Photo, et all,
I believe SD is right. Not going to help a lot with the dissipator if the boat is not grounded.
My personal opinion (AND IT IS A PERSONAL OPINION): If you are primarily coastal and do NOT need a
SSB, do NOT ground.
If you either want an
SSB or are going to be doing a fair amount of offshore: Ground the crap out of the boat and put a dissipator on top.
Either way, you take your chances... but you also take your chances everytime you hop in your car and get on the highway. Do your best, then don't let it consume you (no pun intended).