@Alma check out the choices available at BoatZincs. Know the diameter of your shaft and the spaces available between the prop / strut / and exit from the hull. Armed with this knowledge you will be able to select a zinc design from the many offered.
Doing the job with the boat out of the water is a great way to understand what is needed.
The goal is to keep the zinc about 2 plus inches from the cutlass bearing so water can easily flow through the bearing to keep it cool. If installing it while the boat is in the water, it should be easy to accomplish. This means you want the screws to be captured in the zinc and use a simple tool as shown on the website. Any professional diver like
@fstbttms will have the tools for the job