sea

[dilodi83]

Do they mean the same or are there any substantial differences among these expressions?

rough sea
choppy sea
heavy sea (does it exist?) like heavy and rough weather

any other suggestions?

[5jj]

For me, and the people I sailed with:

choppy sea - lots of small waves; inconvenient, but not dangerous
heavy sea - large waves; potentially dangerous
rough sea - worse than heavy; we would not sail.

We also had a lumpy sea - somewhere between choppy and heavy.

[dilodi83]

Thank you very much.

[5jj]

Thank you very much.

You are welcome.

Please do not take my answers as definitive. What is a choppy sea to a seasoned sailor might appear very rough to a landlubber.

[Rover_KE]

The Douglas Sea Scale describes sea conditions in a nine point classification table.

Rover

[5jj]

The Douglas Sea Scale describes sea conditions in a nine point classification table.

It does indeed. In my experience, however, most of the morons nice people putting out to sea have never heard of the Douglas Sea Scale,Beaufort scale - Wikipedia, the free encyclopedia, or even the BBC weather forecast.

[SoothingDave]

A heavy sea is not made up of heavy water, however.

Heavy water | Define Heavy water at Dictionary.com