check to make sure that "rowboat" is a datablock
I spawned a rowboat on a vehicle spawn and used /getid on it (13235 for my case with that rowboat)
then using the ID in the console, I dumped its data (13235.dump();) and saw that its datablock is "RowBoatArmor"
another way to do it is to use the getDatablock() function, which if you print it will give you a number
you can (probably) then use this number in the change datablock command, or do <target>.changeDatablock(<ID>.getDatablock());
hopefully that will help you with other datablocks too, and not just the rowboat