I own a 2006 Beneteau 373. The zinc for this boat is small. The problem is I must replace it every 5 weeks and have had to since I purchased the boat in 2006 new. As any others had this problem and what advised can you offer?
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Some Ideas for Your Further Investigation
Others will know more, but would doubt that the presumably stock zincs on a recently designed/manufactured boat are so undersized that they need to be replaced every 5 weeks. You could double the zincs and still be replacing in a much too short a time frame. Likely something else is going on.
1) The following might be helpful for an overview of galvanic corrosion and the role of zincs: http://www.boatus.com/boattech/casey/23.htm
2) Your marina is electrically "hot". Use the archive feature of this forum and type in "hot marina" and click on the exact phrase option to find threads for description, diagnosis tips and solution ideas.
3) Being connected to shore power 24/7 I've read ususally will cause the zincs to go faster, lot more so if the marina is also hot. I have a solar panel to keep the batteries topped up and generally only connect to the shore grid when I'm on board working with power tools or want to watch the TV. Just last week a diver was bottom cleaning and replacing zincs on my neighbor's boat and I asked him to take a look at my 10 month "in the water" zincs. The shaft zinc he said had almost no depletion and the prop zinc was still 85% good. The neighbor connected to shore power needs to have his zincs replaced every six months or so.
Lots of variables and people probably have written discertions on the subject. I used to work for a an ocean transportation company operating large bulk carriers (lots and lots of steel needed protection). Sacrificial Anodes (zincs) featured high up in the replacement parts/maintenance budget.
Others will know more, but would doubt that the presumably stock zincs on a recently designed/manufactured boat are so undersized that they need to be replaced every 5 weeks. You could double the zincs and still be replacing in a much too short a time frame. Likely something else is going on.
1) The following might be helpful for an overview of galvanic corrosion and the role of zincs: http://www.boatus.com/boattech/casey/23.htm
2) Your marina is electrically "hot". Use the archive feature of this forum and type in "hot marina" and click on the exact phrase option to find threads for description, diagnosis tips and solution ideas.
3) Being connected to shore power 24/7 I've read ususally will cause the zincs to go faster, lot more so if the marina is also hot. I have a solar panel to keep the batteries topped up and generally only connect to the shore grid when I'm on board working with power tools or want to watch the TV. Just last week a diver was bottom cleaning and replacing zincs on my neighbor's boat and I asked him to take a look at my 10 month "in the water" zincs. The shaft zinc he said had almost no depletion and the prop zinc was still 85% good. The neighbor connected to shore power needs to have his zincs replaced every six months or so.
Lots of variables and people probably have written discertions on the subject. I used to work for a an ocean transportation company operating large bulk carriers (lots and lots of steel needed protection). Sacrificial Anodes (zincs) featured high up in the replacement parts/maintenance budget.
We have to replace ours frequently too
We have a 2001 Beneteau 361 (very similar to your 373) and the prop zinc on our boat doesn't last too long either. Now that we are on a mooring, however, it is much better than before. When we were in a slip, it seemed to disappear practically overnight! As for why we don't use two zincs - there's no room! The only suitable location is right at the end where the prop is attached.
We have a 2001 Beneteau 361 (very similar to your 373) and the prop zinc on our boat doesn't last too long either. Now that we are on a mooring, however, it is much better than before. When we were in a slip, it seemed to disappear practically overnight! As for why we don't use two zincs - there's no room! The only suitable location is right at the end where the prop is attached.
Longer Life for Zincs on a Beneteau 373
In our Marina the Zincs were lasting only about 3 months. I have been able to get almost a year out of my zincs (also on a Beneteau 2006- 373) by installing a galvanic isolater, a shaft brush(purchased from Boat Electric in Seattle) and running a wire from the shaft brush to a u-bolt on the transom to which is connected to a big guppy Zinc that is hanging overboard in the water. However I also bought a maxi-Prop( the orginal prop being totally worthless in reverse) and I found that I had room to put a donut zinc in front of the prop.I leave the shore power on constantly(year around for either the battery charger, fans to circulate air or a heater during the colder months.
In our Marina the Zincs were lasting only about 3 months. I have been able to get almost a year out of my zincs (also on a Beneteau 2006- 373) by installing a galvanic isolater, a shaft brush(purchased from Boat Electric in Seattle) and running a wire from the shaft brush to a u-bolt on the transom to which is connected to a big guppy Zinc that is hanging overboard in the water. However I also bought a maxi-Prop( the orginal prop being totally worthless in reverse) and I found that I had room to put a donut zinc in front of the prop.I leave the shore power on constantly(year around for either the battery charger, fans to circulate air or a heater during the colder months.
Go Fish
I have an Oceanis 370 and had the same problem. I solved the problem in the following way. I went into a marina and you can find a zinc fish. It is a piece of zinc that weight about 10 pounds and is in the shape of fish about the size of a medium size Bass. It has a 10' piece of wire attached to it. One end was cast into the center of the fish and the other end is free. It has a plastic coating on it like and insulated wire.
I have run a wire from my boats grounding strap and one that is attached to the shaft of my boat with an alligator clip to the stern of my boat. Whenever I am in the marina (with or without shore power) I lower the fish over the stern and connect the end of the fish wire to the other wires using a quick disconnect system. This takes about 30-40 sec. Now I am protected and I have found that my very small prop zinc last longer. I now replace the zinc on the prop at my yearly over haul even though I still have more zinc to go.
You can see if the protection is working also. If you leave it in the water for a week and when you pull it out it is still shiny it is NOT working. Mine is very dull looking and cover with a whitish/yellow scale. If you want you can weight it every week for a few months and determine how much it is corroding.
Currently I am going on 2 years and am only half way through my fish.
If you need some pictures I can take some and show you.
I have an Oceanis 370 and had the same problem. I solved the problem in the following way. I went into a marina and you can find a zinc fish. It is a piece of zinc that weight about 10 pounds and is in the shape of fish about the size of a medium size Bass. It has a 10' piece of wire attached to it. One end was cast into the center of the fish and the other end is free. It has a plastic coating on it like and insulated wire.
I have run a wire from my boats grounding strap and one that is attached to the shaft of my boat with an alligator clip to the stern of my boat. Whenever I am in the marina (with or without shore power) I lower the fish over the stern and connect the end of the fish wire to the other wires using a quick disconnect system. This takes about 30-40 sec. Now I am protected and I have found that my very small prop zinc last longer. I now replace the zinc on the prop at my yearly over haul even though I still have more zinc to go.
You can see if the protection is working also. If you leave it in the water for a week and when you pull it out it is still shiny it is NOT working. Mine is very dull looking and cover with a whitish/yellow scale. If you want you can weight it every week for a few months and determine how much it is corroding.
Currently I am going on 2 years and am only half way through my fish.
If you need some pictures I can take some and show you.
Go Fish 2
Just Google "Over the side Zinc Fish" and you will find ALL kind of explanations on why this work so good for so many boats. Also you will see pictures of the product. Cost is $62.00
They also made them in NON fish shape and cost less.
Just Google "Over the side Zinc Fish" and you will find ALL kind of explanations on why this work so good for so many boats. Also you will see pictures of the product. Cost is $62.00
They also made them in NON fish shape and cost less.
The London Metal exchange lists Zinc at
.86-.89 dollars per pound. A zinc fish is just a fancy ingot. See if you can purchase from a local galvanizer.
.86-.89 dollars per pound. A zinc fish is just a fancy ingot. See if you can purchase from a local galvanizer.
zinc plates
or instead of the $40 zinc fish, just buy any of a variety of zinc plates or discs found at any chandlery and attach a wire to grnd the shaft/prop.
All of these zinc source suggestions are treaing the symnptom rather than the cause. If Paul comes back, it would be beneficial to know if the boat is typically on shore power in which case an isolator would be a wise investment. If not, the problem is more insidious and adding another zinc won't solve anything.
or instead of the $40 zinc fish, just buy any of a variety of zinc plates or discs found at any chandlery and attach a wire to grnd the shaft/prop.
All of these zinc source suggestions are treaing the symnptom rather than the cause. If Paul comes back, it would be beneficial to know if the boat is typically on shore power in which case an isolator would be a wise investment. If not, the problem is more insidious and adding another zinc won't solve anything.
Wearing rate..
If my prop shaft consume 1 zince anode annually, would I get through 2 years if I put in 2 anodes ?
If my prop shaft consume 1 zince anode annually, would I get through 2 years if I put in 2 anodes ?
Ken - galvanic action rate
Short answer is no. It's the voltage potential which determines galvanic rate, not the amount of anode. Adding add'l zinc can actually increase the rate of erosion via galvanic action. Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed or adding unnecessary zinc can cause the zincs to erode away arguably faster since they create a larger battery situation where none or little existed perviously.
Short answer is no. It's the voltage potential which determines galvanic rate, not the amount of anode. Adding add'l zinc can actually increase the rate of erosion via galvanic action. Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed or adding unnecessary zinc can cause the zincs to erode away arguably faster since they create a larger battery situation where none or little existed perviously.
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