Creating pressure using water flow 1

[Pdnorenberg]

I am trying to find a way to fill and empty a ballast system on a boat without using any type of pumps. By using an underwater intake the ballast tanks are easy to fill by simply driving the boat at high speeds, forcing the water into the tanks. However, I was trying to find a way that I could use rushing water to create air pressure or suction that would make it easy to empty the tanks quickly and efficiently. If you could give me any basic ideas to experiement with it would be a big help. Thank you.

 

[TheBlacksmith]

Can you open the tanks to the transom area while at speed? I've seen more than a few good old boys "pump out" their runabouts by removing the bilge plug while planed off; the transom tends to be a low pressure area as the water rushes to fill in the hole behind a fast moving boat.

Blacksmith

 

[PUMPDESIGNER]

Easy. I am not sure if they are sold any longer, but 30 years ago you could purchase at any marine store a small die cast hose fitting that went onto the end of a garden hose. It had a small tube that went down into the bilge. Turn on the city water and direct the spray overboard. Through venturi action the hose dropped into the bilge would have negative pressure and would empty the bilge.
Set up any sort of a venturi device and you get the same effect.

PUMPDESIGNER

 

[DLANDISSR]

Pdnorenberg:
Since the water pressure from driving the boat forces water into the tank through (I assume) forward facing inlet you could install another valved outlet facing backward, perhaps in the transome.
The negative pressure from the water flowing across the backward facing outlet would cause the water to flow out of the tank.

This would work similarly to taking a transome plug out and driving the boat to drain water out of the bilge.