knowledge regarding electrolysis but here's my take on un-bonding the system. You ALWAYS have current flow when you put two dissimilar metals in an electrolyte. Now, you cast the bronze body of the valve with Prue silicon bronze and set it aside in a pile of other valve bodies. Now you cast the plug out of another batch of pure silicon bronze and set them aside. Now you cast the handles out of another batch of pure silicon bronze and set them aside. Now you take a valve body, a handle and the plug put them all together and connect the handle onto the plug with a stainless steel cotter pin. Now you install that 4 part valve into a boat and set it in salt water which, in reality is an electrolyte. All of these "pure" silicone components aren't all that pure and you get current flowing between the parts. That's one reason. Another is that the through hull fitting is attached to the hull. All boats end up with a film of salt crystals covering the bilge unless you wash the bilge as often as you do the outside of the boat. Current flows across the salt because it's an excelent conductor so you get current flow between various components through out the boat. All of these currents are very small but over time it adds up. Bonding a boat levels all of this out and connects it to a sacrificial zink.

silicone bronze