Unloading with the hatches open?

[Statmk]

Yes. Some cargoes are stickier than others. Common practice to use hoses to rinse. If that does not work it is knocked loose by hand. Inter-cargo contamination many times is not a big deal (a little limestone or coal followed by an ore cargo). Other times, grain or foundry sand, holds almost clean enough to eat out of. Ore pellets not welcome in almost any other cargo. Also you tell the tunnel crew where to apply vibrators to the hold to knock it loose.

[Up North George]

It is common to open the hatches to make sure visually that the cargo holds are emptied.

[Darryl1]

They are checking to see that ALL the cargo is spelling down to the belt. Also, they could be cleaning out the hold.

[Hobieone]

I've seen pics and videos of boomed bulk carriers unloading. They always seem to open most if not all hatch covers.
Is a cargo hold so airtight that ALL must be opened to allow the contents to fall onto a belt ?
I certainly understand how a container must be vented to allow it to be emptied .......... like a can of gas ............. but ALL hatch covers ?
I would think more than one per hold would be over kill and unnecessary work for the deck crew.
Enlightenment is welcome.
Thanks