Very Important ? Bilge Pump Discharge Vented Loops

[Tuxedo]

I’ve been having water mysteriously appear in the forward bilge whenever I went out fishing in sloppy seas for several years. I checked all thru-hulls, pumps, sinks, the bow thruster, and came up with nothing. Then, I started looking at the routing of the forward bilge pump and shower sump pump hoses, and thought they might be able to siphon water back into the bilge.

I installed vented loops in the lines, and, after a 1,400 mile trip to the Bahamas and back (more on that later), no water whatsoever in the forward bilge.

While in the Bahamas, I heard some dock scuttlebutt about an Albin 31 sinking a few years ago because water siphoned back into the forward bilge while some guys were fishing off the NE canyons. I can’t verify that, but I can verify that water can siphon into the forward bilge area of a 31, and probably other models, if they are not equipped with vented loops in the line.

You all might want to look at the way your forward bilge pump and shower sump pump discharge overboard and see if you need to install a vented loop in the line.

[jcollins]

Tom,
Water in the forward bilge is a popular thread around here. I have always had some water come back into the bilge when the pump shut off. I just assumed it was the water left in the hose.

Can you explain what you mean but vented loops? AND...a trip to the Bahamas? I really want to hear about that!

[Tuxedo]

Here is a vented loop, also known as an anti-siphon loop



And here's a link

http://www.boatersworld.com/product/356350199msk.htm

What I did was disconnect the bilge pump and shower pump hose at the waterline thru-hull, mount a vented loop as high as the hose would reach on the bulkhead aft the head, connect that hose to one side of the loop and add a length of hose from the other side of the loop to the thru-hull.

Regarding other discussions about water in the forward bilge, I discovered that my A/C drained into the bilge, so I plumbed it to the shower sump. Also, as others have suggested, I added a little pump down in the very bottom of the bilge, which I also ran to the shower sump. My forward bilge is absolutely dry.

Sorry I didn't participate in these discussions, but on-line access in the Abacos was difficult. I'll post a trip report after I wade through a month's worth of paperwork.

[DougSea]

Tom,
Water in the forward bilge is a popular thread around here. I have always had some water come back into the bilge when the pump shut off. I just assumed it was the water left in the hose.

Can you explain what you mean but vented loops? AND...a trip to the Bahamas? I really want to hear about that!

Here's a link to the catalog at West Marine with vented loops:

http://ecatalog.westmarine.com/full.asp?page=0501

Essentially a vented loop breaks a siphon when there's vacuum (as opposed to pressure) in a line. Especially on sailboats where the angle of heel when underway puts a discharge port under water you can get a siphon effect which sucks water from outside the boat back in. This is usually considered a bad thing!

I'm going to guess that the forward bilge pump outlet on the 31 might get covered by the bow wave when underway. If the pump ran and filled the line with water and then shut off it could then pull seawater into the forward bilge. If the line has a vented loop it would introduce air into the line when the pump shut off and prevent the siphon from forming. You also often see them on head discharge port since these are usually underwater and always have the potential to pull water back into the boat (and overflowing out of the head - really nice!)

They are good to have on any hose which runs to a pump (bilge, shower) that is mounted below the water line in the boat.

And yes, most of what you're seeing when your pump shuts off is the water that was left in the line.

Hope that helps.

[jcollins]

You also often see them on head discharge port since these are usually underwater and always have the potential to pull water back into the boat (and overflowing out of the head - really nice!)

Interesting. Last season my toilet had seawater in it once that I can remember. It was a rough day while we were fishing. I would think that boat builders would take care of this kind of stuff. The normal guy like me just doesn't know or think about it until there's a problem or sees a post like this. I'm glad I found this board. <smile>

[Denis]

Just a question, as with any drain going overboard, isn't it most important to just keep a part of the drain line above the water line at all times? If there was just a loop put in the line as high as possible, wouldn't that keep outside water out?

[DougSea]

Just a question, as with any drain going overboard, isn't it most important to just keep a part of the drain line above the water line at all times? If there was just a loop put in the line as high as possible, wouldn't that keep outside water out?

Not if the outlet is underwater.

If the outlet is underwater and the inboard side of the hose is lower than the outlet you have a potential problem. Once the pump shuts off you have a perfect siphon setup and water will flow backwards into the boat. (If you don't have a vented loop - also known as a siphon break - or a check valve)

Keeping a portion of the hose above the outlet (which IS above water) will keep the random wave that hits the side of the boat from running down the hose into the boat.

A couple of links:

http://www.boatus.com/goodoldboat/Marine_exhaust.asp

http://www.dnr.state.md.us/boating/pump ... stall.html

Couldn't find any good bilge pump specific diagrams but hope this all helps!