From Naoshima to Koyoto

According to the timetables, there is a ferry arriving at Uno Harbour 17.55 - and there is a train to Kyoto leaving 18.07

Is this enough time to catch the train? Are the feries some times delayed?

The station seems to be very close to the harbour.

A1)
About 5 min walk no worry not so far.
But if return ferry very crawded also no return ticket for train(JR)
Uno stn ticket vending machines and ticket window are not so many.
So should buy return ticket at ticket window(not regular vending machine)
before going to ferry port for Naoshima. (if need)

Republished captured Google MAP add directions.
https://s15.postimg.org/lvia3v5vf/uno_port_to_JRstn.jpg
This is also understanding easier.
https://youtu.be/Cm2Fu7OZhb0

If stay one or more nights in Naoshima buy at ticket window.
(At ticket for reserved vending machine possible by EN menu but need more minutes)
http://train.skygrass.net/railway/jrw/st33/uno.html
http://4travel.jp/travelogue/10435582
Also regular ticket vending machine not covered until Kyoto. (too,far)
No (touch screen) button of oneway fare. (fare table on yr head,too)
https://momotarookayama757.files.wordpress.com/2016/02/img_1480.jpg
(note)
Uno stn has not ICOCA or other IC card ticket(Suica,PASMO or) acceptable gate.
Also fr Kyoto by regular also for Shinkansen until Okayama,too.
IC card NOT covered fr/to KYOTO/OSAKA(as Kinki) area
fr/to OKAYAMA/HIROSHIMA/KAGAWA area and Shinkansen.
http://cool5.sakura.ne.jp/blog/wp-content/uploads/2015/04/wpid-sc_2015...

A2)
Seto naikai(Seto Inland Sea) is one of sea streaming very faster than Ocean
https://youtu.be/V9nz76k980U
but basically wave won't be high just worried super strong wind or deep fog mainly.
Ferry company reported cancel and restart info both .
Last cancel date is MAY in this summer operated everyday all schedule.
http://www.shikokukisen.com/news/traffic-info/
(Use Google translate)

This is not btw Uno and Naoshima ferry route
"Uzusio cruise" in Naruto area far east fr Naoshima.
https://youtu.be/k570zKZpGHE
https://www.uzusio.com/
https://en.wikipedia.org/wiki/Naruto_whirlpools
This is one of huge "ART" of Japan :)

The ferry and train times are coordinated across the day so people can get from the ferry to the train. It is a short walk and a pretty easy transfer.

I am Japanese live in Kagawa.
I think that it is difficult to catch 18:07 train from the 17:55 ferry.
Certainly,it is close to Uno stn from Uno ferry port, but the ferry always arrives at Uno ferry port at 17:55.
So I suggest that you should buy 18:42 train ticket.If you get 18:07 train,you may change train tickets at ticket window.

Thanks for very useful answers. I'll see if i can get tickets to the later train (we are 15 people).

Looking so much forward to visit japan!

Yes, you can see the train station from the ferry, but you have to cross a couple of roads and actually the trains are NOT always coordinated to match the ferries. If you get right to the front of the queue of departing passengers, and you get a move on, you MAY catch the train, but you may not.

There's not an awful lot to do at Uno station, but you can spend 10 minutes checking our the sculptures between the ferry pier and the station, and you can go to the combini on the next street corner and get drinks/snacks for your journey, and by the time you've done that you should have only a short wait for the next train.

You'll probably be so chilled out from your time in Naoshima that you won't be in the mood for rushing. While you're there, I assume you're going to go to the Chichu Museum (you really should, it's excellent). I would also highly recommend the James Turrell/Tadao Ando arthouse project. If you're rushed for time and can't do everything, I'd skip the Lee Ufan - but your tastes may vary.