Another possibility: In the case of the USS Cairo: Could the stands of grape simply been have stored/stacked on the sabots? After 100 years of submersion, the one in this photograph as freshly recovered could have BECOME attached simply from chemical reaction and long contact. Did all of the stands recovered have attached wooden sabots? In the close quarters of a gunboat, it would make perfect sense to stack the grape on the wooden sabots to save space, avoid damaging the wooden decks, and to ensure there were enough sabots for all the stands. I'm not saying this is the case, as the earlier period photograph shows new stands with the sabots attached, but we don't have those examples to examine. Strapping is a possibility and could be easily done today. However, I'm not sure the high-carbon steel strapping that would have been required to apply the needed tension to both the bottom plate and the wooden sabot was availble in this time period as the apparently rabbetted edge on the sabot in the Museum photo would indicate. But, if there were small brad or nail holes in this recessed area, that would support the banding theory as the pressure would only have to be applied to the bottom plate.