When you go to Blokzijl, please use the big free parking spot outside the village before entering the village. From the parking place it's just a small walk to the village centre.
The reason is: Blokzijl itself doesn't have a lot of parking space & there are some very small streets where you can't pass each other.
Getting to Blokzijl is quite difficult by public transportation. You have to go by train to Steenwijk from where you will have to take a special bus. I never took this little bus, but the times are quite inconvenient. It is better to take the train taxi (€3,75) and be brought all the way to Blokzijl.
Easier is to drive to Blokzijl yourself, or include on your boat trip in the Provincie of Overijssel.