Must I install a thru-hull for new bilge pump?

[Lou 14643]

I'm thinking of installing a new (never had on boat) automatic bilge pump. I currently have only a manual pump on my O'Day 272. Is it possible to "T" the new pump outlet into the manual pump line, using the same thru-hull, or must it have its own discharge point? If I can use a "T" does it cause loss of efficiency? Thanks very much!

 

[Ross]

I would use a "Y" any time you add a turn

you add the equivalent of length in the plumbing run. Also you must be certain the the water doesn't return through the manual pump.

 

[Lou 14643]

Ross, please elaborate

Do you mean a Y with a valve in it, or just a y-shaped connection?

 

[Ross]

Just a "Y" fitting. Adding ball valves to each leg

would isolate the two pumps. You will need a valve in the auto pump line if you use the manual pump as there are no check valves in the electric pump. If the through hull is not out in the open I would put in another and not fool around with valves.

 

[Lou 14643]

Thanks Ross. I was worried about...

the possibility of pumping back down the other side of the line, rather than overboard. I guess a second thru-hull makes most sense.

 

[Ross]

Less complicated and fewer pieces

I violate the rules and discharge my bilge pump into my cockpit drain. But then I justify it because my cockpit drains are straight flow to the stern, 2" pipes, one port and one starboard.

 

[Boat Babe]

speaking of bilge pumps.....

whenever I run my bilge pump, it pumps out all most all of the water (except the last 1/2"), then when it shuts off, the water in the tubing which goes to the transom runs back into the bilge, thereby never completely emptying it. Should there be a check valve in the line preventing the back flow? Thanks

 

[Ross]

I am not certain about bilge pumps but

I always put a check valve in sump pump lines in houses. Nancy calls our boat her little house on the water so I guess I would put a check valve in the bilge pump discharge.

 

[Lou 14643]

Don Casey recommends two pumps for this reason.

In This Old Boat, he talks about the problem with one large pump having too large a hose. A line large enough to handle the flow from a large pump will hold enough water when the pump clears the bilge that, even with anything other than a perfectly clean, unobstructed check valve, it will eventually flow back through to the bilge and cause the pump to cycle on and off. He suggests 1) the shortest hose run possible in order that the hose does not hold a very large volume of water, 2) a smaller pump located below the level of the large pump, just to keep the bilge completely dry, eliminating not just a nuisance, but also, and more importantly, the damaging effects of water on the hull lay-up that can cause blistering from water migrating through the resin from the inside of the boat.It was reading this section of his book this morning that got me thinking of the original question I posted on this thread.

 

[higgs]

If it were me

If I could easily fit a T to the existing pump - and install a check valve to to stop the auto pump from pumping into the manual set up, I would do that. If it was easier to put a thru hull above the water line for the new pump I cwould go that route. KISS. Do what is easier.

 

[Ross]

Lou, The only way I have ever gotten ALL

of the water out of the bilge is with a vacuum cleaner. The pumps can't get close enough to the bottom to get it all. I can get all but the last 1/4 inch with the pump. The rest just evaporates. I wish that when I had redone the bilge I had built in a true sump. That way I would be able to dry all but a 6 inch square.