Quote Originally Posted by cougarmeat View Post
Something to bear in mind when the, "DCF is used for boat sails so it should withstand the wind" thoughts enter is ... They are not holding the sailboat back against the wind. They are not anchored to the ground, a tree, etc. holding the wind back. On a sail boat, they are filling the shape of the sail and going with the wind. That's not to say too much sail won't have problems in a storm - it's that the dynamics are different.

How does a sailboat move? Most people picture it being pushed by the wind in the sail. Sometimes, yes, when the wind is at the stern (back). But usually - the boat is "pulled". Imagine an airplane wing. The air over the top creates a pressure difference that causes lift - pulling the plane up. Now imagine that horizontal wing in a vertical position - that's a sail. The shape of the sail causes that same pressure difference but instead of pulling a horizontal wing up, it's pulling vertical wing forward. The DCF sail is moving with the wind.

So I'm not saying DCF isn't strong. I'm just suggesting that thinking a DCF sail on a boat is the same dynamic as an anchored down tarp, could be a little off.
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.