ASA and PSIA Instructor
Join Date: Apr 2000
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The tension knob is called a wheel brake, and its primary purpose is to lock the wheel when it is not in use, although you can also cheat and use it to hold the helm say if you are beating and need run below to get a beer...
As to play in the wheel, there should be NO play in the steering system at all. If there is, then something needs adjustment or replacement and you should attend ot it. Too much play and a cable is going to jump off the radial drive, always at the worst moment...
Crawl underneath and see how the system can be adjusted, also check for any wear.