Multihull / Multi-bulkhead Bilge Pump Solutions?

[SailingHarmonie]

QUOTE=Matt Johnson;3946370]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.[/QUOTE]

Interesting. I’m not a cat expert, but none of these one I have been on had anything remotely resembling watertight doors in the bulkheads. I am sure there are some that do I haven’t seen.

My boat has watertight doors, and limber holes that have easily reached valves to isolate a flooding compartment. Kind of the best of both worlds, at least imo.

[Matt Johnson]

In our case, we don't have any openings through the bulkheads. The access is from the deck making them completely separate.

The sole/floor in our hulls are basically at the waterline and sealed to create a double bottom. Each transverse webbing shown under the sole breaks these areas into sealed and watertight cells (some are used as the fuel tank). Not shown is the longitudinal stringer running down the centerline and further dividing the area into even smaller sections.

Great if we were to strike anything, but it does make it more difficult to repair.

This has been commonly done on custom/semi-custom built catamarans since their beginning.

[SailingHarmonie]

Originally Posted by Matt Johnson

In our case, we don't have any openings through the bulkheads. The access is from the deck making them completely separate.

The sole/floor in our hulls are basically at the waterline and sealed to create a double bottom. Each transverse webbing shown under the sole breaks these areas into sealed and watertight cells (some are used as the fuel tank). Not shown is the longitudinal stringer running down the centerline and further dividing the area into even smaller sections.

Great if we were to strike anything, but it does make it more difficult to repair.

This has been commonly done on custom/semi-custom built catamarans since their beginning.

Attachment 295638

I’m thinking you and I have a very different idea of what a “watertight compartment” is. A small box under the cabin floor is not at all what I had in mind.

My boat is quite different. The watertight compartments are;
The chain locker, the forward cabin, the main cabin, the engine room, the aft cabin, and the aft locker. The only penetration between compartments are at deck level, or valves.

In the event of catastrophic flooding each compartment can be isolated from all the others. With one compartment flooded, the boat sits no more than 10 deg off her lines, she stays afloat with any two flooded.

Assuming these under sole boxes are actually effectively sealed, why do they need bilge pumps? And how do you install a bilge pump into such a space and maintain watertight seals?

[Matt Johnson]

OP doesn't list what type of cat they have. So I can only speculate and explain why we have a similar number of bilge pumps. Keep in mind that for our boat, bilge pumps are only really for nuisance leaks.

You don't put bilge pumps into each of the cells under the floor. They are completely sealed and can't be accessed. But one cell is left open from the top and that's what is considered the bilge... it gives an area for any water on the floor to drain, plus below waterline access for through hulls and depth sounder.

The fwd compartment - sail locker - is again a completely separate from the living area and accessed from the deck. It needs its own bilge pump to any nuisance leaks from the deck hatch or fittings. Same with the aft section.

Engine bay - in our case under the aft berth - needs is own bilge pump since it has water intakes, exhaust and prop shaft penetrations.