My father gave me an old 14" Polarkraft 14' jon boat with a 16" transom. Today on the lake my 15 " shaft outboard kept getting fouled with leaves. Does that mean I need a long shaft?
No that just means you are driving in the weeds.Be careful that it keeps pumping water weeds can sometimes block and/or plug the water intakes.
If the weeds aren't too dense you can sometimes get them off by reversing.
It's important to try to avoid them if possible.