Square tops

Originally posted by JimC No, it was awful for 50 years ago too. Untapered mast, Solo sail planform with a extension above the top batten, we knew better even then too.

Fair comment, I sometimes tend to forget most of the junk I remember from the 70s was made in the 60s. Some of it before the 60s.

I think in theory a square top should be a good idea for dinghies for a given mast height. In light winds when you have more RM than power you can generate lift up high where there is usually more wind and cleaner winds. Then when the breeze pick up and you have all the power you RM can balance you can dramatically lose power from up high, which lowers the CoE in sails which allows your available RM to hold down more power. 

In practice, generating power up high in light winds may sound great, but is limited by tip losses. If you force the wind to do something hard where nearby there is an option to just go around, it will usually just do that. Similar to setting a really deep foot and them all the wind dropping out under the boom. Obviously the theory to elliptical sail shapes is to taper off toward the tip as it becomes increasingly inefficient to try and generate lift toward the end. 

If you could end plate the sail against the deck, and put wind lets on the head then it would be really nice... but both are impractical in many cases.