high voltage question

1978 johnson javelin
85etlr78c

While running today, I noticed that voltage on my fish finders were reading 16.8 - 17.0 while running at any speed on plane. Came off plane and idled and it would drop to 13.5 or so. Am I right assuming its the regulator gone bad?

I would put a digital volt meter on the battery and check it. Also if you have wing nuts on the battery replace them with stainless steel lock washers and hex nuts.