Seacocks, Thru-hulls & Ball valves. 10 to replace:(

Hermit Scott · Mar 4, 2009

After doing some, I don't think that $500 a piece is unreasonable. 6k sounds reasonable for all that.
I personally don't agree with bonding that seacocks. They are all one type of metal and if they are isolated, I don't understand how they could get eaten up by electrolysis. I would like to know these things before I get to my marina though.

jibes138 · Mar 4, 2009

Electrolysis

Scott,
Electrolysis can happen within the metal itself not necessarily between different components. Metals are typically alloys so they have multiple elements with varying electrical potentials in the form of free electrons. In the presence of moisture you can get pitting and corrosion as positive cells give up atoms to negative charged cells in the same metal object. The purpose of a sacrificial anode is that it is much more noble than the other metals in the system and thus will sacrifice its' atoms before the rest of the metal does. It is basically a plating process with the anode losing atoms and the cathode attracting them. So my suggestion is to make sure you bond all metal object under water to the sacrificial anode. In an airplane all the parts are bonded to allow lightning strikes to conduct through the plane and not cause major damage. Another reason to bond everything, if the boat is hit by lightning you will have a conductive path to ground (the water) otherwise you have a high potential charge that will jump the resistive (air) gap to the closest conducter. I've heard stories where this could cause a through hull to be blown out of the boat.

Hermit Scott · Mar 4, 2009

Your through hulls are connected underwater to anodes?

jibes138 · Mar 5, 2009

Grounding

All the underwater through hulls, the mast step, rigging, are connected together with ground wires and connected to the keel bolts (lead keel) and the engine which is connected to the shaft that has a zinc anode on it.

jibes138 · Mar 5, 2009

Bonding Definitions

Scott,
I may have confused you by using the term "bonding" in discussing your through hulls and sacrificail anodes. Bonding in this sense is "electrically bonding" the parts or in other words connecting them together with a wire so that they all can conduct electricity amongst themselves and they are all connected to whatever has the sacrificial anode, in this case your propeller shaft. So don't confuse this with adhesive bonding which is a mechanical joint. Your through hulls probably had a copper wire attached with a hose clamp and that wire would run to various other through hulls and eventually be part of the grounding system for the boat. I know for a fact my old catalina 25 didn't do this but it was an outboard so there was no shaft. Your 30 may not have this either. I don't have a photo and won't see my boat for a while so maybe someone else could post a picture to show scott what this looks like since he is replacing his through hulls he should include the ground wire. I think from a photo that the flanged adapter looked like it had a vertical rib with a through hole. This may be just a connection point for a bolt to attach an electrical wire. Not sure why else that feature would be on the adapter?

Maine Sail · Mar 5, 2009

Hermit..

There are differing schools of thought on bonding. Some are in the "must bond" camp and others are not.

There is plenty of good info out there and you can read till your eyes turn blurry. I personally do not bond my seacocks but others choose to. If there is one thing that is a constant is that EVERY boat will react differently if the on board electrical systems or the marinas electrical systems are funky.

Hermit Scott · Mar 5, 2009

Jibes- I do believe the little flange on the side of the flange adapter is for bonding. From what I understand the zinc must be in the electrolite(seawater) to work as a sacrificial anode. For instance, you can't put a zinc on top of your engine and expect the inside not to corrode. Also the anode on the prop shaft must be in the water not in the boat in front of the packing gland.
It seems to me that to make electrolosys you need a difference in potential. If you bond a through hull in the bow of the boat to a through hull in the aft of the boat, and an electrical current is traveling through the water, there can be a differnece in potential that can cause electrolosys. One becomes the anode the other the cathode. Basically you are creating a circuit and a battery when you bond the distanced through hulls.
One is an anode, one is a cathode, the seawater is the electrolyte and the bonding wire completes the circuit.
I do not grasp a full mental picture of the actuality of the situation here, so I am repeating what I have read. So if I am mistating something please correct me.

jibes138 · Mar 5, 2009

You are pretty close.

Think of it this way. You can run a wire from each through hull individually to the zinc in the water, or you can connect all of them along one wire, these are not series connections, but parallel connections. So while current will flow along the path to the various grounds the most noble metal will sacrifice itself before the less noble metals. Zinc is an extremely reactive metal so it sacrifices itself first. I'm not suggesting zero corrosion on the rest but the rate is so slow as to not be a problem over a lot of years. If you only have a single through hull not bonded to a zinc it is possible to have dissimilar metals within the same part act as anodes and cathodes and the result is pitting of the part. I've seen this extensively in manufacturing precision machined parts (parts held to millionths of an inch tolerances). In the presence of a conductive fluid you can get pitting on parts just sitting isolated in trays. No metals are pure because of contaminants and most metals are alloys so to the extent they are not perfectly homogeneous you can get this dissimilar metal effect. If you want to research corrosion and electrolysis you can read a lot more than i can type. I understand Maine Sails comment on two schools of thought. Mine tends to the bonding option. Zincs are cheap compared to a 500 dollar through hull replacement.

Hermit Scott · Mar 5, 2009

I see what you mean; everything is bonded in the boat but they are all in contact through water and somewhere under the water you have a zinc connected to metal.

So how is leaving them isolated a problem, like in a marina with rouge currents? What happens?

Don S/V ILLusion · Mar 5, 2009

[FONT=&quot]Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be un-bonded' does not take into account the individual situation the boat may be in. There are three types of corrosion underwater metals are subjected to---Electrolytic, Galvanic, and Stray current. Bonding underwater metals (and installing a zinc) will cure/prevent the first two types of corrosion but will cause or speed up the last. It is best to find out what type of corrosion your boat is experiencing before deciding on the cure and if you are not experiencing a problem, leave well enough alone.
[/FONT] [FONT=&quot]Only bond underwater items that are showing symptoms of electrolysis. If it ain't broke, DON'T fix it. Once you bond it unnecessarily you have CREATED the circuit rather than DISCONNECTING it. [/FONT]
[FONT=&quot]

[/FONT]

Hermit Scott · Mar 5, 2009

Is 'stray current' from the boat or from another boat or marina?

Don S/V ILLusion · Mar 5, 2009

[FONT=&quot]Stray Current[/FONT][FONT=&quot](or Electrolytic) corrosion results when an applied current flows through immersed conductive materials, other than an intended electrical circuit.
Stray currents can come from an outside source either internal or external to your boat. Internal sources involve a short in your boat’s wiring system, such as a poorly insulated wire in the bilge, an electrical accessory that may be improperly wired, or a wire with a weak or broken insulation that is intermittently wet.
External sources are most often related to shore power connections, or other boats on the dock .

To generate electrolytic corrosion, the stray current must flow onto the metal at one location and then flow off the metal at another location. [/FONT]

sailingdog · Mar 6, 2009

I don't think that bonding metal through-hulls is all that important on a fiberglass boat. On a steel or aluminum boat, it would be far more of an issue. If they are not connected electrically to anything else, there's far less chance of them getting eaten away in a hot marina, as Don points out.

The only real reason I'd see for bonding them is lightning protection.

sailingdog · Mar 6, 2009

Pitting isn't usually the problem with bronze through-hulls. Dezincification is. Clean off the through-hull and see if it has pinkish spots... if so, then you've got a problem. If it's all shiny and the same color, you're probably okay. Here's a photo, courtesy of Maine Sail's photo site, showing what dezincification looks like.

Maine Sail · Mar 6, 2009

sailingdog said:
Pitting isn't usually the problem with bronze through-hulls. Dezincification is. Clean off the through-hull and see if it has pinkish spots... if so, then you've got a problem. If it's all shiny and the same color, you're probably okay. Here's a photo, courtesy of Maine Sail's photo site, showing what dezincification looks like.

Dezincification of seacocks is only a problem if you are using substandard products. Most all thru-hulls & seacocks should be made of a high quality Bronze for below water application.

Spartan for example makes their seacocks using 85% copper, 5% Zinc, 5% Lead (for machining) & 5% Tin. This particular type of bronze is referred to as "85 three 5" Bronze. High quality Bronze will contain very low to no amounts of zinc. Apollo/Conbraco also use "85 three 5" (85, 5, 5, 5) Bronze...

I have yet to ever see a Spartan seacock with signs of dezincification and they have been making them for over 30 years.

That image on my web site is a BRASS ball valve, from a home center, and they WILL dezincify and fail because they are nearly 40% zinc!!