ASA and PSIA Instructor
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If, when under sail the boom hits the dodger, something needs to be changed. But not the rigid vang. You should be able to sheet in hard with the main up without hitting anything. If your vang is adjusted to prevent this, then you won't be getting the proper sail shape.
Perhaps your dodger is too high or your sail is not cut properly.
Ditto to Steve's comments, and additionally you don't want to try to resolve this situation by adding a topping lift. If you were to do so, you would be putting an risky load on the boom, if you trim the main hard with a tight topping lift, you could easily break the boom (been there, done that...).
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