The odd thing is that many sailors fair to consider how the force of the wind
actually moves the boat when sailing. We know it comes from the wind
and we trim sails
to optimize sail shape but the forces on the sails
are all translated first to the edges of the sail where it connects to the boat - mast, boom and headstay and halyards and sheets
, vangs, preventers, poles. All these are loaded up from wind pressure.
But there is all the system that supports the rig... the mast step, and the standing rigging, which includes the chain plates.
It's all a great big vector diagram. The vertical loads are not moving your forward, the weight of the rig, but the components of the vectors point forward are what does it. Although the forces may seem very large because a boat is pretty heavy, it doesn't take all that much to move a slippery shape through the water
. The key thing to understand is all the forces to propel a sailboat are operating at the main points of attachment of the rig... mast, standing rigging and sheets
blocks and winches.
One can see why the chainplates must be strong and well anchored because it is through them that most of the forces pass.