"Gary Warner" wrote in message
...

I'd like to install some kind of valve setup so that my raw-water
intake for my engine cooling can come from the sea-water
scoop or from a garden hose.

It doesn't need to be that sophisticated.

Put a "T" in the water intake line. Put a valve on the T side, and then a
female hose fitting.

Under normal use, the valve is closed and the pump draws water up from the
thru-hull as normal.

When you are on the trailer (I assume that is why you want to run it off a
hose) you connect a hose and open the valve. When you turn the hose on, the
water flows through the fitting and out the thru-hull fitting. When you
start the engine, the pump draws the water up from the T. If the hose is
providing an excess of water it will flow out through the thru hull, thus it
can't over pressure the water intake hose. If the pump wants more than the
hose is providing, it will just suck a little air and thus assure that the
vacuum doesn't collapse the garden hose and pinch off the water supply.

As I wrote this, it occurred to me that your objective might be to flush the
engine of salt water while the boat was still in the water. In this case,
you would need to be able to shut off sea water intake otherwise the pump
might still draw a little from the thru-hull. If your boat is to stay in
the water for extended periods then you should have a ball valve mounted
directly on the thru-hull, so you can shut it off there.

Just don't forget to close the valve on the hose fitting when you are done
with the hose!

Rod