[hooligan6a]

I hauled last month and replaced zinc in the shaft had to haul yesterday and the new zinc is half gone. Only 15 days in the water and all at sea not in a marina.
what should i look for?

 

[kd3pc]

name brand zinc from a reliable supplier...not the $1 knock offs. Call Jamestown Distributing or your local engine yard that services your engine brand. Even West Marine

You may have some electrical issue, I would test for leakage as soon as practical.

 

[denverd0n]

I would not assume that it is a bad zinc. More likely is that you have some sort of serious electrical leak that you need to find and fix.

 

[Delta-T]

+1 on the electrical problem. Assuming it actually was changed out!

 

[Fstbttms]

I hauled last month and replaced zinc in the shaft had to haul yesterday and the new zinc is half gone. Only 15 days in the water and all at sea not in a marina.
what should i look for?

Bare wires bleeding 12vdc into a wet bilge can destroy big metal parts in a hurry.

This ocurred in a matter of weeks. Despite resolving the problem (broken insulation on a bilge pump wire) the prop eventually fell off.

 

[RichH]

First, start with a galvanic isolator on the incoming ground wire of your AC supply. If you dont have a galvanic isolator, your AC ground wire will 'connect' your boat to ALL other boats (some with BAD wiring) on the entire AC supply circuit of your dock, etc.
Yandina.com makes very good galvanic isolators.

You also may want to detail the cause of the 'leakage' by using a 'standard reference electrode' probe to measure the potential differences around your boat. This will indicate HOW MUCH of a zinc to use for anode protection: Corrosion Reference Electrode Product Specifications

Other posters have listed the need to purchase 'quality' and reinforced zinc anodes ... a lot of 'asian schlock' is being sold as anodes these days.

 

[Minnewaska]

+1 on the electrical problem. Assuming it actually was changed out!

Good point. Wouldn't be the first time a boat was splashed and the yard didn't actually do what one asked, or even what they said they did.

If the OP is certain it was replaced, there's a short somewhere.