I agree with Jake and Yurdle. The dolphin striker post takes the full downward force of the mast. This force is transfered to a tensile force within the striker rod which is counterd by an axial compressive force along the main beam. With the dolphin striker securely fastened to the main beam and properly tensioned, the main beam should see no bending load due to the downforce of the mast (only compression along it's length due to the force of the striker rod pulling inward). The compression tube is there simply to prevent the user from over-tightening the dolphin striker post bolts and accidentally crushing the main beam. Case-in-point, boats like Hobie 16's & 18's (which don't use a double-nut sriker post) don't require a compression tube.
The compression tube in your boat is most likely stainless steel in order to prevent it from corroding and seizing to the dolphin striker post.
sm
Nearly....
MOST work thus:
Mast sits on a ball; this ball is attached to the a threaded rod that goes thru the main beam and attaches to the dolphin striker. However; the rod is also fastened via 2 or maube 3 bolts to the main beam.
The beam AND the DS take the load. THis is why it us usefull to apply some positive (up) prebend in the front beam.
For a while, this was the only setting I would change on the Hurricane I owened. More wind; more prebend so more rig tension. It does NOT work on my F16 in the same way!
