I'm very familiar with Friedman's "U.S. Small Combatants," but that book doesn't deal with minesweepers. Actually, I'd be hard pressed to think of a definitive book on that topic. There of course was the recent title "Wooden ships and iron men: the U.S. Navy's ocean minesweepers, 1953-1994," but I'm not sure that there's any reference to the successor aluminum hulled ocean minesweeper that would have been a follow on to the Agile class?
There's an article by Norman Friedman on US Minesweepers from the late 1940s to the mid-1960s in
Warship 1994.
The 220ft Aluminium-hulled minesweeper is not a follow-on to the
Agile class, but instead a very early preliminary design for said class, dating from 1949. This was 220 × 37 × 8-6ft, 910 tons light (925 tons standard, 1180 tons fully loaded), it used five 1500hp low-magnetic diesels, two for propulsion driving CRP propellers via reduction gears, and three for sweep current. BuShips were considering diesels from GM, Fairbanks-Morse and Cooper-Bessemer. Armament was a single 3"/50 with a Mk 63 fire control system, and four twin 20mm. Ammunition was to be placed as high in the ship as possible to avoid underwater explosions.
Aluminum ship construction wasn't all that mysterious by the 1950s, although all aluminum hull construction might not have compared favorably in terms of cost with the composite aluminum frame/wooden plank hull construction. The material costs are obviously quite expensive in comparison to steel and aluminum welding tends to be somewhat more specialized.
The smaller wooden design selected cost slightly greater than half of that of the aluminium hull.
I'm inclined to say the technical issues were rather minor and that the cancellation must have been tied to changing priorities rather than the issue of aluminum hull construction itself.
The aluminium hull has several major issues, the first being shortage of supply, US wartime consumption has increased from 120,000 tons per year to 1 million tons, and was 360,000 tons per year in 1949, it was one of the three materials under the Controlled Materials Plan because sources of high-quality bauxite ores had been heavily depleted, and production required significant electrical power and BuShips feared that the US was already nearly running at full generating capacity.
This was by itself not enough to kill the aluminium sweeper, but it did force designers to look at smaller 180ft aluminium and 160ft wooden hulls.
Aluminium construction had to be dropped as it turned out rolling and pitching would create eddy currents (which in turn had magnetic consequences, although Friedman does not explain how).
To put the issue in perspective, the RN cancelled the much better known 1955 Ocean Minesweeper in this period, although as far as I know, that was a conventional steel hulled ship similar in many respects to the earlier Algerine class. The USN was apparently much more concerned about amagnetic construction in this period?
The US was more concerned about amagnetic construction in this period, surprisingly more seriously than the Royal Navy, they had to convince them to change the construction of the
Ton class, which at the time had aluminium frames, decks and bulkheads, with African mahogany planking, to be replaced with American-style laminated-wood framing. The initial British view was that eddy currents would not be an issue, as these would occur only in conditions when the ship was incapable of sweeping, but Canadian trials bore out American fears, forcing the British to make changes. American were also unhappy with the amount of magnetic materials being used in the Mirrlees and Deltic engines.
