Bilge outlet routing

[selene]

I currently have a single Rule2000 bilge pump, not automatic, which joins the cockpit drain on the port side (after it's venting loop).  I am looking to add a second pump, with a float switch, bit higher than the first, as backup.

The question is - where to I route the outlet?

My current ideas are:
(1) out with the shower sump - stbd side. Only problem is that the outlet is a smaller bore than the pump (~3/4"? vs. 1-1/8")';  it would be a pain to change the through-hull.

2) Run it to the transom - the manual bilge outlet is on the stbd side, there is a covered-over hole in the same position on the port side.   Put a new marelon through-hull there.  Longer run - not sure where I would put the venting loop; it would have to be high enough so the water would go downhill to the thru-hull.

Any suggestions?

[selene]

Would appreciate any comments on how your bilge pump is configured....

[Dolce_Vita]

I recommend a completely separate discharge, above the waterline.

On Dolce Vita,  the Whale Gusher manual pump, and the automatic Rule pump
both have dedicated hose runs to independent thru-hulls on the transom.

[selene]

Thanks, Ed!  Incidentally, where is your venting loop for the Rule? I was thinking of epoxying a wooden plate to attach the loop right next to the manual/whale pump.  Should be high enough. Then out the transom. 

[Dolce_Vita]

With the discharge above the waterline, no vent loop is required, as a siphon can't start.

[selene]

Appreciate the feedback, Ed; I'll give it further thought. I read on another site:
"Even if the outlet is normally above the waterline, water may siphon into a heeled or well-laden boat, as mentioned previously. It may he driven up by following seas; or, in an otherwise calm anchorage, be forced up the pipe by repeated wakes from passing boats or water-skiers. This phenomenon is known as water hammer. I heard of an interesting case of this recently in which waves, deflected off a seawall, repeatedly hit the stern of a boat, eventually sinking it."

Of course this is not a problem with the valves in the Whale Gusher; probably not with the Rule routed out on the transom, either....just wondering what other folk do!

[Dolce_Vita]

I read on another site:
"Even if the outlet is normally above the waterline, water may siphon into a heeled or well-laden boat, as mentioned previously.

True, but that's why mine is on the stern, and high enough that it never goes under.

 

It may he driven up by following seas; or, in an otherwise calm anchorage, be forced up the pipe by repeated wakes from passing boats or water-skiers. This phenomenon is known as water hammer."

Quite true, but an anti-siphon valve won't help with this.  Anti-siphon valves break open under suction, to stop the siphon.  They close under 0 or positive pressure.

The check valves in the whale gusher would prevent this, but the bilge pump lacks any kind of valve, and would benifit from a check valve.