interface Module with the Display Panel
Setup is really simple: Install the Display Panel, connect it to the Interface Module with the Cat 5e Cable, Connect the 3 sensor harnesses to the Interface Module and attach the Sensors to the sides of the tanks.


Of course, running the wires from the Sensors to the Interface panel is going to be an issue, The interface panel could be placed anywhere, but it's probably best if it is near the boats Main Electrical Panel, that means some of the tank wire harnesses will need to be extended. Not a big problem, the directions state that can be done. The bigger problem is finding an unobstructed side of the tanks. The holding tank is very well secured in the boat (definitely don't want that tank moving about, particularly when it's full!). The Midships Fresh Water tank is also very secure, I don't think there is an open side on that tank at all. The Aft Fresh Water tank should be easy.

Installing the Display Panel

The Display Panel has no moving parts (except an adjustable potentiometer on the back for varying the readings on an LPG tank but we're not using that option.)

It requires a flat surface 5.5" by 3.5" and a cutout of 4.5" x 2.25". I intend to install it at the Nav Station along with the existing Air Conditioning Control Panel.

It has to be connected to 12v and I'll connect it to the 12v DC Panel Meter wiring with an inline 1amp fuse.



My Harbor Freight Vibro saw gets plenty of use at home and on the boat. Marked out the panel position so that it was level with the adjacent Air Conditioner controller and then cut into the woodwork.

Once the hole was made, easy to just screw the panel in place, run power lines to the -ve bus behind the electrical panel and connect the +ve to the Water Pressure Circuit breaker (that's the only 'water' relevant breaker).







Here's a pic of the Nav table (the bulkhead that houses the VHF, Stereo, Engine Hour meter, AC Controller, and now the Tank monitor panel, is an addition by a previous owner. It certainly gives plenty of room for the additional electronics.








Installing the Interface Module


This module has a self adhesive pad on the back, so it's just a case of choosing where to install it and sticking it to a flat surface. It needs a few inches of space in front of the module in order to be able to connect the cables.

I'll install close to the back of the Display Panel.

Note. the module has 2 Cat 5 connectors, the 2nd is for connecting an optional remote display, no need for that on a 34' boat.
The Sensor plugs are labeled Fresh, Grey, Black and a 4th for LPG.


Installing the Midships Tank Sensors

The pic shows the forward side of the midships tank and the glassed in bulkhead that helps keep the tank in place. There's about a 1" gap on the inboard side (left in the pic).

I was able to clean the tank side with a paper towel taped to a 16" metal rule and soaked with 91% isopropyl alcohol, did that a few times. Then taped a sensor to the end of the rule and guided it into position, once it touched the side of the tank it stuck! So just a push on the rule detached the tape from the sensor and twisting the rule 90ยบ I was able to use it as a lever and apply additional pressure to the sensor. It's definitely stuck in place. Repeated the process with the other 3 sensors. 

Ran the wire temporarily across the cabin and plugged it into the Interface module. Press the button and WooHoo, works.


Installing the Holding Tank Sensors

I used  my Vibro Saw to cut a 2" slot in the end panel that secures the holding tank in place. To protect the tank, really did not want to puncture the tank with the saw and have a poop leak! So I inserted my 16" metal rule between the aft end of the tank and the retaining bulkhead. It only took a few minutes to cut the slot. Turns out the bulkhead is glassed nearly all the way around except at the deeper part of the tank bottom so it does not need to be modified after the sensors are installed. Otherwise I'll attach a wooden plate over the slot to reinforce the end panel.
The sensors were easily adhered to the tank.


Then I temporarily connected the sensor wires to the Interface module to test the tank. Uh Oh! It shows the tank as being 3/4 full, but it's empty! Ok, perhaps we did not do a good pump out last week. So I opened the vent at the top of the tank and peered in (that's a first). With a flash light I could see the bottom of the tank below the vent, but very little else. The tank appeared to be almost totally empty, a small amount of sludge on the inboard side of the bottom of the tank. I could see an almost crystalline residue on the visible part of the tank bottom. Hmmmm!

Possible issues:

  • Sensors are bad (I should have tested them before sticking them to the tank)
  • There could be a 30 year old build up of crud (salt, poop, calcium) on the sides of the tank, similar to that which is visible on the tank bottom, that might interfere with the sensor operation.
  • The tank could be more than 10mm thick, a limit described on the SensaTank instructions.
I've sent an email to the manufacturers asking for advice, but I think the most likely issue is the build up on the tank sides, so I'm planning on adding an inspection port to the top of the tank and giving the tank a good clean. There has to be some pluses with that process, but it sounds like a crappy job. It can wait till the haul out in November.

Installing the Aft Tank Sensors

The aft tank is in the Aft locker and a pain, literally, to access. However, not too difficult.

Just empty the aft locker, remove the shelf that covers the rudder quadrant and then get into the locker. There's room for a couple of stowaways down there. 

The sensor wire will have to run to the port side then over along the back of the fuel tank, behind the bathroom cabinets through the hanging locker and into the Nav station area. Easy!








Pretty easy install. The pic shows the sensors applied to the back end of the Aft Water tank before I cut off the wire ties.

Using a cable fish rod, I ran it through the holes in the cabinet above the Nav Table aft into the Head and then aft into the void under the Port side Coaming and into the area behind the Engine Control Panel. I was able to attache the end of the sensor cable to the fish and pull it through into the head cabinet. The wire is only 15' long, so I had to butt join an extension to be able to reach the Interface Module. As I keep the electrical kit onboard, that was easy.

With the aft tank sensor attachment complete, I ran the wire from the midships tank aft to below the galley counter, then over to port above the hot water tank, down under the cabin sole into the are of the Holding tank, then ran both the holding tank and the midships tank wires up the port side near the main battery cables and behind the electrical panel into the area with the Interface module. Easy.

Testing the System

The Aft Water tank sensors are connected to the 'Fresh' tank connection on the Interface Module, the Midships to the 'Grey' tank connection and the Holding tank to the 'Black' tank connection. The Aft and Midships tanks are working fine, but the Holding tank is reading 3/4 full even though it's empty.
Talking to the C34 owners, I'm leaning towards the issue being a build up of crud on the inside face of the holding tank where the sensors are attached. But that will have to wait till I install a surface mount inspection plate in the top of the holding tank - a crappy job to say the least! Meanwhile we're trying a chemical clean of the tank, I don't hold much hope of that working, but it's cheap and easy, so worth a try.

Looks like we're going for a sail this week, probably Thursday or Friday, wooo hooo!

We really will see you on the water.

Paul