The USCG as of 2013 is asking the law be changed. The old law states that any vessel from 39'4" and above (MUST) have a copy of the Nav rule hand book onboard the Vessel.
The USCG is asking the rule be dropped from 39' 4" down to 16 feet. I have not hear if they have gotten their wish as of yet and if it is the law.
I do know under the old law a Hard copy of the hand book must be onboard the Vessel. The reason being If a Vessel's power fails the Capt of the vessel still have a hard copy of the the hand book to use. That is what the USCG told us in a class any ways. But however, if this new Law has passed they may have change that as well I do not know, but a simply call to the USCG will tell you if you still need a hard copy of the book or not.
Also here is a good link that may help some people with the Nav Rules.
All the best.