Above post makes sense but seems to speak more for building in aluminum. In large commercial vessels the weight of the hull built in steel has less of an impact on performance. As size decreases this becomes a greater concern and the strength may be viewed as overkill. In short one is incurring unnecessary weight with need for greater sail area and larger engines. With aluminum strength,puncture resistance,weight are more in keeping with size and actual use. Although galvanic concerns exist issues with coating do not. Hence, one reads of the extensive use of aluminum but not not steel by Alaskans for their skiffs and high latitudes sailors for their hulls. Unpainted aluminum still allows a very aesethically pleasing hull.
Unpainted aluminium in the tropics gets hot enough to fry eggs on. I had to paint the back of my aluminium dinghy white inside, so it wouldn't burn my feet. A couple I met in Tonga, in an unpainted aluminium boat, said it took them til2 AM to get to sleep because of the heat buildup during the day. It's extremely difficult to find effective antifouling paint which wont have electrolysis problems with aluminium. Aluminium welding is only 60% the strength of the surrounding metal while steel is 100%. Its far easier to screws up an aluminium weld , steel is far more forgiving and far less expensive. When the steel for my 36 was $3800 the aluminium was $20,000.
Most 36 ft steel boats are lighter than many plastic hulls, such as Westsails, Cape George cutters, Herreschoff Nerias, Ingrids, etc.
Steel is more corrosion prone above the waterline , where you can see it. and easily deal with it. Aluminium is more corrosion prone below the waterline , and happens more quickly, where it can go along way before you notice it.
Some boats have been built in steel with aluminium cabin tops, which while being trickier, can save weight up high. I just replaced a plywood cabin top with aluminium, on a steel boat this spring . Worked out well.
Steel is far more abrasion resistant on coral or rocks should you go aground and is far more floating container resistant. You can build an engine driven portable welder for steel for under $50. Aluminium welding is far more complex .
Check out the origamiboats site ( yahoo groups ) for more info.