A couple of ther things you can do to stabilize a floating dock are: 1) If you are using plastic barrels for floatation, partially fill each barrel so that it sits lower in the water. Imaginge a totally empty barrel and how it will be very tipsy on the water surface versus a 50% filled barrel that is partially submerged. 2) Add ballast to your dock. Hang an engine block off each corner of the dock 2-3 feet below the surface. This accomplished the same end result as adding water to each barrel. Both methods "plant" the dock a little lower in the water increasing stability. If you chose to partially fill each barrel, you'd want to do this during the construction phase. If you chose adding external ballast, you could determine how stabile your dock was first, then add ballast until you get the desired stability you want. With such a large floating dock, it may be more stabile than you'd think.
