Charles:
A route video is on the link below. (The video goes from the 13.1 mile point (ish) to the finish, so you sort of start at the end). http://www.fitprorob.biz/marathons/
You can do some very crude calculations based on the video, just in minutes of cycling. Of course the cyclist will have gone much faster on the roads than the beach/mud, so it's likely that the % below is too low on road/concrete and too high for mud/beach. Anyway it looks like the route is about:
40% road/pavement/concrete
45% track (gravelly path: can get puddles, but not really slippery mud)
15% track/beach (not so gravelly: these bits could be muddy)
I've done it the last 2 years, and whilst there's some puddles, and sometimes a bit of mud, it's quite minor. Unless you're planning a 2:30 or something
. Definitely trainers not trail shoes. See you on Sunday!!