Multihull Seasick …. a new Phenomenon?

High-speed catamarans are known to roll and pitch in a way that is quite different from a monohull but there has been little research on the effects this may have on the passengers. The first real opportunity to study the effects of ship motion on military personnel on a high-speed catamaran arose when the Royal Australian Navy chartered HMAS Jervis Bay, a vessel built by INCAT Tasmania. It was discovered that the motion of the catamaran was quite different to a monohull and in rough weather the roll was very small, but when it did roll, it did not have the gently rolling action associated with a monohull. Instead, the vessel moved in a "stiffer" way and in beam seas the roll was enough to cause discomfort, particularly as the stiffness of the roll increases at high speed.

Pitch was also significant in rough seas. It was also found that in high seas the slamming of the centre hull, became an important factor, as it tended to cause significant longitudinal accelerations. Following seas in rough conditions were not a problem. Observations were made that although the catamaran may or may not cause an increased incidence of seasickness, it sometimes did affect individuals who did not normally suffer seasickness.

HMAS Jervis Bay has demonstrated its ability to transport troops and equipment quickly to a neighbouring land. In its troop carrying role, to have an understanding of the effects of ship motion in comparison to a traditional monohull is important when future acquisitions of troop carriers are carried out. This information may also help in command decisions. Knowing the percentage of military personnel likely to suffer seasickness given the expected sea state conditions, and travel duration, could provide a measure of the readiness of the troops on disembarkation.