All designs incorporate compromises to fit their purposes. There isn't a boat built that doesn't have compromises. This doesn't mean those compromises are inadequate. To achieve shallow draft, the Allures 44 uses two smaller rudders, separated off the centerline as far as possible, canted so that one of them is always at a near normal angle of attack and connected to 2" shafts.

Other than the canted part, does this setup sound familiar? Why is this setup considered highly as "blue water" acceptable on one boat and not the other?

How much steering do you need on a boat? Our boat turns within its own length with shallow rudders and has never lost steering control due to not enough steering surface (I can't say the same for several full-keeled monos I have sailed). Why does it need deeper rudders? Yes, your statement is true - deeper rudders have more steering surface than shallow rudders. Why doesn't your boat have an even deeper rudder? Is it because the rudder surface you have is adequate for all steering conditions you will experience? Why doesn't your rudder cant? That would make it much more efficient. Sounds like you made some compromises.

I won't argue engineering with you, because I am out of my depth there (but I do actually have much experience with catamarans ). However, some logic and statistics may help. There are may be 30,000 catamarans sailing around right now (actual number open to debate, and I suspect this number is low). A few of them have lost rudders because of breaking/bending of the shaft - let's make that number 50. I now personally know of 2 (Alpha is one), so 50 sounds right to me, although I suspect this number is high. I have never seen a rudder stock on a