Rules concerning alternate modes of travel?
 

After reading the rules for the Guinness record for cycling around the world on Mark Beaumont's site, I was wondering if there are any rules as to time discounted when it is necessary to travel by sea or air on a brevet or similar long distance ride. If a brevet took place on a small island and a boat ride was necessary to complete the trip, would the time spent on the boat be taken from the total ride time?

This doesn't have any real-life implications for me, I'm just bored and letting my mind wonder a little too much.

You might browse around the BC Randonneur and SIR sites for the answer to your question ... I believe both have rides which include ferries.

http://www.randonneurs.bc.ca/
http://www.seattlerandonneur.org/