depth for deck footings

My wife and I have been working on an old house we purchased late last year. Before starting on the porch I wanted to check the footings and make sure we had a good base to build on. In the back of mind I knew I was opening a can of worms but it just had to be done. The results were worse than I thought.

2 4x4 posts go down into concrete, they appear to be the only thing holding the porch up at this point, both are wet and easily marred with a hammer. The one in the middle is just gone. The construction of the porch looks solid otherwise.

My plan is to use those paper forms to cast new footing and put new posting up to the 2x6. My question is how deep for this area?

Pictures were gnarly but just won’t upload.

2 feet will good as long as the soil is dry and not marsh muck

and do http://www.strongtie.com/products/connectors/lcb-cb.asp#

Woodfloats?