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Old 29 October 2007, 09:39   #21
Country: UK - England
Town: Over here
Boat name: S.S. Nobstick
Make: Three Wise Monkeys
Length: 3m +
Engine: 44lbs of thrust....
Join Date: Nov 2003
Posts: 2,115
Originally Posted by Nasher View Post
The supplier is supplying exactly what I've asked for, being a below decks componant.
Above deck spec is altogether different.
But both Stainless.


Now you’ve piqued my curiosity… what grade did you order then? And for what purpose? I’m only curious because I found in my crewing days that anything in the damp salt laden air of a yacht was fecked in no time if it wasn’t “proper” marine equipment……

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Old 29 October 2007, 12:42   #22
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,620
Originally Posted by Pete7 View Post
Yep then cover bolts and washers in a big dollop of sealant, though I do accept lining the holes with a layer of resin would be good practise.
There's 2 avenues of problems caused by the drilling of the bolt holes: 1) You want to keep water out of the structural part of the transom, hence sealing the bore with epoxy, glas resin, or similar. 2) you want to seal around the bolt, so water doesn't weep through to wherever the hole ends up on the inside, and to prevent anaerobic bacterial corrosion from eating away at the bolts (I'll explain that one below, in case you're not familiar with it), hence the sealing of the bolts into the holes.

Most likely, taking care of one problem will take care of both, for a while. If, for whatever reason, the bolts are removed (or even just loosened and retightened), you open both avenues back up again. Most people will not go through the trouble of re-sealing the holes again, and the problems are likely to start there. By taking care of each in turn, there's less likelihood that both will start happening.

The anaerobic bacterial corrosion happens in tight locations, where water gets in and doesn't dry out. In essence, the existing bacteria is active as long as oxygen exists in the water, then dies off as it's consumed. The anaerobic bacteria then begins feeding on the ex-aerobic bacteria, giving off sulfuric acid as a by-product. The acid eats away whatever it can, including stainless steel. This type of corrosion is pretty common in stainless-to-stainless threads that are submerged. The simplest way to avoid it is to use a non-soluble filler for the threads (i.e. sealant, caulk, etc) which will prevent water ingress in the first place.


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