Talador: "I am having a devil of a time trying to figure out why the sailors want flaps?"

The devil ain't in the detail. It's plain to see.

It's the total drag package.  All that drag above and below the water must be overcome.  And you need lift to overcome it.  Your single element will either have to be so tall that you must depower before you generate much lift, or so squat that its draggy anyway. 

Aircraft don't use symmetric foils.  They don't fly upside down, at least not much better than a bucket of bricks when they try :).

Aircraft are symmetric in plan view.  Lift is balanced around the fuselage.  Sailrocket is symmetric.  Single element wing and Bruce foil balance.  Low drag makes sense.  Problem is they needed a draggy base ventilated foil because of the speed.

You need a full VPP and testing.  The big bucks of Oracle and TNZ went this way.

If you just want to compare it to a triangular sailed sloop you are setting the bar low.  If you are building a wing you should be benching it against wing + sail and 2 element wings in a VPP.  You are dealing with the same logistical problems of reduced capacity to reduce lift and drag aloft when it blows.

It makes sense for GreenBird to use the single element.  Apart from the keel, the whole package is low drag with minimal controls - necessary for an unmanned craft.  But don't forget that keel.  Are you going to put a 6m weighted keel under a HarryProa in order to ensure selfrighting?  Is your bridgedeck proa (as I understand your intentions) going to be low drag?

These questions are rhetorical (i.e. intended to make a point) - I have no plans to respond to any responses.  My apologies, but I'm too busy building to be further drawn on this topic.