Another Mesmerizing Maintenance Mystery!

The other day, our macerator pump stopped macerating. (This is the thing that empties your waste tank.) If you can't empty your waste tank, you'll soon no longer have a working head (toilet). This is not a good situation to be in, obviously.

I wish we could say that the first thing we checked was the ground wire on the electrical panel and that it was loose and we tightened it and everything started working as it should…

But it didn't happen that way. 

It started innocently enough. We could hear the pump running, as always, but this time the tank level wasn't going down. We thought maybe it just needed a little longer, so we ran it for 15 minutes or so and still no joy. Since it was running but not pumping anything, our guess was that it was not getting primed. Usually, this happens because one of the one-way duck valves leading into or out of the pump is clogged.

Oh yay!

So Kevin climbed down into the lazarette (involving an intense set of yoga moves) to get into a position where he could begin to remove the raw sewage hoses from both ends of the macerator pump. Some serious contortionism is required to get into this position in the first place…add the need to use tools and avoid spilling raw sewage, and you've got yourself some drama right there! 

Kevin removed both duck valves, carried them topside, cleaned them completely and made sure they were working correctly. Oddly, they looked just fine. He then reinstalled the valves, hooked the raw sewage hoses back to the pump, flipped the switch to try it again.

Nothing.

Now the pump wouldn't even run. He figured he must have accidentally unplugged an electrical connection or something, so back down into the lazarette he went. He checked all the electrical connections, and then checked that power was being applied to the pump when it was turned on. Power, check! The volt meter said 14.2 volts…because we were under way. (Did we mention we were under way when all this was happening? Oh sorry, forgot that part.) So 14 volts is being applied to the motor but the motor is not running. Bad sign.

Next theory: Maybe we overheated the motor while running it for 15 minutes and it's got a thermal cutoff. Usually if a motor has a thermal cutoff, it resets itself automatically after it cools down. So we waited for half an hour. The motor is now cold. We try again.

Nothing.

Maybe we burned the motor up? Kevin read in some online boating forums that sometimes these motors can be fixed by cleaning the brushes, so Kevin went back down into the lazarette, removed the pump, then removed the motor from the pump to see if the motor itself worked when power was applied directly to it.

Nope. 

Okay, time to get serious. Next, he disassembled the entire pump and motor assembly, cleaned the commutator and brushes (see first photo, above), and oddly, everything looked fine. He reassembled the whole thing, and tried it again.

Nothing.

Looks like we must have ourselves a dead macerator pump. Once we arrived in Prince Rupert, we headed over to Sea-Sport Outboard Marina Service & Clothing, picked up a different kind of macerator pump (a Jabsco Self-Priming pump, because they didn't have our brand, a Whale Marine "Gulper"), then walked a few more blocks up to Saanich Heating & Plumbing to get a bunch of clamps and adaptors so we could plumb the new, different pump into the place of our existing pump, and returned to Airship to start the Pump Replacement Project.

Step 1: Attach the correct connector to the wires on the new pump.
Step 2: Plug it in.
Step 3: Flip the switch.

Nothing. Wait, what???

Step 4: Unplug it and check voltage at the connector. Yep, 12.8 volts.
Step 5: Plug it back in.

Nothing. Could the brand new pump be bad??

On a whim, we tried plugging the new pump into a completely different circuit (the one for the raw water washdown). We flipped the switch and the pump started right up.

At this point it gets really weird, because remember, our pump was running (just not pumping) before.

Just for kicks, we plugged the old pump into the new circuit, and guess what? The old pump worked fine too! Could we miraculously have developed a wiring problem, right when our pump was having a mechanical issue? 

We checked the voltage on the circuit when the pump was plugged in and the voltage showed almost zero. What this means in electrical terms is that the circuit is not completely broken, but somewhere in the wiring between the battery and the pump, something has high resistance. The most likely suspect would be one of those little in-line fuses, which could of course be hidden anywhere in the wiring of the boat. Kevin meticulously followed the wire from the batteries through the electrical panel, behind and underneath access panels, through the engine compartment, up to the switch that turns the macerator on and off. Then, he followed the wire all the way from there (through the entire boat) back to the lazarette.

Nothing.

He followed the positive wire everywhere he could find to follow it (checking the resistance with a multimeter), and it all looked fine. (He checked the positive wire because that's where any fuse, switch, or other thing that might have failed if the circuit overheated would be located.)

That only left two choices. Either he'd missed something in following the journey of the power wire through the entire boat, or…is there any way it could possibly be the ground wire??

Having something wrong with the ground wire is super unlikely, because it just runs from each device (the pump, in this case) straight to a big metal bar inside the electrical panel where all the ground wires from the entire boat are connected together.

Just on the "maybe we'll win the lottery" off-chance, he plugged the power wire from the pump, together with the ground wire from another circuit. The pump started right up.

Unbelievable.

That only left one thing to check. We opened up the DC electrical panel, found the big metal bar with about 52 wires running to it from every circuit on the boat, looked through all of them until we found that one that was labeled "macerator pump" and guess what?

The screw was loose.

We turned the screw half a turn to tighten it, went out and plugged everything back together, and the (old) pump worked perfectly. Not just perfectly, it ran about 4x faster than we'd ever heard it run before. So apparently, this screw had been loose for a long time and our pump was always just barely running. (Because of the loose screw, the voltage would be lower, so the pump wouldn't be getting as much power, or if things jiggled wrong, it would have no power at all.  On a boat, things jiggle!)

Now, two days later, after several more yoga sessions in the lazarette, a bunch more grunting with hose clamps and raw sewage lines, wiring, zip ties, and crimped connectors, everything is back together and working better than ever. 

At least this mystery was a solvable one!