6

David Fickling on Twitter: "Here's a story about how a ship-eating clam hel...

 3 years ago
source link: https://twitter.com/davidfickling/status/1344404814256504832
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.

Conversation

Replying to

The naval shipworm Teredo Navalis is an under-appreciated marker of globalization.

It's a type of highly adapted clam that bores into waterlogged wood using the remnants of its shell as a rasping saw:

Image

No one is really sure where in the world it originated, but it seems clear it's an early example of a marine invasive species.

Its marine wood diet suggests that it evolved among mangroves, but we first find written references in ancient Greece where mangroves were absent:

Image

References in Greek texts from the 4th century BC are IMO suggestive of early voyages to the coast of West Africa, the nearest navigable mangrove forests (unless shipworm managed to somehow get carried across the Sinai isthmus):

https://academia.edu/34223273/Effects_of_shipworm_on_the_performance_of_ancient_Mediterranean_warships…

Image
Shipworm have bacteria living in their gills that allow them to digest cellulose. This makes them astonishingly efficient at turning submerged wood into sawdust. Unprotected timber in shipworm-infested waters can completely disintegrate in eight or ten years.
Image

This becomes a really big problem with the Age of Sail. Ships plying the oceans are eaten from the inside out as they travel.

You also end up with external fouling from goose barnacles and other organisms.

Image

This slows wooden ships down drastically and eventually destroys them.

Shipyards came up with various ways to solve the problem. Some boats had double hulls, with a cheap wooden outer surface that could be periodically replaced in dry dock.

Tar paint was also used, and lead or copper plates were bolted on to the keel from relatively early times.

The metal solution was probably most effective, but it had a problematic side-effect: it turned the ship into a giant battery.

With seawater acting as an electrolyte, the copper or lead sheathing would become the positive cathode and the iron bolts holding the ship together become the negative anode.

Anodes quickly turn to rust, so again your ship is destroyed.

Image
BUT copper sheathing was so effective at preventing shipworm that from the mid-18th century the British navy decided it was better to replace the iron bolts (and update them with more corrosion-resistant alloys) than to replace all the timber instead.
The American Revolution provided the real spur to this. Copper is a relatively expensive metal. But with the British Navy fighting a trans-oceanic war, fouling and shipworm was a national security problem that had to be fixed, so the entire fleet was coppered in short order.
Image

That required a LOT of copper. Luckily for the British, there were large domestic deposits.

Cornwall and Devon had been mined since classical times as one of the ancient world's most important sources of tin, which was alloyed with copper to make bronze.


About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK