Sense or Nonsense Hanging Zinc Anode Overboard?

[Goudurix]

In our marina (Belgium, seawater) more and more GRP sailing boats start to hang extra zinc anodes attached to a S/S wire, overboard, as (extra) cathodic protection.
On european boats we do not have the shore power earth connected to the boat 12V negative DC ground system.
So what is the sense of hanging an extra anode overboard (wire connected to engine blok or DC negative or propeller shaft etc) if one has the adequate zincs alreay installed "according to good practice" = on propeller shat close to the propeller nd if possible and extra one on the propeller retaining nut?

I see them installing commercially available stuff consisting of a stainless steel cable attached to a heavy zinc. Other side of the cable to be hung over a stanchion or similar (providing this stanchion is bonded into the DC ground....)

I thought that to provide good cathodic protection a zinc should:
- be fixed/connected electrically as good as possible (eg. fixed ON the shat or ON the propeller providing a tight electrical contact) => the S/S wire plus"hanging" it over a stanchion doesn't sound like a good low-resistance tight connection to me...
- as close as possible to the metal it should protect

Your comments?
Does it make sense or is it a waste of money?


Jan