Saildrive Anode Depletion

[Ammonite]

I've just hauled out after 7 months afloat and the zinc anode on my 120SD saildrive has virtually disappeared. The engine is an MD2040 and its isolated from the drive (I've confirmed there's no continuity). The prop is a Brunton's Autoprop with its own zinc anode and its fitted with an Ambassador ropecutter which by design bridges the usual Autoprop isolation. The zinc prop anode is only circa 20% depleted. There is no shore power on our pontoon and we have probably plugged into shore power (no galvanic isolator) for something like 30 days this year. There's an additional zinc pear anode attached to the gearbox (and nothing else) as a backup for the saildrive anode in direct sight of the saildrive about 2ft away. This has lost very little but I'm assuming the saildrive anode would need to dissappear completely before this does anything. There is another zinc pear fitted as standard (Moody 36) that is connected to the rudder, keel cooler, keel and dc negative and ac earth. What's the most likely cause of the excess depletion and what can I check to confirm this or is the make up of the Autoprop such that the Saildrive anode gets depleted first? Under normal circumstances the Autoprop prop anodes apparently don't last very long but mine does. I'm planning on changing the dedicated gearbox, saildrive and prop anodes to aluminium next season. Thanks

Edit - there is a good connection between the prop and prop anode

 

[Daydream believer]

I have always used 2 autoprop anodes a season & one saildrive (120s) anode every season -coupled to a volvo 2020. Plus Ambasador clone rope cutter (Did have an Ambassador but it wore out).
Only connected to shore power when away from my own marina on holiday, or at home when needing a battery charge up- usually prior to departure. Jefra advise no anode should be connected to the rudder on a Hanse. ( Aluminium rudder shaft) There is no other anode on the boat. Galvanic isolator fitted.

The prop is connected through the rope cutter to the saildrive. The bearings do not isolate it.

Now I have a 2030 engine the anode has less metal & I have re used the old anode. It has been in the water 3 months & I do not expect to be in long next year before the boat will need a mid season scrub.(Coppercoat). I will monitor progress & change then if needed. Ambassador anodes are expensive so I buy the standard ones & machine them to suit. It is awfull cutting away all that zinc but it saves £40 a pop. Brunton anodes are stupidly expensive as well. Adrian Miles sold me a stock before he retired.

I have saved all my anodes for the past 20 years. I have nearly finished a small forge & will mould my own. Unfortunately the split ones for the saildrive are harder but at least the prop does not have to be removed to change them on the current saildrive with my new Volvo D-2030 engine fitted recently.

 

[vyv_cox]

My Bruntons Autoprop is on a shaft drive protected by its own anode and a shaft anode. The Autoprop anode typically lasted for one season and the shaft anode for two (six months in the water in Greece, water temp between about 24 - 29C). I painted the prop with Hammerite plus Velox antifouling, pretty effective, but as a bonus the anode life has doubled. Two years for the Autoprop anode and at least four years for the shaft anode, would probably do more. Propeller antifouling with Velox

 

[Ammonite]

I should have added that the prop is painted