Pumps do not do what you think - Page 2 - SailNet Community
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post #11 of 22 Old 06-20-2013 Thread Starter
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Re: Pumps do not do what you think

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that was a great video!.
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I am hoping my setup would buy me some time. I have a 500GPH and a 2000GPH pump in the bilge along with a hand operated pump from the cockpit.
Probably not really. Based on my tests, you will be lucky to be getting 600 GPH total in REAL pumping ability from all of these.

1" hole is 2,400GPH coming in.

With your pumps running you still have 1,800GPH or 30 gallons per minute. Make a guess and say that's about 5-6 minutes before your cabin is underwater......


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post #12 of 22 Old 06-20-2013
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Re: Pumps do not do what you think

Two crew with two one gallon pails, with sufficient motivation and coordination would move 25 gallons per minute, 1500 gallons an hour....
...for a while.
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It's 5 o'clock somewhere:


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post #13 of 22 Old 06-20-2013
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Re: Pumps do not do what you think

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Originally Posted by vtsailguy View Post
So I did some real world tests and calculations on my pumps.

Four pumps will net me about 160GPH

A one inch hole lets in 2,400GPH

Nowhere near enough for even a relatively small hole. Basically all pumps are useful for is open windows and children's dribble?

I made a video, the math is at the end, can this be right?

That Sinking Feeling | Sailing With Kids
Out of curiosity, how long are your hose runs? Are there any back flow prevention valves on these hoses? Is the hose diameter sufficient throughout the run of the hose? How old are your pumps? How high do your pumps have to pump? Have you verified that the vanes of the pumps are clean?

Tim R.
Our Carina is for sale
1997 Caliber 40LRC

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post #14 of 22 Old 06-20-2013 Thread Starter
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Re: Pumps do not do what you think

The pumps are pretty new and the hoses are to spec. You should try the test yourself, you might be surprised!


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post #15 of 22 Old 06-21-2013
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Re: Pumps do not do what you think

I've always figured that 12V electric pumps are only going to buy me a little time to find/stop the leak unless it's just a small one. Any serious hole is going to sink the boat if it can't be plugged or slowed down.
Most boaters seem to be overly impressed with the "GPH" rating of their pumps without doing the math to find out what that equates to in the much more important "GPM", to say nothing of the friction losses and head.

John
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1988 Brewer 40 Pilothouse

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post #16 of 22 Old 06-21-2013
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Re: Pumps do not do what you think

This is not at all unusual for a centrifugal style bilge pump. I always figure on 1/3 or less of face value rating as installed.

Some things most are not aware of:

#1 These pumps are rated at the open bucket rate. This means a ZERO head rating.. This is a VERY DISHONEST way of selling a bilge pump to unsuspecting buyers..... I personally find this type of marketing disgusting at best. Almost as bad as companies selling "marine" tankless LPG fired water heaters that meet NONE of the safety standards. Caveat Emptor.......

#2 These pumps deal horribly with added head pressure and can pretty easily lose 50-75% or more of their rating as installed.

#3 These pumps are rated at charging voltages. This is NOT completely honest as most sailboats would not have the motor running when the bilge pumps was in use. All one needs to do is look at the amperage consumption to see how much the voltage can affect these pumps. A Rule 2000 will draw 12A at 13.6V and just 8.4A at 12.0V....... The current a pump draws is directly related to GPM/GPH volume

#4 Corrugated hose adds a LOT of head restriction.

#5 Check valves should not be used on the outlet of the pump because the pumps often don't have the oomph to overcome the standing water in the hose or the check valve sticks.

#6 Every elbow or turn adds more head restrictions.

#7 The height from bilge to siphon break creates even more head.

#8 Undersized wire can add yet more unwanted voltage drop to the pump causing even more reductions in output.

#9 Discharging below water, such as teeing into a sink drain, can also slow the pumps capacity...

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post #17 of 22 Old 06-21-2013
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Re: Pumps do not do what you think

I was wondering about the corrugated hoses. Thanks for the info, Maine.
This will help me in my upgrade plans.

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post #18 of 22 Old 06-21-2013
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Re: Pumps do not do what you think

This thread confirms step 1 of damage control during flooding into the ship: STOP THE LEAK!

You have to reduce the leakage to less than your dewatering capacity before all your reserve bouyancy is lost.

Nothing else can save your ship from sinking.
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post #19 of 22 Old 06-21-2013
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Re: Pumps do not do what you think

A pump is not there to "unhole" the boat. It is there to help empty the water out, while you are plugging the hole. There's a reason why serious dewatering pumps are driven by gasoline engines and resemble medium size gensets.
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post #20 of 22 Old 06-21-2013
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Re: Pumps do not do what you think

One of the best stock setups I have seen was the big Edson manual pump mounted at the foot of the companionway on a Santa Cruz 52. Slot in the sole section gave it away...
The broker told us that owners often referred to it as their "Oh My God" pump!
Gallon a stroke!
Handle was about 4' long.

You'd still have to have someone finding the leak and doing damage control, as others have pointed out.
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