GUPPY I Program
The prototype GUPPYs, Odax and Pomodon (both Portsmouth-built Tench boats), appeared in 1947. Externally, they featured improved streamlining of the bridge and shears structures, and periscope and radar mast supports. To reduce hydrodynamic drag, one of the periscopes was deleted. No snorkel was fitted, due to difficulties in adapting the snorkel to the fleet boat. Deck guns and their associated containers were removed. An SV radar aerial was added to the top of the sail, creating a distinctive side bulge. All capstans, cleats, and rail stanchion supports were redesigned so they could be retracted or removed when rigged for dive. Most notably, the sharp V-shaped "fleet boat bow" was replaced with a distinctive rounded "Guppy bow" that improved submerged performance.
These modifications changed not only the boats' appearance, but also their terminology: After a GUPPY conversion, the faired structure around the boat's conning tower and mast supports was called the "sail."
Internally, the boats underwent considerable rearrangement to accommodate larger battery wells and batteries of greatly increased electrical power. The batteries were of a new design. Compared with the original Sargo battery, the Guppy battery used a greater number of thinner plates that would generate higher current for a longer time. However, these batteries had a shorter life, 18 months versus the five years of the Sargo battery, and took longer to charge. They also required ventilation to remove hydrogen gas, and required cooling water to the battery terminals and termination bars. Four 126-cell batteries were installed in enlarged battery wells that replaced former storage, ammunition, and refrigeration spaces. These four batteries could be connected in series or parallel, providing a wide range of voltages and currents, and thus a wide range of speeds.
In the maneuvering room, two or four of the earlier high-speed motors and reduction gears were replaced by slow-speed motors. All open-front switchboards were replaced with enclosed splash-proof cabinets. Lighting and other "hotel" electrical loads were converted to use 120 volt 60 hertz alternating current, and ship electronics to use 120 volt 400 hertz AC. A new air conditioning system of greatly increased capacity was also installed.
In service, these boats offered greatly improved underwater performance. Pomodon reached 17.8 knots surfaced and 18.2 knots (33.7 km/h) submerged, Odax slightly less.
Read more about this topic: Greater Underwater Propulsion Power Program
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