This is NOT normal for grounding to the "engine". A bare starter bolt perhaps...
I ALSO ground my alternator
BTW, with a "separate" smaller - wire, not relying solely on the engine's main battery - wire. This is a more reliable, low loss connection.
Unless bonded, the strut is not normally connected "electrically" to the shaft at all, as the rubber lined cutlass bearing separates it from the shaft.
In my case, I isolated the engine from the AC and DC system (except when its running), by installing an on off switch in the black - wire, as well as the red + one. I shut off both during the 99.9% of the time that its not running. This minimizes any stray current, that eats zincs.
For galvanic protection of the shaft / strut / and prop... The one shaft zinc alone does the job for a year. It is bonded internally from a bolt on the strut's inside surface, to the shaft "brush". This provides contact between the shaft and strut. If you're not using a shaft brush and bonding wire, your strut is not protected by the shaft's zinc at all.
These changes have eliminated my early problems with rapid zinc consumption
from 16 years ago, and all underwater metal is stable.
I also isolated my mast's lightning ground from the AC and DC system, as well as aft bonding wire. This required that I isolate things like the base of the VHF
antennae, which is common with the DC-. By using diodes to connect the SSB
radio's copper strap to the grounding plate, it transmits RF energy, but NOT DC current.
This was partially after consultation with Stan Honey, 15 years ago, who helped diagnose my problems. I was an ABYC member
while building our boat, and had wired it with ONE common ground, as ABYC specified. In my case, this created a battery of stray currents that was eating zincs at an astronomical rate! I was also OVER zinced at the time. My one shaft zinc is now all that I use, (for the drive train), and the copper plate, as well as rudder hardware
What works on one boat will not necessarily work on another. You may need to experiment
. Bear in mind that the ABYC standards are a great starting point, but may not work for you. Their orientation seems to be toward safety of the "occupants", and minimizing a manufacturer's liability, as opposed to safety of the diver under the boat...
For me, "being" the manufacturer, (can't sue myself), and diving
on the bottom every two weeks to wipe off the slime, I was more concerned about zinc consumption
, (requiring more marina dive time), and my safety IN the water
, than IN the boat, (which has all double insulated AC accouterments). Bear in mind... I do check for proper ground to the dock's AC pedestal
, (with a small testing plug
in device), every time I hook back up, or at a new marina. If I feel the need, a flip of a switch turns the "safety ground" back on.
In any case, there are a lot of ways to wire these boats up, and some careful prioritizing and experimentation may be called for.
Best of luck,