Adding a Bilge Pump -- Question about Discharge Hose & Thru-Hull

[garry]

I'm buying a 1987 CAT 34 which has the driest bilge this side of the Mississippi, however, I believe in automatic bilge pumps and want to install one. I can install it, no problem, but I'm wondering if I should run a separate discharge hose to a new thru-hull or somehow connect into the existing discharge hose and/or thru-hull for the manual pump.  Do they make anti-siphon (anti-back-flow) valves for discharge hoses? That would make the junction easier and safer.  Whatcha think?

Any chance you can respond to me at gms@san.rr.com?

Thanks,

Garry

[Ted Pounds]

Garry,

The second bilge pump should have it's own outlet, ABOVE the waterline.  I think the best spot is next to the manual discharge, at the stern.  That's where mine is.  If the discharge is below the  water line you run the risk of siphoning back in.  Anti-siphon valves can fail.  If you connect to the manual pump line then one pump can end up pumping back into the bilge via the other.  The discharge line should have a loop that is higher than the discharge outlet.  An anti-siphon might be a good idea however. to get max output from the pump you need to make sure it doesn't restrict the flow.  A recent blurb in "Seaworthy" magazine advised against any sort of backflow or other valve.  Just a few thoughts...

[Ron Hill]

Gary : Ted is correct.  You want a separate hose for your added bilge pump. 
My electric pump discharges on the starboard side of the transom, about 4 inches higher than the large center manual bilge pump exit.
You never want to put an anti syphon valve in a bilge pump line.  It could get clogged or fail and not let the water flow thur it to the outside of the boat.!!

[Ken Juul]

My second electric bilge pump is plumbed through the Air conditioning out flow thru hull above the water line on my stbd side.  Much easier than running a second line all the way to the stern.  I only have one discharge in the stern that both the manual and primary electric bilge pump use.  Guess I'll have to do some investigating to figure out how one of the POs plumbed it.  I have observed the bilge, not getting any back flow through the manual.  Perhaps the manual pump location higher than the outlet is forming a anti siphon loop preventing back flow

[Fred Jackson]

One more point about hose routing:  If your outlet is on the starboard side, your hose should run down the port side, or loop up to the port side before going to the exit.  This is so if you are on beam-end after a knockdown, and your outlet is underwater, it does not become an inlet.

Fred J.
Amante Catalina 36 #2209

[Ted Pounds]

Which is why it's just as easy to run it to the stern.

[Fred Jackson]

Ted,

I'm not sure you understood the point.  Even if you run the pump outlet hose to the stern, at some point, it needs to traverse the boat laterally.  This ensures that if you are knocked down and sitting on beam ends for a period, you will have a portion of the hose above the suface of the water, blocking water entry.

Fred J.

[Ron Hill]

Gary : Fred makes some interesting points, but I believe the "righting time" on a C34 is in seconds - from a knockdown. 
I'd be more worried about an open companion way!!   Then again the righting time on a C36 may be much longer??
The longer the hose from the bulge pump the more of a back flow of bilge water when the pump stops pumping. 

[Ted Pounds]

Fred,

It doesn't need to traverse laterally,  It just needs to to be looped high above the water line.   If you're on beam ends an outlet on centerline will be above the water (as will the loop).  If the centerline outlet ends up underwater then, as Ron said,  I'd be worried about the companionway.