How Long Will Your Bilge Pump Last in Emergency?

[Steadman Uhlich]

I would like to pose a question that I think is good to consider. I hope you will answer based on the simple scenario outlined below, and post your answer in comments below, and please restrict your answer to the scenario and the conditions outlined in it. I have selected a single high volume bilge pump model (recommended by others in another thread in another CF Forum) and a single battery, to keep this scenario simple.
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The Emergency Scenario: Taking on Water: "Start the Bilge Pump!"

Assume your 35 foot boat is taking on water through a 2 inch hole, 3 feet below waterline. That hole puts 4,152 Gallons Per Hour (GPH) into the boat.

Assume your engine will not start, after several failed attempts. It is not usable in this emergency. You have no generator, no gas powered pumps, and you have no time to charge any batteries by using solar panels (which you don't have).

Remember this scenario condition: You only have ONE 12V battery available now to run your electric bilge pump.

You have only a single dedicated 12v Starting Battery (an ordinary wet cell that is a few years old, but still holds enough charge to start the engine when needed) that you have just been using to try to start the Diesel engine. You tried to start your engine about 8 times with no success. You are now concerned about discharging it further as you need it for your electric bilge pump. Your other "house" battery is not available or charged, due to previous discharge during the stormy night and then some short due to rising water in the bilge that rose over the batteries which were stored low in the boat.

You want to use a high volume bilge pump to dewater the boat ASAP, or as much as possible given these limits. The pump is a Rule Evacuator 4000GPH model pump, one you selected based on recommendations in a CF thread about high volume emergency bilge pumps. It is attached by alligator clips to the Start Battery, when needed, which is NOW. So, while your legs are wet as water sloshes over the cabin sole, you connect the alligator clips for the emergency bilge pump to the partially discharged engine start battery, and start pumping.

The pump has the following specs:
Rule Evacuator Pump 4000GPH uses 20 Amps, 1.6 HP, 12 volts.

How many Watts does that take? You found a formula and calculated:
I (Electrical) HP = 746 Watts. Therefore P(Watts)= 746 X 1.6 HP = 1193.6 Watts.

Big Question: How long do you think that pump will run (at rated speed, not a trickle) if you have only that one (start) battery available to use?.

Please post your guess below.
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Why is this scenario written as it is?

The scenario is written as it is to restrict the pump's use to a single battery that may be usable and movable to a higher position if needed during water rising over the sole.

And while some boats may have large and very heavy battery banks, I think it is best to consider what one would do in a case where you have the minimum available to you (i.e. A single battery), and, in this case a single electric pump.

What is the correct answer?
Because we don't know the actual charge of that battery and its condition, it is the big variable. So, there is no "correct answer" to this question above. Instead, I hope you will make an honest and sincere guess, based on your experience with boat batteries and the situation described in the scenario. More importantly, this post was made as a "challenge" for you to consider what you would do if you were faced with a similar scenario in real life.