Jim
On the old hulls say pre 67 at least they sat tall of the water and had relatively short afterplanes and a lot of lift and ran tail down. If you ran a parallel blade rudder the leading edge would tend to flutter as it would be canted forward relaitve to the top of the rudder and suck the tail down in a turn . they fell off too much anyway.
Plus the prop designs made them pretty squirrely in the top end. the effect of the trail on the leading edge is to ensure the rudder blade isnt forward fo the shaft and so tend to stay straight, so the nose of the boat wanders less and will hold higher top speed.
A lot of boats ran castor too. The shaft is closer to the transom at top, further out at the bottom, some times several degrees. This castor reinforced the trail in straighline and if whether or not it lifts in a turn at least doesnt bog them down. Running in a boat which is very similar to a 59 Jones they sure needed all the lift they could get.
The modern boats which run flatter for an after and laterally can run straighter setups because the arent going to have the front of the blade canting forward as the tail drops and with wider tracks and better fins and props they are more stable in a straightline.
