Here is how the bow sprit is mounted. A pole extends from the main beam above the cross bar and is held down by non-stretch wire or rope attached at the end of the pole and back to bow of each hull.
And from the bow of each hull line or cable goes to the mid pole for a bit more security.
All cables or lines are tightly secured.
The bowsprit is NOT attached to the crossbar.
In that way the luff load can be very taut.

If you tied the bowsprit to the crossbar, you would indeed bend it and the bow sprit. No matter how tight you tie the bowsprit, it will initially rise a bit, but will get to a point that allows the luff tension.

My first attempt at the Hooter was without the bow spreader bar in a 21-mile upwind race to Put-in-Bay. I started off well by staying ahead of the H16s and one TheMightyHobie18, but soon the boat got slower and slower, and the luff was sagging off more and more.
It was then I noticed the bows were starting to curve inward. I quickly took down the Hooter and sailed bald the rest of the way.
And upon arrival immediately ordered the spreader bar. Now everything works wonderfully.
I have been unsuccessfully trying to get a longer pole, a bigger Hooter and bigger self-tacking jib set up, but each time has met with a small disaster. Been to the drawing board a number of times on this one. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />

Hope this explains it.
Rick