Example 1 - Unprotected aluminum corroded by the curing solvents used in many marine goops. Note the epoxy coating in the 2nd pic served to protect the parent tin.
Example 2 - SS bolts through an aluminum rail without any protection or isolation. Recall that due to the corrosive effects of dissimilar metals (aka 'galvanic corrosion') the aluminum being the weaker metal on the materials charts of noble alloys, like a battery, the aluminum will bleed it ions out of itself, in deference to the higher charged SS. This "white frosting" you see is indicative of the effect. Over time the tin will be weakened ... a matter of not if, but when ... and then it will be structurely defficient. Note it will happen significantly faster on boats used in saltwater where saltwater is a perfect electroyte to carrry that electrical current imposed.
The 'white' area around those bolts will be cleaned and scrubbed with white vinegar and then new SS bolts will be added, where the bolt bodies will be covered in heatshrink and nylon washers will bear up against the tin on the side of the rail where the washer are needed against the tin.
Example 3 - Severe example of aluminum and stainless steel (SS) - In this case a SS slide track (to the mast) affixed to an aluminum gooseneck that held the boom on a small one-design sailboat caused the tin to lose all its strength! Now yes, it took 30-years (some years the Owner reports the sailboat wasn't used, he wasn't the original owner, and we don't know 'how long' it may have been used in the saltwater environment), but the aluminum piece broke off the other day and the boom nearly killed the sailboat Owner when it let go. I saw it happen, they're OK and I towed the boat in.
Once he got the tin gooseneck out of the boom, we were able to crumble the remaineder of the gooseneck block just by using our fingers, like breaking apart a hard cookie!
Example 4 - 'Crevice corrosion' of a SS bolt through a wood transom, no tin involved. Remember, SS is 'stain less', it is the O2 present in the atmosphere that helps protects the SS from staining or corroding, but when trapped in its hole through the glass/wood layup transom, there's no air to 'protect' the bolt. This corrosion is exacerbated when under 'stress' and of course tightening that bolt to hold the swim platform certainly puts a huge stress load on the fastener.
This is 304 series SS, the BEST CHOICE for safety/deck hardware on a boat - especially in saltwater - is 316L series which is passivated.
Example 2 - SS bolts through an aluminum rail without any protection or isolation. Recall that due to the corrosive effects of dissimilar metals (aka 'galvanic corrosion') the aluminum being the weaker metal on the materials charts of noble alloys, like a battery, the aluminum will bleed it ions out of itself, in deference to the higher charged SS. This "white frosting" you see is indicative of the effect. Over time the tin will be weakened ... a matter of not if, but when ... and then it will be structurely defficient. Note it will happen significantly faster on boats used in saltwater where saltwater is a perfect electroyte to carrry that electrical current imposed.
The 'white' area around those bolts will be cleaned and scrubbed with white vinegar and then new SS bolts will be added, where the bolt bodies will be covered in heatshrink and nylon washers will bear up against the tin on the side of the rail where the washer are needed against the tin.
Example 3 - Severe example of aluminum and stainless steel (SS) - In this case a SS slide track (to the mast) affixed to an aluminum gooseneck that held the boom on a small one-design sailboat caused the tin to lose all its strength! Now yes, it took 30-years (some years the Owner reports the sailboat wasn't used, he wasn't the original owner, and we don't know 'how long' it may have been used in the saltwater environment), but the aluminum piece broke off the other day and the boom nearly killed the sailboat Owner when it let go. I saw it happen, they're OK and I towed the boat in.
Once he got the tin gooseneck out of the boom, we were able to crumble the remaineder of the gooseneck block just by using our fingers, like breaking apart a hard cookie!
Example 4 - 'Crevice corrosion' of a SS bolt through a wood transom, no tin involved. Remember, SS is 'stain less', it is the O2 present in the atmosphere that helps protects the SS from staining or corroding, but when trapped in its hole through the glass/wood layup transom, there's no air to 'protect' the bolt. This corrosion is exacerbated when under 'stress' and of course tightening that bolt to hold the swim platform certainly puts a huge stress load on the fastener.
This is 304 series SS, the BEST CHOICE for safety/deck hardware on a boat - especially in saltwater - is 316L series which is passivated.
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