Does anyone know how the vertical posts are attached to the hulls on a hobie16.

It looks to me as though there is silicon sealent around the posts as they come out of the top of the hull. Does this mean that they are only attached at the bottom and are not glassed in at the top. If so why? could this be to allow for different expansion of the fibre glass and Aluminium?

I want to know because I am building my own boat and want to follow a tried and tested method.