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Discussion Starter #1
Hi there, I'm a brand new member here, although I have been reading threads for quite some time, info here has proved invaluable...what a resource!

My question for debate is as follows..
I am trying to design a bilge pump system for a 42' Zulu, rebuilt recently, that has 3 watertight bulkheads, hence 4 compartments. I have so far thought that all hoses that come from strum boxes in respective compartments should come to a manifold via taps. This means that if compartment 1 is filling, you open tap 1 and then choose your pump, open the tap to that pump (manual, electric or engine clutch pump), close taps to other pumps so water will not back down them, and Bobs your mother's brother. This was explained to me by a friend who worked on ships systems...

The problem arises when i am away from the boat and she springs a leak. When i am away, I planned to leave all compartment hose taps open, as i would not know where a leak might come from, and leave the electric pump on auto with float switches. BUT, if a leak occurs in compartment 1, and all hose taps are open, the electric bilge pump will also be sucking in air from the three remaining dry compartments...... see attached drawing....

This system also means that I should have 8, yes 8! float switches, one normal and one high water for each compartment!

Is there a way round all this?
 

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In my opinion watertight means watertight, which means no connnection of water to other compartments. Therefore it is best to design individual pumps for each compartment with their individual seacocks.
 

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Discussion Starter #4
So how is it done on major ships with water tight bulkheads then? I am trying to build redundancy into the pump system, so I have manual, electric, and engine pumps available. aft in one compartment.. if i have a pump system for each compartment, that would mean 12 pumps (three for each), and four exit holes instead of one (manifold). Phew! Thats a serious pump system for a 40 footer....
 

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Discussion Starter #5
But I take your point, well made, that if the four hoses are left open to the electric pumps while I am away, one compartment could flood another by backing down the next hose.....Doh!
 

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One compartment one pump. Each pump one auto/manual switch. You can limit through hulls with check valves. EG 2 pumps one TH or 3 pumps 1 TH. Easy.
 

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Discussion Starter #7
Thanks for your reply...So I will end up with 4 electric pumps that handle the whole boat ( probably with their own batteries), and a manual and engine pump that only handles one compartment...? There has to be a way for the whole boat to be covered by one electric, one manual and one engine pump with canny piping. I have never had watertight bulkheads before, which I am glad to have, but the bilge system is foxing me! Anyone out there with bulkheads that have got around this problem with less pumps? thanks again Sea Hunter...
 

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Whoa there; batteries? Batteries need a charging system of some type; if you're a going to run wires for that you might as well just send them directly to the pumps. Sounds like you need a qualified marine electrician as induvidual batteries are not required for each pump.
 

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Discussion Starter #9
I can wire up myself, but would rather solve the problem with fewer pumps and a better piping/hose system. Also, if I have 4 electric pumps, one in each compartment, and one compartment floods entirely it could short out the whole batt system. I would rather have all batts, pumps and taps aft, in one place and to hand. Not a big fan of having lots of non-return valves if I can avoid it as they clog, and consequentely cease to function. One electric, one manual, and one engine pump should handle it from the aft compartment, keeping electric lines short and everything to hand.

The question is the hosing layout which will not allow water into a dry compartment if another one floods, or allow air to be sucked up from a dry compartment when the float switch activates in a wet one...........hmmmm.....
I am trying to build in ease of use and redundancy, without 6 pumps and 8 float switches which seems excessive for a 40 footer!

Actually, there will be 2 manuals, 2 electrics and one engine pump but the song remains the same.....how to hose them with watertight bulkheads and leave the boat safe in the knowledge that the float switches and hose layout will kick in satisfactorily....
 

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Maybe it's just me, but the two phrases "keeping it simple" and "four watertight compartments" on a 42' boat appear to be diametrically opposed...

If you intend to maintain the integrity of each compartment, then you'll need to dedicate independent pump systems for each one.

I think you are overestimating the risk involved in powering all of your electric pumps from one battery location. As long as you are diligent in your selection of materials, how you route your runs and ensure you make good watertight connections you can eliminate most of that risk. Will it be totally safe from failure? Of course not. However, if you add a battery bank to each compartment then you'll be adding a bunch of weight, wiring, complexity, and maintenance and emptying your wallet.

I guess my bottom line is this: You seem to be over-engineering this one. My assumption is that the designer of the boat intended that she could remain afloat with one compartment flooded. If that happens, you are going to be calling for help. If you suffer a hull breach that compromises more than one of your compartments, you will be in deep doo-doo regardless of your bilge pump set up.
 

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Discussion Starter #12
Thanks for your reply Porfin....I am where I am, at 42' and with bulkheads; no point taking them out!

Redundancy to me means that if one type of pump doesn't operate for whatever reason i can reach for another. Therefore, if redundancy is to be followed, and according to the advice previously given in this post (which i am greatful for), it would mean having three types of pumps in each compartment, a total of 12 pumps, which quite naturally would be rediculous, nay impossible.

You may have your wires crossed in thinking that i was advocating an electric pump and battery in each compartment. That is what i want to avoid through clever hosing.

What I want is one of each type of pump (electric, manual and engine driven) in the aft compartment, next to the batteries. While I am aboard I am able to operate taps and pumps so there is no problem. It is when the boat is left for a week or two unattended that gaps in the system arise.

Imagine just two compartments...
...they both have a strum box and hose that go to a third where they join in a manifold to an electric pump. One of the compartments leaks and triggers the float switch which starts the electric pump. A non-return valve in the dry compartment's hose will stop the water from the first from flowing down it and flooding the dry compartment.....BUT the pump will suck air in from the dry one aswell as water from the wet one, substantially reducing the pumps output.

The 'air suck' issue is the sticking point in an otherwise simple, minimal and sensible pump layout for when on the boat.

Do boats with watertight bulkheads all have three kinds of pump in each room, hermetically sealed from each the others? Or do they have one electric in each? Do they have two float switches in each compartment?

I cannot find anything on the net on this subject, despite days and days of searching. My only supposition is that they either have dozens of pumps and through hulls (which I want to avoid) or that they are vulnerable when left unattended.

Anyone out there with bulkheads? I'd love to know how your pumps are laid out!
 

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Non return valves work very well when they are clean. Debris will keep them at least partially open. That is if one compartment has water in, and water is pumped, you can be sure that something will block the non return valve of that section. Next time there is water in a different bulkhead,the water will find its way to the first bulkhead.
 

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Discussion Starter #14
How about a valve that closes the bottom of the bilge pipe when it has no water? See attached diagram. It would ALL need to be housed in a mesh to act as a strainer, and need tinkering with to get the float right, so the pumps don't suck the valve onto it when active, but it could solve the problem of sucking air from a dry compartment when a wet one is being pumped...any thoughts?
 

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As a passenger vessel I' m required two water tight bulkheads. Each bilge has it own electric pump with high up thruhulls and backflow stoppers, controlled from common panel. Each bilge has two sensors ,one for auto pump and other (separate circuit) for flood alarm.Each bilge is hard plumbed to engine driven Japsco thru ball valve manifold and valves at each bulkhead which are normally open.Everything is tested every year by CG so I know it works and couldn't be simpler.
 

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Discussion Starter #16
Thanks for that...is it mandatory for passenger carraige to have a dedicated pump for each compartment? When you have your engine Jabsco running does it suck air up from dry compartments? Or do you have to shut the valve first?
 

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It sounds like you have 1 very large pump, and wish to have 4 pipes, 1 sucking from each compartment?

Usually in smaller boats you have a smaller pusher type submersable pump in each compartment.

The purpose of watertight bulkheads is to prevent a sinking if one compartment is flooded. Having a seperate pump for each compartment accomplishes this, (the redundancy is the number of compartments, it is not neccessary to have redundant pumps in each compartment as would be if the boat had NO bulkheads.

I.E. My 36 ft boat has one bilge running the entire length of the boat, I have two bilge pumps one forward, one aft that are on seperate batteries, one on ehouse, one on engine starting, one has a higher float than the other and comes on only if the first one is overwhelmed.

Since you have multiple bulkheads 1 pump each, is twice the redunduncy of my boat already.

If you really want the one pump rules all method, there is in fact a solution. Parker makes a sealed solenoid valve that operates from 12vdc, (or 24vdc), it comes in a variety of sizes from 1/4" to 4", their 3/4" or 1" valves should be in the ballpark of what you need. Simply plumb one valve in line to each pickup, and wire to a float switch in that compartment. When the float activates it will open the correct solenoid, as well as signal the very large master pump to turn on. Problem solved.
 

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Normally a bilge pump manifold is all closed. If there is a problem ,open the appropriate valve and turn on the pump.The automatic electric bilge units in each compartment should take care of small stuff if that's too complicated.
 
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