US citizens do not need and in practice cannot get a Schengen short-stay visa. For all stays that fall under the Schengen visa system (i.e. stays of less than 90 days in any 180-day period), US citizens can present themselves to the border and enter without a visa. As long as the total stay does not exceed the maximum duration and you meet all the usual requirements, you are also allowed to leave and reenter as often as you like so that the visit to Turkey is not an issue.

US citizens do not need and in practice cannot get a Schengen short-stay visa. For all stays that fall under the Schengen visa system (i.e. stays of less than 90 days in any 180-day period), US citizens can present themselves to the border and enter without a visa. As long as the total stay does not exceed the maximum duration and you meet all the usual requirements, you are also allowed to leave and reenter as often as you like so that stopping in Turkey in the middle of the cruise does not create any special issue for you.