How connect two bilge pumps to ione thru hull

[kapnd]

Separate systems for each pump!
Check valves are notorious for causing problems, I don’t like to use them if at all possible. They foul easily, and many pumps will not have the pressure to open them when they’re holding a tall head of water, especially if the pump is in any way compromised, like by debris in the bilge water or low voltage.
I set the height of my secondary pump within a couple of inches of the primary so that if the primary fails, the secondary will take over before the bilge water height reaches disaster level.
I’ve seen many secondary pumps and high bilge water alarms mounted ridiculously high above the primary, a recipe for disaster!
My current boat has an open bilge bow to stern, where a few inches of water equates to hundreds of gallons, and multiplies exponentially as the water level rises. Don’t want to go there!

[garyfrankovich]

ABYC H-22.8.8 states: If the discharges of several bilge pumps are manifolded to discharge through a single thru-hull fitting, the system shall be designed so that the operation of one pump will not back feed another pump, and the simultaneous operation of each pump will not diminish the pumping capacity of the system. A check valve shall not be used in the discharge manifold system

[Auspicious]

Originally Posted by Uncle Bob

The concept of a sea chest is that one hull perforation below waterline supplies water to all equipment requiring sea water to operate from the one point, sized appropriately.

True. Common on military and commercial ships and some recreational craft, like Amel.

Originally Posted by Uncle Bob

If one transfers that principle to discharge

But you can't. You are missing the relationship of pressure and flow rate.



Do not do this. It won't work in extremis. If your boat sinks your insurance company may say you are responsible and they won't cover. Your boat may sink. It is a bad idea. One bilge pump to one outlet. Loops are okay, check valves are not.



Thus spake the naval architect.

[01kiwijohn]

I did this the other way 'round.
In the main bilge, I have one electric pump, that goes overboard through a, ta Dah, thru hull.
I wanted to back this up manually so I now have a manual pump, accessible from the cockpit, with a three way valve, so I can pump out the engine / stuffing box bilge (no electric pump here, I like to know how much water is coming into the boat normally) and switch over to pump out the main bilge if necessary. Both strum boxes have check valves, but they do leak back over time. There is only one thru hull for this manual pump arrangement.
So far, it has been satisfactory.

[mcon12000]

I think it was wisely stated above, stick with two thru-hulls. If the boat sinks you’ll be at fault as far as your insurance company is concerned and if you’re self insured you’ll learn what they already know.

The fewer moving parts in a design the better and for me (my opinion not proven) this proposed system appears far more dangerous than the existing thru hull you’re trying to eliminate don’t you think?

Forgive me for only reading the first few pages skipping to the last and posting.

[Rob.Lovelace]

Originally Posted by GILow

Oh no! The dreaded non-return debate is about to begin. Makes guns and anchors seem like a sewing circle discussion.

I'm getting myself a spot on the fence.

what, is there a down side to non return valves? I have one i’m about to fit (japsci) please advise if i’m wasting my time.

[Olddan1943]

Originally Posted by Rob.Lovelace

what, is there a down side to non return valves? I have one i’m about to fit (japsci) please advise if i’m wasting my time.

Check valves (non-return valve) can and have been known to stick.
If it sticks open, your screwed, if it sticks closed, your screwed.

You are setting yourself up for 'failure' and perhaps a denial of an insurance claim.

The price of putting in the through hull doesn't cost much and then the job will be done correct, the first time. Sweeping bends and turns, NO fittings in the hose either.

Remember, one pump, one overboard.

[AuroraGH]

Originally Posted by Olddan1943

Check valves (non-return valve) can and have been known to stick.
If it sticks open, your screwed, if it sticks closed, your screwed.

Ok, I have a check valve attached to the 90 that routes my pump outlet upwards. After the check valve, there is about a 4 foot rise to max height, then a u-bend down to a thru hull that faces downwards (because wineglass hull's aft do that) a bit above the WL.

I do not understand how I would get rid of it. In fact, I did remove it and the pump empties the bilge, sucks air, shuts off, stand pipe flows back into the bilge which triggers the pump again....and it will do that forever.

What am I missing?

[Olddan1943]

Originally Posted by AuroraGH

Ok, I have a check valve attached to the 90 that routes my pump outlet upwards. After the check valve, there is about a 4 foot rise to max height, then a u-bend down to a thru hull that faces downwards (because wineglass hull's aft do that) a bit above the WL.

I do not understand how I would get rid of it. In fact, I did remove it and the pump empties the bilge, sucks air, shuts off, stand pipe flows back into the bilge which triggers the pump again....and it will do that forever.

What am I missing?

Does the stand pipe have a have a vacuum breaker on top? If not, investigate putting one at the top of the inverted U.
Vacuum breaker are common on the sanitary overboard line.

[transmitterdan]

Originally Posted by AuroraGH

Ok, I have a check valve attached to the 90 that routes my pump outlet upwards.

In fact, I did remove it and the pump empties the bilge, sucks air, shuts off, stand pipe flows back into the bilge which triggers the pump again....and it will do that forever.

What am I missing?

Nothing. But check valves (non-return valves) are a critical element with parts prone to clogging/sticking. You are correct that the water up to the siphon break will flow back into the bulge. You can raise the level of the float switch a little and leave a puddle of water in the bilge. Then the pump won’t endlessly cycle.

You can also install another small diaphragm pump with a lower switch and let that drain the bilge dry. This pump needs it’s own siphon break and thru-hull. The diaphragm pumps have a built-in check valve so they are also prone to clog/fail but at least that cannot stop your main dewatering system.

If you have a boat that constantly takes on water consider an upgrade to stop that. Many boats do not take on water all the time.

[GrowleyMonster]

Yes you COULD use one of the posted solutions to eliminate a through hull. It might generally usually work okay. But it is MUCH BETTER, MUCH SAFER, to follow recommended practice, which is to have a through hull discharge for each and every bilge pump.



I don't know about you, but I don't want my bilge water elimination system to generally usually work okay. I want it to always work perfectly as designed, due to prudent and proper redundancy. I don't even have all my electric pumps powered from the same battery. Never. Not. No. Nein. Absolutely positively never never nevernevernever. I certainly won't have two pumps eliminating through the same fitting. I have and continue to do certain things that violate or bend or massage certain accepted safety practices, I will admit. But I won't take a chance on my boat sinking due partly to my own shoddy bilge pump installation. It is too easy to just do it right and an above the waterline through hull and hose clamp is just a few bucks.

[Olddan1943]

Put it back to factory specs and walk away.
I suggest, any modification contrary to the factory installation and then the boat sinks, the builder will not assume any responsibility even if the factory design is wrong.
Add another bilge pump? Add another hull penetration about 12 inches above the water line.

[pcmm]

Originally Posted by Rob.Lovelace

what, is there a down side to non return valves? I have one i’m about to fit (japsci) please advise if i’m wasting my time.

check valves have 2 issues
1. they reduce water flow a bit (a bit is important with bilge pumps)
2. they often get stuck. Not so bad when they get stuck open really bad when they get stuck closed or partially closed.

[Auspicious]

Originally Posted by AuroraGH

What am I missing?

What the big boys do is have a small stripping pump that runs the water down to the bottom but can't keep up with a leak. Above that is a real bilge pump. Above that is "I'm really in trouble" pump.

[David M]

The downside to this is that when observing by looking at the overboard discharge you will not know which bilge is being dewatered. The USCG on inspected vessels prohibits doing this. Your choice with a pleasure boat.

You will also be depending on 2 check valves to prevent water from being pumped from one bilge to the other. Do you trust check valves enough to put your boat at risk? I have seen them stick both open and closed.

The more complex you make a system the more likely it is to fail. I don't see it as worth the risk.

Also, never discharge anything other than the head discharge below the waterline. You need be able to confirm if your bilge pump is working by looking at its overboard discharge. Also by discharging below the waterline you are increasing the risk of sinking your boat by creating another source of water entry into your boat.