Re: 50 horse water pump help
If you have the motor submerged to at least 6 inches above the 'split' between the lower unit and the center section (AKA "exhaust tower" or "mid section") that should be plenty. If the water is just up to the 'split' that's probably not enough. If you have a set of "muffs" you can be sure that you're getting adequate water to the motor. With the motor running, you should adjust water pressure such that some water spills out the muffs.
At any rate, if you're sure the water supply (whether in barrel or via garden hose) is OK, you probably have a bad impeller and it's time to drop the lower unit.
Check the FAQ section of the iboats forums for impeller changeout procedures and/or pick up a good manual. Just don't run it any more once you figure out for sure that it's not getting water; you can burn up the powerhead in short order if you're underway, at speed, with no cooling!
HTH......ed