[nicthesailor]

Seafarer here. This is basically correct, but the problem is mainly storage before loading.

Ideally, is mined, then either stored somewhere dry, out of the weather, or delivered directly to the ship in a covered train/conveyor belt.

In reality, it's usually mined, then stored in a big pile outside in the weather for weeks/months until it's loaded. It won't pass the pre-loading transportable moisture limit (TML) tests, so they falsify the results.

A cargo with a slightly high TML can appear dry on loading, but the vibration causes the moisture to migrate down to the bottom of the hold and cause the cargo at the bottom to liquify. When the ship rolls, this layer shifts, and the rest with it.

Obviously, if the TML is way too high, the whole thing turns to slurry.

[russfink]

Can they just pump the water out?

[nicthesailor]

To pump out, we need it to settle out of the cargo so that we can get it to the pumps. That works for certain types of cargo (iron ore and most types of coal are easy), but if it forms slurry instead, we can't get it out unless we can somehow pump the slurry out.

Normal bilge pumps can't cope with slurry.