If one is good are two better?

[PapaBruce]

Morgan 416 in a marina. If one zinc is good on the propshaft, are two better? I've searched the forum and can't find an answer - then again, I'm a guy and guys can't find anything!

[djmarchand]

Yes, if you have room for two on your propshaft that will give you better zinc life. Some will say that you can overzinc, but I don't think you can get there with just two on the prop shaft.

David

[gello]

yep u can overzinc.
consequences:

on fiberglass boat: mostly benign
bonded- alkali bottom paint attack around thru hulls. kind of dissolves paint off hull leaving a rough moonscape for a few inches in the paint around metal items.
unbounded-not much of an issue unless your prop is painted. watch rubber components like cutlass bearing which are in close proximity and may not like alkali.

on wood boat: depends
bonded: alkali ears soft wood and destroys hull integrity around thru hulls. exhibits white feathery spider webs on surface of wood. very bad.
unbounded: same as fiberglass above. remember however wet wood often creates an accidental bonding system so be careful.


on aluminum boat: death
over zinced is as bad as overzinced. u live in a battery. get a good silver half cell and a millicolt meter and keep your voltage in the 800 to 900 mv range. certainly below 1100 mv.

good luck. I carry a home built corrosion meter and measure regularly.

cheers

gello

[PapaBruce]

thanks!!