i had a similar experience with our starwind 19.
a friend and i were sailing delevan lake and i piloted us through some tall grass just under the surface.
we were able to get her out of the grass, but when we tried to retrieve the boat at the ramp, the centerboard wouldn't raise all the way.
grass was had wrapped around it and now, the board was stuck half way. i too used a dowel to push the board down, unfortunately, it didn't work and i spent over an hour diving under the boat pulling grass and yanking on the centerboard.
so, like your friend tom, don't allow me to take the tiller in grass choked coves.
(it happens that my friend with me that day is named tom)