Theis,

There is great wisdom in your words. A high volume electric pump would be a wonderful addition to any boat with electrical power regardless of battery capacity.

I think that this thing about the advisability of one-way (flapper) valves in manual bilge pump systems deserves some commentary from the manufacturers and other persons with technical knowledge in the matter. The pump manufacturers also build the valves, and presumably they do so for some reasonably valid purpose. Boat plumbing professionals should also be consulted.

Although it may be true that about could be lost due to a blocked flapper valve, the lack of working one-way valves could result in a siphoning problem in any system where the exit thru hull is below the water line, as ours might be on some point of sail.

Although it might be unlikely that both of the flapper valves that are integral to a manual pump might fail simultaneously, a small amount of bilge trash sucked into the line could do that very thing, I suppose. A third flapper installed in he lazarette locker would provide some further protection in that case.

As you note, a third valve in the lazarette would also increase the risk of complete blockage of the system. So we are into arena of conjecture and opinion on the advisability of adding a one-way flapper valve in a bilge pump line when it comes to manual pumps.

Now, a flapper valve in an automatic electric pump system might be a completely different matter, because of the possibility of the valve becoming blocked while the boat is unattended. Those folks with inboard engines would need to seriously consider the alternatives and consequences of those alternatives.

I guess that the problem is that with limited resources, the lack of space for redundant systems, and the inevitable setting of priorities for maintaining a reasonably safe boat, we all must make compromises. Surely, the only safe alternative is never to go to sea. I recall thinking about the alternatives if I were to break a leg in the backcountry during my ski patrol days, and it all came down to that two way radio. A experienced sailor I once knew had a simple answer to questions about whether this or that boat was seaworthy. His answer was, "If you have a good radio."

Fortunately, we have a basically seaworthy boat in our Ariels, but the failure of a thru hull, or other piece of plumbing on any boat at sea would change your priorities quickly. If you are far enough off shore at the time, you would be well served by two electric bilge pumps installed as per Don Casey's recommendations, with plenty of juice to support them, and a couple of well placed manual pumps just in case.