ok i'm give it a shot

a system where the rudders kick up is easy, a system where they go back down is either impracticable or impossible, otherwise makers would be selling it. we all want it!

the problem is pre-load. enough to kick the rudders up before damage is possible as is a pre-load to pull them down

but both working together and against each other would mean rudders at about half way tending to steer poorly, not kick up correctly or stay down either.....can't see how you can have your cake and eat it too

same for optimum dagger board length

optimum length for upwind performance is probably infinite length.....but that's too long so they make them shorter

how much shorter depends on the maker. hobie think zero length is best while modern a-class boat makers think very long is good. the amount of variables that come into play is enormous. hull design, cost, weight etc

any engineer can build a better system if he is allowed to make it heavier and more expensive. where they earn their keep is by making them lighter and cheaper