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How does a water-ballasted boat compare with a lead-ballasted boat of the same length, beam, draft, freeboard and interior headroom, and the same weight of ballast?

Water ballast is much lighter for trailering, as it can be drained. A water tank is cheaper than the same weight of solid lead. These benefits are purchased at a cost however.

The water-ballasted boat will have less static stability, This is because the less dense ballast cannot be concentrated as low in the boat. The water-ballasted boat therefore cannot carry as much sail as the lead-ballasted boat, but will have similar resistance to motion. This means decreased speed. Also, this ballast occupying relatively high areas of the boat will require a deeper shaped hull for the same interior headroom which leads to a shorter (vertically) fin or centerboard for the same total draft. This adds up to worse windward performance. These are the costs of the more convenient trailering and lower expense.