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The problem is that most of what has been published and routinely discussed, (even in US high schools) etc. on how sails (wings, etc) work has been wrong since the time when the Wright Brothers empirically discovered an entirely different reason for 'lift' (and such applies to all fluid dynamics - hydrodynamics as well as aerodynamics). Suffice it to say that such sciences are definitely NOT intuitive; yet, when using tell tales on sails or combinations of sails one can under exact conditions see the effect of air apparently 'circulating around' such sail and sail combinations.

Without getting into discussion of fluid dynamics and losing everyone via 'glassy eyed stares and nods', sails 'work' aerodynamically (going upwind) simply because the flow air has 1. 'friction' and 2. the apparent oncoming boat/sails causes some proportion of that airflow to go FORWARD on the windward side of the sails which in turn cause an 'upwash' way out in front of the boat causing a circulation effect of air flow. This is not dependent on whether the boat is mast headed or fractional rigged - its just the total area of the sails moving forward that causes effect ... and the effect is air circulating 'around' the sails/wing/propeller/turbine, etc.
The seminal articles that 'unveiled' such strange behavior to the sailing community was introduced by Arvel Gentry (aerodynamicist and sailor) in the early 1970s. Do websearch for: airflow+sails+circulation
The same applies to all fluid flow about 'foils'.

http://ljjensen.net/Maritimt/A Review of Modern Sail Theory.pdf
https://cld.pt/dl/download/10d8878b...ht - The Aerodynamics Of Sail Interaction.pdf

Again, such fluid flow is NOT 'intuitive' yet once you begin to understand exactly what is happening, you can under the 'right' conditions see these effects when using a full set of tell tales (or smoke tracers) on sails/wings, etc. To reach such understanding you will have to ignore everything you previously ever learned about how wings and sails 'work'. Under the 'right' conditions when sailing aerodynamically, usually when the air speed flow is exactly matching the forward speed of the boat/sails, you will notice that the windward side tell tales will not be streaming aft but will be streaming FORWARD ( a vectorial SUM) !!!!!! ... streaming forward on the windward side and streaming aft on the leeward side --- the 'total' flow is 'circulating' around the sails and in so doing is causing an optimum amount of 'upwash' well out in front of the boat/sails; hence the ability to 'point' (and point higher, etc. than when attempting to explain or rationalize by the 'wrong' and long held theories). The 'upwash' is simply air moving out of the way of the oncoming boat/sails and moving aside towards the apparent 'lower pressure' (leeward) side and long before it gets even close to the boat/sails. The windward side of the sails moving forward is causing 'some' of the air on the windward side to flow FORWARD .... its simply caused by the square foot of sail / wing material moving forward and doesnt matter if its all held up by a masthead rig or a fractional rig ... its 'just' the amount of sq. ft. of area moving forward. The 'keys' here are twofold: 1. air flow is 'circulating' around sails and 2. air has viscosity (friction).

A lot of articles and reply commentary have been written about 'sails and their recirculation flow regimes'. Do a websearch but be warned that some of the aerodynamic theory will be difficult to understand, .... at least on the first few readings. If interested, do read and reread and reread again such articles several times and then transfer that knowledge to YOUR sails with telltales installed .... you will eventually state "oh yeah, I think I can SEE what is happening; but, you have to have a full set of tell tales and 'gentry tufts' installed to see this.
Your high school science teacher was entirely WRONG about wings and sails and propellers, and what causes 'lift' etc.

;-)
 

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I'm an engineer, but I skipped the fluids course, but now regret that.

As a cruiser, I like the fractional rig for practical reasons. Usually, the mast is further forward, allowing the boat to balance reasonably even with the jib rolled up. Small jib is easy to tack, a bigger fully battened main is easy to handle, you can hold a full jib into an increasing wind while reefing the main only (partially rolled jibs usually don't hold their shape well), the boat will sail to windward on main alone when short tacking allowing someone to easily work the foredeck to get the anchor ready or grab a mooring, and a furling code zero (a super easy to deploy light wind sail for cruisers) can be launched easily in front of the rolled up jib.

I read a little about Bernoulli and Reynolds numbers, but cannot remember any of it:)
There is no need to review Bernoulli, Reynolds or even Prandtl, etc. All you have to do is keenly observe that most frac rigs (compared on an equal/similar basis) overwhelm masthead rigs when going to weather; and on the 'down side' the very same frac rigs will invariably use a spinnaker to beat the pants off a masthead (using a large LP genoa) 'going down'.

Such kind of strongly suggests that a masthead rig is only a compromise ... using the BIG jib/genoa instead of a 'proper' downwind sail and at the expense of 'pointing ability' for going uphill, to boot. It also suggests that the 'aerodynamics' of sailing more or increasingly 'optimize' with the fractional rig.
No 'iterated numbers' or 'theories' required, the 'ratings' databanks, the compilation of racing result over many many years seem to confirm this; all the while, the 'modern' (post ~1903) theories of aerodynamics help to explain 'why' that is.

All this stated, I still dont want an overly-tall rigid wing-sail on my crab-crusher 'Perryboat', thank you. But yet, I still fly a staysail 'under' a yankee topsail, as the speedo results show an increase of forward speed & VMG when pointing with this 'combo' .... and even that the staysail doesnt visibly seem to be 'drawing' - thanks to modern theories of aerodynamics.

;-)
 
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