Hull and Rudder Zinc.....Yes or No? (Cutwater)

[GulfSailor]

What are the pros and cons of bolting a hull zinc to the transom and bonding it to the ground system?
As most hull zincs have galvanized inserts molded into them, what material should be used for the securing bolts?

Same pro and con question for installing a zinc on the rudder. I notice that few of our boats (Tugs and Cutwaters) have either fitted.

I'm not sure the answer is "If they were needed the factory would have installed them", as the trim tabs certainly need them and mine don't have any.

I'm going ahead with a galvanic isolator and trim tab zincs, but I'm on the fence about the hull and rudder.

All input welcome, especially from Andrew. 😉

 

[abcandjrc]

The quick answer is "It can't hurt but night not help." Part of it depends on how hard your environment is on zincs. Your water's salinity, your marina's wiring, your boat's potential, and your neighbors' boats' potential.

I guess the con is that it is one more area for a leak, and if the transoms are cored (I suspect they are not, but do not know for sure) a risk for high repair bills.

The other answer is stainless steel.

 

[Andrew Custis]

This is a great topic so thanks for involving me.

There are many different opinions on transom zincs and ways a boat should be bonded. I will keep this one as simple as possible.

1. Would a transom zinc help? Absolutely. A transom zinc is designed to tie your existing bonding system to a large anode mounted on the transom of the boat. Your bonding system consists of your thru hulls, multiport strainer and engine anodes below the water line bonded with an 8 gauge green wire tied to your battery negative. A transom zinc ties into this system taking the attention off of these metals that would be exposed to stray current. A cheap version of a permanently installed transom zinc would be the grouper zinc. This type of anode would need to be hauled into the boat and disconnected from the battery negative each time the boat is used. I have attached a link to what this would look like. This would give you a few different options. Ranger Tugs and Cutwater Boats do not install transom zincs on any model other than the Ranger 29 and Ranger 31.

You asked about material used to install the transom zinc? I am assuming the question is what kind of sealant is used to stop leaks from happening? If that is the question, I would use a 4200 or 5200 marine grade sealant made by 3M.

http://www.boatzincs.com/hanging_anode_zinc.html

2. Now on to the trim tabs. Trim tabs are not bonded to anything else in the bonding system. With that said, adding anodes to your trim tabs means they are not increasing the anode protection on your vessel one bit. They are simply protecting the metal on the trim tabs. Ranger Tugs only puts trim tab anodes on boats that are bottom painted at the factory and for local deliveries. Bennett trim tabs are the brand of tab used on our product. After speaking with Bennett about adding anodes to their tabs, they say these are not necessary. Having an anode certainly wont hurt the tab but will add a cost to the end user that is not necessary.

3. The rudder is also an item tied into the bonding system. With this said, a transom zinc or grouper zinc would protect this. Also keep in mind one thing. Bronze has natural corrosion inhibitors in it that fight against corrosion. I am not a fan of adding anodes to the bronze rudder we use.

I can get into galvanic isolators another day. Hope this information helps. 😀

 

[GulfSailor]

Thanks for both replies so far.

To Andrew, in regard to fixing a zinc to the transom. Because many hull zincs have a galvanized insert for the mounting bolts, I was wondering whether galvanized bolts or stainless bolts should be used to secure it and the bonding wire.

This is the zinc I was thinking of installing: http://www.boatzincs.com/dp-612.html

As to the trim tabs, Bennett do recommend using a zinc, but only for salt water use.

This is what the Bennett Owner's manual says: "(SALTWATER ONLY) To deter electrolysis, a zinc anode should be attached to the top of each trim tab. Zinc must make direct contact with stainless steel. Do not paint zinc. Do not ground trim tabs to other underwater appendages."

Thanks for the valuable input, and based on what you say I'll forget about the rudder zinc but go ahead with one on the transom, and as I'm in both salt and fresh water I'll add a pair to the trim tabs.

I'd also be very interested to hear your thoughts on galvanic isolators if you can find the time; I'm sure it would be of interest to many others besides myself.

Thanks again!

 

[Andrew Custis]

We use a 3/8" X 4" Silicon Bronze stud with double nut and washer inside and out. Thank you!

 

[baz]

As I've just installed a below water-line stern/transom zinc I can tell you what I used.

Silicon Bronze threaded studs (yes - I used two studs) with silicon bronze double nuts on outside (provides a lock nut capability) and also inside of the zinc and a silicon bronze washer against the stern. On the inside of the transom accessible from the starboard side lazzarette I have the same material for washer and double nuts. The nut that is against the washer on the water side of the transom is welded to the stud so that it can be held with a wrench to avoid the stud from rotating when removing the outer lock nuts for replacing the worn zinc.

Oh -- and as Andrew has mentioned, use 8 gauge wire for bonding the zinc. Also solder the ring connector to the wire used for securing to the stud inside the boat.

After mounting the stern zinc I checked for leaks over two days. None found -- but put this on my list of things to check periodically.

Two pieces of advise...

1) When I first drilled two horizontal holes in my transom zinc I made them vertical centered. After installing and checking to see if the zinc was completely submerged I observed that 1" remained above water line. This has caused me to relocate the two holes in the zinc to be 1" off vertical center.

2) Have a 2nd zinc that is already drilled out with two holes using the first as a template. Thus when replacing you will not have a problem with the holes NOT aligning on the studs. Always keep a reserve zinc with pre-drilled holes for this reason.

BTW -- The transom mounted zinc is easily replaced with the boat in the water. You may have to lay flat down on your dock, but that's a minor issue. If you trailer, not a problem... 😀

 

[baz]

Gulfsailor: Be sure to add a wired between the tabs and their hinge portions attached to the stern. I found after 2 1/2 years in salt water with factory installed trim tab zincs the hinge portion attached to the stern had several rather large holes (1/4" dia) caused by corrosion. The added trim tab zincs should help reduce or eliminate this type of corrosion. The 'hinge' is simply a crimp (at least on my MY2010 R25 it is) and suspect because of this there's little solid connection between the tab and it's attached hinge on the transom and thus without the wire bonding I mentioned there little protection offered by the trim tab zinc for the transom mounted metal hinge.

 

[baz]

This is a great topic so thanks for involving me.

There are many different opinions on transom zincs and ways a boat should be bonded. I will keep this one as simple as possible.

1. Would a transom zinc help? Absolutely. A transom zinc is designed to tie your existing bonding system to a large anode mounted on the transom of the boat. Your bonding system consists of your thru hulls, multiport strainer and engine anodes below the water line bonded with an 8 gauge green wire tied to your battery negative. A transom zinc ties into this system taking the attention off of these metals that would be exposed to stray current.

...snip...

I can get into galvanic isolators another day. Hope this information helps. 😀

I also assume the prop shaft end zinc's erosion rate is reduced some by having a large stern mounted zinc tied into the bonding system, right ?

Look forward to the "another day" when you post your thoughts on the usefulness of a Galvanic Isolator... 😉