I've had my Thunderjet Chinook OS for four years now and have never changed the zinc on the lower transom. Although I inspect it every time I go out. I bought a new one, teardrop type, but have never had to install it. I never keep the boat at a marina, other than a few days on the creek in Port Renfrew, and wash/flush it with fresh water after EVERY use. Both the motor zincs are showing signs of powder formation on them but I haven't had to change them either, just a good cleaning with a SS wire brush. BTW - the boat has 106 hours on it as of July 27th, 2015 and I use braided line on my downriggers.
Does this sound normal?