Decks, Patios, Porches and Docks - driving 6x6" dock posts thru muck to bedrock?

My aunt has commisioned a friend and I to build a new dock/pier for them at our lake. They want an 8' wide 48' long pier, straight out from the seawall. Looking at other docks, we have decided on either 6x6" or 6x4" posts, every 10 to 12 feet, 8' apart. At the seawall, the water is only 2' deep, progressing out to about 7' at the end of the pier. I have done a little calling around, and found a place that rents a post driver, but will only drive a 4x4" post. Any help on what or where i should look for something to drive these posts?

My uncle on the same lake (small freshwater lake infested with zebra mussels) said he had to go down almost 18' (below the muck bottom) till he got solid bedrock. He was smart and did all his post driving in the winter when the ice was frozen, which we can't do. This is the closest thing I have found to a pier forum, for information on building a dock. Other suggestions would be appreciated.

Thanks,
Jaime

the two basic methods are platfom mounted drivers (rams) or jetting in the post with water pressure. you need a decent pressure pump to jet them in and you need to place the intake hose upstream from the debris flow so as not to suck up the mucky water. 1/2" inch pipe with a 3/8" reducer in the end seems to work well. you might be able to use the home's water supply if it's around 50 or 60 PSI with good flow rates.
it's a three man job at least as one runs the jet, one holds the post and one hammers it down. with the possibility of having to go 18' i would consider a floating dock.

the two basic methods are platfom mounted drivers (rams) or jetting in the post with water pressure. you need a decent pressure pump to jet them in and you need to place the intake hose upstream from the debris flow so as not to suck up the mucky water. 1/2" inch pipe with a 3/8" reducer in the end seems to work well. you might be able to use the home's water supply if it's around 50 or 60 PSI with good flow rates.
it's a three man job at least as one runs the jet, one holds the post and one hammers it down. with the possibility of having to go 18' i would consider a floating dock.

Could provide a little more detail on 'Jetting' them in? Do you just jab the pipe down along the sides of the post to assist in allowing it to sink down into the muck?

Could provide a little more detail on 'Jetting' them in? Do you just jab the pipe down along the sides of the post to assist in allowing it to sink down into the muck?

yes, you have the idea. you're blowing out the muck with the pipe and water pressure and the post follows it down. you need a balance of pressure and volume. overkill on pressure (pressure washer ) will not work. i've rented our small Echo two stroke pumps for this a few times and have sold a couple of the Homelite fire fighter pumps to contractors in the past for this application. you need enough pressure to displace the material and then enough volume to wash it away. too little of either one and it won't work.