It stiffens the trailing edge of the cover. I added one piece of angle and it still had an audible buzz to it, so I added the second angle and that did it. Airboats are similar to aircraft from a vibration standpoint. Resonance, fatigue and bolts loosing up are a constant issue. I install everything with two locking methods, such as a lock washer and loctite, nyloks with loctite, or loctite and safety wire. You don't want anything coming off and hitting the prop.