I've mentioned this befo you should simply parallel the bank and
install a small starting battery. If you want it to be high quality
and "idiot proof" and a battery combiner (the smaller ones are cheap.
Why invest in an "emergency" starter when the same money give you a
proper solution?

BTW, the small Yanmar will *usually* starts with under 5 seconds of
cranking, but it isn't self bleeding, so it can get balky if the line
gets dirty or airbound. I just started my two engines after winter
layup - one fired quickly, but the other took about 30 seconds of
cranking. My point is that in real life problems always come in
groups - the morning your battery dies could also be the morning the
fuel filter clogs. Why rely on a pack of D cells that cost the same
as a proper battery?


Roger Long wrote:
It's amazing how complicated simple things are when you start thinking
about them.

A little research in Calder's book shows that he, at least, considers
bilge pumps on the battery side common.

But..

I've already decided to run both my batteries as close to parallel as
possible to minimize the depth of the discharge cycles and get maximum
life out of the expensive AGM cells. This goes against the
conventional wisdom of always maintaining a dedicated starting
battery. I'm going against the grain because:

a.. This is a sailboat and I will not be helpless if the engine
doesn't start. I've cruised in boats with no engine at all.
b.. The engine can be hand started, at least in warm weather.
c.. I'm going to be mostly daysailing and short cruising this year.
d.. I have very minimal ship's service loads so it is unlikely that
I'll run the batteries flat.
e.. I can start this little engine with a portable emergency
battery. It's even been done with a handful of flashlight batteries.
So, if I want a dead ship except for the bilge pump, I have to decide
which battery to use. That means that a long run of pumping with the
charger off, as could happen with the boat unattended in a storm,
would drain one battery down. I also would only have half the battery
capacity for bilge pumping under the same circumstances. That is not
ideal. Worse, if one battery did die, I would have to get into the
panel and switch the bilge pump. That's not good.

I guess that, for now at least, I'll just leave things as they are
with the bilge pump wired into the bus. That means leaving the switch
on "Both" when putting the boat away and being sure to turn everything
except the bilge pump off.

A good solution for my situation would be two bilge pumps, one on each
battery. That would provide redundancy. It should be simple to run a
second line and another through hull in this boat. I'll just wire them
into the same float switch. I'm going to take a look tomorrow. We're
doing a lot of through hull work anyway and we'll have the equipment
right there to punch one in above the waterline.

The ramifications just go on. I just realized that the bilge
discharge fitting is 3/4 and the pump hose is 1 /18. That means there
is a reducer somewhere. That's a kludge I'd better track down. That
would be another reason to go to two pumps of the same total capacity.