erratic voltage, bogs motor

[True North]

So just to update and finish the thread. I replaced the alternator with a marine-grade replacement that I bought online. Once installed, ran the motor and the voltage spikes were non-existent, at least while under idle and up to about 1800 rpms. True test will be when I splash, but wanted to thank everyone who chimed in to assist. Now onto the next project of installing a new Fishhawk X4 speed/temp sensor!