Bill I am extremely grateful for your shared research, without it I would have no idea of what any of these vessels looked like as I have gleaned only basic data from my UK sources and these inspections reports plus other snippets of information you have written down are priceless. I am but a dwarf standing on a giants shoulder because without your data I would know nothing.
Here is an interesting calculation , the Mobile had a nett tonnage of 282 tons. which means she was rated as being able to carry such a weight in cargo. One cubic foot of iron weights 491 lbs , slice that into thirds and you get the weight of 4 inches of iron plate one foot square as 163lb. The smallest dimension of a Arkansas type casemate for 4 guns (assuming the lowering of the boiler made the deck flush) would be 15ft for each pivot gun and 10 feet for each broadside gun plus 10 feet for the stack and engine room ventilation with a minimum deck height of 8 feet to work the guns. We now have a casemate 60 feet long by 8 feet high. Taking the weight of the iron.
we have (60 + 28) x 2 sides x 8 ft = 1408 ft squared ,
weight of iron armour 1408sqft x 163lb = 229504 lbs ,
converted into tons we have 229504/2000 = 115 tons
Calculating the backing of 12 inch pitch pine timber at 52lb per cubic foot (not including the weight of the timber frame) , we have
1408sqft x 52lb = 73216 / 2000 = 36 tons.
Total weight for 4 inches of iron plate with 12 inches of pitch pine backing = 151 tons of extra weight .
The use of green timber would increase this weight still further and you would need to add the weight of the framing material plus grating and also the weight of the 4 guns and carriages plus stores and ammunition but this would probably make the total weight of around 170 tons. now this is not 170 tons stored below the waterline in the hold but a large amount of top weight amounting to 60% of her cargo capacity situated above the waterline which would call into question her stability, this being a calculation of a vessels beam when taking into account her topweight. Of course the size of the casemate is open to argument as is the amount of wooden backing as we just don't know and I am only quoting typical figures but either way it gives some indication of the issues converting a vessel of a modest size into a Arkansas style ironclad.
One other historical fact of note is the lack of any type of armour available let alone rolled 2 inch plate at this time. When Montgomery's RDF vessels came North partially completed from New Orleans, the vessels stopped off at various riverside towns and begged for railroad iron and in many cases it was not forthcoming or had to be obtained from the local authorities by force, such was the shortage that probably only the front glacis of some of the RDF vessels was armoured and some failed to obtain any iron at all. I suspect that the same situation existed on the Yazoo during this time and any iron, let alone iron plate would be virtually unobtainable .
Here is an interesting calculation , the Mobile had a nett tonnage of 282 tons. which means she was rated as being able to carry such a weight in cargo. One cubic foot of iron weights 491 lbs , slice that into thirds and you get the weight of 4 inches of iron plate one foot square as 163lb. The smallest dimension of a Arkansas type casemate for 4 guns (assuming the lowering of the boiler made the deck flush) would be 15ft for each pivot gun and 10 feet for each broadside gun plus 10 feet for the stack and engine room ventilation with a minimum deck height of 8 feet to work the guns. We now have a casemate 60 feet long by 8 feet high. Taking the weight of the iron.
we have (60 + 28) x 2 sides x 8 ft = 1408 ft squared ,
weight of iron armour 1408sqft x 163lb = 229504 lbs ,
converted into tons we have 229504/2000 = 115 tons
Calculating the backing of 12 inch pitch pine timber at 52lb per cubic foot (not including the weight of the timber frame) , we have
1408sqft x 52lb = 73216 / 2000 = 36 tons.
Total weight for 4 inches of iron plate with 12 inches of pitch pine backing = 151 tons of extra weight .
The use of green timber would increase this weight still further and you would need to add the weight of the framing material plus grating and also the weight of the 4 guns and carriages plus stores and ammunition but this would probably make the total weight of around 170 tons. now this is not 170 tons stored below the waterline in the hold but a large amount of top weight amounting to 60% of her cargo capacity situated above the waterline which would call into question her stability, this being a calculation of a vessels beam when taking into account her topweight. Of course the size of the casemate is open to argument as is the amount of wooden backing as we just don't know and I am only quoting typical figures but either way it gives some indication of the issues converting a vessel of a modest size into a Arkansas style ironclad.
One other historical fact of note is the lack of any type of armour available let alone rolled 2 inch plate at this time. When Montgomery's RDF vessels came North partially completed from New Orleans, the vessels stopped off at various riverside towns and begged for railroad iron and in many cases it was not forthcoming or had to be obtained from the local authorities by force, such was the shortage that probably only the front glacis of some of the RDF vessels was armoured and some failed to obtain any iron at all. I suspect that the same situation existed on the Yazoo during this time and any iron, let alone iron plate would be virtually unobtainable .
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