Well the way I look at it is that fibreglass boat does not have a "chassis ground" as such.
So you dont really need to tie anything to your vessels hull. Secondly you dont want current to be running into your steel hull normally or if you have a faulty electrical item. If current flows in your hull you are going to eat away your electrodes. However its difficult to avoid because technical your engine is mounted onto the hull through engine supports which may be insulated. The only reason you would want earth bonding to the hull is for "equi-potential bonding" for lighting or things like a HF radio to prevent interference. You dont want DC, RF or 240AC at different potentials. Its a hazard for shock, Lightning damage, RF problems and safety. So the ideal is to have one ground reference point for all systems and that does not require you to use your hull if you have a proper ground return bus bar that is not attached to your hull but is floating and not bonded.
When I had a steel boat I just had a heavy copper ground bar. This was my negative DC return and negative bond point for all dc circuits. I did have a switch that grounded this ground bar to the hull when lighting was around through a heavy duty switch. You will have some DC bonding to your hull through the HF antenna tuner, the negative is bonded to the mounting bracket which you will screw to your hull for RF ground. I did bond my tuner to the steel hull but the tuner was floating and not directly connected to the hulll. It was grounded through a RF choke for lightning and RF ground purposes but the choke blocked noise from other circuits interfering with the HF radio. At that time I was using Pactor email and did not want any noise.
The bottom line is that is ONE one ground in the electrical world, and you can call it what you want DC, RF or whatever its essentially the RF or DC current return path. On metal hull you want to be careful about electrolysis and dont currents running through the hull by design or accident like cars that use the cars body as a negative ground wire.
