Quote:
Originally Posted by DickR
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.
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I have seen some aluminum docks with a very high triangle at the pivot point at the shore. The cable angle is increased considerably, along with the mechanical advantage because the cable comes from the top of the shore triangle high above the dock and often hangs over it a bit, and attaches near to the end of the dock. The cable angle is at least 45 degrees - and higher - to the horizontal and therefore the amount of force required to lift and hold the dock is quite a bit less.
Maybe this is similar (or identical) to what you are describing. I have never looked closely to see how such an arrangement is constructed. Perhaps the triangle lays into the dock frame somehow when the dock is down. In any event, it's a very good system and when I have to rebuild the dock some day, this sort of arrangement - whether wooden or aluminum will be in play!!