Nelson & His World

Having failed O-level science ignominiously many years ago, I'm rather hesitant about posting this question. Here goes:

I dimly remember that metal is corroded by salt. 18th century ships were protected with copper sheathing to avoid the attachment and growth of marine life that wooden ships were hampered by. Was there some additional process in use that protected the copper sheets from corrosion by sea water?

Anna

This may not be what you are referring to - but I know that the original pure copper sheathing used through the Nelson era was later replaced by a copper alloy which became known as Muntz metal.

There is some information here.

It is rare for more than a couple of weeks to go by without me being reminded of this product.

I regularly go into Birmingham City Centre along the canal bank. And this runs past the back of Muntz's former Birmingham works. The Muntz name was painted on the canal side of the rear wall and is still visible - although becoming progressively faded.

MB

Different metals corrode at differnet rates in the presence of water and oxygen. Salt in the water speeds up the process of electro-chemical corrosion. Help! any chemists present?

In my younger days, the steel used by MG and British Leyland seemed to suffer particularly badly!

Copper barely corrodes at all in pure water (hence its use for water pipes!), and corrodes only very slowly in sea-water. Copper (and some other metals such as aluminium) resist corrosion by building up a protective layer of oxide (green when exposed to the air, and brown under water - take a look at HMS Trincomalee next time you are in Hartlepool!). Unfortunately, in the case of copper sheathing on ships, this layer of oxide significantly reduces its anti-fouling capability, although it is still effective in its primary purpose against ship-worm, providing it was undamaged. Ships were therefore still docked from time to time to have their bottoms scraped. This scraping removes some of the oxide, and so allows the oxidisation to speed up again, and hence the copper gradually corrodes. Ships therefore had to be regularly re-coppered, and from some fairly limited analysis I have done previously, this was perhaps about every 3 or 4 years during the Napoleonic wars, and occasionally even more fequently. For example the Bellerophon was re-coppered four times between 1800 and 1810 (excluding more minor repairs to damaged copper).

The cost of keeping the Navy's ships coppered was therefore very substantial.

I think I am right in saying that there were many earlier experiments than Muntz with copper alloys that would corrode more slowly, but their anti-fouling capabilities were either less effective than pure copper, or they were too expensive. From the link provided by Mark, it seems that Muntz metal provided the right combination of cost and anti-fouling ability.

It is clear from documents at the time that the main objective of coppering a vessel was to reduce attacks by the worm and to extend the time needed before she had to undergo a major repair. The Navy Board, which under Middleton advocated the coppering process, estimated in 1783 that, whereas an uncoppered ship required six monthly docking or careening and a yearly bottom scrape, a coppered one would only need docking for repair or recoppering every three years.
This figure fits in with Tony's example from the ‘Bellerophon’. However, copper varied in quality and whether a ship was deployed in warm or cold water seemed to have an effect, so the period after which they needed this attention varied considerably. ‘Doris’ for example, seems to have only needed it on average every nine years. To establish the reason for these differences, the Navy Board carried out regular experiments to establish the rate of corrosion but was able to come to few conclusions. Sir Humphrey Davy in the 1820’s had a go, and showed that copper, when mixed slightly with another metal performed much better. Perhaps this was the origin of the Muntz process mentioned by Mark
It was the opinion of many captains that the slight disintegration of the copper caused by oxidation not only stopped the worm but deterred marine growth, so that coppered ships went much faster. They would have gone faster still without any oxidation at all; but in terms of the alternatives, the increased speed given by coppering was a key feature of British tactical success in battle, certainly in the late 18th century. The Navy Board (obsessed with the problem of the cost of repairs) were not much concerned with this feature, but sailors naturally were since it gave them the edge. The French noticed it too. I recall a report that one frustrated French captain gloomily observed ‘The bottoms of English ships are sheathed with copper; ours with oysters.’ They of course soon followed suit.

Brian

That sounds rather like the nineteenth century equivalent of that scene from the 'The Battle of Britain' where, I believe, Goering asks the disillusioned Luftwaffe pilots if anything can be done to turn the battle in their favour. One turns to him and says something like, 'Yes! Give us Spitfires!' (Although he said it in German, of course.)

It might be worth mentioning that the whole subject coppering was something of a learning curve for the navy. I believe the first RN ship coppered was around 1760, but in the early years there were problems with ships that had been so treated – the chief of which was in keeping the plates secured to the hull. About the time of the War of Independence, it was eventually deduced that the reason for this was that the bolts securing them were iron and that a reaction was activated between the two metals, so causing the problem. Copper bolts were then substituted for the iron ones and the problem was largely solved.

Incidentally, I read somewhere that the Cutty Sark was originally coppered with Muntz metal. I don't know what they will use now – that's if you will be able to see it under all that glass that is!

I've been away from the site for a while (perhaps nobody noticed) in the annual move to the cottage, from where I am writing this. Unfortunately, we have been off line for about a week due to the move, reconnecting etc., but all is up and running now – hopefully. At least I had a lot to catch up on!

I had been meaning for ages to take a photo of that obscure sign on the back of Muntz's old factory.

At long last here it is!

I feel a sense of Turner's "Fighting Temeraire" here. i.e. The old fading away and the new taking over !!

ah the muntz familly,they still live in the area,in tanworth in arden own farms there and also the childrens farm,also station approach in dorridge ,the forest hotel(happy days for me lived a stones throw away)most of the shops on the approach still belong to the family ,the station its said has every train stop even though a tiny station as a concession to be allowed to build it there, also muntz street in birmingham small heath is named after the familly who made a fortune from their special metal process
proccess