Boat electrolysis

18' sled.
Aluminum.

If the big motor has a good zinc but the gas 9.9 kicker has a little one in poor shape do you need to replace it or will the one on the big motor suffice?

100% replace. Electrolysis is direct through the part, so Zincs must be directly connected to any item which requires protection. I.e. the one on your big motor isn't going to create a "force field" of protection - that's not how it works.

Thanks.

For that I would use electrolytes.

Also, if the zinc on the big motor appears to have a good coat of oxide on it, brushing it with a clean stainless steel wire brush helps for continuity (or so I've been told by the boat shop I use).

Look up post " How Much Zinc Makes a Boat Fishy " from Iwannagofishn on this board, if your interested in some science and details on boat zincs to catch more fish.

Might want to add one to the hull as well.

Might want to add one to the hull as well.