The attitude characteristics of two small research vessels, a 539 displacement ton monohull (R/V Point Sur) and a 419 displacement ton SWATH (R/V Western Flyer) are compared. The comparison is based upon 134 (147) motion measurements carried out on the Point Sur (Western Flyer) in 2003-2005. Measurements were made using a tilt meter and a vertical gyro. When hove-to, rms pitch and roll (vertical acceleration) increased with increasing sea height on the monohull at three (six) times the rate of the SWATH. When cruising, the fins on the subsurface hulls of the SWATH effectively damped the pitch (roll) caused by head and bow seas, reducing the amplitude by a factor of 2 (10) compared to those observed while hove-to; accelerations were reduced by a greater amount as the frequency of pitch and roll was reduced. In contrast, cruising motion (pitch, roll, acceleration) on the monohull increased when seas were on or forward of the beam. The only point where the cruising monohull appeared to out-perform the SWATH was for pitch in quartering/stern seas > 10 ft.
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