As Alfred Giddings reveals in an article published in Naval History magazine in 1998, sometimes submarines benefit from a little help from above—on the surface, that is. The article, entitled “Rudder Assist” appears below.
“By 1955, the early success of the first nuclear-powered submarine—the USS Nautilus (SSN-571)—made it obvious that a new class of submarines should be built to exploit the revolutionary power source. The Nautilus design (as well as that of the Seawolf (SSN-575), the second nuclear submarine) was not suited well for direct class reproduction, so what became the Skate (SSN-578)-class design was begun. [The author of this piece was a member of the Preliminary Design Team for SKATE and would go on to be lead engineer of the LOS ANGELES (SSN-688)-class submarine project.] The design included several innovations, one of which was tested at sea on the USS Thaddeus Parker (DE-369), a World War II destroyer escort.
“The submarine navy was fully committed to twin-screw propulsion. The hydrodynamic and acoustic virtues of a single-screw, body-of-revolution hull form were just being realized in the conventionally powered Albacore (AGSS-569), but adding these hydrodynamic innovations to the more dramatic innovation of nuclear power posed too many simultaneous risks. Important factors in the hull-form decision included the standard requirement for after torpedo tubes, and the need to configure the bow to accommodate torpedo tubes and a sonar without a large additional development program. Accordingly, the Navy adopted a hull form resembling a smaller Nautilus.
“It soon became evident that the submarine would lack the rudder authority to meet the maneuvering specifications. The maximum surfaced draft of the boat would be determined by the length that the lower rudder projected below the baseline. In older World War II fleet boats, the upper surface of the afterbody was almost horizontal, so that the lower surface rose up smartly toward the stern; for them, a large, low-aspect-ratio rudder beneath the hull was adequate when surfaced as well as when submerged.
“High-speed turns in snorkeling GUPPY submarines after the war, however, had given submariners a healthy respect for the maneuvering effects the imbalance of roll moments produced when all the rudder area was beneath the hull while the (necessary) bridge fairwater was completely above the hull. This, plus experience with the Albacore, led to the requirement to have the rudder area almost equally divided above and below the hull. Also, the depth of the hull form in way of the rudders was determined primarily by the needs of the after torpedo room. The then-standard criterion for submarine rudder area for adequate surfaced maneuvering called for the immersed rudder area to be a specific and standard percentage of the lateral projected area of the immersed hull. This could not be met using a hydrodynamically efficient rudder plan within the constraint of maximum draft. For submerged maneuvering, the upper and lower rudder areas are compared to the total submerged later projected area of the boat, and a similar percentage criterion prevails. We needed the most from each square foot of rudder.
“Flaps had been used on aircraft for many years to increase the lift capability of a given area, and the approach looked promising. Articulated flaps were used for the same purpose on some of the antirolling fin installations used in passenger ships and warships. A portion of the trailing edge area was hinged to the main portion of the movable control surface, and a linkage caused the flap to rotate to an angle larger than the rotation of the main body of the fin.
“For the Skate, a four-bar linkage was selected; when the main rudder rotated to the usual hard-over angle of 35 degrees, the flap rotated an additional 45 degrees relative to the rudder’s main body. The resulting cambered surface had about twice the effectiveness per degree of rudder angle as did a standard design rudder at the same commanded angle. The slight right-left asymmetry of movement of the flap between extremes was of little consequence.
“There were major concerns about the design’s ruggedness and maintainability. The linkage was close to the hull, reasonably protected from damaging impacts, and compact enough to minimize the risk of fouling with cables and other debris, but the entire concept needed testing.
“We looked for ships operating over the same speed range that sported rudders of approximately the same size as those planned for the new submarine. A 1,350-ton, twin-rudder John C. Butler (DE-339)-class destroyer escort seemed to fill the bill. The Parker—due for overhaul—was selected.
“We designed a pair of rudders for the Parker using plans almost identical to those for the Skate. (The rising slope of the DE’s bottom was not exactly the same as the taper of the Skate’s afterbody, but it was close.) Each rudder had a hinged trailing-edge flap operated by the four-bar linkage. Sea trials in August 1956 were distinguished principally by the lack of excitement. Turning performance was at least as good as with the original rudder; backing performance was essentially unchanged; and no new noises or vibrations were observed.
“Afterward, the Parker took her flapped rudders to the fleet. We had no special news from DE-369, and, as with many new items of special interest—no news was good news. The Skate class operated successfully at sea for years.”