DC Connection To Hull

[Doug Criner]

Titanic's electrical system used the hull as a return path (like automobiles that use the steel body for the return path).

Theoretically, the polarity should have been hooked up so the hull was a cathode, thus reducing galvanic corrosion - but I've seen to reference to that. Was Titanic before a general appreciation of galvanic corrosion?

Also, I haven't seen reference to sacrificial anodes installed on the hull below the water line.

By the way, has any consideration been given to attaching sacrificial anodes to the wreck to slow down corrosion?

 

[Bill Sauder]

Wow, there's a lot of questions here¦

The Titanic did use the 'single wire' system of delivery in which current is delivered to the appliance, which is bolted to the ship's steel structure that acts as a return path. The system was widely used in the 1870-80s as a way to save on the cost of copper electrical cables, but badly out of favor by 1910.

First it was an immense fire hazard. In a two wire system, the hull is supposed to be neutral, so if a wire breaks and touches the steel, it's a less serious 'current leak' and there's an indicator light on most ship's main electrical panel to indicate which polarity has the fault (Queen Mary 1936) With the single wire system, EVERY wire that touches steel is a 'dead short' and vast amounts of current can be drawn out of the system causing sparking and large heat jumps.

The second problem is that in the early style systems, the current found its own path back to the generator, often causing damage. Condensers tubes and propeller bearings were particularly vulnerable to stray currents. The application of an electrical current caused very accelerated wasting of dissimilar metals at the tubes and bearings.

The 'Shipbuilder's' writers knew of the system's reputation and drops the subject of distribution as soon as possible, so there's very little elaboration. It does mention by way of an apology ''¦ but the returns are carried back and bonded in such a way as to avoid stray currents.' (p110)

My interpretation is that every circuit domain had a switched delivery (positive) running to each appliance, and a collection (negative) cable that was attached every few deck beams so that every appliance was within a relatively small radius of a current collection node, rather than let the current 'run wild' to find a path of least resistance. It also helps control sparking if the ship makes contact off-ship grounds.

I believe from partial schematics that survive that Titanic was Negatively Grounded, and that the generator control pillars, and main switchboard dealt primarily with control through the positive legs of the circuit. It's been too long since I had chemistry to remember if a negative ground system is favorable or unfavorable to hull corrosion.

I'm sure I've seen zinc sacrifice plates bolted onto Olympic, that's a detail I wouldn't remember clearly because all ships have them and not noted because it's the standard set up.

Nobody's suggested installing zinc sacrifice plates on the wreck so far as I know, I'm not sure anybody has the authority to do so. That will probably change shortly. The hull probably would be receptive to them: when table silver is recovered from the wreck it is pristine if in contact with a sacrifice metal, but a catastrophe if it is simply in the mud: The ship's silver is actually silver electroplate over a copper core, and it's very common for the copper to disappear leaving only a double silver shell, the remains of the interior and exterior plating fragile as tinfoil.

Philosophically, its begs the question, why do this? It strikes me as trying to embalm a long-dead corpse.

 

[Doug Criner]

Bill, very good info. Thanks.

Yes, I think all steel ships after a certain date must have had sacrificial anodes. They should be shown on the hull plans, not the electrical schemes.

But, to your thoughts about whether to install sacrificial anodes on the Titanic wreck. Is it too late? Certainly for the corrosion that has already occurred, of course.

But, I frequently read on these pages and others that "this or that" must (or must not) be done because Titanic is rapidly deteriorating. Maybe you think that Nature should be allowed to take its course, which will happen sooner or later anyway.

I don't know. Strapping on a few sacrificial anodes should be much simpler that what has already been done, salvage-wise. But, then, the sooner the ship totally disappears into the muck, maybe there will be some peace - Titanic remembered, but no longer explored.

But, if the goal were to preserve the wreck as long as possible, I think installation of sacrificial anodes could extend its present life some considerable number of years. Anodes will protect ferrous metals, but nothing else. Of course, it's the ferrous metals, iron and steel, that are the structural support of the ship - the failure of which is causing the ship to cave in and collapse.

Of course, there will always be non-ferrous artifacts in the debris field: brass, china, etc. Those may be discoverable many decades from now.

 

[Bill Sauder]

The problem with attaching sacrifice plates is that they have a limited radius of protection and they must be tapped and screwed into virgin metal to work. Even assuming a large radius of protection you need a fantasticly large number of sacrifice plates, including the interior decks, uptakes, etc. You are talking about an operation of tens of millions of dollars. For protection that is temporary and disfiguring. Who will pay for it?

The other problem with the sacrifice plates is that they only protect from chemical attack. The steel is being consumed by iron-eating bacteria as well (hence the rusticles).