Overlapping schooner sail plan

I am working on a design for a proa with schooner rig with sails overlapping. Since a proa, the sails will be identical as the boat sails in both directions. Looking for input/ guidance on:
Aerodynamic flow
Sail shape

 

Why the odd configuration? What are the advantages of that rig?

 

Instead of a schooner rig with masts in line and the aft sail receives bad air from forward sail, the forward sail will make in theory one sail.
Also, easy to shunt.

 

"...the shift to a non-overlapping jib setup for optimum IRC performance. This shift in sail plan has had a significant lessening effect on the boat’s light air performance due the headsail area reduction.

To compensate for this reduction in power, the class uses an inhauling system – this narrows the slot between the mainsail and headsail, in turn increasing the power of the entire sail plan."
J/109 INHAULING FSI STUDY TO GAIN SPEED & POINT - UK Sailmakers https://www.uksailmakers.com/2019/03/21/2019-3-21-j109-fsi-study-to-gain-speed-amp-point-by-inhauling/

While a lot of pressure testing shows the foresail doing most of the work, the presence of the aft sail (mainsail) can have a dramatic positive effect on the foresail's effectiveness.

Tightening up the slot can increase the pressure variance on both the forward and aft sails.

-Will

 

There is likely a drag penalty for overlapping sails. But this penalty does not entirely cancel out the added area. And only the area that is overlapping suffers this penalty. And this says nothing about the overlapping sail fairing what I call the "mast bump turbulance" of the sail that is being overlapped. So, even though there may be a drag penalty, it is more than made up for by the improvement of the airflow over the sail being overlapped.

 

Most designers and sailmakers like a bit of fore sail overlap, given their druthers- Irens and North Sails came up with generally the same sailplan, IMO, as you are proposing on Fafarer- see pics above. There MIGHT be a bit of imbalance toward Lee Helm with more power in the front sail, but that could be balanced with foil deployment. It might be worthwhile to look up biplane and tandem wing aerodynamics if you want to dive deeper into things- the CFD is pretty if nothing else. (The mischievous part of my brain is suggesting some sort of lug rig, especially dipping lugs, but that will make shunting more, um, entertaining- on the other hand, dipping lugs are very powerful. For modernized standing lugs, check out Micheal Storer’s Goat Island Skiff performance racing rigs- you might be able to go to freestanding rigs with gust response, which could be useful given pacific proa dynamics, and localizing rigging tension off the hulls and on to the masts. Unless that’s what you’re already doing- it’s a bit hard to tell.).

 

Makes me think of a gollywobbler- a very large quadrilateral staysail set between the foremast and mainmast of a Staysail schooners.
Starling Burgess NIÑA had a gollywobbler sail and it would take the place of the staysail and would be added to or replace the fisherman.
I have heard a gollywobbler will make you fly.

 

I am also thinking of a dipping lug on a proa too, but as a single sail. What could speed up the shunt considerably is one more sail and yard lying on deck which is lifted on a new tack after the "old tack" sail is lowered.

 

When it comes to the aero flow and sail shape for that rig, there's a few things to keep in mind. With them overlapping sails, you gotta make sure the airflow ain't getting too funky and turbulent between 'em. Them sails'll be fightin' for clean wind if they're too close together. My two cents? Give 'em a good separation so they can both breathe proper-like. You don't want that leeward sail just chokin' on the turbulence from the weather one. Plenty of folks make the mistake of packin' the sails too tight.
Greetings, Vincent

 

No doubt you have checked out Sidecar? It might be worth a Tasmanian holiday to have a close look at it?