To join the group, which is a public group, go to your User CP and along the left sidebar, there's a link towards the bottom called "Group Memberships". Select the Boat Crew group and Submit it, then Paul will approve you if he sees fit.
Once you're approved, you will have an option in the same Group Memberships area that says "You may choose to be identified as a member of the follow groups: CR Boat Crew". Hit "Update", and your title will change to reflect this and you're set.
If you have questions, ask Paul and if he can't help you feel free to ask me.