Originally Posted by
Devon77
But suddenly, the needle is hitting something in the bobbin mechanism
If I had to guess I'd say your use of a domestic machine to sew heavy canvas has caused the timing to slip.
Very easy to fix but it will probably happen again if you keep using it to sew sails together again. If you really want a domestic machine to do this, a 201 would be my choice: It will take more punishment than the 306, and they're very cheap nowadays.