Last fall, a team of engineers from Naval Surface Warfare Centers, Carderock Division and Philadelphia Division flew across the United States to execute Rough-Water Trials on USS Zumwalt (DDG 1000). The trial evaluated the seakeeping and structural response of DDG 1000 and was conducted under the Performance and Special Trials (P&ST) program, which is a collection of tests to develop class-baseline hydrodynamic, structural and machinery performance information.
Separated into two phases, the first phase of the Rough-Water Trials was performed in October 2019. The team evaluated the seakeeping behavior, structural response and operability of DDG 1000 in mission-relevant conditions in Sea States 3, 4 and 5. This assessment also evaluated how the ship motion conditions affect crew performance.
During the second phase of the Rough-Water Trials in October and November 2020, the trials team tested DDG 1000 in more severe wave conditions. The trial was conducted across two storm events, the first near San Francisco, which peaked at mid-Sea State 6 wave conditions, and the second near Ketchikan, Alaska, which produced conditions through the top of Sea State 6. The storm-driven conditions exceeded expectations in terms of exposure time and wave steepness and enabled the team to satisfy all objectives of the testing.
Unlike the Calm-Water Trials, which were conducted near San Clemente Island close to the ship’s homeport of San Diego, California, the Rough-Water Trials required conditions that were not benign. The Rough-Water Trials Director, Stephen Minnich, explained why his team chose to move further north for the second phase of trials, citing a good rule of thumb: storm intensity tends to increase the further north you go in the Eastern Pacific. Wave climatology studies informed the selection of test locations and schedule to increase the likelihood of finding the required wave conditions. The team used a variety of wave forecasting models to guide the actual execution of testing.
“We chose locations and times to conduct the testing that would correspond with what forecast models were indicating would provide the wave conditions required to complete our test matrix,” Minnich said. “We deployed wave buoys that drifted on the sea surface, which helped us to quantify the seaway in terms of the wave height, period, and direction. We were completely at the mercy of Mother Nature during the testing, but those devices were critically important to the characterization of what we were seeing in terms of ship motion and structural response and for the situational awareness they provided to support safe execution of the testing.”
Minnich and his team were encouraged by the results of the Rough-Water Trials, noting that there were no exceedances of critical motion criteria limits. This is important because it confirmed prior characterization of the seakeeping behavior of DDG 1000 in severe wave environments. In early November, the team disembarked in Everett, Washington, after more than two weeks onboard for the trial. The conclusion of the second phase of the Rough-Water Trials means that all of the at-sea testing for the P&ST program is now complete.
Next on the agenda for the group will be to replicate the conditions of the second phase of Rough-Water Trials at model scale in the test facilities at Carderock. This includes reproducing the wave environments and the ship loading conditions for a Seakeeping Correlation test. The model test will take place in Carderock’s Maneuvering and Seakeeping Basin beginning in late March 2021.
“Effectively, we will be re-running critical portions of the trial at model scale onsite at Carderock,” Minnich said. “This will enable us to quantify the differences between our model-scale predictions and our full-scale observations.”
Minnich said he appreciated the team’s dedication, time and sacrifice – especially in an elevated risk scenario. The team was away from home for nearly four weeks to support the trials in the midst of the ongoing COVID-19 pandemic. In spite of the personal discomfort of conducting Rough-Water Trials, Minnich said the entire team rose to the challenge and executed the test successfully.