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post #1 of 16 Old 05-05-2019 Thread Starter
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Bilge pump overboard discharge

Just wondering if anyone has tied in their bilge pump and deck drains into the engine exhaust discharge? I know of a couple of cases where it has been done to clean up a lot of thru hulls and keep water stains off the hull. Has anyone done it and if so could you provide some details. Obviously you don't want the engine discharge water going back to the bilge but the idea does have some merit provided it can be done safely.

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Re: Bilge pump overboard discharge

Another concern would be backfilling the exhaust, under certain heeling and pitching conditions. Backfilling the exhaust could allow water into the cylinders. Dedicated makes more sense to me.


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Re: Bilge pump overboard discharge

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Another concern would be backfilling the exhaust, under certain heeling and pitching conditions. Backfilling the exhaust could allow water into the cylinders. Dedicated makes more sense to me.
That makes no sense... If the engine exhaust is not back filling as you write... why would adding a Y and bilge water cause back filling?

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Re: Bilge pump overboard discharge

Much would depend on the angle of the plumbing .Does the engine exhaust runs good downhill from high point Well above wl. Bilge T'd in as close to thru hull as possible so you don't fill the hull with fumes. As I am big proponent of shut off valve at the transom to prevent engine flooding in some sailing conditions I wonder where the bilge pump would put it!!
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Re: Bilge pump overboard discharge

When you are done doing that I have a wheel that needs re inventing. all that work to eliminate one small above the waterline fitting?
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Re: Bilge pump overboard discharge

Makes no sense to me....I know no one whose boat is set up this way

Engine discharge comes from the raw water pump....now you want to connect the bilge pump into that. Suppose the engine is already running...arenít you giving the engine water a second outlet into the bilge as well as the normal discharge thru Hull. Also suppose both are running at the same time...( bildge and engine pump) . Which one wins getting its water discharged through the same opening.


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Re: Bilge pump overboard discharge

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Originally Posted by SanderO View Post
That makes no sense... If the engine exhaust is not back filling as you write... why would adding a Y and bilge water cause back filling?
You meant to say that you canít make sense of it. It does make sense.

When the engine is running and pumping water, there is positive pressure pushing the raw water out the exhaust. Havenít you ever heard of flooding an engine with raw water, if you crank too long and she doesnít start? The raw water can back up the exhaust in some engine geometries.

The OPs idea would be putting water into the exhaust at some point downstream, which I presume they would be wise enough to consider a spot that drains by gravity. I was trying to point out that whatís downhill at the slip isnít always downhill. If the bilge pump is evacuating water, while underway without the engine running, Iím not sure Iíd be convinced where it was going.
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Re: Bilge pump overboard discharge

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Originally Posted by Minnewaska View Post
You meant to say that you canít make sense of it. It does make sense.

When the engine is running and pumping water, there is positive pressure pushing the raw water out the exhaust. Havenít you ever heard of flooding an engine with raw water, if you crank too long and she doesnít start? The raw water can back up the exhaust in some engine geometries.

The OPs idea would be putting water into the exhaust at some point downstream, which I presume they would be wise enough to consider a spot that drains by gravity. I was trying to point out that whatís downhill at the slip isnít always downhill. If the bilge pump is evacuating water, while underway without the engine running, Iím not sure Iíd be convinced where it was going.
It depends on the geometry of course. I assumed the engine exhaust loops up well above the water line even if heeled.... my does. Bilge hose should as well... mine does.

I was unaware of sucking water in by cranking the engine. Learn something new every day!
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Re: Bilge pump overboard discharge

Each bilge pump hose exit needs to have its own thru hull. Any future survey will look for this.
While not all of the requirements found in a survey might seem equally applicable in the Real World, this is one that Does.

If you ever get involved in a potential sinking situation, you Will want All of the dewatering devices to work right on the first try. (!)
(I have been a "first responder" to a near sinking of a large sailboat and know that it takes everything on the boat and an additional gasoline pump on the dock to completely reverse the down flooding...)

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Re: Bilge pump overboard discharge

When a motor floods from cranking it over, I thought it was because the impeller is pushing water in but there is no exhaust force to get rid of it.
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