Limber Hole Debris Screen
This is a grill that inserts in the limber hole of my boat to keep leaves and other debris from plugging it up. I've had these in place for four months now, and they work well.
I have a similar design for the transom and splashwell drains at http://www.thingiverse.com/thing:448673, and for the bed of my pickup truck at http://www.thingiverse.com/thing:464492.