Sea ores are generall a great think but pain to build (also if you needs fluids in it). So why there are not a Mining Ship for this job?
A cargo ship with a crane on it. You build a ship station near the field, the ship goes there and red field and if xy time goes some ore at the field delete and the ore are in the cargo from the ship. (so long it is full)

(https://mods.factorio.com/mod/Water_Ores) - perfect combination with a mining ship!

You might like https://mods.factorio.com/mod/dredgeworks

• why here are no delet button for doubble posts? Sorry for this.

I use that mod dredgeworks (it was in the pack "All the Overhaups") but i cant deinstall becouse than the water ores are gone - original "Water Ore" dont destroy by landfill but with dredgeworks landfill destroid the ore and cant be deinstall for this savegame) - THATS the reson i wish me a digging boat. And the modder from dredgeworks found the idear interesting but cant design it. So maybe you and he can work together?

This is our conversation https://mods.factorio.com/mod/dredgeworks/discussion/65175ecf113bc41c4d3d76eb

This is beyond the scope of Cargo Ships. I'm only able to maintain it, I don't have time for new features.

The API allows new boats to be added by other mods with the ability to run on rails, or for a car-type boat to have extended-range enter/exit ability. I can help you with using the API.

I thought there was a mining train wagon but I can't find it. That could be applied to a mining ship on water rails, if it exists.

I have absolute no skills in programming. And use for english translators. So i thing for me this are much to complex to write it myself.
i will try to find "a mining train wagon" in the mod list. But more than copy paste other codesnipes and tray and error stupid things i cant do.
I mean i have need 2 houres for understand and changing in dredgeworks the belts from 15 to 30 per second. And use faster miner. And this was only change two words.

But thank you for youre answer.