Multihull / Multi-bulkhead Bilge Pump Solutions?

[bredlo]

Hi all,
56' catamaran liveaboard, here. Each pontoon features 6 bulkheads, for a total of 14 individual sections. Thankfully, for plumbing purposes all are easily connected to one another via several inches of clearance below the floor, running along the central "hump".

I'm hoping to design a solution for pumping out individual bilges from a single source -- ideally with pre-placed hoses, and allowing the pump to remain stationery. Put another way, it would be an octopus - perhaps with a manifold - to pump out any section from a central location. Does not need to be automatic via water sensors or anything too fancy. Thoughts?

[Tin Tin]

Do you want to make them separate airtight compartments?

[MWGDVC]

How will you keep the dry sections from sucking air, preventing the water from being drawn out from the wet sections?

[Sparx]

A single pump in each hull with a valved hose running to each compartment would work. Locate the valve manifold close to the pump and in an easy to reach location. Choose a pump that is good at pulling air, such as a diaphragm pump. This pump would be in addition to at least one automatic bilge pump in each hull.


The design you are describing with many partial water tight bulkheads is unique. Often I see limber holes in partial structural bulkheads that allows water to drain to a central location, where it would be expected to find a bulge pump.

[Miyalk]

I run a single Jabsco ¾" 24v pump in my cockpit locker, it has a inlet and an outlet manifold with valves on each inlet/outlet. One of the inlets is a thru hull which is normally open and one of the outlets is to the deck hose. So I can pump out of any compartment and switch the discharge to overboard to use as a bilge pump.

Very happy with the setup.

[bredlo]

Thanks for all the replies. Tin Tin, they're already watertight against the other sections unless the water topped the center "hump", at which point all bets would be off.

MWGDVC, good question. I assumed that if the manifold I choose has valves, it will allow me to maintain a vacuum because they would all stay off until I need to open just the hose running to the compartment with water.

Sparx, I think I'm following what you're describing. I do like the idea of one pump in each pontoon... combined with the valved manifold idea, it might be a pretty reasonable set up.

As for the unique design, it's pretty nifty, actually. The pontoons are large, and each section is 6 feet long, and about 4 by 4 feet wide and high. It's sort of a "Titanic" design in that the bulkheads are both structural, and provide enough waterproofness to give one extra time to pump out if there's a localized puncture.

The open design of the center "hump", where water would eventually overflow into the other compartments... is really the achilles heel, along with the fact that I had to remove parts of a few bulkheads when adding 100 gallon black and gray tanks.

[bredlo]

Miyalk, that sounds exactly like what I'm after. Thanks so much - I'll see if I can find a similar pump and start shopping the other parts.

[SailingHarmonie]

There are a number of issues here that are not well addressed by comments so far. You can certainly set up a manual system to pump out the individual compartments.

But--there are things to consider. Are these ACTUAL watertight compartments? or are they just spaces without proper limber holes? Very few boats of this size are built with real water tight compartments. The proper solution here is to have limber holes so all spaces drain to the lowest point, then you can use a single bilge pump to drain them all. This is standard yacht design. Skipping limber holes is just a cost saving choice by the builder, and a REALLY crappy one at that.

If they ARE real water tight compartments, that are truly designed to prevent flooding between compartments with water tight doors and the associated hardware, you have a tougher job. You need to be sure that you do not compromise that design.

Based on what you posted, nobody knows which of these cases is the actual situation, maybe you do not know yourself..

[MWGDVC]

Bredio,
More questions:
How will you know a compartment needs pumping?
What if a flooding event occurs whilst you aren't aboard?
The compartment size you describe will weigh approx. 5500 Lbs. each if flooded. How many compartments flood before more serious events occur?

[Lee Jerry]

Originally Posted by bredlo

Thanks for all the replies. Tin Tin, they're already watertight against the other sections unless the water topped the center "hump", at which point all bets would be off.

[snip]

As for the unique design, it's pretty nifty, actually. The pontoons are large, and each section is 6 feet long, and about 4 by 4 feet wide and high. It's sort of a "Titanic" design in that the bulkheads are both structural, and provide enough waterproofness to give one extra time to pump out if there's a localized puncture.

The open design of the center "hump", where water would eventually overflow into the other compartments... is really the achilles heel, along with the fact that I had to remove parts of a few bulkheads when adding 100 gallon black and gray tanks.

I don't follow the compartment arrangement and, as others have said, don't the get the water tightness. What is the "center 'hump'" you refer to? Is it the bridgedeck? When you say "easily connected to one another via several inches of clearance below the floor" do you mean you can drill through bulkhead there?

Regardless, a couple comments. The hoses will presumably be dry when not in use and will therefore take a long, long time to prime the pump. Put the pumps near midships to minimize run lengths. Obviously, this also means using a self-priming, run-dry pump. There will also be lots of losses in this system, so the pump will need to be "oversized." Probably a lot.

Finally, what about redundancy? In a typical arrangement where water drains to a common bilge (as SailingHarmonie described), it is not unusual (actually recommended) for there to be multiple ways to pump out said bilge: primary electric pump, back-up electric pump, manual pump accessible below deck, and manual pump accessible above deck. At a minimum, you would need to duplicate the system in each hull, for four total pumps.

What is in there now?

[bredlo]

Great points, good questions. Thanks everyone - I'll reply soon with a better diagram, but briefly:

Yes, the system I'm imagining is manual only, and I'd have to check each hatch if I suspected something was wrong. I can't imagine this system being automatic unless each of the 14 compartments had its own pump and its own float gauge or moisture trigger (not sure of the correct jargon).

There are no limber holes; the bulkheads are sealed from the bottom of the hull to the underside of the main floor / deck -- shown incorrectly in my original drawing as open below the floor. However, the "hump" in that illustration is open between the two pontoons, and open between all the hatches, providing me with the ability to route plumbing and electrical lines anywhere under the floor.

I'll continue thinking about this and come back with better diagrams in order to get more accurate suggestions, I appreciate the replies so far!

[nick83]

@bredlo,

The way I solved it on our Cat was to have 8 bilge pumps, each on their own manual circuit breaker. 4 for each hull: main bilge midships, fwd storage locker, head, and engine room.

All these compartments are separated from each other. Not totally watertight, but somewhat. For instance, the engine room would have to have about 18" deep water before it would start working through stuffing tubes to the midship bilge. The engine would be halfway submerged.

I also have a separate Auto circuit that is currently hooked to 5 bilges (2 midships, 2 engine room, and the head we take a shower in). So those will kick on automatically anytime they sense water. I'm using "water witch" switches which work fairly well.

One nifty thing is that if any of the bilges kick on automatically, it lights up the LED next to that circuit on my board so I can visually see which bilge pump is kicking on.

I'm still planning to add 2 more high-water bilge pumps with alarms and greater capacity in the midship bilges.

In this picture I found from when I was installing the panels, the red auto switch is off, but I do leave that on generally.

[SailingHarmonie]

Originally Posted by nick83

@bredlo,

The way I solved it on our Cat was to have 8 bilge pumps, each on their own manual circuit breaker. 4 for each hull: main bilge midships, fwd storage locker, head, and engine room.

All these compartments are separated from each other. Not totally watertight, but somewhat. For instance, the engine room would have to have about 18" deep water before it would start working through stuffing tubes to the midship bilge. The engine would be halfway submerged.

I also have a separate Auto circuit that is currently hooked to 5 bilges (2 midships, 2 engine room, and the head we take a shower in). So those will kick on automatically anytime they sense water. I'm using "water witch" switches which work fairly well.

One nifty thing is that if any of the bilges kick on automatically, it lights up the LED next to that circuit on my board so I can visually see which bilge pump is kicking on.

I'm still planning to add 2 more high-water bilge pumps with alarms and greater capacity in the midship bilges.

In this picture I found from when I was installing the panels, the red auto switch is off, but I do leave that on generally.

Attachment 295625

EIGHT bilge pumps? How on the earth’s oceans is that a better solution than just putting in limber holes that should have been added by the factory?

[Matt Johnson]

Originally Posted by SailingHarmonie

EIGHT bilge pumps? How on the earth’s oceans is that a better solution than just putting in limber holes that should have been added by the factory?

It leaves the watertight areas intact. It's not uncommon on catamarans.

Ours is similar. The first 13' of our boat is separated by a full height bulkhead. Main hull living space is 17' and has its own bilge. Engine (aft berth 6.5') is in a cofferdam and if we were to get a catastrophic leak, won't sink the boat enough to put the top anywhere near the new waterline. And in our case, the aft 8' is also separate from the main hull.

[GordMay]

A [½"∅] Snap Handle Baitwell/Transom Plug, will enable sealing, and unsealing, the limber holes, between compartments.