bilge pump routing

[osprey877]

My bilge pump outlet hose connects by Y joint to the sink drain and then drains directly below through a seacock (there is an anti siphon loop before it gets to the Y joint). The sink drain seacock is 2" dia and is about 2 feet below waterline. The bilge pump hose is 1.5 inches diameter. My question is whether or not there is any danger of the pump filling up the sink (and then overflowing back into the boat) or will it always be easier for the water to go out through the seacock rather c than up to the sink? Calder seems to say connecting to the sink drain is common to avoid long hose runs, and he doesn't mention any risks associated with this practice.
I also wonder if I am losing pump pressure by having the open sink drain acting as an air vent in the system. If the hose discharged directly to the seacock it would be a closed system other than the anti siphon valve thatcclosea once the pump starts. Or is this no different than discharging to a throughull that is above the waterline and thus "open" all the time.
I'm sure its a simple "physics of plumbing" issue but I can't figure it out! Thanks

[tkeithlu]

While I prefer bilge pumps to discharge above the waterline (my boat has only two below the waterline seacocks, and one stays closed), the only problem I can see is if there is blockage between the Y and the seacock. That could happen if 1) greasy gunk from the galley sink builds up, and 2) you forget to open the seacock (!). Bilge pumps normally operate at very low pressure, and are centrifugal in any case, so you're not likely to cause a geyser in the galley.

[osprey877]

Thanks. What about the pressure issue? Am I losing pressure with an open vented pump?

[Lepke]

As tkeithlu said, bilge pumps are low pressure. If you put your pump in a bucket of water and point the hose up, you will get a few inches of bubbling water like an old fashioned water fountain.
The pump in your system will move some water up the sink hose until the weight of the water offsets the pressure the pump creates. Then the flow goes out the thru hull. Flowing water seeks the path of least resistance.
That said, having salvaged and repaired many large boats, I prefer to have bilge pumps on their own system and thru hull, a proper vented loop, and no restricting check valves. Plumbing out of sight tends to get no routine maintenance. Thru hulls below the water line, open but rarely used, can get blocking marine growth.

[zboss]

I've read that Fatty Goodlander routes a bilge pump into the cockpit and then it drains through the scuppers. This way, he is always aware when the bilge pump is running!

[steamgoat]

My small auto pump also exits in the cockpit. Easy to see if I had a leak ! The large electric and manual pumps exit well above the waterline,no valves involved.

[zboss]

Originally Posted by steamgoat

My small auto pump also exits in the cockpit. Easy to see if I had a leak ! The large electric and manual pumps exit well above the waterline,no valves involved.

It really is a brilliant idea. I'm going to do the same. I'll have to explain to the broker why it set up as such. Also, I'll probably hear no end of it from people who believe that ABYC is the letter of the law.

[robwilk37]

thought i was the only one with bilge routed to the cockpit. but then again i have a visceral fear of thru-hulls and would never bury one out of sight.

[denverd0n]

Originally Posted by steamgoat

My small auto pump also exits in the cockpit. Easy to see if I had a leak ! The large electric and manual pumps exit well above the waterline,no valves involved.

This seems to me like a good way to do it. You want your main, "save the boat," bilge pumps to have their own outlet, above the water line, and without any check valves. The smaller, "keep the bilge dry," pump can empty into the cockpit so you can see how often it is running and how much water it is pumping.

I wouldn't want my main pumps to empty into the cockpit unless I had an open transom, or REALLY BIG scuppers!