Model Boat Mayhem

Mess Deck: General Section => Full Scale Ships => Topic started by: Colin Bishop on October 24, 2008, 10:24:18 am

Title: One Way Wiring in Ships
Post by: Colin Bishop on October 24, 2008, 10:24:18 am
I have picked up in a book on liners that prior to WW1 and maybe after, the wiring systems were one way which posed a considerable fire risk if the insulation chafed as a result of the "working" of the ship in a seaway. I assume that this means that the hull and ship's structure was used as a joint neutral/earth. I found that quite interesting - does anyone know more? There isn't much in the way of detail on the Internet that I can find.

Title: Re: One Way Wiring in Ships
Post by: BarryM on October 24, 2008, 04:40:02 pm

Yes it was used back in the very early days. You can see the attraction for owners; half your wiring installation costs at a stroke. If my ancient copies of MacGibbon's or Sotherns throw any more light on it I'll let you know.

Barry M
Title: Re: One Way Wiring in Ships
Post by: BarryM on October 24, 2008, 05:19:34 pm

Did not have to go too far back. The following is extracted from "Electricity Applied to Marine Engineering" published as recently as 1966. Well. 1966 is recent to me....

The Single-wire System
Although this system is considered to be obsolete for use on larger ships Lloyd’s Rules for Electrical Equipment states that ‘distribution systems employing single-wire with hull return may be submitted for special consideration’. The system is therefore described below
In this system the hull of the ship is used as one of the supply leads, only one cable being used to carry the electricity between the generator and the consuming apparatus, lamps, motors, fires, etc. The principal thing in favour of this system is cheapness. From an electrical point of view it is in many ways undesirable for the following reasons.
A failure of the insulation on the live conductor at any point will, or should, cause the protective gear to function, that is either a fuse blows, or a circuit breaker comes out causing an interruption of the electric supply. If the protective gear failed to function there would be a dead short circuit on the generator.
For this reason all fittings used in damp places should be watertight. Where cables pass through bulkheads, insulated bushings must be used. Also, because of the magnetic effect of the current, a single live cable must not be laid within 30 feet of steering or standard compasses. A person touching any live cable, or live portion of a switch or other piece of apparatus, immediately gets a shock to earth. For these reasons only low voltages should be employed. To avoid electrolytic corrosion, the positive pole of the generator should be earthed. If the negative pole is earthed and there are any leakage currents due to damp, the armouring of the cables will be eaten away and deposited on the hull of the ship.
The question is sometimes asked as to what would happen if two ships lying side by side in port, one with the positive earthed, the other with the negative earthed, were to swing against each other and come in contact. The answer is precisely nothing. They are in electrical contact all the time via the sea water. Unquote.

As I suspected it was used to keep costs down, Shipowners don't change.


Barry M
Title: Re: One Way Wiring in Ships
Post by: Colin Bishop on October 24, 2008, 05:48:42 pm
Thanks for taking the trouble to dig that out Barry, very interesting. I know that's the way they wire cars but I didn't realise you could use it on a 50,000 ton liner! Apparently the wiring installations on the big German liners such as Imperator (Berengaria), Vaterland (Leviathan) and Bismarck (Majestic) were poor quality and in the case of the latter two gave problems all their life and resulted in the early breaking up of Berengaria. The Americans took over Vaterland in WW1 and afterwards the defeated Germans wouldn't give them the plans for the ship so the Americans resurveyed her from scratch and rewired her, Apparently it was a massive undertaking and eventually rather a waste of time as she was a commercial failure.

In fact a number of German ships were badly designed and constructed compared with those of other nations. The Imperator was top heavy and unstable and required a lot of work to make her properly seaworthy including lopping the tops off the funnels, stripping out marble fittings in the first class bathrooms and pouring thousands of tons of cement into the double bottom. More work was done when Cunard took her over. The later Bremen and Europa also suffered from electrical faults and weak construction. The French took over Europa after WW2 and virtually rebuilt her as the Liberte after the Americans said they didn't want her because she was in such a poor condition.

Mind you, the British didn't always get things right either. The Queen Mary was a notorious "roller" until stabilisers were fitted in the 1950's and much of the stern had to be rebuilt and stiffened to cope with vibration. More recently, they got the calculations for Canberra wrong and the weight of the engines aft caused the ship to sit bow up. This was also cured by adding solid ballast in the bow sections which was a dubious solution as the weights at the ends of the hull imposed a lot of strain on the mid sections. Fortunately she was very strongly built and able to cope with the stresses. Although Canberra was the better looking ship, the Oriana was held to be a superior engineering solution and handled better too.

It all makes you feel a bit better when you make mistakes on your model!