Boat, no tripod. Also some wading.
For wading, the only solution I've found is a short neck strap. Any other connection point will allow the camera to hit the water. Not always that comfortable, but that's life. Anything that has some length to it will allow the camera to hit the water (unless very shallow water). One issue I've had is that if wading in waist high water (or higher) and using a physically long lens, the end of the lens could hit the water regardless of attachment point.
In a boat, a wrist strap is OK unless in rough water where you may need to unexpectedly brace yourself. Your hand automatically reaches for a handhold and your camera bangs the boat. A chest harness might work, but I haven't tried one.
So the only solutions I have used (and think will work) violate your "no neck strap", no "wrist strap" rule.