Wednesday, December 11, 2019

Investigating the rudder shoe

When I started the bottom job project, I had a chance to check the rudder fittings. I noticed a crack in the fiberglass over where the rudder shoe was located at the aft-end of the keel. I was concerned that the crack may be a sign of corrosion in the bronze rudder shoe itself.  Bronze doesn't rust but it does suffer from electrolytic corrosion. The boat rudder rests and rotates on top of this shoe, which is bolted onto the keel. If the rudder shoe fails, the rudder may fall down to Davey Jones' locker.  That would be bad. 

A crack in the fiberglass over the rudder shoe.


Sanding away at the fiberglass layer over the rudder shoe, I discovered that the rudder shoe is fine, with no external signs of corrosion. (Can't find the photo! But trust me.) Because the rudder shoe is made of bronze (note the green oxidation stains) which suffers far less from crevice or pit corrosion in oxygen-deprived environments, there's no need to remove it entirely to additionally check the inside of the shoe for corrosion (unlike chainplates made of stainless steel which do suffer from crevice/pit corrosion and so should be removed entirely when checked.)  The crack was just a thin layer of fiberglass matting that had delaminated off of the bronze rudder shoe. Bronze is far superior to stainless steel for underwater use but like any metal it is subject to electrolytic corrosion aka stray current corrosion. Also, fiberglass-to-metal bonds never last, and inevitably will delaminate. Potentially this exposes the bronze underwater fitting to stray current corrosion once the bronze touches seawater. But this was not a big problem to fix since there was no corrosion. All I had to do was scuff up the shoe surface so it had some "tooth"and then encapsulate the bronze shoe under new layer of fiberglass to isolate it from the external sea water & so avoid electrolytic corrosion. 

The rudder post seemed fine but
we'll see more once I drop the rudder entirely

Investigating further, the rudder post seemed fine, the rudder itself seems fine and is made of solid fiberglass (as with the centerboard) with no signs of water intrusion or delamination. I had repacked the rudder stuffing box but since I've decided to drop the rudder entirely, I will be loosening that up again too.

Here's the funny thing. While stripping the bottom plain off of the rudder, it became apparent that someone had put epoxy barrier coat (gray) over the bottom paint (red). Bottom paint which is not meant to be permanent, is hardly a good base for epoxy barrier coat paint, which is meant to be permanent. I'm guessing someone was doing a rush job, ad instead of sanding off the red bottom paint, decided they could hide it all under a layer of gray barrier paint anyway, so who would know? Not the owner.  Luckily the epoxy barrier coat did stick, mostly.  I'll have to it all off of course, but this, to me, is yet more proof that in the marine services industry, you really have to do it yourself and can't rely on yard workers to care as much about your boat as you.  


No comments:

Post a Comment