I know that the Alpha One operates with a water impeller in the outdrive.

Does the Bravo One also have an impeller in the drive in addition to the water impeller pump mounted on the engine? What is drawing the water up from the drive to the motor? Is it by just suction from the engine mounted pump?

You are correct, just the one on the engine. Its crazy how they work, alot of good videos on youtube.

No a Bravo does not have a impeller in the drive, and neither Alpha nor any other boat impeller "sucks".
The impeller moves water from one side to the other. This is a reason you cannot run a drive in a bucket or drum. Some do this with the Alpha but even then the impeller is running somewhat dry.

Only motor which can be run from a bucket is the outboard

When the boat is in the water, the drive is submerged enough to bring the water to the impeller. When moving the intake holes on the drive are angled forward to force the water to the impeller

The above video clearly shows otherwise. Put your hand over the intake side of a Bravo 1 pump and rotate it. Submersion depth of intake holes and forward motion of boat only enhance pump flow but are not requirements.

most Mercury outboards use nearly an identical pump to an alpha. The pumps absolutely do have suction and will draw from a bucket etc. Many boats have the water pump above the water line.

Agree with above. An automotive water pump, or the circulating water pumps on the front of our engines, have metal impellers that do not create a seal to the pump body. This type of water pump is what AllDodge is referring to, this sort of pump does not create suction or pressure. Instead, they simply create flow.

The rubber impellers in a tight-tolerance housing, create a seal to the housing, allowing for the creation of negative pressure (suction).

My pumps create suction as soon as the engines start I can see the water going through the intercooler dumps as soon as they light up .

Wait. When a boat is in the water and drive submerged, does the water reach the engine mounted pump? I would think the water in the drive would be lower that the impeller meaning there is suction involved.

With boat in the water remove the hose going to the pump

While there is some its very little suction. There is all kinds of threads here where folks have trouble getting a slightly used impeller to pump. Ya'll have your opinions and I have mine, they don't agree but what else is new.

Anyone with a Bravo, with boat on the hard put your drive in a bucket. Fire it up and see how long your impeller last, I'll wait

Remember, when you back your boat into the lake, your drive is submerged but your water impeller pump on the motor still is above the water level line. When you start the motor , it take a bit of time for the water to exit the exhaust.

Thanks