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Old 26-07-2011, 07:55   #1
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Bilge Pump Discharge at Waterline

Hi All -

The boat I purchased about 5 months ago has the bilge discharge positioned about 3 or 4" above the flat water line - obviously, it's well below the heeled water line.

I see no signs that this was not the original setup, or that there was ever accommodation for a vented loop or other siphon break. When I bought the boat it did not have a check valve. I don't think the bilge has a check valve, because when I turn it off, the water column that hasn't been discharged flows back into the bilge pump.

The boat has been sailed often and hard - what am I missing in this setup that has kept it from sinking when heeled?
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Old 26-07-2011, 08:46   #2
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Re: Bilge Pump Discharge at Waterline

I'll guess that water flowing past the bilge outlet is moving at a high relative velocity. Bernoulli's principal indicates that fluids moving at a higher velocity are at a lower pressure (conservation of energy), so the water doesn't flow in (much).
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Old 26-07-2011, 08:52   #3
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Re: Bilge Pump Discharge at Waterline

Interesting - would that be considered a basis for design of bilge system 30 years ago?
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Old 26-07-2011, 08:56   #4
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Re: Bilge Pump Discharge at Waterline

I have a similar setup on my compac . Makes me nervous . I would put a big loop in the bilge hose if I were you. I have had water come in when the little boat had a knock down .
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Old 26-07-2011, 08:59   #5
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Re: Bilge Pump Discharge at Waterline

It sounds like a vented loop would be a good idea. If you can't put in a vented loop, a lot of people do use check valves but it's not as good a solution. It doesn't sound like it's really been a problem. I like allanpeda's theory. You won't heel unless you're moving. Heck, the low pressure might even suck water out of the bilge!
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Old 26-07-2011, 09:00   #6
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Re: Bilge Pump Discharge at Waterline

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Originally Posted by sandycohen View Post
Interesting - would that be considered a basis for design of bilge system 30 years ago?
Hey, I'm just riffing. Bernoulli is old school (18th century) physics, but empirically people would observe as much. Or maybe a prior owner removed the check valve / loop.
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Old 26-07-2011, 09:05   #7
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Re: Bilge Pump Discharge at Waterline

both my bilge pumps in my formosa are similar in set up as the description you gave. my hoses from pump to exit loop up near the deck--NO vent. is perfect-- does not back flow, even when rail is in seas.
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Old 26-07-2011, 09:13   #8
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Re: Bilge Pump Discharge at Waterline

Zeehag - it does not sound like yours exit close to the water line (exit loop up near deck). If the exit is always above the waterline, at all heels, I don't see what a loop or vent would do.

All - I don't have access to easily add a loop above the max waterline, but I can add a loop that goes above the current high point. Is this better than nothing, or is there no reason to have a loop that can be below waterline? Plus it adds head pressure.
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Old 26-07-2011, 09:16   #9
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Re: Bilge Pump Discharge at Waterline

Quote:
Originally Posted by sandycohen View Post
Zeehag - it does not sound like yours exit close to the water line (exit loop up near deck). If the exit is always above the waterline, at all heels, I don't see what a loop or vent would do.

All - I don't have access to easily add a loop above the max waterline, but I can add a loop that goes above the current high point. Is this better than nothing, or is there no reason to have a loop that can be below waterline? Plus it adds head pressure.
the EXIT is less that 1 ft from water line. the LOOP is made in the hose BEFORE it exits. both sides. i8 have 2 pumps and 2 hoses and 2 exits near the water line with 2 hoses looped up near the deck.
\in MOST boats i have sailed/owned/ had experience with the set up is without the loop in the bilge pump exit hose. doesnt make difference. water flows out, none comes in. must be a design flaw.....if it worries you, add more hose and make it make a loop at the deck level, as the skeereded previous owner of this boat went and did.
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Old 26-07-2011, 09:18   #10
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Re: Bilge Pump Discharge at Waterline

Sounds as though this is the type of issue that is not a likely problem. If you see water coming in from the bilge pump, then deal with it. If you really hate the setup, move the bilge outlet through hull to the stern and plug up the old one.

I'll bet you could find ten other things to fix first that are of greater concern.
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Old 26-07-2011, 09:18   #11
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Talking Re: Bilge Pump Discharge at Waterline

Quote:
Originally Posted by sandycohen View Post
Hi All -

The boat I purchased about 5 months ago has the bilge discharge positioned about 3 or 4" above the flat water line - obviously, it's well below the heeled water line.

I see no signs that this was not the original setup, or that there was ever accommodation for a vented loop or other siphon break. When I bought the boat it did not have a check valve. I don't think the bilge has a check valve, because when I turn it off, the water column that hasn't been discharged flows back into the bilge pump.

The boat has been sailed often and hard - what am I missing in this setup that has kept it from sinking when heeled?
If I were you, I would change this set up.

Let's say you go cruising... and wind up in Georgia.

Let's say (hypothetically) that you go up a creek to anchor for the night, and learn that the significant tidal range in that creek is MUCH greater then what you are used to.

Now, let's say that you sit in you dingy, watching your boat slowly lay ALL THE WAY over in her side....

... Now, you watch as the water comes back in.

You want that loop to be high enough that there is no way water can ingress through the discharge and fill the boat before she floats.

... hypothetically.

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Old 26-07-2011, 09:19   #12
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Re: Bilge Pump Discharge at Waterline

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Originally Posted by zeehag View Post
the EXIT is less that 1 ft from water line. the LOOP is made in the hose BEFORE it exits. both sides. i8 have 2 pumps and 2 hoses and 2 exits near the water line with 2 hoses looped up near the deck.
I like that setup. This fall I want to add a second smaller bilge pump with a lower float to do most of the day to day drainage.
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Old 26-07-2011, 09:20   #13
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Re: Bilge Pump Discharge at Waterline

Wow - All we hear Nigel Calder and his legions say is that vented loop bilge pumps are the only way to not sink a boat most of the time.

I added a check valve - I know it's not the best, but it seems better than nothing.

Although one could make the argument the boat stayed afloat for 30 years. I am now putting a device in that potentially could block the EXIT of water should the bilge actually have a demand.
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Old 26-07-2011, 09:20   #14
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Re: Bilge Pump Discharge at Waterline

There is a valve there, no? If you get into a wacky spot, like shoaling, close it. You have plugs right?
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Old 26-07-2011, 09:23   #15
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Re: Bilge Pump Discharge at Waterline

Allanpeda - Plugs yes, valve no.

I am a bit nervous about disconnecting the hose at the through-hull that perhaps hasn't been touched in many years, and finding things that gall or stick or don't fit back together while trying to add a valve.
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