Composite fender board.

Features:

• smooth round edges — less of a chance to dent the hull
• concealed vertical holes — protects lines from getting chafed
• two holes on each end — one goes to the vessel, the other to the fender's bottom loop
• modular design — allows full customization to best suit your vessel
• unsinkable — could be used as personal flotation device in emergency situations
• lightweight — lighter than wood, makes your boat go faster
• versatile — can be used to patch the hull in case of a serious collision

The core should ideally be made out of foam (Airex, Last-a-Foam, Rohacell, Divinycell, etc), cut on a CNC (please see “Fender Board - Core” design for reference).  A Nomex or Kevlar sandwich panel can be used as well, but the round edges might require some filler prior to lamination.  If you feel adventurous, printing the core could save you money and weight, but I wouldn't be able to tell how strong that'll end up being when compared to closed-cell foam or even plywood.  The board's total length and position of holes needs to be calculated based on the vessel's size and where exactly it is planned to be hanged from.

The designs are 1" thick, 6" wide, intended for ½" lines.  Once completed with FRP, primed, and painted, the dimensions will become slightly larger.  If dealing with metric system, or e.g. to compensate for cutting a 24" foam board into 4 pieces, uniformly scale all parts down to be 25mm thick.

Printing

PLA could work, but something stronger (e.g. ABS) is preferable.  The problem is, epoxy heats up while curing, and that could easily deform PLA.  Not to mention exposure to the sun's heat, especially if you use dark paint.  Since this thing is going to be scratched a lot during use, it might be a good idea to use some kind of bio-resin, e.g. epoxy from R*Concepts: https://livingrconcept.com/products/

10% infill should be sufficient, since the build needs to be reinforced either with glass, basalt, aramid, or whatever else you have in mind.  Carbon fiber might be light, but will likely shatter and crack from being bumped and rubbed against pilings, so please only use it if you really know what you're doing.

3D honeycomb should be a good choice for the infill pattern, but there might be more suitable patterns for this build, especially considering that almost all impacts will come solely from one direction (the dock).