"I think the engine pumps are more trouble than help." (CarlF)
I'm inclined to agree, in the case of the cooling pump, but how about an extra engine-driven pump purely for disaster "de-watering" (not previously in my nautical vocab!)
Either belt-driven or in-line via a muff coupling from the crank or camshaft, or - for propshafts low in the hull
, there used to be (ten years ago, may still be available) a very high-throughput option which was the ultimate solution for any diesel installation
with a well engineered air intake:
I think it was axial flow, like a really crude waterjet unit, all cast metal, quite sizeable, with a split impeller which could be bolted around the shaft, and a split housing (with plenty of clearance on the tips of the impeller)
It didn't need an inlet; water just flowed into it at the suction end, IIRC.
(Maybe that's something like the "Waterwitch" referred to by rebel above?)
Used to be made by Ericson
Now by these guys:
Something like this would have saved the Bounty, I reckon. A few hundred horsepower can shift an awful lot of water.
(When I first heard the news, it occurred to me that manual pumps, much less efficient than the Edson referred to above, were sufficient to keep the original Bounty afloat during several months
of trying to battle the wrong way around Cape Horn during the wrong season against conditions which would surely have sunk the replica....
but then I realised that was probably an uncharitable thought, considering how many people were available to man the pumps on the original. And they were not perhaps the happiest of possums thereafter.... )
It seems to me axiomatic that electric pumps cannot be included in any list of disaster-dewatering assets, but engine driven pumps (given a carefully thought-through snorkel, connected also to all breathers) will run indefinitely with the engine completely submerged.
If there is a smaller diesel, say for genset duties, this should be the one with the engine driven pump if the larger diesel cannot be started without electricity.
(I've done several trips on a 78' yacht with a 6LXB Gardner, which could be started by human power. The galley
was designed with removable partitions, and the handles from one of the grinder installations detatched and brought below. Four big boys could kneel on the floor in the galley
and get her up to speed for one cylinder to fire, the other five being decompressed. The flywheel was then heavy enough to allow bringing the remaining cylinders 'on-line' one at a time.)
Hydraulically (oil-)driven waterpumps are available, but have no relevance to the OP's question. Even if electric pumps are unconditionally submersible, it's hard to ensure that any battery
bank, contactors, isolating switches etc will all survive
They clearly represent overkill for anyone likely to read this, except perhaps on very large vessels with multiple watertight spaces distant from the engine.