I am building an 8ft x 16ft Residential fixed dock and plan to use pressure treated 4x6 posts embedded in concrete for the vertical supports (placed on 4ft-8in centers). The dock is on a freshwater lake. The dock will be in a no wake area so I will not have that much force on the dock.

The water level is dropped about 6 feet during the winter to prevent damage from ice. The posts will be 3ft above the water line in the winter. I plan to dig the post holes by hand this winter, set the 4 x 6 posts and pour the concrete. I plan to use an 18 inch dia tube for the concrete forms.

My questions are:

1) How deep should I dig the holes?  The frost line is 20 inches in my region.  Is 24in depth sufficient?

2) Do I need to add some rebar to the concrete?

3) Is it OK to embedd the treated post in the concrete or is it better to have concrete extend to the waterline and then use treated posts above the waterline?  (I am looking for 10 years service).