I'm telling you - on the deck of a monohull healing at 20 degrees punching through chop without the aid of a trapeze line....it's livable gription barefoot and great with shoes. Most certainly that can be applied to trapezing.

To get technical about it - the static friction while barefoot remains the same...perhaps reduced a little initially. Static Friction while wearing deck shoes goes up dramatically. Kinetic friction while barefoot goes down dramatically (i.e. once you start slipping it's more slippery) while wearing shoes it is still increased a good bit.

Static friction can be losely interpreted as how grippy a surface is when neither of the contact surfaces are moving relative to each other - they are "static"... i.e. how much pressure it takes to get your foot to move while it's planted on the hull. Kinetic friction is resistance to motion between two surfaces when there is already motion between them (like resistance while you are already sliding). They are two very different values and the static friction is typically greater than kinetic friction. In this case, while barefoot, the static friction remains about the same while the kinetic friction becomes a good bit less.