Comparison of SWATH and monohull vessel motion for regional class research vessels

Abstract

The attitude characteristics of two small research vessels, a 539-ton monohull (R/V Point Sur) and a 419-ton SWATH (R/V Western Flyer), are compared. The comparison is based upon 134 (61) motion measurements carried out on the R/V Point Sur (Western Flyer) in 2003 and 2004. Measurements were made using a tilt meter and a vertical gyro. When the vessels were on station, root mean square roll on the R/V Point Sur (Western Flyer) increased 0.23 (0.12) degrees and pitch increased 0.12 (0.06) degrees per foot of sea height for seas between two and twelve feet. Corresponding on-station rates of increase for vertical acceleration for the stern at the side were 0.18 m/s2 (0.03 m/s2) per foot for the R/V Point Sur (Western Flyer) and reached 1/4 g for the R/V Point Sur for 15-ft. seas. Similar accelerations were observed at full speed when seas greater than 10 ft. were forward of the bow on the R/V Point Sur. For R/V Point Sur, observed directional response at full speed and pitch and roll damping were in good agreement with values obtained from tank tests in 1979.