Rusty Stanchion Fasteners? Not Good.
Stainless steel fasteners threaded into embedded aluminum plates need to be carefully sealed to prevent crevice corrosion.
May 23, 2014
The rust stains showing below this stanchion base mean that the stainless steel fasteners are falling prey to crevice corrosion. They need to be replaced.
Question: The photo I sent in was taken on the inside of my boat. What you see are the four bolts that are holding one of the stanchion bases onto the hull. Those are obviously rust stains that seem to be coming from the stainless steel. That's not supposed to happen. Furthermore, I don’t understand why there aren’t longer bolts in place with washers and lock nuts installed. Can you explain what’s going on here?
Answer: What you are showing represents one of the fears I have with an approach to mounting deck gear that is frankly becoming a trend on many new boats: to insert pre-drilled and tapped aluminum (not stainless steel) plates into the laminate as a combined backing plate/fastening fixture for the deck gear. The raised section of the laminate that is visible in your photo is where the plate is encapsulated inside the hull laminate. The stainless steel screws or bolts that are holding the stanchion base in place are threaded into the aluminum, but they need to be totally sealed so that no water can migrate past the exposed head of the bolt or screw and down the threads.
What I don’t see in your photo is any sealing compound pushed through as the bolt was tightened in place. This tells me the sealer was probably forgotten when the stanchion was installed. Stainless steel that is exposed to moisture but is deprived of oxygen will indeed rust, because it never gets an opportunity to develop the oxide layer on its surface that keeps it from rusting. The result of this is crevice corrosion and the ugly rust stains shown in your photo.
Rusty stanchion fasteners can lead to trouble. The danger here is that the bolt will corrode enough so that it is vulnerable to breaking. Hope you’re not hanging on to the lifeline the stanchion supports in a rough sea when it breaks!
The solution is to replace the bolts that are in there now, and apply lots of sealer to the threads and bolt before you insert them into the stanchion. What you want to see after you torque the bolt into place is sealer oozing out from around the entire circumference of the bolt or screw head. This ensures adequate sealing to keep the water out. If cosmetics are a concern, you can clean the excess sealer with a rag and some acetone.
