I am working on a scratch model of Commissioner Hamilton's gunboat and have started rigging, using the attached drawing from the NMM. I have a very limited understanding of rigging practice and am puzzled by the function of the block and lines area circled in red. Presumably the line going behind the sail is attached to a pendant and can be tightened or loosened as required, but it looks to me that all that would do is lift the boom. What is it that I am missing? Any help gra