It's useful to note how aluminum frame docks typically handle this. There is an arm, hinged at the shore end, that in the down position helps support the decking. For lifting, that arm is raised considerably above deck height by the lifting cable, and there is another cable (or perhaps an extension of the main cable) going from the end of that arm out to the end of the dock frame. This creates a triangle between the two cable sections and dock frame. The main cable is thus pulling at quite an angle above the center of gravity of the dock, approximating the effort of your raising the wood dock frame to 45 degrees or so while the dock frame itself is raised a lot less.
The "right" angle to use when there is no lifting arm depends a lot on how far above the dock level you have the shore end of the cable placed. Imagine if the attachment were on a huge tree at 40 feet above ground. Imagine also if the attachment were only a foot above the dock; the initial cable tension might well crumple the dock before lifting it.
|