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Old 21-06-2018, 21:20   #1
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Corrugated hose or smooth for bilge pumps?

I read something recently that bilge pumps should only use smooth hoses and not corrugated ones. Smooth hoses supposedly can move more water and corrugated ones are less efficient.

It turns out that I am replacing all my bilge pumps and found that my bilge hoses are all corrugated. Should I eat the expense of replacing all these hoses?

The previous owner also had added flap valves on the bilge hoses. The water can go out but not come back. The outlets are all above the water line. Are these flap valves a good idea? Or will they come back to bite me in the future?
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Old 21-06-2018, 21:28   #2
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Re: Corrugated hose or smooth for bilge pumps?

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Originally Posted by Bigjim View Post
I read something recently that bilge pumps should only use smooth hoses and not corrugated ones. Smooth hoses supposedly can move more water and corrugated ones are less efficient.

It turns out that I am replacing all my bilge pumps and found that my bilge hoses are all corrugated. Should I eat the expense of replacing all these hoses?

The previous owner also had added flap valves on the bilge hoses. The water can go out but not come back. The outlets are all above the water line. Are these flap valves a good idea? Or will they come back to bite me in the future?

Yes, corrugated hose reduces flow. The only advantage is that it is cheap.


Check valves (flappers) on bilge pump hoses present two hazards.

  • They can catch debris.
  • They hold water in freezing weather, allowing the hoses to freeze between cycles and the boat to sink (if the hose drains back to the bilge, it's OK, because the bilge does not freeze in the water).
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Old 21-06-2018, 22:10   #3
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Re: Corrugated hose or smooth for bilge pumps?

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Originally Posted by Bigjim View Post
I read something recently that bilge pumps should only use smooth hoses and not corrugated ones. Smooth hoses supposedly can move more water and corrugated ones are less efficient.

It turns out that I am replacing all my bilge pumps and found that my bilge hoses are all corrugated. Should I eat the expense of replacing all these hoses?

The previous owner also had added flap valves on the bilge hoses. The water can go out but not come back. The outlets are all above the water line. Are these flap valves a good idea? Or will they come back to bite me in the future?
First, internally corrugated hose can have a HUGE impact on the amount of water flow. Depends a bit on the pump curve, but good practice is to use smooth bore hose. Note that some hose that is smooth on the inside is corrugated on the outside. Those are fine.

Flaps are a crutch. You are better off looping the hose as high above the waterline as practical inside the boat. Flaps reduce flow, and cause other problems. Flaps are better than using check valves in a bilge pump outlet, but not by much. Depending on the geometry, you might need some type of syphon break.
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Old 22-06-2018, 10:27   #4
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Re: Corrugated hose or smooth for bilge pumps?

The outlets are above the waterline. Obviously, this could change if the boat takes on lots of water. But under normal circumstances the ports are a foot above the water.
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Old 22-06-2018, 11:23   #5
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Re: Corrugated hose or smooth for bilge pumps?

The corrugated hoses for bilge pumps that I've seen are smooth on the inside. The corrugations keep the hose from being easily kinked and/or crunched reducing the volume of the hose. Nothing will decrease flow more than having a heavy object flatten it or a kink.
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Old 22-06-2018, 11:29   #6
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Re: Corrugated hose or smooth for bilge pumps?

When I bought my boat it had 3 bilge pumps. 2 of them shared an exit hose. there was a bronze flap type check valve near the Y in the hose. It was stuck in such a position that one pump was useless and the other nearly so. The third pump had a check valve that was also stuck. I now have 4 bilge pumps each with a dedicated smooth bore hose, antiphon loops and no check valves.
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Old 22-06-2018, 11:46   #7
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Re: Corrugated hose or smooth for bilge pumps?

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The outlets are above the waterline. Obviously, this could change if the boat takes on lots of water. But under normal circumstances the ports are a foot above the water.
A foot above the water is a good start, but if the hose does not loop higher than that inside the hull, every time a wave rides past that hole water will flow down into the bilge.

Assuming you sail places where the waves are higher than 1 foot....

This is really basic marine plumbing. Water likes to flow downhill, and not uphill. Always force water that is trying to come into the boat to flow uphill. Gravity is far more reliable than any check valve or flap will ever be.
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Old 23-06-2018, 09:27   #8
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Re: Corrugated hose or smooth for bilge pumps?

I assume that when heeled the outlet is below the waterline.
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Old 23-06-2018, 09:54   #9
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Re: Corrugated hose or smooth for bilge pumps?

I have had failures of the cheap corrugated hose. I heard the pump come on then water pouring into the bilge! A good look found a crack with no obvious cause. Now I've replaced all with thick wall smooth pvc
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Old 23-06-2018, 14:33   #10
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Re: Corrugated hose or smooth for bilge pumps?

Any recommendations as to which type or brand of smooth bore tubing one should use?
I recently replaced a bilge pump discharge tube using the cheapest corrugated tube at West Marine but am having second thoughts. I intend to add a second pump as backup so I could at least have one with the best line.
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Old 23-06-2018, 14:39   #11
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Re: Corrugated hose or smooth for bilge pumps?

I use non-toxic PVC internally reinforced with polyester mesh, for all bilge outlets, and I vent them above the waterline through siphon breakers. I do NOT use flap valves or any spring-loaded valves. They just add unnecessary resistance--far more than the foot or two extra lift for the efficient use of siphon breakers.

I also add swimming pool salt to the bilges, a good idea on any wooden vessel but has advantages in fibreglass too. Nor recommended for steel boats however! The salt stops rot and pickles any timber. Cockroaches dislike it. It stops bilge water going rotten to some extent--salt is a good preservative--and it stops your bilge water freezing.
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Old 23-06-2018, 15:02   #12
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Re: Corrugated hose or smooth for bilge pumps?

seem several check valves that were stuck, and or installed incorrect, I do not use a check valve in my boat
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Old 23-06-2018, 15:52   #13
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Re: Corrugated hose or smooth for bilge pumps?

There does seem to be a lot of hostility towards check valves here. There are good reasons for having them in a bilge pump system, especially for maintaining prime. I have two 1-1/2" manual diaphragm bilge pumps, each with its own pickup which includes a foot valve. The foot valve is a joker valve, the same as in the output of the manual bilge pumps and just as reliable. My cockpit pump is 6'-7' above the pickup, so takes some doing to create enough vacuum to draw the water up to the pump initially; having it primed is an advantage. Also, after pumping and without the foot valve the hose empties back into the bilge, undoing some work. Presumably the electric pump(s) is turned off, or otherwise it will be restarted by the rise in bilge level at the sensor. My electric pumps are submersible, so I have a valve right after the output - otherwise the contents of the hose from about 8' up drains back into the bilge and restarts the pump causing unnecessary cycling.

Most boats probably don't have the high lift that I do, or even the large hoses I use with the main electric pump, so back-draining and loss of prime are less of an issue. YMMV - I just note that blanket condemnations are often not appropriate.

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Old 23-06-2018, 16:26   #14
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Re: Corrugated hose or smooth for bilge pumps?

I also had 3 check valves. All frozen. Now high loops up underneath the cockpit seats with exit over 1 foot above the waterline.
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Old 23-06-2018, 17:40   #15
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Re: Corrugated hose or smooth for bilge pumps?

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I also had 3 check valves. All frozen. Now high loops up underneath the cockpit seats with exit over 1 foot above the waterline.
All check valves are not the same. What is the design of your frozen ones?


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