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Old 02-07-2020, 04:53   #1
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2 pump Bilge Diagram; Asking for Technical Review

Hello, I hope everyone's sailing season is going well!

I recently purchased a 1979 Cape Dory 27 and it came with no electrical bilge pumps. I would like to rectify that situation with a well thought out bilge system and believe I have the electricals worked out.

The physical system is pretty basic right now. I plan to have a small nuisance pump at the bottom of the bilge. Physically higher than that by some amount will be a large crash pump. The thought is that the nuisance pump running is not really a big deal, but if the crash pump should start then I want me, any crew, the whole marina/anchorage/state to know the boat needs help.

Notes: I haven't calculated current at all points yet, or have distance runs, so wire gauge, switch/relay size + inrush current, etc. if noted are just guesses right now. Since I view the dewatering system as "mission critical" "must never fail" I've created the following schematic that I hope will fill the following design requirements.
  1. Allows for future expansion of the boat battery system. ("Any" amount of "ins" can be attached to the bus bar BUS1_2)
  2. Allows for future addition of pumps. ("Any" amount of "outs" can be attached to the bus bar BUS1_2)
  3. Allows all pumps to draw from all batteries until depletion, bypassing any low-voltage safety systems.
  4. System runs independent of any battery selector switch and is always ON and cannot turned OFF.
  5. System maintains battery independence.
  6. If any battery should become disabled or the links to that battery are severed, allow all pumps to draw from any remaining batteries until depletion. Each cable, fuse, and isolator (diode) from a battery to bus bar BUS1_2 should be appropriately sized to carry the full current of ALL pumps.
  7. Design will prevent the user from accidentally disabling any pump (no "OFF" selection).
  8. Control panel will visually display what mode the pumps are running in and that voltage is available. (ex. "Green LED is ON" indicates pump is in AUTO mode and that there IS voltage)
  9. Control panel silently indicates when small/nuisance pump is running (amber LED)
  10. Control panel visually and audibly indicates when pumps are running manually (red LED and alarm)
  11. When large crash pump is activated the user is notified visually and audibly (red LED, siren loud enough to alert sleeping crew, hopefully helpful neighbors, the next town over, etc.)
  12. Exterior high-decibel alarm for crash pump can be manually shut off. Circuit will automatically reset when the crash pump has stopped running, preventing future alarms from being accidentally disabled by the user.
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Old 02-07-2020, 09:08   #2
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Re: 2 pump Bilge Diagram; Asking for Technical Review

The idea of a nuisance water pump and a crash pump is excellent; I have installed many systems in just this way over the years.

I like the idea of supplying the vital bus from both batteries but that begs the question; why do you have two batteries. We have moved away from a two house battery setup and now try to have only one house bank.

The details in your schematic show that you understand electrical circuitry. i would therefore recommend that, if you must keep the two battery system, that you consider using a zero drop isolator (Sterling, Victron) in lieu of the two isolating diodes that will induce a voltage drop.

All that you have designed is available in a pre-packaged form from WaterWitch and others. Here is a link to the WaterWitch bilge alarm family for 1 to 6 bilges:

I use their electronic switches exclusively because they are bulletproof and some have a 5 year warranty while others have a 7 year warranty. This is unheard of for electronics in the marine industry.

I use toggle switches for control, not the more decorative Contura type. The Contura switches don't provide enough tactile feedback and can be too easily bumped out of the desired position.

Finally, the toggle switches that I use have two positions: AUTO and RUN. The RUN position is not momentary and there is no OFF position. I try to make this system operator error proof.

As always, it is your boat (IYB).
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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bilge, cal, pump

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