It's very matter of fact. Spavens was a disabled seaman. He had lost a leg and wrote the memoir to supplement his pension. He assumes, almost certainly correctly, that his readers will have little or no idea about how the navy works so he explains all the routine stuff; who does what, how watches are kept, what the rations were and how they were cooked, how a battle was fought at sea. There are a few juicy court martial details and some oddities like which yard arm someone was hanged from (it depended on rank). And so on.
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