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Old 03-12-2007, 13:24   #1
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Grounding all throughulls?

Hi guys,

I've noticed on my boat that some through hull fittings were grounded to the engine, while others were left alone. Why was this done? I'm figuring they tried to use the shaft zinc to protect a few of them... but what about the others?

I'm converting to an outboard, so a the moment I'm unsure how to proceed. Ground to the battery, or yank the wires?
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Old 03-12-2007, 15:09   #2
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Hi guys,

I've noticed on my boat that some through hull fittings were grounded to the engine, while others were left alone. Why was this done? I'm figuring they tried to use the shaft zinc to protect a few of them... but what about the others?

I'm converting to an outboard, so a the moment I'm unsure how to proceed. Ground to the battery, or yank the wires?
ALL metallic through-hulls should be grounded to protect against electrolysis. I suspect that someone removed the ones that are not wired.

My boat actually has 3" wide copper strips glassed into the hull, running to all through-hulls. This eliminates the possibility of a wire corroding through or becoming detached somewhere.
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Old 03-12-2007, 18:53   #3
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Are all the thruhulls metal???
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Old 03-12-2007, 19:16   #4
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Are all the thruhulls metal???
Not all through-hulls are metal. I don't know about yours. Some through-hulls are made of varying types of plastic, including carbon fiber. They're more common on boats less than 30'.
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Old 03-12-2007, 19:25   #5
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Grounded is not really the correct term. Bonded is a better term, as they are bonded (connected) to a zinc to cut down on electroytic action.
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Old 03-12-2007, 20:37   #6
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I have had boats with bonded and non-bonded thru-hulls. I personally go unbonded having had to replace some thruhulls that had turned pink and had been bonded. This is just my experience. I understand that Calder thinks this way also but don't quote me on that.
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Old 03-12-2007, 20:38   #7
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Most of them are metal, theres one marelon bilge pump throughull.

The two of the three seacocks under the cockpit sole were bonded, the other was not.

Since I will not have an inboard engine, should the seacocks be bonded to the negative post of the battery, or just all linked together?



Yes, I know the cockpit drain needs a high quality hose... not the radiator hose pictured. (Still sorting her out!)
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Old 03-12-2007, 20:46   #8
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They should be bonded to a zink to prevent electrolysis/corrosion.

Where was your boat built??? That looks like a plug valve. They are just not that common, that small, in the USA. Or it's old! Have you actuated it lately?
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Old 03-12-2007, 20:50   #9
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Its a 1961 Pearson Triton.
Hopefully built in Bristol, RI!

As far as the origin of the valve, I'm not sure. Both of these are smooth as glass. It's a 1.5 in, thinking about stepping up to 2-3 inches for speedy cockpit draining.

So, for a boat that has no inboard, and fiberglass, how would you guys suggest I add a zinc? Should my rudder shaft have a zinc with the lack of prop shaft?
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Old 03-12-2007, 20:58   #10
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Any metal parts that are submersed should have a zink or bonded to a zink.

Some zinks are attached to the transom with bolts where it is always underwater, even while underway.

Others can be attached to large metal parts and bonded thru-out the rest of the boat, like if you had a bronze rudder (Power boats).
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Old 03-12-2007, 21:13   #11
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Its a 1961 Pearson Triton.
Hopefully built in Bristol, RI!

As far as the origin of the valve, I'm not sure. Both of these are smooth as glass. It's a 1.5 in, thinking about stepping up to 2-3 inches for speedy cockpit draining.

So, for a boat that has no inboard, and fiberglass, how would you guys suggest I add a zinc? Should my rudder shaft have a zinc with the lack of prop shaft?
I have those same valves on Kanani. I really like them. If they get stuck, you can just lossen that nut, turn the handle back and forth until it is free. It will probably leak so then slowly tighten the nut as you keep turning the handle until the leaking stops.

When you haul-out, take it apart, clean it up real pretty and lube it with a marine grease and they should last for many years. Mine are the originals from 1980. I have serviced mine in the water by jamming a wood pug up from the outside (although I don't recommend that to others).

I modified mine by drilling a hole through the threaded shaft and using castle nuts. That way I put a cotter-pin in them to keep the nut from backing off.

To see if the valve is having electrolysis problems, put a little Muriatic Acid on a brush and touch the bronze with it. If the bronze is good, it will turn gold and shiney. If it is bad, it will turn black.

Be sure to wipe the valve clean with baking soda to nuetralize the acid.
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Old 04-12-2007, 05:03   #12
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We are in fresh water and have decided to not bond the through hulls. We are not as concerned with corrosion as we are with removing a path for lightning to exit via the through hull. We reconnect the bonding when back in salt.
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Old 04-12-2007, 05:04   #13
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We have used automotive lapping compound to reseat these valves. Just make very sure they are clean of all the compound prior to greasing and reassembly.

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I have those same valves on Kanani. I really like them. If they get stuck, you can just lossen that nut, turn the handle back and forth until it is free. It will probably leak so then slowly tighten the nut as you keep turning the handle until the leaking stops.

When you haul-out, take it apart, clean it up real pretty and lube it with a marine grease and they should last for many years. Mine are the originals from 1980. I have serviced mine in the water by jamming a wood pug up from the outside (although I don't recommend that to others).

I modified mine by drilling a hole through the threaded shaft and using castle nuts. That way I put a cotter-pin in them to keep the nut from backing off.

To see if the valve is having electrolysis problems, put a little Muriatic Acid on a brush and touch the bronze with it. If the bronze is good, it will turn gold and shiney. If it is bad, it will turn black.

Be sure to wipe the valve clean with baking soda to nuetralize the acid.
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Old 04-12-2007, 09:32   #14
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Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be unbonded' 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.

Richard
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Old 04-12-2007, 10:21   #15
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We are in fresh water and have decided to not bond the through hulls. We are not as concerned with corrosion as we are with removing a path for lightning to exit via the through hull. We reconnect the bonding when back in salt.
This brings up a "whole new topic". I will just say that if your boat gets hit by lightening, you won't have to be concerned about it any more.

I have seen two boats hit by lightening in all of my years of sailing. Actually, one was hit, the other was close to a lightening strike. The 1st one (hit) was in Tonga. The boat immedialtey sank, in the marina (about 10' of water). When the boat was raised, everything metal on the boat was gone. There were holes in the hull where the chainplates were. Evidently, the charge hit the rigging (first) and found it's way to the water, through the hull. All of the thru-hulls were blown out, even though the boat was not bonded.

After pulling the wreckage from the water, it was discovered that all of the F/G had delaminated from the heat of the strike, turning all of the moisture that was in the glass to steam (all F/G boats have a small % of moisture. Wood boats have a lot).

The 2nd vessel (in Florida) had a "Nearby" strike. All of the electronics were fried (even though the owner unplugged everything).

It has been my experience that lightening will strike where it will strike. Your mast and rigging, (although they seem huge to you) are tiny in the total relm of things. Water is a huge conducter of electricity. If a boat gets hit, it is a totally random event IMHO. Anything that you do or don't do, will make little if any difference. If your boat gets a direct hit, nothing you can do will carry that current to ground. We are talking millions of volts/amps of electricity. IMO, steel boats would probably have the best chance of survival in an lightening strike. If lightening is a big concern (and it shouldn't be), get a steel boat.
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