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Old 27-03-2014, 14:22   #31
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Re: My crash pump idea

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Originally Posted by cal40john View Post
Head is determined from inlet to outlet. The lower the outlet the less head and the faster a centrifugal pump pumps. I forget the term but there is another head which is how high the pump can lift water with none in the downhill part of the hose. This determines how high the top of the loop can be...
John--I'm not clear on your conclusion, here.

High on the hull, in the size boats we're dealing with, will be a few feet above the normal waterline. When you start the crash pump you don't want its outlet submerged, creating excess back-pressure and another path for water ingress if that pump fails.
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Old 27-03-2014, 15:33   #32
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Re: My crash pump idea

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A power boat with a couple 300hp cats maybe worth it, most sail boats under 100hp, not gonna help compared to a 8400 gal per hour electric pump.

Not so good, huh? Hopcar is right; I've got twin 450-hp diesels, and they each pull water through pretty quickly

-Chris
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Old 27-03-2014, 15:41   #33
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Re: My crash pump idea

You probably have a built on genny that could power a high volume electric pump and not mess with the engine intakes. It's been debated here much before and people love it or hate it. I'm an engine guy and don't care for it much. You could get all sorts of bronze valves, strainers and plumbing to do it really nice or spend the same money to do electric. 6 one way, half dozen the other.
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Old 28-03-2014, 04:32   #34
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Re: My crash pump idea

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Originally Posted by Horror Hotel View Post
You probably have a built on genny that could power a high volume electric pump and not mess with the engine intakes. It's been debated here much before and people love it or hate it. I'm an engine guy and don't care for it much. You could get all sorts of bronze valves, strainers and plumbing to do it really nice or spend the same money to do electric. 6 one way, half dozen the other.

Fair enough. In our case, I already had the valving in line... so we only have to attach a hose in the fitting and throw a lever, maybe 45 seconds worth of work. OTOH, if Dave's engine won't pull enough water fast enough, I see your point.

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Old 28-03-2014, 04:46   #35
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Re: My crash pump idea

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Whether you proceed or not...

Does your main engine (diesel?) have a water pump? If so, it's relatively easy to configure a T-function in your raw water inlet, so the engine can suck from outside or from your bilge. Groco sells relevant valves and strainers... probably other's do, too...

If that could work, it could be another way to solve it... or it may give you more leeway in design of an augmentation system...

-Chris
I see a couple of problems with this approach:

1. A sailboat engine of 100 hp or less will have a lower raw water flow rate than even normal bilge pumps. For crash pump duty, this is not nearly enough.

2. Main engine raw water pumps, nor the rest of the raw water system, are not designed to pass solids. Bilge water in a flooding emergency -- if you've ever witnessed a flooding emergency -- is full of all kinds of solids. Risk is high -- actually, it is highly probable -- that you will clog the pump and the raw water system and lose engine power, on top of your flooding emergency.

3. Most sailboat main engine installations are below the waterline, so the main engine will be one of the first things to get flooded in case of a flooding emergency. No main engine = no pumping. This same argument applies to engine-driven mechanical pumps.


That's why I think an AC powered electrical pump is better. It should be matched to whatever generating capacity you have. A Honda suitcase generator is a good power source in that it is likely to be high and dry and usable despite other systems failing (like the ship's batteries). But the pump needs to be matched to its capacity. Some pumps have soft-start capacitors.

I have a diesel generator which is mounted above the main engine so quite high above the waterline. It is started by a completely separate battery which is also above the waterline. I have not implemented this yet, but I plan at some point to install an outlet on the top of the generator where I can plug in an electrical trash pump. I can then disconnect the generator from the boat's electrical systems and just run the crash pump from it. The generator should not be flooded until the boat is practically sunk already. The generator is 6.5kW so will run any conceivable size trash pump.

Remember also that trash pumps need large diameter discharge hoses to deal with the solids which will have to be passed through. In my opinion it is unrealistic to permanently install such a thing. But for that there exist folding fire department type hoses which you can lead out the companionway and over the side. That means that your whole crash pump system will be portable, so in case you come to the aid of another boat with flooding, you can use it for that, too.
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Old 28-03-2014, 06:09   #36
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Re: My crash pump idea

I like everybody's idea here and have been planning to install a crash pump system with a semi-dedicated semi-permanent mount... Basically like a Fire extinguisher mount for the pump with the suction side just above the main bilge pumps... Hard hose with bayonet fitting to an above the waterline through hull... Extra soft hose for use in another location... AC wired straight to the genset AND mains panel...

Ready to to dewater in it's storage spot, but basically portable...
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Old 28-03-2014, 06:29   #37
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Re: My crash pump idea

Like others here i have many times experienced overload of a Honda 2000i. I have a device that draws 2100W for about 10 seconds when it first starts. It struggles for a few seconds and then gives up. I don't think it will manage the 23A startup, or even come close to it. That's approaching 150% of the rated output.......
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Old 28-03-2014, 13:52   #38
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Re: My crash pump idea

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Originally Posted by Terra Nova View Post
John--I'm not clear on your conclusion, here.

High on the hull, in the size boats we're dealing with, will be a few feet above the normal waterline. When you start the crash pump you don't want its outlet submerged, creating excess back-pressure and another path for water ingress if that pump fails.
Here's how I think this all works.

Pump head is the difference in height between the water surface level where the water is being pumped or height of the outlet opening of your pipe, and the water surface level above the pump (This is a correction of my earlier post).

My outlet is a little above the water, I could probably mount it 2 feet higher. This is 4 feet of head versus 6 feet. On my Rule 2000 that's about 200 GPH difference, or about 10%.

The cross sectional area, waterplane, of my boat increases from bottom to top. At normal loads my PPI is about 1200 lbs/inch. Let's say I sink the boat 2 inches, I've added 2400 lbs to my boat or about 300 gallons of water. My pump is about 3 feet below the floorboards and the waterline is maybe a foot above that so about 4 feet below original waterline. With all the lead and tanks down low it only takes 12 gallons to get to the bottom of my pump, then the volume of the keel increases. Total guess here but let's say 300 gallons gets me to the floorboards, or 3 feet of water above the pump. If my outlet was underwater to begin with, I've increased the head by 2 inches at the outlet and decreased it 3 feet at the inlet, so a net decrease in head of 2 feet 10 inches. Not an insignificant decrease in head. This website states the velocity effects are negligible, so I'm guessing that the outlet pumping into air versus water is a small effect.
http://www.pumpfundamentals.com/imag...l/tutorial.pdf

Those with no sump the head is probably small to begin with so the above isn't nearly as important. Also the OP was talking about a pump that probably has a much higher total head so the %age loss with a higher outlet will be much smaller than normal bilge pumps.

My hose loops up to just under the deck amidships and has a vent.
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Old 28-03-2014, 19:31   #39
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Re: My crash pump idea

Thank you, John. Though I believe the pump must be capable of the head pressure created by the height of the loop (it must lift the water that high, to start).

I would prefer to locate the crash pump such that its maximum head easily reached the high-on-hull outlet location (which will likely be much closer to the water during the emergency), and that it could keep the water below the floorboards. It is unnecessary that it completely dry the bilge sump, as there must be other pumps for that, once an emergency repair has been achieved to stop/slow inflow.
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Old 28-03-2014, 21:11   #40
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Re: My crash pump idea

If I was going to run a pump off a portable generator I wouldn't install it permanently because it would be much more likely to be used on someone else's boat than mine.
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Old 28-03-2014, 23:43   #41
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Re: My crash pump idea

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Originally Posted by Terra Nova View Post
Thank you, John. Though I believe the pump must be capable of the head pressure created by the height of the loop (it must lift the water that high, to start).

Yes, the top of the loop must be lower than the total head capability of the pump, but some people don't get that the down part of the loop affects pump performance in a good way.

I would prefer to locate the crash pump such that its maximum head easily reached the high-on-hull outlet location (which will likely be much closer to the water during the emergency), and that it could keep the water below the floorboards. It is unnecessary that it completely dry the bilge sump, as there must be other pumps for that, once an emergency repair has been achieved to stop/slow inflow.
The pump I described is conveniently sitting on top of the lead. The keel is around another 1.5 feet deeper in another place, so this isn't my dry the bilge pump. What I do like about the placement is that I have an alarm on this pump, it has never run except when I ran a garden hose into the boat to test it. Anyway the water is still well below anything but the keel when the alarm goes off giving me a chance to look for leaks while they are still above water.

The pump could be mounted higher and a switch to an alarm placed as low as you decided was to point that you wanted to look for leaks.

I don't really consider the Rule 2000 to be a true emergency pump, but it is the biggest I have so far. A real crash pump will be acquired before I take off.
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