Here's a preview from the 3rd edition of Moon Nicaragua, due on the shelves later this year. Also have a look at
http://www.bigcornisland.com/river.html:
Contact the Emusepci office just inside the gates of the municipal dock for current ship schedules (open 7 a.m. - 5:30p.m.), or call their office in Rama (tel. 505/572-1467)
Also consider the San Nikolas, a weekly RORO freighter between El Rama and Corn Island, which will actually arrange your entire overland journey from Granada. The ship leaves midnight on Thursdays from Rama and arrives Corn Island at 4.00 pm on Friday. Cost is $17 each way Rama/Corn Island (tel. 505/277-0970,
www.semarflu.com).