No, that's what you get for being wrong.
Please note this is from a site that discusses these materials in terms of DIY small boat construction ?
A "strength-equivalent" aluminum structure, having used deflection (stiffness) as the design criteria, will have been built using roughly 50% greater plate thickness. We might then say that this strength-equivalent "one and a half inch" thick aluminum plate will yield at around 51k per square inch of surface area (around 29% greater yield strength than the "equivalent" region of steel plate), and will fail at around 67.5k psi (around 12.5% greater ultimate strength than the "equivalent" region of steel plate).
Of course these broad generalizations are intended only as a way of illustrating the approximate relative strengths of the materials. However, from these considerations we can see that the aluminum vessel will have a greater overall strength than the steel vessel per square area of plate. The reason for this is that the aluminum plate will, for the sake of stiffness, be 150% the size of the steel plate.
The result in practical terms is that a boat built in aluminum will be far less easy to dent by running into stuff (roughly 29% higher regional yield strength), and will have a slightly higher resistance to ultimate failure (around 12.5%). As an added bonus, this means that the aluminum yacht will resist distortion all the better while being welded during construction. As an extra added bonus, the aluminum structure will weigh considerably less than the equivalent steel structure.
Dave Gerr has equated the two materials similarly, referring to a material's structural efficiency. By this, he means the ratio of a material's stiffness to the density of that material. Per those equations, aluminum is shown to have a "structural efficiency" much greater than steel. In more precise terms, for columns that are designed to an equivalent stiffness an aluminum column will weigh 57% of the equivalent column in steel. For beams and panels (frames and plating) designed to the same stiffness, an aluminum structure will weigh 48% of the equivalent structure in steel.
