I beg you to critique my bilge pump outlet line-- it's siphoning

[niftyc]

I bought an unusual custom 63' steel trawler that is a fixer-upper. Since everything is custom, figuring out the systems is quite a puzzle.

A leak somewhere in the engine room had me stumped. I've been laying toilet paper traps and I even considered dye. Finally it dawned on me that the bilge pump itself is the source of the water. I thought it was a little bit of backflow from the outflow line but now I see it is far more water than can be in the outlet line itself.

I've read the threads on here about plumbing bilge pump outlets. I'm thinking this isn't the correct way to do it. Here's what I've got:



The outlet line is below the waterline (marked in image as a horizontal blue line) and I believe the line is siphoning. It looks like the line has a one-way valve that has failed and is now leaking, and it has no anti-siphon valve. The outlet is to starboard. The line leads to a Rule 3700 submersible pump that is wired to operate ONLY automatically via float switch. There is no other bilge pump in this compartment.

How should I fix this if I do not move the through-hull? (e.g. it remains below the waterline?) A mechanic wants me to just replace the ball valve.

P.S.
I really appreciate the generosity of people on this forum who volunteer to help new owners like me. I don't know anything about plumbing and I'm trying to learn fast.

[Sailmonkey]

I would put a siphon break at the top of the loop. Being steel you can just drill and tap the pipe to accept something like this.

https://marinesan.com/vacuum-breaker...MaAi1gEALw_wcB

[BillKny]

If your outlet is below the waterline it MUST have a siphon break. Otherwise it will... siphon the ocean back into the boat until the bilge pump fails and the boat sinks.

I hope the rest of the boat was built with better understanding of the ocean then your bilge pump system.

[Uncle Bob]

Originally Posted by Sailmonkey

I would put a siphon break at the top of the loop. Being steel you can just drill and tap the pipe to accept something like this.

https://marinesan.com/vacuum-breaker...MaAi1gEALw_wcB

Only if the loop is significantly above the waterline, if not you should make it so.

[Madehn]

It needs to 3 feet higher than waterline in my opinion. Your mechanic doesn’t have a clue if he thought a new ball valve was sufficient. Might be a good mechanic but I wouldn’t be taking any advice from him on anything but engines

[Cpt Mark]

Anti siphon valve is an easy fix. Get a bronze one. You must be able to take it apart and clean it. 3' above waterline, absolutely.

Better yet, next haulout remove the ball valve (which every through hull should have) and have that hole repaired. Move the exit point to above water.

[Cadence]

Not trying to be cute but i hope the rest of the "custom" is better than that. Move the discharge to above the waterline.

[zstine]

Originally Posted by Madehn

It needs to 3 feet higher than waterline in my opinion. Your mechanic doesn’t have a clue if he thought a new ball valve was sufficient. Might be a good mechanic but I wouldn’t be taking any advice from him on anything but engines

the siphon loop itself doesn't have to be 3 ft higher than waterline. he can run the air break in a tube up higher if needed, with the loop as is.. not ideal but.... but I agree that a siphon break is needed.

[Nord Sal]

Originally Posted by Cadence

Move the discharge to above the waterline.

I agree with this. Why put another hole below the waterline when you don't have to? Why depend on a siphon break when you don't have to?

[Hermia II]

Please start by studying thru-hull fittings, make sure they are made from bronze (not some kind of brass which is not uncommon), both the thru hull fitting and the valve. Hose up with a u-turn, as far as possible from the waterline, on which there is a siphon breaker (essentially a check valve letting air in but not water out when pumping) and down to the pump.
Sometimes the boat heals so that water reaches the gunwale, The U-turn should in this situation be above the water level. If not, the check valve on the pump-hose is needed but that is a compromise since crud will deposit on the check valve and it will start leaking, which is what you experience now.

[niftyc]

I really appreciate all the help.

Hermia, as far as I can tell there is no through hull fitting, it is a straight pipe welded to the hull with what looks to me to be a standard plumbing valve that you would find on a pipe placed a few inches in. I can try to take a better picture when I'm out at the boat.

Thanks to everyone for the advice, I wonder if anyone had thoughts about the pipe material. The metal pipe turns to a flexible line just out of view. I think they used the wrong kind of flex line. The bilge has had diesel in it at some point and it seems like diesel has dissolved the flex line -- black clumps are coming off it. Or anyhow that is my speculation as to what has happened. (There is no diesel in there now.)

[Hermia II]

If you use laminated PVC hose, it will do fine with contaminants like diesel as well. Don't keep the old flexible tubing if you don't trust it 100%

[deblen]

some sources and info. cheers/Len


https://www.defender.com/category.js...243574&path=-1


https://www.defender.com/category.js...574&id=2243585


https://marinehowto.com/

[Dockhead]

I wouldn't have galvanized steel piping or fittings on any boat used in salt water. It rots from the inside out and will fail at the worst possible moment, perhaps sinking your boat.

Plumb that with good plastic hose to an above the waterline through hull, with a loop far above the waterline and a syphon break.