Hello John,
Your work is superb, nothing you do is rubbish. I don't wish to turn this into a 'Yazoo Monster' thread and I don't have all of my references at hand but to summarize my thoughts they are as follows:
What is known about the 'Yazoo Monster'?
16 September 1862 - Mallory authorizes Weldon & McFarland to begin construction acting as 'Agents of the Department', an arrangement similar to the Tifts. They are 'entering upon the duties of constructing a warship, according to the plans and specifications which after mature deliberation with the aid of the judgements of the Engineer (Williams) and Constructor (Porter) of the Navy, been determined upon... Rf- NA RG 45 M-625, R 410, Pl 867-868
23 September 1862 - Mallory orders Brown to superintend construction and assist Weldon & McFarland. Rf- NA RG 45 M-625, R 410, Pl 873-874
October 1862 through February 1863 - Brown and Paymaster Nixon submit several payment claims amounting to hundreds of thousands of dollars for materials used and construct.
In addition to the 'Yazoo Monster', Brown was constructing the river obstructions and defenses south of the yard and converting the Mobile into an ironclad. From Smith's account it is likely that defensive measures took priority. Construction work ceased during the winter and early spring due to excessively high water. At that time, apparently, most of the hull frame was up. However, the ways had partially collapsed resulting in a hull list and probable damage. During this time at least two ship carpenters fled to Northern lines and reported on the construction. Their accounts differ as to the machinery arrangements and hull size. Although, the English carpenter accurately describes the work on the Mobile and Republic.
April - May 1863 - The decision is made to evacuate the YZNY due to the declining military situation. The yard and its vessels are torched. Three days after the yard is set afire the first USN officers approach Yazoo City. They are immediately greeted by civilian authorities who request that private property be respected and protected. These authorities describe all of the Confederate military activities that have been occurring there, including the construction at the YZNY. It is the civilian description of the 'YM' that the lieutenant cites in his report that is later repeated by Porter. USN officers inspected the grounds but did not conduct a formal survey of the remains.
This raises questions -
1) The ship carpenter informants obviously did work on the vessel but it is highly unlikely that they had access to the formal plans and design office. By only having the frame up it would have been difficult to know the actual machinery arrangements and planned armament. There were probably multiple sets of machinery available in the yard from salvaged vessels. But would they have known the final design and appearance? Probably not.
2) The civilian authorities knew about the construction but again, it is unlikely that they would know the design in detail. Did they exaggerate what was known? It is possible.
3) The Nashville was contracted to Montgomery & Anderson on 16 September 1862, the same date as the 'YM'. It is known that Porter, out of necessity, developed the large sidewheel ironclad design in the summer of 1862 to take advantage of locally available HP machinery. The Memphis was authorized that fall to Shirely & DeHaven who like the Tifts and Weldon & McFarland, acted as agents of the department. While there were differences in all CSN ironclads it is accepted that Porter attempted to design and build them in classes or series. That these three vessels were authorized in the same time period for use in shallow waters and with sidewheels, strongly suggests that they were of the same design. This came from Porter in Richmond.
Could it have been modified and enlarged? Certainly, however, being the first project with the department I would think W & McF would follow the plans as carefully as possible. No correspondence has been found suggesting such changes were requested as occurred with the Mississippi. In the spring of 1863 Mallory attempted to contract another one of these ironclads with Smoker in Shreveport. He refused the terms of the contract because HP machinery had become scarce and inflation would render his earnings worthless. He would have accepted the contract had it been given the previous fall.
4) Aside from his preoccupation with defensive works why did Brown not complete the 'YM' like he had done with the Arkansas? The Arkansas was structurally complete when he assumed command. She needed to be fitted out and finished but most of the necessary components were already there. The 'YM' was built from the keel up and no materials were on hand. It was an entirely different undertaking.
Yes, the evidence is circumstantial and inferred. But we don't have much else to go on. These are the basic reasons why I believe the 'YM' was a Nashville class ironclad. Perhaps one day the state of Mississippi will authorize a survey of the YZNY. I think they would find a few spikes in the mud in a hull shaped pattern. And I would wager a fine Kentucky bourbon that they would extend about 250' and not 300'.
All the best,
Bil