a) In 1/48th, don't bother! Unlike some boilers and bridges, round headed rivets weren't used on hulls, but rather countersunk with flattish/oval headed forms. After a few years of use and several coats of paint, they are almost invisible.
b) One of Tom Gorman's book, I forget which, shows some typical riveting patterns.
c) But you will have rows of rivets on maybe a 4 inch spacing:
All along each plate edge, where it is either lapped over the next, or backed up with a strip behind each butt joint;
Along each plate edge that is joined to what I'll call an edging piece-- stem, keel, stern post, deck edge;
And where each plate overlaps an underlying frame (rib), which may be spaced every foot and a half or so.
d) Image below shows a smaller fireboat (built along tug lines) with all-butted plates, somewhat unusual... but see the rivet pattern at the stem and elsewhere, and note how flush the rivets are.
e) For my 1:24th tug "Dearborn", I did do the rivets, as they can be seen in such a large scale... I used glue drops.
See them going on at
http://www.rcgroups.com/forums/showthread.php?p=8824641#post8824641and how I used a laser to align the ribs' rivet lines:
http://www.rcgroups.com/forums/showthread.php?p=8832752#post8832752and the final result at:
http://www.rcgroups.com/forums/attachment.php?attachmentid=1795972