Many thanks for the reply Anders, I'm pretty clued up on the points that you have made. I've followed a few tutorials using the birail tool. My problem is using the tool to create a boat hull I just can't get my head around how I go about about it. The tutorials I have followed seem quite basic, which use two rails and 2 profiles. I just can't get my head around which curves do i use for the profiles and rails, and should i be creating a complete hull with the birail tool or just half? Your help is much appreciated.