Here in Florida, I have installed 20 foot poles, 10" in diameter, 7' deep in the silt bottom. Here every thing is sand so a 5 horse water sump pump with a 3" diameter end on a 8 feet length aluminum pipe, is enough to shoot the sand out while you set the polls. It takes about 20 minutes to set a pole using the water pressure. If necessary The last foot or so is driven with a heavy weight off a 25' high boom that is used to lower the pole in place. Cost here to have it done is like $250.00 a pole and $250.00 to set each one.($500.00 each.) I have a friend that did my pole work with my help, when I revamped my 2 boat lifts. I did my first lift pictured in my avatar last spring.
Karl