Bilge Pump Reality

The ratings on bilge pumps are big, impressive numbers like 1000 gallons per hour.  But in reality, that's only 5 to 8 gallons a minute.  In other words, not as fast as bailing with a bucket.

Here's the calculation.  First divide the 1000 gallons per hour by 60 to go from hours to minutes. That's 1000/60 = 17 gallons per minute. 

But pump manufacturers rate their pumps with zero backpressure, meaning no uphill and no friction in the discharge hose.  By the time you factor in pumping 2 or 3 feet uphill plus the friction loss in the hose and elbows, you're down to about 50% of "rated" capacity.  Divide your 17 by 2 and you get 8.5 gallons per minute.  It's worse if you have that corrugated hose, which would take you down to about 5 gallons per minute.

This week's assignment is to add up the capacity of all your bilge pumps, and convert it to actual gallons per minute.  Assume each 1000 gallons per hour capacity actually works out to 5 or 8 gallons per minute.

Is that enough to save your boat if you have a serious leak?  No. And the answer isn't to add more pump capacity.   Just understand that bilge pumps are for clearing nuisance water, but not for saving your boat. 

But do keep a couple of square buckets aboard.  It's amazing how much water a couple of scared people can move.

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