Emergency dewatering: Multiple pumps, collapsible discharge hose? - SailNet Community
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Emergency dewatering: Multiple pumps, collapsible discharge hose?

I have a manual and two electrical bilge pumps. Both of the electrical pumps are smallish. Nothing wrong with the hand pump but if I should experience a half-way serious amount of water coming in, I would like to take care of stopping it rather than sitting on the cockpit bench manning the hand pump. So, I decided I need some emergency de-watering system. For reference, we are talking a 32' boat here.

I am looking mainly at Shurflo since Practical Sailor ranked them highest but I suppose the following applies to other brands, too. I could buy a hulking big centrifugal pump, like 4000GPH or so. I would not want to install it permanently but keep is easily accessible and only deploy it (=throw it in the water-filled bilge) in case of substantial water ingress that my regular pumps cannot handle.

But the price structure of bilge pumps is weird: the cost for a 1000GPH Shurflo is about $35.- while a 1500GPH costs about $100.- So my first question: Is there anything wrong with buying a few smaller pumps rather than a big one? It is cheaper and I get redundancy (aren't we sailors supposed to always have redundant systems?). So, I would buy 2 or 3 of these pumps, mount them on a board with electric cables attached to them. The other end of the cable will have large alligator clamps (like from a re-purposed car starter cable) ready to clip on a battery.

My second question: Is there anything wrong using collapsible discharge hose for the pump(s)? Like this (but there are many others, for pool use, agriculture etc) Watts 1-1/2 in. I.D. x 150 ft. PVC Flat Discharge Hose-RCDR - The Home Depot
Takes very little space compared to rigid hose, it is not too costly, and made exactly for, well, discharging water, which is what a bilge pump does. Each pump would have its hose permanently clamped to its outlet with a hose clamp, ready to go. To start emergency de-watering, I would only have to attach the alligator clips to the battery, put the board with the pumps in the water and throw the other end of the hoses over board.

Anything wrong with these two ideas?

Last edited by MastUndSchotbruch; 3 Weeks Ago at 10:38 PM. Reason: typos
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

The public thinks an airplane with four engines is twice as reliable as one with two engines, but the people who build 'em all point out that having twice as many engines (and parts) means you'll have four times as many failures, so less is more.

Of course bilge pumps fail more often than airplane engines.(G)

Robustly installed and plumbed with real-world discharge flows and all...in theory I'd vote for more small pumps because they all s**k anyway. When you buy them, buy a spare too, because you'll need it soon enough. Same for the float switches.

I think I'd rather see solid pipe or firm hose for the hoses though. Park a car on a fire hose, and the nice collapsible hose does collapse. (Then the firemen come and do wonderful things to the car.) Somehow, I wouldn't want to place bets on just what would fall on the collapsed hose, or get wedged or jammed onto it, and obstruct the flow.
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

A single big pump permanently installed in the bilge with proper hosing is the way to go. Even if everything works fine with a portable system, I would prefer to use my time for searching the reason for water ingress and trying to cover it instead of trying to find the pump, insert it in the water, work with the collapsable hose.
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

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A single big pump permanently installed in the bilge with proper hosing is the way to go. Even if everything works fine with a portable system, I would prefer to use my time for searching the reason for water ingress and trying to cover it instead of trying to find the pump, insert it in the water, work with the collapsable hose.
Agree. Lots of small diameter discharge hoses will cause a lot of 'head loss' due to friction and undue and detractive turbulence (ability to pump efficiently). BIG pump with BIG diameter hose is the best way.

Would be the same with a scared sinking sailor with the choice between many little buckets or one BIG bucket.
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

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Originally Posted by hellosailor View Post
The public thinks an airplane with four engines is twice as reliable as one with two engines, but the people who build 'em all point out that having twice as many engines (and parts) means you'll have four times as many failures, so less is more.

Of course bilge pumps fail more often than airplane engines.(G)

Robustly installed and plumbed with real-world discharge flows and all...in theory I'd vote for more small pumps because they all s**k anyway. When you buy them, buy a spare too, because you'll need it soon enough. Same for the float switches.

I think I'd rather see solid pipe or firm hose for the hoses though. Park a car on a fire hose, and the nice collapsible hose does collapse. (Then the firemen come and do wonderful things to the car.) Somehow, I wouldn't want to place bets on just what would fall on the collapsed hose, or get wedged or jammed onto it, and obstruct the flow.
Not only "the public" thinks that redundancy in the form of several independent engines is safer than relying on only two. This why aviation authorities require ETOPS ratings fro twin-engine aircraft.

I agree with you that a collapsible hose can, ehm, collapse. This is one of the reasons why I am asking this question. Maybe I need to do some experimentation to see how real this problem is on a boat (where few cars park
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

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A single big pump permanently installed in the bilge with proper hosing is the way to go. Even if everything works fine with a portable system, I would prefer to use my time for searching the reason for water ingress and trying to cover it instead of trying to find the pump, insert it in the water, work with the collapsable hose.
I can see the argument. It would, however, require a lot of modifications to the boat, including an additional hole (thruhull). And one would still rely on a single pump which may fail or get clogged. And all that at higher cost than multiple smaller pumps.
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

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Agree. Lots of small diameter discharge hoses will cause a lot of 'head loss' due to friction and undue and detractive turbulence (ability to pump efficiently). BIG pump with BIG diameter hose is the best way.

Would be the same with a scared sinking sailor with the choice between many little buckets or one BIG bucket.
That is the beauty of collapsible hose: it would NOT be "lots of small diameter discharge hoses" but "lots of LARGE diameter discharge hoses." They are compact enough to have a dedicated 1" 1/2 hose for each pump (or whatever the pumps want, the hose comes in many sizes).
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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

One large pump is also far more efficient than multiple small pumps. As for the collapsible hose, it adds a lot of friction to the system, again reducing pumping capacity. A single large pump with a large smooth hose will pump the most water/amp, which is typically the restriction faced, at least until you switch to trash gas pumps.

Keep in mind a few things...

My general recommendation is that the emergency pump should be sized to a failure of the worst case thru hull. Normally this is the engine thru-hull. The larger it is and the deeper it is the worse the situation can become quickly.

1) most bilge pumps are rated at zero head, and zero back flow preassure. Adding either can dramatically reduce pump volume.
2) a realistic installation will reduce pumping capacity by about 25% at the pump, then 1% for every foot of hose 2% for corrugated hose.

3) a 1" hole 12" below the water line will let in 1200 gallons/hr.
4) a 1.5" hole 12" below the waterline allows in 2500 gallons/hr

Personally I think electric bilge pumps are at best barely ok for this purpose. But they need to be massive, and probably wired directly to the alternator. A gas powered trash pump or PTO trash pump is far better.

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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

My first boat had a Rule bilge pump of around 450-500 GPH rating. I installed a 2nd pump rated at 1100 GPH and was feeling pretty good about my ability to get water out of the boat until one day cleaning the bilge I had the water hose (standard garden hose hooked to the marina fresh water system) flowing into the bilge and found that with BOTH pumps running I could just hold even, with either pump shut off the boat would fill.

My thoughts are unless you have one honking big pump you won't keep the boat afloat on the pump alone, you need to stop the ingress of water ASAP.

I keep leak stop supplies readily available, consider the pumps mostly useful for keeping the bilge dry and pretty - not so much for saving the boat.

If I had room for a big honking pump I would have one.

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Re: Emergency dewatering: Multiple pumps, collapsible discharge hose?

Flat hoses are only for manually deployed systems to put a collapsible hose in an automatic system just is not the thing to do. Now if you are on board always and it truly is a manual deployment then never mind. Basically a flat hose is a bad idea in a bilge system, just my opinion, unless its a big dewatering pump when the hose is impractical to stow in a rigid form.
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