Bob,
You seem to know what your talking about when it comes to corrosion.
I've seen anodes on some out boards and understand the principle but
don't really have a handle on what I need.
My K-350 will be ready for launch soon so it's time for me to get the
anodes I need. I have a painted carbon steel hull with several pieces
of stainless steel mounted to it, two aluminum props and one bronze
prop. A real pea soup when it comes to corrosion. Most of the time I'll
be diving in fresh water but sometimes sea water. I doubt it will stay
in the water for more then a day or two at a time.
If your familiar with the K-350 design and size, can you give me an idea
of the size anodes I need and where to best place them?
Thanks, Dan H.
----- Original Message -----
From: Bob Duncan <mailto:katsurencho@yahoo.com>
To: personal_submersibles@psubs.org
<mailto:personal_submersibles@psubs.org>
Sent: Monday, March 08, 2004 7:44 PM
Subject: Re: [PSUBS-MAILIST] Interior paint (was: Scuttle valve)
To add to my last e-mail. I would like to talk a little about
corrosion and corrosion control. Which is usually the primary
purpose of a coating system (corrosion control). It takes 4 things
to make corrosion: An Anode, a Cathode, a metal path, and an
electrolyte. Oxygen is the primary electrolyte. Oxygen is contained
in water, and of course a normal atmosphere. The salt in sea air
(not only sea water) is a strong electrolyte.
The easiest and most common method of corrosion control is to put a
barricade on the metal surfaces to prevent the electrolyte from
contacting the metals (anode and cathode). Since any structural
metal is an alloy ie: steel is an alloy of Iron and Carbon you
alread have an anode and cathode in contact with each other. We
can't prevent this.
There are charts available in corrosion control manuals, or
corrosion engineer manuals that list how far apart metals are from
being the cathode or the anode. The anode gives up electrons or is
the one to rust away (if you don't mind these terms "rust") We put
zinc anodes on steel ships to save the steel. The zinc anode is
eaten away instead of the steel, then as a rule of thumb, the zinc
anode is replace when it is half gone.
Anytime you put a metal fastener thru metal, you again create a
corrosion problem. As the fastener is seldom the same alloy as the
material it is holding together.
I'll try to keep this short, and simple !!!
When you add electricity to the system, you have more electron
flow, and increase you potential for a corrosion problem. It's very
difficult to keep electricity out of a modern boat!
Once all the metal is welded it is probably (possibly depending
on the situation and design) the best time to clean the surface.
Apply a chemical conversion if you are going to, prime the surface
and apply a top coat. Then add the systems. It is very important to
coat all metals used in the marine industry. There are few
exceptions, one being that when you use an anode (such as zinc on
steel) that the contact surface be bare. As it wouldn't do much good
to put the zinc on a painted (or coated) steel surface.
Corrosion control is an ongoing war in the marine industry.
Bob
Bob Duncan <katsurencho@yahoo.com> wrote:
Hello,
I would think that if it is an ambient pressure submarine,
that you should be able to use the same kind of coating that is
used in hyperbaric chambers.
For a 1ATM submarine, i would use epoxy or polyurethane primer
and topcoat. We dont' use the word paint, because paint is a
decorative, and these are a coating system. I'm sure you will
have a fair amount of condensation, on the inside of the boat.
bob
Michael B Holt <tlohm@juno.com> wrote:
On Mon, 8 Mar 2004 15:05:26 -0800 Steven Mills writes:
>
>I had not thought of water-proofing the interior, but it
makes sense.
>Paint or plastic? Would there be residual out-gassing over
time from
>the plastic if one used spray-on vinyl like used in beds
of pick-up
>trucks?
>What would be the curing time of paint versus plastic?
Hey, let's talk about this. What sort of paint can be used
safely on the interior of any sealed cabin? Some paints
have an odor that lasts for a long time.
Mike