Dave,
It is any help, I too start feeling sea sick if I try to tie knots on a stationary boat, never mind a moving one ( I find it the quickest way of feeling ill ).
Taking your eyes off the horizon and concentrating on some other task, I start to feel rough in 15-30 secs or so.
Mind you, I found it is not so bad now I have had the boat for 3 years or so.
PS: Just looking at the picture of some guy eating a huge pizza slice whilst typing this