Ballast tank filltime

[91nautique]

Any one good at math?

Im building a fiberglass ballast tank for the bow section
of my boat,and what I need to know is-

Using two, inch and a half scoop fittings ( facing forward) what
would be the fill time of a tank with capacity of 330 pounds,
from empty to full @ aprox 22 mph ?
Both fill lines will be fed into the tank from the top- ie no restiction
to flow and vented

Any body know how to roughly calculate this?? Or done something similar?

Thanks