Windsailor
9 volt batteries are small and that would be nice to carry.   One 9 volt battery would be too low a voltage and 2 in series would be too high.  There is not enough capacity to run a detector for very long.  Your suggestion of lighting got me to thinking.  I have found area lighting uses a lot of power but if you can light only the area you are working in it would greatly reduce the power required.  Like the cap mounted led lights.  I could see mounting one on the gunnel.  Your comments bring visions of trying to tie a knot in the dark and what would help would be a light mounted near your hands.  Something that was easy to turn on and off would last for years.  If you come up with something that work well let us know what your find.