That will depend on the type of boat, but it can be done in as little as 2 hours in a high speed ferry.
Not directly, you can take the Dublin Ferry to Holyhead Wales or Liverpool England then take a Train to Newcastle.
Dublin is in Europe, so you could say the answer is zero. The nearest European country would be Wales, which is less than 2 hours by boat. To mainland Europe, which is probably what you mean, it can be done in less than 2 days. There are no actual ferries from Dublin to any mainland Europe country.
Fishguard is in Wales, not Ireland. You'll need to take a ferry to get from Fishguard to Dublin or Vice Versa. There are daily ferries, they take a few hours.
The only way to sail from Wales to Orkney is by sailing boat, so the time taken will depend entirely on wind and weather conditions during the voyage.
The two main places to sail from are Dublin and nearby D
16 hrs 50 min from Dublin to Bishkek
You can be in Scotland from Dublin by air in less than 40 minutes.
how long will it take a small boat from england to Greece
a while
It is about 9 hours.
About 14 hours
About 40 minutes.