[C320-list] P-Bracket Dezincification

[Dennis Cookson]

Bruce, thanks for your reply.  Never heard of a strut made from fibreglass, very interesting. I don’t know anyone here in the UK that could do that but I have time to find a bronze replacement. CatalinaDirect have it but the price is quite high even before import duty, VAT, shipping etc. Can you remember the name of the original supplier that cast them?

Dennis Cookson
‘Catalina’ #0577


> On 29 Oct 2024, at 19:28, bruceheyman via C320-list <c320-list at lists.catalina320.com> wrote:
> 
> HI Dennis,Probably at least 10 years ago we saw signs of galvanic corrosion on the strut.  At the time it did not have a zinc and it was not bonded (that I could find) to the vessel ground.  We did add a smallish disk zinc at that time to the strut.  The monthly diver added it to the inspect/replace as needed list.   
> At our last dry dock we found that the strut had cracked along the surface where it comes out of the hull.   We found the original company that cast them for Catalina but they were going to take 8 weeks to get the part to us as they had zero in stock.  I choose to let the yard machine a new one out of G10.   Problem solved as we will never have to worry about galvanic corrosion again....at least for that part.BruceSomerset Los Angeles
>    On Tuesday, October 29, 2024 at 12:10:59 PM PDT, Dennis Cookson via C320-list <c320-list at lists.catalina320.com> wrote:  
> 
> I had a marine engineer booked to replace my cutlass bearing today but things didn’t go exactly to plan. After removing the propeller he fitted a Strut-Pro tool to push out the old bearing but immediately found that the leading surface of the P-bracket/prop strut sleeve around the bearing started to flake away revealing a bright pink rough area. This is apparently bronze that has become dezincified, whereby the zinc content of the bronze has been leached away by either chloride corrosion or galvanic corrosion. Either way, it is irreversible, and the engineer informed me that the P bracket would need to be replaced as it would be weak and prone to further damage.
> 
> I’m wondering if any other 320 owner has encountered this, or has knowledge of why it might occur. I replace my sacrificial zinc anode annually, which is bolted to the hull, and grounded. I haven’t yet determined whether the P-bracket is connected in the same way. We’re rarely connected to shore power as the boat is kept on a swinging mooring during summer months and lies on the hard over winter.
> 
> Is your P-bracket bonded to your electrical system?  Or do you have a zinc anode fitted directly to the bracket, as suggested by Catalina Direct <https://www.catalinadirect.com/shop-by-boat/capri-26/engine/props-etc/prop-strut-zinc/>?
> 
> Dennis Cookson
> ‘Catalina’ #0577