[Liam]

A power washer will remove the growth no problem on a properly treated bottom,a decent power washer will remove the paint too,and the gel coat if there is any damage to it.
If you plan on cleaning and painting the bottom yourself then investing in a pair of stands is the way to go. There are ways off moving the boat on the trailer to work around the rollers but the job is awful enough with the boat on stands.
Unless you are dedicated to the job or money is an object you may find redoing a bottom is something you tackle just one time then decide its money well spent to have someone else do it