Re: [PSUBS-MAILIST] Paint on Galv.

[vbra676539@aol.com]

Better than monel is isolation. Nylon washers (one machined with a shoulder to fit through the aluminum lug) then SS hardward, flat washers against the nylon (or delrin) and self locking nuts for safety. The tanks themselves need to be completely isolated from the pressure hull, if possible. Monel conducts electricity. Although more inert that SS, it does not protect you from shorts to ground, which will turn aluminum into a battery component. Perry used magnesium anodes on the aluminum bits, isolated the mounting brackets as I have described (dive planes, rudder, etc.) and built their MBTs of 316L SS. It's a solid combination, if your pockets are deep enough, and it works a treat.

 

I've seen the magnesium anodes do everything but sizzle with an electrical short in a thruster (1hp/120volt). We had to change the anode, but the aluminum component it protected went unscathed. Keep in mind, anodes must be bedded to improve the electrical connection (if any). Don't depend on retaining bolts to do the job. We used white lead paste, which worked pretty well.

 

As to coatings on mild steel, I would skip any of the metalizing processes and go to high quality paint, which will work better and cost less (although probably not MUCH less). We used US Navy milspec Amercoat products (Dimetcote). The total coating consisted of a zinc base, then an epoxy tie coat, and finally the vinyl top coat(s) and I'm here to tell you, it's very to ugh to beat. With proper applications, we never even had pinholes to deal with. Keep in mind, the Amron stuff was designed for ships that would be staying in the water. We hauled the boat out and rinsed with fresh water after every dive, let her drip dry, and went on about our business, which wasn't much stress on the coatings comparatively speaking.

 

That quality of paint allowed us to use coatings on virtually every O-ring sealing surface on the boat. The shiny hatch mating ring on the conning tower was monel cladding on hull material, put there because that is the only O-ring mating surface regularly unseated. It was for toughness rather than beauty. Everything else was painted. The topcoat used to cost $600/gallon. Don't know what it is today, and it is solvent based, not water based, which is an EPA problem in this country (US). But if you can get it, and stand the freight, you won't regret the results.

 

Vance


-----Original Message-----
From: Hugh Fulton <hc.fulton@gmail.com>
To: personal_submersibles@psubs.org
Sent: Thu, Sep 10, 2009 4:14 pm
Subject: [PSUBS-MAILIST] Paint on Galv.

Hi All,

I just had a talk with a company Altex about having my buoyancy tanks grit blasted, then zinc metal sprayed then painte d.

They said don’t Zinc metal spray.  Aluminium metal spray is OK.  What they said is that the water will penetrate the paint and activate the zinc and paint will come off.

I guess the same applies for galvanizing then painting.  Does anyone have any comment on this.  Also with Aluminium bolted to stainless steel they said don’t use stainless bolts use monel.

If it is true what they say it is another caution for P-subbers falling into traps.  Hugh

 

Problem with getting older is that I’ve forgotten whether I have forgotten or never knew!   

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