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STERNDRIVE LEG BONDING

J

jungpeter

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My Pursuit 2460 is equipped with a Volvo Penta 5.7l Gi-Gf engine and (unknown model) duo-prop drive leg. It is moored 24/7 in fresh water, at a marina that provides 110VAC shore power. On the propellor housing is a magnesium anode surrounding the propellor shaft, between the stainless steel propellors and the aluminum outdrive leg. On the shield (the aluminum interface casting between the leg and the transom) is another magnesium anode. The boat is not equipped with a separate and discrete bonding system within the boat, typically linking all the various metallic through-hull fittings to a transom anode.

I'm adding a shore power and battery charging (110VAC) system (power cord, AC panel, charger, etc.) to the boat. I need to interconnect the AC safety ground leg with the DC ground system in the boat. To ensure this common ground, is is safe to assume that the engine block will provide this "common ground" via the transom shield and the outdrive leg, hopefully galvanically protected by the propellor and shield anodes? And can I also assume that the engine block will provide a sufficient common ground to also add a bonding system between several metallic through-hull fittings that are not currently protected?

I recognize that this 24' boat is designed to be stored on a trailer, with battery maintenance provided by a temporary trickle charger. As a trailer boat is not afloat, galvanic corrosion is, therefore, not an issue. However, afloat in a marina, connected to shore power and surrounded by other boats also connected to shore power, not only is stray current protection required, but galvanic isolation and polarity monitoring necessary.

Regards,

Pete

This is sort of a "big boat" question, and I'm admittedly trying to add a "big boat" (110VAC and battery charging via shore power) feature to my small boat. But not only is corrosion an issue, but most importantly, safety. I surely don't want to inadvertently energize my surrounds with 110V stray current, and electrocute some poor swimmer.
 
They used to make Galvanic Isolators, to connect the AC system's Ground wire to the boats bonding system (usually the block) while isolating the AC components...
 
I'm a retired marine tech in MN that did this upgrade a few times.

I'm not saying to not do this, but study first. We had a boat at the marina next door that a land based electrician did this to his boat. Killed a dog and would have killed some kids but the parents grabbed them before they jumped in to "save" the dog. Big lawsuit.

Yes you NEED to ground to the engine. I don't know how much research you have done but this wire needs to be pretty big and high quality (tinned copper) low resistance is critical. On a 25' I'm guessing at least #6 awg maybe #4. Do a some research on the bonding system. Back then testing showed to not bond everything. Some things like S.S. trim tabs and S.S swim platform supports are usually better to have their own anodes and not be part of the bonding system. Testing must be done so you don't "over protect" yes that's a very real problem. This was something that was up for debate at the time. Seems that water quality played into it and I can only speak to my market because I never paid much attention to other areas when I took classes. I don't know if Pursuit is still owned by the Slikkers family, but I would sure give them a call for Up To Date advise.
Make very sure ALL of the Volvo bonding wires from the engine ground stud all the way back to the drive are perfect. Test them.
Yes you NEED a Galvanic Isolator
Keep your grounded conductors separate from your grounding conductors. This isn't a house you're wiring.
Google --- Volvo ACP I'm pretty sure you want this impressed current system.
Google --- silver/silver chloride reference electrode You will want one for this project.

Think about joining ABYC, they publish a manual called Standards and Recommended Practices for Small Craft. That thing is the BIBLE of stuff like this. I did and it was worth it for doing stuff like this. But Volvo also puts out a corrosion manual that has some good info, you just need to pay attention to what water you're in.

What ever you do ---- resist the urge to use land based components for this. Yes I know they are probably about 1/3 the cost nowadays. But even simple stuff like GFCI outlets are very different. Electrical leakage is a thing, even the very cheap boats use marine components.
 
muc said:
I'm a retired marine tech in MN that did this upgrade a few times.

I'm not saying to not do this, but study first. We had a boat at the marina next door that a land based electrician did this to his boat. Killed a dog and would have killed some kids but the parents grabbed them before they jumped in to "save" the dog. Big lawsuit.

Yes you NEED to ground to the engine. I don't know how much research you have done but this wire needs to be pretty big and high quality (tinned copper) low resistance is critical. On a 25' I'm guessing at least #6 awg maybe #4. Do a some research on the bonding system. Back then testing showed to not bond everything. Some things like S.S. trim tabs and S.S swim platform supports are usually better to have their own anodes and not be part of the bonding system. Testing must be done so you don't "over protect" yes that's a very real problem. This was something that was up for debate at the time. Seems that water quality played into it and I can only speak to my market because I never paid much attention to other areas when I took classes. I don't know if Pursuit is still owned by the Slikkers family, but I would sure give them a call for Up To Date advise.
Make very sure ALL of the Volvo bonding wires from the engine ground stud all the way back to the drive are perfect. Test them.
Yes you NEED a Galvanic Isolator
Keep your grounded conductors separate from your grounding conductors. This isn't a house you're wiring.
Google --- Volvo ACP I'm pretty sure you want this impressed current system.
Google --- silver/silver chloride reference electrode You will want one for this project.

Think about joining ABYC, they publish a manual called Standards and Recommended Practices for Small Craft. That thing is the BIBLE of stuff like this. I did and it was worth it for doing stuff like this. But Volvo also puts out a corrosion manual that has some good info, you just need to pay attention to what water you're in.

What ever you do ---- resist the urge to use land based components for this. Yes I know they are probably about 1/3 the cost nowadays. But even simple stuff like GFCI outlets are very different. Electrical leakage is a thing, even the very cheap boats use marine components.
Click to expand...
Hi Muc,

Thanks for your reply. As I mentioned in my original posting, I am very aware of the issues with stray currents around boats moored in fresh water, when hooked to shore power. As I consider my posting on this forum a small part of "research", I'm doing that also.

My question is NOT do I NEED to ground to the engine. I recognize that the engine block is, truly, common ground. Therefore, ALL grounds within the electrical systems in the boat (110VAC and DC electrical grounds, and the corrosion control bonding system) must be connected to common ground (the engine block). What I'm unfamiliar with is if the outdrive leg and shield rely on their various bolted connections to provide continuity between these submerged elements and the engine block. And given your response, I now understand that answer to be NO, there are various "...Volvo bonding wires from the engine ground stud all the way back to the drive..." that should be located and tested. Thanks for that answer.

I do have a galvanic isolator in my 110VAC shore power electrical system. I just didn't include it in my system description.

I'm confused by your statement "...Keep your grounded conductors separate from your grounding conductors." Do you mean keep my DC electrical grounds separate from my corrosion bonding? If that's what you mean, then yup, I never rely on my bonding system to provide DC electrical ground. I agree, my boat is not my house.

While not a member of ABYC, I am well aware of their various standards, and have read them extensively. But I cannot locate a "Volvo corrosion manual". Do you have any reference link to this manual?

Lastly, roger, roger, I never use "land based components" in my boats. Fisheries Supply and I are on a first-name basis, and my bank account proves it!

Thanks again for your input. Much appreciated.

Regards,

Pete
 
Parts of the drive do ground to each other thru bolts, like the upper half to the bottom half. But basically anything that moves will have a bonding wire that will make it's way back to the engine. I bring this up because you have a trailer boat of unknown age that has lived in freshwater. I have worked with many techs (and I was one a long time ago) that feel all these "extra wires aren't needed. So it's possible they didn't get put back on during service. It might be good for you to use this link to find out what outdrive your boat has. If you enter the serial number from the engine, transom or drive (and the boat was registered with Volvo) it will tell you what it came with.

www.volvopenta.com

Manuals & handbooks | Volvo Penta US

Workshop manuals, owners manuals and service protocols for your engine. Get your manual and service protocol here.
www.volvopenta.com www.volvopenta.com

I was talking about the 120 volt A/C system. Grounded conductor is what a land based person calls the neutral in a house and Grounding conductor is the ground wire in a house. On a boat they can never touch, except if there is a generator or inverter installed. But that's a whole new subject.
Yes, you are correct that the bonding system can never be used as an electrical ground. Funny story, a 34' that we had sold new was one of 3 boats that started shedding the paint from the drives. It was found when the boat was hauled for winter storage the first year. Boat was on a river about 50 miles away and I was sent down to check it out. Took me a full day to find that when the builder installed a CO detector in the cabin they had used the 120 AC grounding conductor for the CO monitor ground. That boat and the other two that had even weirder issues are what inspired my employer to ask me to go down the rabbit hole that is corrosion analysis and correction.

The Volvo manual is something I got during one of my classes at Volvo. It's title is Corrosion measurement part number 7747458. I'm not sure if this is something available to consumers. It starts out with "This Service Manual is produced primarily for the use of Volvo Penta workshops and qualified Volvo service technicians". It was mainly written for the DPH/DPR & IPS drive systems, but the theory and testing applies to all drives. If you can get a copy, it's a good read.

You mentioned that you have studied the AYBC standards. Could you share a way to see them without spending the $600 to join? I'd love to see what's been updated since I retired.
 
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