1/32 of an inch per foot. So an 8 ft long piece can expand and contract up to a 1/4 inch over I believe a 40° temperature range. There is plenty of lumber that does that as well. Also living in Ft. Lauderdale you probably won't have to worry much about that. Hope this info helps
What thickness of Starboard will do the trick? I looked at the new Grady's at the boat show and recall thinking that the toe rails were thicker then 3/4 inch. Also they were shaped some - i.e, run through a router with a beaded edge.
I did not use starboard to replace the duratrim toe rails on my 1994 Tournament 192 for this exact reason. Any expansion/contraction for me seemed unreasonable. I used good quality teak and it looks great. Will require maintenance, but it's such a small amount of teak that it doesn't bother me.
I used 1 inch thick Starboard. Slotted the holes a bit, 1/8" on each hole and no noticable changes in summer. Snugged up the screws and they are not loose at all.