It really is kinda the same. Sail, Tarp, Propeller, Rotatory wing, or fixed wing. It all comes down to a Pressure over an area. DeltaP/A. This is the load and force into the structure. Now on a tarp the sheet will have to react the full load out the tie outs as what it ties too is fixed. In a sail the Force is all there also and is transferred through the structure to accelerate the boat. (F=MA) and overcome the water friction.
The biggest difference in a sail and a tarp is how it is held. Most main sails are held the full length of the mast and boom providing a large reaction area to the overall load at any one "tie-out" is greatly reduced. In a tarp it is held at 4 points. This is one reason I favor a CRL under the tarp. In a windy situation the tarp load is transferred to the ridgeline over a larger area than an Over the tarp hang.
The difference you may be are eluding at is real in that the relative speed of a sail boat to the wind can diminish the perceived wind speed. i.e. a boat cruising at 20mph in the same direction as a 30mph wind experiences a 10mph relative wind.
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