You can get the average speed by just dividing the distance by time (not time by distance). For example, if you travel 120 miles in 2 hours that’s 120/2 or 60 miles per hour.
This site will give you the distance between two points:
It comes up with a distance of 4550 miles. There are probably several other apps out there that can give you distance as well.
However, if you look at the map from the above site, it doesn’t make much sense to use that as a calculator for a ship. You’d have to sail over parts of Connecticut, Newfoundland, and Nova Scotia, and then once you get across the Atlantic you’d have to sail across France and the island of Sardinia. Most ships don’t handle the overland parts of that journey very well.
I don’t know of any online map that can do it, but you can take a piece of string and place it along the surface of a globe to follow the path that a ship would take. When you get to your destination, pull the string out straight and measure it. Use that against the scale on the globe and you can get a rough idea of the distance. If you know how fast a ship travels, you could then use that to figure out roughly how long it would take for the ship to go that distance.
You may be able to do the same sort of thing with google maps, but it wanted me to log in to create an account in order to access the “my maps” application there so I didn’t try it.
Let’s say for example though that you end up with a sailing distance of 8000 miles, and your ship travels at 25 knots. 1 knot is 1.15 miles per hour, so 25 knots would be 28.75 mph. 8000 miles divided by 28.75 miles per hour is 278 hours. Divide that by 24 and you get about eleven and a half days.