Crack in propellor

[hollmanr]

Hi, the haul out today brought me 2 "presents". A crack in the propeller (picture 3) and 3 gauge marks on the back of the keel (picture 1). The gauge marks are slighly bend to the side, which to me looks like the marks from when my bow line dropped overboard and wrapped itself around the propeller (there are also similar but smaller gauge on the front of the keel (picture 2). (I haven't ran aground since the last haul out when there weren't any of these gauge) I think I can rule out galvanic corrosion as the saildrive itself as well as the propeller don't show signs of pitting. But please correct me if I'm wrong. Any ideas why an aluminium propeller could crack like that ? Could it have happened when the line fouled the propeller ? Boat is a Bavaria 32 cruiser (2005). Thanks !

[Yngmar]

Wow, that must've been some rope!

But yes, the sudden stopping with force acting on a single blade only is able to rupture the propeller like that. It looks like the crack happened some time ago though? There is quite a lot of pitting on the propeller, both old and new, which may have weakened the hub. I see the insulating washer under the cone is installed, but did you check it is working? There should be no electrical contact between propeller and cone or saildrive leg. You can check with a simple multimeter.

I can't quite tell from the photos, but it looks like the nicer lead-antimony keel rather than the cast iron. IIRC it was a 2% antimony alloy and while strong enough, it remains much softer than cast iron, so this makes some sense, but still, that's quite some chunks!