We have had one day that you couldn't go out to the Island in 4 trips. And that was before they got the new boat. In all honesty, some of the time you can't go to the Island, you wouldn't want to go to the Island. It is only one part of the trip anyway, they still have a beach and the Island of Jamaica to enjoy.
In six trips, we have one day when we couldn't use the island and CTI shuttled couples over to CSS. They did have a limit on the number they would take over. If it's a MWF, they go to CSS as the trading places day.
We have been going to CTI since 2004 and only one day out of 10 trips (approx. 2 weeks long each) in September we were unable to go to the island. Looking forward to our arrival on 9/6 and also visiting SSB at CSS while there.