Scott,
Zincs.....and galvanic corrosion require both an electical connection and a conducting medium (salt water) to complete a circuit. Dissimilar metals along with the two previous items form a battery. The use of zincs is to provide a more active (less noble) side for the circuit so that the zinc is consummed rather than your boat part. Zinc is a very active metal, asi is aluminum.
This raises two points. The first is that in order to work, zincs need to be connected electrically (by wire) with the other metal items that sit in the salt water. If it doesn't sit in the water, it doesn't need to be bonded. And zincs not connected to the other items may corrode for other reasons but will not protect your boat.
The second point is more debatable, by some. There is a the thought that to bond (connect) your through hulls to the other metal in your boat is an invitation to disaster. If the zincs are consumed and the through-hulls are now the most active metal in the system, you now have a battery eating up the one thing between you anad the bottom of the harbor. There have also been some reports I have seen saying that galvanic corrosion can cause problems with the surrounding material, especially wood and soften and weaken them. I can't speak with any authority about that but I have heard it from some. So my recommendation is to bond everything but your through hulls.
There are two systems tying things together electrically in your boat. The first is the bonding system as mentioned above. The second is a grounding system tying all metal items above the water to the same electrical point, for lightning protection. Code requirements currently (sorry,,,I couln't resist) are for the main discharge path to be 4 ga copper wire or better and ohter paths to be no less than 6 ga or 20 ga copper strips. This may be the source for wire tying your shrouds and stantions together and might lead to a through hull (argghh).
If you have any questions, drop me an email...Also a shameless plug for the Power Squadron. Their Marine Electronics course (for members) is an excellent resourse for this and other information. Join a local squadron and avail yourself. (I am an ME instructor)
John G.
Valhalla
Commander No 287