Don't laugh! I have heard it mentioned, but I have no idea what it does?

Thanks.

Look at the front of your motor. They are usually mounted at the lower left. Driven off of you belt. This is the seawater, also know as raw water pump that sucks the water up through the outdrive and into the engine.

Hope this helps.

If you go to the tech tips how to section it shows one being rebuilt in detail.

Dock's got it covered.

Only note I want to make is that on Bravo models, the sea pump is belt driven on the front of the engine(similar to automotive, but impellor is rubber not metal) and on Alpha models the pump is in the drive itself.

What about a sea strainer?

On a volvo penta (original) they are mounted on the front of the harmonic balancer.

BT

Here is a pic of a sea strainer. There are several Businesses in the Links section that sell them. It helps keep debris out of your engines.
http://www.stainlessmarine.com/strainers.html
http://www.imcomarine.com/imco/index.html
http://www.marinemachine.com/home.htm

like doc say's, it on the lower r.h. side
of mercruiser/bravo and above applications,
and it supplies cooling water to the engine.
now the "REAL" discription,
it's the device that always fails at the
most INOPERTUNE time, and, depending
on boat, can be a REAL SON OF A B-TCH
to get to, and some times results in
HARSH language useage.
ALWAYS CARRY A SPARE IMPELLER !

BajaDaze, your response is slightly misleading. When you say "on front of engine"' you are refering to the "Circulation Pump" that works in conjunction with the "Seawater Pump" / "Raw Water Pump" (Bravo Drive setups). Both pumps are belt driven.
Runnin A Fever, the circulation pump is and can be removed in favor of a "crossover", but this is a whole other subject. The "Seawater Pump" is mandatoryand a pain in the ass to service as described above. DO NOT RUN IT DRY.

Late model mercruisers have the fuel pump and sea water pump as one unit that is mounted like an accessory and driven like an alternator off the front of the engine. The circulation pump is not what I consider an accessory. To locate the pump is easy find the most inaccessable spot on the front 1/2 of the engine an eliminate the power steering pump and alternator and what you have left over is probably it.
Access (unless you have REAL LONG ARMS) is not enjoyable.
Unless you like being bent over with your face on the thermostat.
That didn't sound good did it?
Yes carry a spare impeller KIT. one that you can install in an emergency. And replace every season or sooner (for when they take a U^&%(&^%&$)
Running dry can equate to getting airborne off a good wave. So don't figure "Gee I don't leave my engines running on the trailer?" as the only time the pumps can run dry

RLW, you're right. Thanks, I was a bit vague.