bobofthenorth
Guru
- Joined
- Oct 18, 2009
- Messages
- 570
- Location
- Canada
- Vessel Name
- Gray Hawk
- Vessel Make
- Defever 43 Offshore Cruiser
OK - so we've got a Wesmar bow thruster on Gray Hawk and its bonded with #8 wire more or less directly to 2: 6 x 12 zincs mid hull.* It also has a "B" prop nut zinc directly on the thruster prop.*
When we pulled Gray Hawk for the survey the prop zinc was pretty well gone.* The PO didn't change it at that time but I hired a diver shortly after we closed and he replaced that zinc.* At the same time he added two eggs to the prop shafts which already had an egg apiece on them.*
Fast forward three months and we are changing marinas so I hired a diver to have a look-see and he reported a consumed prop zinc on the bow thruster, which we replaced again.* The rest of the zincs showed what seemed a more "normal" rate of consumption.* The plates are eroding but not abnormally as are the shaft zincs.* The oldest shaft zinc "eggs" were pretty well gone so we pulled them and put on new ones but the ones that we added in Seattle were still in good shape.
So what's the problem?**I don't know if that rapid erosion on the Wesmar zinc is "normal"?* I don't have any baseline so I look to the collective wisdom of this group for your input.*
I thought that the rapid erosion must indicate a bad bond between the bow thruster and the plate zincs but tonight I checked that out with a VOM capable of .001 ohm measurements and it shows 0.000 ohms between the bow thruster case and the plate zincs.*
It seems to me I have three possibilities:
- this is normal erosion of the bow thruster zinc which means I need to be checking it more often than every three months
- I've had some localized hot spot (dunno if that is even possible) in which case it will have a different erosion rate going forward
- my diver in Seattle neglected to change this zinc, despite the fact that he charged me for it and presented a consumed zinc
What am I missing?
When we pulled Gray Hawk for the survey the prop zinc was pretty well gone.* The PO didn't change it at that time but I hired a diver shortly after we closed and he replaced that zinc.* At the same time he added two eggs to the prop shafts which already had an egg apiece on them.*
Fast forward three months and we are changing marinas so I hired a diver to have a look-see and he reported a consumed prop zinc on the bow thruster, which we replaced again.* The rest of the zincs showed what seemed a more "normal" rate of consumption.* The plates are eroding but not abnormally as are the shaft zincs.* The oldest shaft zinc "eggs" were pretty well gone so we pulled them and put on new ones but the ones that we added in Seattle were still in good shape.
So what's the problem?**I don't know if that rapid erosion on the Wesmar zinc is "normal"?* I don't have any baseline so I look to the collective wisdom of this group for your input.*
I thought that the rapid erosion must indicate a bad bond between the bow thruster and the plate zincs but tonight I checked that out with a VOM capable of .001 ohm measurements and it shows 0.000 ohms between the bow thruster case and the plate zincs.*
It seems to me I have three possibilities:
- this is normal erosion of the bow thruster zinc which means I need to be checking it more often than every three months
- I've had some localized hot spot (dunno if that is even possible) in which case it will have a different erosion rate going forward
- my diver in Seattle neglected to change this zinc, despite the fact that he charged me for it and presented a consumed zinc
What am I missing?