Problems Solved: Diaphragm Bilge Pump Installation

9 Nov

I practiced what I preached, and finally installed a diaphragm bilge pump to improve the situation in my deep and creepy bilge. I wrote about this in my bilge pump opus, All About Bilge Pumps.

The principle at play here is that the bilge pump that keeps your bilge dry may not be the same bilge pump that keeps you from sinking: Centrifugal bilge pumps, the workhorses of the bilge pump world, can’t pump all the water out and always leave an inch or more behind. To really get the water level down you need a diaphragm pump attached to a strum box (intake strainer), and with this arrangement you can get it down to a quarter inch deep. Add a check valve and you can keep the water from flooding back down the hose after pumping. Aside from getting down there with a sponge, this is about the best you can do at keeping your bilges dry.

My bilge has the added complication of being deep and narrow, so narrow that a centrifugal can’t sit on the bottom. The centrifugal pump sat about 8 inches off the bottom, and this 8 inches usually contained a deadly emulsion of sea water, diesel, dead ship’s rat, and some substance that resembled dirty margarine when I sucked it into the shop vac. I also found all manner of hardware and tools that had been lurking down there. It’s hard to capture deep dark places in a photo, but here it is:
On the left is my new intake. On the right is my Aqualarm Smart Switch. The bilge is too deep to reach the bottom. If I lie on the floor of the engine room, with an engine mount stabbing me in the ribs, I can only reach to about a foot above the bottom, so it’s about 4 feet deep.

I installed the Johnson Viking Power 16, which I liked even more once I got it home and started futzing with it.
It turns out the pump and motor can be reoriented any which way, so I was able to make it fit in the best place with the hose connections on the most convenient side, and still keep the electric motor above the wet end of the pump. The plumbing connections were straightforward, with the outflow going overboard through my existing thru-hull, and about a 5-foot run straight down to the bottom of the bilge for the intake. Because of the odd, narrowing shape of my bilge, a standard strum box wouldn’t even fit, so I made this custom intake out of a bronze cap and an NPT to hose barb fitting:

I know this homemade intake strainer will be prone to clogging, but this is just the pump to keep my bilge dry, not the pump to keep my boat from sinking. For that purpose I’ve got a 3700 GPH centrifugal pump, which sits outside this sump.

While I was at it I figured I’d replace the hoses, both to this new diaphragm pump and to the manual pump, whose plumbing runs alongside it. There was some old fiberglass heat shield stuff wrapped around the two hoses, which I removed, to reveal this:

Both hoses had been badly melted, though not ruptured, by the heat. But wait, they weren’t near anything hot anymore, because I replaced the standpipe exhaust with a wet exhaust….in 1997. This means I sailed around the world for ten years with most of my bilge pumping happening through those pathetic, nearly completely occluded, melted hoses. Lucky I didn’t sink, and here I am giving other people advice about bilge pump systems. Ahem.

I also practiced what I preached with wiring, and ran the bilge wiring to a terminal strip inside a waterproof plastic box. Actually, I’d done this a few months ago as part of my engine room re-wiring job, so to add the diaphragm pump I just had to screw and unscrew well-labeled wires from the terminal strip, where everything will stay dry and electrically sound.

These Cantex plastic electrical boxes are about $5 at Home Depot, and I use them all over the place with appropriate watertight fittings. For marine use you’ll want to replace the screws that come with them with stainless, and a step drill bit is the right tool for drilling clean holes through plastic.

All this wiring leads to my Aqualarm bilge pump monitor console (on left side of panel), which, combined with the Aqualarm Smart Switch will get you to Bilge Pump Nirvana.

This article was syndicated from The Adventures of the Vessel Condesa


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