Lots of bad information being posted here.
NEVER ground to the aluminum hull. You'll cause galvanic corrosion and it will eat away at your hull little by little! You need to have a ground block that run all the way back to the battery.
HUH!?!?!?
Nothing grounds out into the water. And just where do you think the engine and the starter are grounded too. There is no electrical connection from the boats electrical system to to the water through the lower unit. The sacrificial anodes are there because when you have dissimilar metals in close quarters in and electrolite(like salt water) you will get electric galvanization, which will eat away at the softer metal. Essentially electroplating. The anodes don't transfer energy or make a connection to anything.
Bill
