Rock used for ballast in ships around the 12th century,what size and shape?

[bear]

Wanted to know for a Cog ship what shape of ballast rock was used and about what size? Rouned rock or sharp shaped.

 

Thanks Keith

[wefalck]

As always, the region you are looking at is important re. the availability of rocks. In fact, most of the southern Baltic and adjacent North Sea areas, where cogs originated from and in which they traded are areas of glacial moraines with little outcrop of bedrock. What you would find there are so-called erratic blocks, well-rounded due to glacier and melt-water transport. These would also be the areas of aboundant rounded pebbles on the beaches. The rock-types would be mainly granites and gneisses.

 

There are sandstone and limestone outcrops on the Baltic islands of Gotland and Bornholm. Sweden and Finland have exposed outcrops of granites. In Denmark and Northern Germany there are only a couple of outcrops of limestone.  Along the coasts of the British Islands and France, one would find a greater variety in rocks along the exposed coastal cliffs.

 

Apart from those erractic blocks and the pebbles picked up on the beaches or when ploughing fields, there has been for centuries a trade in cut stone-slabs from Scandinavia to Denmark and Northern Germany as ballast. These were used in construction and to pave sidewalks. On the return trips the ships were ballasted with sand instead. However, I don't know, when this kind of trade started.

 

Concerning sizes, in those moraines you can find anything from car-sized blocks to gravel and sand. I gather people used what they found and what could be man-handled - keep in mind that a block of rock weighs about 2.5 to 3 times as much as an equally sized glass of beer ...

 

[Kenchington]

Another general consideration is the difference between permanent and temporary ballast. Vessels that don't have major changes in the weights on board (e.g. fishing craft) get "permanent" ballast that stays in place all season. Dense rocks are good. Vessels that carry cargo may need temporary ballast if the paying load isn't enough for stability under sail. Then sand or gravel is best, as it is easier to load and discharge, though a major consideration becomes the cost of material that will be dumped at the end of the voyage -- unless there is some market where it can be sold.

 

Given the shape of a cog's hull, I would guess (no more than that) that they rarely carried much permanent ballast.

 

As to well rounded, wave-washed beach-rock versus angular, ice-shattered field stone: It need not be an either/or. As a generality, large, rounded pieces could be locked in place with smaller, angular ones -- depending on what was readily available locally.

 

For the specifics of cogs, try searching scholar.google (https://scholar.google.ca from here) with the two search terms "cog" and "ballast". That gives me 6,000 hits. Not all concern the intended meaning of "cog" but the first few include a study of ballast sand in Wismar Harbour, two reports on the Bremen cog and a Mariner's Mirror paper in cargo handling in cogs.

 

Trevor

[wefalck]

As a geologist (who received his basic university education in the geographical area of question), I would say that there are no 'ice-shattered' rocks ...

 

On the sand vs. rock ballast, one has to make a difference between the regions: in the continental North Sea regions boulders or pebbles were difficult to come by, while in the Baltic region pure sand is more difficult to find.

 

Sand has the risk of clogging up pumps ...

 

In the harbours in the region in question regulations for where to discharge (sand) ballast were put into place quite early, as 'wild' discharges near the quays led to sanding-up issues at a time, where dredging was in its infancy or no means were available at all. Pebble and boulders on the other hand were valuable building materials for e.g. foundations or paving.

 

[tmj]

There's a lot of truth in what wefalk states! While in Florida, I occasionally did metal fabrication and repair work for a 'salvage company'. I was told that the origin of a wreck was oft times determined long before the actual wreck itself was located, if located at all, due to the type of ballast stones found trailing along the bottom. Proper types of stones let them know they were on the right track. Improper stones meant a new, uncertain 'something' worth noting... but nothing to usually get excited about!      

Edited 13 hours ago by tmj

[wefalck]

In fact, some of the boulders that may have been used as ballast can be traced by geologists without any scientific instruments to very specific locations in Scandinavia. However, this does not mean that they have been picked up there, because these boulders have been transported by the glaciers during the various ice-ages over hundreds or thousands of kilometers to what are now the southern shores of the Baltic.

 

With the aid of trace-element analysis today, geologists (and criminologists) can now trace many rocks to very precise locations around the world. In this way we don't necessarily know the origin of a wreck, but we know, where it has loaded ballast.