Put a period at the end of the sentence and it changes from

> Segelschiffe in rauer See verlangen Ärger.

to

> Segelschiffe in rauher See sind ein Problem.

The translating software can't distinguish between 'sailing ships' the noun, and 'sailing' (verb) 'ships' (noun) the act. The latter is what is probably intended. It is also missing chances of using idiomatic expressions in the translations.

Well, 'is' is singular so it can’t be the correct verb associated to 'sailing ships' if the latter means multiple sailing ships rather than the activity of sailing ships.

I like that I can clikc a word in the target box and choose an alternative translation while the system updates the result accordingly. Previously, I had to play with different translation alternatives manually in Google or Yandex translate. I think deepl also learns from such user choices.

Google Translate lets you do that too..

It used to, but not anymore for long sentences. That is one big reason that I switched.