A basic dock has a number of uses including a location to moor a small water craft, to fish from, and a platform to sit on and enjoy the water. You can make a dock with a simple shape from basic lumber and recycled plastic barrels. Damaged drums can be replaced, at relatively little expense when compared to other flotation devices. It is important to remember that a 45 gallon barrel will float about 200 Kilogram. Make sure that you use enough barrels for the size of your deck. An 8 by 8 foot square is a reasonable size dock for four 45 gallon drums to support.
Cut the four by four post down into 8-inch sections using a circular saw.
Lay out the frame for your dock. Do this by laying out the four 2 by 8 boards in a square. Stand the 4 by 4 posts up in the corners of the frame. These will anchor the corners and give you something to screw into.
Screw the corners of the frame together, using 2 1/2 inch deck screws. Put at least two screws in each side of the four corners, or a total of four screws in each corner.
Create cradles for the barrels to sit in under the frame. This not only holds the barrels in place, but also prevents them from rubbing against the decking. Do this by running 2 by 4 support beams across the frame. The distance between the support beams should be equal to the barrels' width. On top of these support beams, run two 2 by 4s perpendicularly from the top to the bottom of the frame, at a distance equal to the length of the barrels. Screw the 2 by 4s into position using 2 1/2 inch galvanised screws.
Reinforce the structure by putting L brackets at all the locations where the 2 by 4s cross one another.
Seal the barrels. Tighten the cap on the barrels and go around them with silicone sealant to prevent leaks.
Turn the dock over so that the frame and cross braces are facing up. Lay out the deck boards perpendicular to the cross braces. Screw each board down to every cross brace using two of the 1 1/2 inch galvanised screws per cross brace.
Turn the deck back over. Check to make sure the barrels' fit under the dock. It is important that the barrels fit snugly inside the cradles at the four corners of the deck. If the barrels fit too loosely, use shims between the frame and the barrels to tighten the fit.
Transport the dock to its permanent location and set it afloat, barrels down, in the water.