Jump to content

2nd Automatic Bilge vs. Constant Power to Existing Float Switch

Recommended Posts

Hi All, new owner of a 2003 183SS.  Our boat stays in the water at our dock for the season and currently the bilge float switch is wired through the master; no power to the pump or float switch w/ the battery master off.   The pump will operate automatically via the float w/ the master on as well as with the helm switch.  I want an automatic bilge pump powered at all times.

What are the experts' thoughts and experiences on the two options:

1) Add a second automatic pump tee'd into the existing hose w/ backflow valve (w/ appropriate fuse, etc.).    Plusses are redundancy, not cutting into the existing harness, etc.   Concerns here are the added complexity of the tee and valves as well as mounting the second pump. 

2) Wire the existing float switch to the battery (add fuse, etc.).  Plusses are no backflow valve, tee, not mounting second pump.  Concerns are cutting into the existing harness.

I will be using a larger group 27 AGM battery either way.  I have a lot of classic auto and airplane experience and understand good wiring practices, etc., but am new to the boat environment. 

One other question; Can I mount a second pump by carefully drilling and screwing (stainless fastener, proper sealant) the mount to the stringers under the engine?

Thanks all, Merry Christmas and Happy Holidays.



Link to post
Share on other sites


If it was me, I would add a constant hot wire to the pump. This would do 2 things, If you left the helm switch on to the pump. By shutting the battery switch the pump would than shut off too. Also with the battery switch off, if the float switch came up the pump would turn on. I would add a 2nd (even connecting it to a 2nd battery) pump total independent on the 1st. pump. Don't forget to fuse and hot wires you add.

By teeing of the first pump, it may not be able to handle the extra water flow. It most likely was not rated for that.  

Yes, you can mount it under the engine. As long as you use the right length screws and say 3M's 4000 sealant or its equal.   


Link to post
Share on other sites

Remember a long rain can cause batteries to run down TOO low to start the engines.  Happens. On my bigger boats. Only........1............of the batteries can be run too low by a big rain.  You do not need to put the second pump in a difficult place or position. It is a SPARE / AUX. pump tied into the battery system.  ONLY controlled by a switch in the engine room . Put it in a easy place to reach.  Some  boats have a problem. The electric for the raising of the engine hatch is tied to the same battery as the pump.  Dead battery ?   No hatch opening.  Figure out how you can survive a dead pump battery easily. I would like you to install a second battery,  pump, float switch & fuse the 2nd pump to the second battery.

Never share 1 pump circuit parts with another. Risk is 1 circuit can kill both batteries and or float contacts.

Link to post
Share on other sites

Thanks all, debating the second battery project.  Not a lot of space to add the second (in front of trim pump?) and a fair amount of addt'l weight at the stern.  We are at the place most weekends so the boat isn't unattended for long periods, but the 2nd battery is probably the ideal situation.  

Link to post
Share on other sites

If possible you can mount the 2nd battery anywhere there is room for a totally enclosed battery. Some electrical knowledge is required to make sure the 2nd battery wires can carry FULL alternator currents. If it gets run down also.

I carry heavy duty 20' battery jumper cables on all the bigger boats. You can simply jumper the batteries to start a engine.

You may need a charging ...isolation diode...... to prevent both batteries from draining each other thru the alternator charging  leads.

Link to post
Share on other sites

Thanks again.

I am installing a second pump tee"d into the existing bilge hose w/ backflow valves.   I picked up a Rule automatic pump locally, but when I opened it up and read the documentation it indicated that it senses water by running a few seconds every ~2.5 minutes and draws ~.2ah/day without actually pumping.   I am not sure I want to use that style of pump so I am looking for a float or other sensing design.  Probably a conventional Rule automatic or Whale.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...