[PSUBS-MAILIST] Re:Stainless in aluminum

[VBra676539@aol.com]

Brian,

Maybe Hugo will catch this question and help me out here with some product 
names, but I can tell you that the answer to your question is yes and no.

At HBOI, we used a stainless steel insert which was threaded inside and out. 
Bore the hole to the insert size, tap, screw the insert itself into the 
aluminum with a mandrel and then hammer in the locking dogs. The insert should be 
well bedded in one of the super whammydine Loctites (or epoxy or something) in 
an effort to exclude seawater from the outer threads. It's going to become a 
permanent fixture anyway (as you might well imagine) so you might as well nail 
it in there the best way you know how.

The inserts come in all sizes, so that their inside thread size will match 
whatever bolt you have in mind. The trick to using them successfully is to 
grease the bolt with nonsoluble grease every time you install it, and I mean grease 
it GOOD!!! Otherwise, and as I remember it, about the only otherwise we ever 
found, was that salt would creep in there and build on the threads--which gave 
you a twisted off bolt head, more often than not, when you tried to pull it 
later.

One more hint: Don't use machine threads for this kind of application. 1/4 20 
is about as fine as you'd want to risk. The coarser threads, when being 
reluctant on removal, are easier to rock back and forth, thus easier to persuade 
out into the light.

We used Almag hatches in the early days at Perry and had to fight corrosion 
quite a bit, and as I have said somewhere (somewhen?) else on this page, we 
used magnesium anodes on the aluminum dive planes and rudder assemblies. I have 
actually WATCHED them corrode, with fumes streaming off and little bits of 
metal flaking into the water, when a DC circuit shorted to ground.

You can, of course, bolt straight into aluminum, but the damage will happen 
on the aluminum end, and you probably won't see it until it gets pretty 
bad--and it won't be pretty--just pretty bad. Beware. Some days it's like diving in 
battery acid. A single dive with a pesky short can cause some BIG problems.

Best Regards,
Vance



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