It should be so tight that boat does not move forward or back along the dock in the wind or current.
Follow these steps: 1  Approach the dock slowly at a shallow angle with the boat completely under your control, as shown in this photo. 2  If you have a choice, it’s easiest to come to the dock with the bow into the wind or current, whichever is stronger, letting it slow you as you approach. But docking is like any other sailing skill: learn how to dock your sailboat the right way, pay attention to your boat and the wind, and soon enough it will be second nature. The steps below are for docking under power; docking under sail only is described here To minimize chafe on dock lines in breezy conditions (or generally), do you tie the lines relatively tight so that the boat sits close to the dock and has less room to move back and forth, or do you tie the lines a bit more slack so that there is more room to move? This is with galvanized metal cleats at the dock. Fore and aft lines not so tight, have slack. I run the springs straight from the dock cleat to the boat's cleat, winch or rail. The chocks are the chafe problem. If the stretchy line does not turn thru a chock or anything it lasts for years. Docking Plan. Before approaching the dock, one end of the docking lines should be secured onboard; fenders readied and speed reduced. If the wind is onshore (blowing toward the dock), the boat is brought to a position parallel to the dock and about two feet off. The wind will blow the boat in.  And...because boats don't drive like cars, it is another learning experience. A boat steers from the stern and pivots on its axis. So, when you steer to the right, for example, the stern of your boat moves to the left (which may be why you are bumping into the slips on the next dock over). Try visualizing pushing your boat in to the slip (somewhat like a shopping cart on ice) This boat is making good use of spring lines to keep the boat in place at the dock. When a boat is docked where the tide will go up and down, there are several ways to ensure that dock lines remain relatively tight and the boat does not move forward or back along the dock in the wind or current. With properly set spring lines and bow and stern lines, any boat can be made to rest alongside a piling or set of pilings. Properly deployed fenders or fenderboards will protect the boat from the dock no matter what tide, wind, or current condition may come along. i like the lines tied so as not to have jerking or tugging on them, as that is a cause of breakage. when i am in a marina, mine are not loose nor tight--tight is not comfortable and on my boat causes much chafe. my formosa likes to run in a circle, and if that is impeded, i have loss of lines due to chafe. some folks like to tie tight, saying this keeps chafe down, but it doesnt work that way for my boat. Fore and aft lines not so tight, have slack. I run the springs straight from the dock cleat to the boat's cleat, winch or rail. The chocks are the chafe problem. If the stretchy line does not turn thru a chock or anything it lasts for years. The boat can be tied tightly to the dock and it will simply ride up and down with the dock. Some docks are equipped with sliding tracks on the pilings, and the boat can be secured with a short midship breast line to the slide car, which will move up and down with the tides. With properly set spring lines and bow and stern lines, any boat can be made to rest alongside a piling or set of pilings. Properly deployed fenders or fenderboards will protect the boat from the dock no matter what tide, wind, or current condition may come along. I think tight lines are hard on the boat, lines and dock. I can't address locations where excessive surge exists, as I've never berthed a boat under those conditions for any length of time (and hope I never do!). I highly recommend mounting fenders to the dock instead of hanging them off the boat for various reasons.  A floating dock floats in the water and maintains the dry area between the water and the base of the dock. A pier is stationed into the ground, under the water. This enables the dock to fluctuate with the water. Steel docks are the preferred dock if you are considering adding a roof system to your dock. Finger Docks generally require additional flotation at the end of the dock to reduce deflection. Depending on your site conditions, several types of anchoring can be used, including; cables, winches, underwater chain anchors, and spud poles.
http://sailing.about.com/od/learntosail/ss/howtodock.htm http://www.cruisersforum.com/forums/f90/how-tight-do-you-tie-your-docklines-94715.html http://www.boatsafe.com/nauticalknowhow/docking.htm http://boatsafe.com/nauticalknowhow/moredock.htm http://www.tropicalboating.com/2010/04/tying-boats-to-docks-using-springlines http://www.cruisersforum.com/forums/f90/how-tight-do-you-tie-your-docklines-94715.html http://www.tropicalboating.com/2010/04/tying-boats-to-docks-using-springlines http://www.sailnet.com/forums/general-discussion-sailing-related/73249-dock-lines-tight-loose.html http://www.tigerboatdocks.com/30/resources/faqs.htm
how tight should boat be to dock