Logging messages and a bug fix

Hi @smith6 ,

I've added debug-level logging in a few places.

Also, corrected a bug in the Ocean class. (The @origin attribute of the interpolators was not being set correctly when the Ocean class was being initialized.)

Can you take a quick look and accept the merge request if you are happy with the changes.

Will the version no. be incremented and new version be published to PyPi automatically?

Thanks, Oliver