Will the Starlink constellation provide an alternative to the Inmarsat?

Iridium not Inmarsat - Sorry!!

Not for inReach purposes. Starlink requires a tri-pod mounted 19 inch dish. Also, service for a particular account is constrained to an individual cell. Even if you lug the equipment, you cannot travel far and still receive service. Bottom line is that it might be fine Internet service (1Gb - OTOH, it requires an insanely clear field of view), but it's not a substitute for iR devices in the field.

Pity about the single cell requirement.  I was thinking that Starlink would be a far superior solution for internet on the high seas than any current solution.

Guess not.

Thanks Guys, it was looking promising... oh well 

Elon isn't interested in the niche group of a few thousand people who want better internet during international expeditions. He's targeting the billions of people who want to ditch their regular home internet providers, because that's where the money is. Those customers don't mind having to use a stationary 18-inch satellite dish.

The market segment for people who want better internet connectivity on the high seas, or in the wilderness, is too small. So we probably won't see a lot of new technology for that in the near future, beyond what we already have.