An oceangoing craft security barrier (1, 16, 24) comprising: a substantially planar support element (2, 25) having a top edge and a bottom edge, wherein a top first attachment site is formed at the top edge of the support element and a bottom first attachment site is formed at the bottom edge of the support element; and a bulbous barrier element (9, 21, 28), which is separate from the support element (2, 25), the barrier element (9, 21, 28) having a top edge and a bottom edge, wherein a top second attachment site is formed at the top edge of the barrier element and a bottom second attachment site is formed at the bottom edge of the barrier element, with a curved protruding section extending between the top edge of the barrier element and the bottom edge of the barrier element, the protruding section extending away from the plane containing the top and bottom edges of the barrier element, wherein the support element (2, 25) and the barrier element (9, 21, 28) are configured to be releasably connected to each other by way of the first and second top attachment sites and the first and second bottom attachment sites, so that the support element (2, 25) and barrier element (9, 21, 28) define an internal space therebetween which is configured to receive a horizontal rail raised above a surface, and wherein the oceangoing craft security barrier (1, 16, 24), in use, is configured to be rested on the rail, a vertical plane being defined between the rail and the surface, so that the rail lies at or near the top edge of the support element (2, 25) and the top edge of the barrier element (9, 21, 28), the support element (2, 25) extends close to the vertical plane, and the protruding section protrudes outwardly from the vertical plane. a substantially planar support element (2, 25) having a top edge and a bottom edge, wherein a top first attachment site is formed at the top edge of the support element and a bottom first attachment site is formed at the bottom edge of the support element; and a bulbous barrier element (9, 21, 28), which is separate from the support element (2, 25), the barrier element (9, 21, 28) having a top edge and a bottom edge, wherein a top second attachment site is formed at the top edge of the barrier element and a bottom second attachment site is formed at the bottom edge of the barrier element, with a curved protruding section extending between the top edge of the barrier element and the bottom edge of the barrier element, the protruding section extending away from the plane containing the top and bottom edges of the barrier element, wherein the support element (2, 25) and the barrier element (9, 21, 28) are configured to be releasably connected to each other by way of the first and second top attachment sites and the first and second bottom attachment sites, so that the support element (2, 25) and barrier element (9, 21, 28) define an internal space therebetween which is configured to receive a horizontal rail raised above a surface, and wherein the oceangoing craft security barrier (1, 16, 24), in use, is configured to be rested on the rail, a vertical plane being defined between the rail and the surface, so that the rail lies at or near the top edge of the support element (2, 25) and the top edge of the barrier element (9, 21, 28), the support element (2, 25) extends close to the vertical plane, and the protruding section protrudes outwardly from the vertical plane.