I have a newly purchased 1973 American 16. I have a question about the centerboard--why are there two lines on the top of the trunk that are to operate the centerboard? The one aft seems to do all the work, whereas the forward line does not seem to do anything? I've sailed it once, with the centerboard in what I think was a fully down position and seemed to track properly, but am just curious about the correct use of the two control lines. Any help is appreciated. Thanks.