Overnight a really good question came in from Dave in California about some comments that were made by a marine surveyor on a report to a potential boat buyer. Its worth sharing this because it raises several good points; one about the integrity of some surveyors and two about the limits of AC power on board that is provided by a DC to AC inverter.

Inverter Collection

Of all the things that a boat owner can install on their boat an inverter is perhaps one of the most magical. With an inverter you can take battery power and turn it into almost the same thing as the shorepower that comes down the dock and through that fat yellow cord into your boat. The stuff you need to run hairdryers and flat screen TV's. But, there are some limits here. First to the question that Dave sent in:

Ed,

"Recently a surveyor called out the following as an issue with a boat's wiring system:

"The inverter is wired to power all the circuits of the AC electrical panel. The inverter should only power the 'outlets' breaker."

The boater knows for example not to run the inverter to heat his onboard water but Is there any specific code in the ABYC standards that says having the boat wired this way a no-no? The boat does have a provision to make it impossible to have the shore power and inverter powering the AC hot bus bar at the same time; and it has been test run this way with no issues. Thoughts?"

Dave

OK, so lets sort this out. First of all the surveyor is presenting his opinion only. There is nowhere within ABYC Standards where this statement is made. The Standards do dictate that a break before make switching configuration be provided to ensure that a boat owner can't inadvertently activate shore power simultaneously with inverter power but as for how much equipment the inverter is connected to on the boat, well that's between the installer of the inverter and/or the boat owner. ABYC is silent on that issue.

What the boat owner needs to understand is that all inverters have a finite limit as to how much power they can actually create. Further, there is a trade-off and some loss from the battery power used to create AC power within the inverter. The loss will vary, but it runs from about 10%-15%. No inverter is 100% efficient, although some I've tested within the last two years were running at up to about 93% efficiency.

What I'm referring to here is the amount of DC amps it takes to create X amount of AC wattage.

At the end of the day people this all boils down to two things, the rating of the inverter, 1000 watts, 2000 watts, 3000 watts etc. and secondly how long you intend to run the appliance. I refer to this as your "appetite for amps". The table below which comes from my book entitled "The Powerboater's Guide to Electrical Systems" explains how you go about calculating your own appetite for amps based on an assumed 90% efficiency for the inverter. Keep in mind that all AC applicances used will have either operating volts and amps or operating volts and watts embossed on a label somewhere on the appliance. By dividing volts into watts, you can calculate the amperage needed to run the appliance. also keep in mind that if you own a sailboat and not a power boat, the above mentioned book will serve you just as well, the electricity involved here really has no idea what type of boat it is on.......

When all is said and done, the size of the battery bank needed to supply and feed that appetite for amps will be the limiting factor. Most boats run out of real estate to store batteries. Keep in mind that to ensure acceptible battery cycle life, you really only want to discharge conventional batteries down to about 50% of their amp-hour capacity, for for example a battery with a 100 amp/hour capacity should only use 50 of those amp hours on a regular basis.

My Ask Ed section has been getting a workout this week! All good because it means people are finally thinking about their boats and less about shoveling snow or how to get away from it. Tom wrote in overnight with a really good question that needs sharing. Here's his query:

Ed,

I'm finding whatever AC amperage is being used by the load I switch on shows up in the ground wire of my shore power cord; any ideas on how to find the source of this leak? Inverter on or off and taken out of the system makes no difference. This is a 240 50A supply. The dock master isolated the leak to my boat by switching off the surrounding boats.
My visual inspection didn't reveal anything obvious.
Thank you!

This is a very common problem unfortunately and usually occurs because a land based and trained electrician has done some work on the boat. The issue that Tom is describing is caused by what is known as a false ground. On a boat these can be found in several locations, one of the common ones is at the back of a 120/240 volt appliance such as the photo of an electric range shows below: (clothes dryers can also be culprits)

The photo above was scanned from one of the chapters in my book Advanced Marine Electrics and Electronics Troubleshooting. You can get your very own copy by clicking on the Amazon photo in the left column of the site here.

In Tom's case I believe that the problem is actually located behind his electrical panel on board vs. at an appliance. Somewhere back there he has a buss bar with a bunch of green colored wires going to it. He also has another buss bar with a bunch of white colored wires going to it. Somebody along the way has connected these two buss bars electrically. They must be isolated from one another! Tom's boat is lethal. Anytime he plugs in at the dock and turns on an AC appliance on board, some of the AC current is actually leaking out of the bottom of the boat into the water. The fault current is splitting between the AC neutral and the gounding conductor, which is also part of the boat's bonding system. This means that underwater metals like sea cocks and the like are connected to this same system. (See yeaterdays post) If a swimmer gets near the boat when this appliance is turned on, they will swim through a voltage gradient in the water and could quite easily be electrocuted.

Tom, get this attended to immediately!  The ABYC Standards are quite clear on this matter. The ONLY  place where the AC neutral (white) and ground (green) are connected together on board is at sources of AC power on the boat, such as inverters and generators. In the case of inverters they are only linked when the inverter is actually producing AC power.  

I love it when readers write in. Eric wrote in over the weekend with what I think actually ends up being three good questions. One of them has to do with bonding and grounding, the other anode consumption, and the third with transducers and fairing blocks. For those of you who have no idea what the bonding system on your boat looks like, the photo below shows a green wire connected to a sea strainer. That wire is there to attach the strainer to the boat's bonding system.

So, let's get a look at Eric's note so you can all see what's going on in his case:

HI Ed
Got a question about my 28' Cape Dory flybridge. After my first full season with the boat I noticed my prop zinc just about gone and the two disc type zincs on the trim tabs (I installed last spring)nearly gone as well. The boat is kept on a mooring in Salem harbor all season. I also have a dyna-plate for bonding. The thru-hulls are bonded by a bare copper wire to the dyna-plate and there is what looks like #8 green leading to the rudder post. I noticed a break in the bare bonding wire with green corrosion. I was planning on re-bonding the whole system with #8 wire. Is there anything I should be looking for or should I add a zinc plate on the transom as well? BTW it’s a Chrysler 360 and no generator. Also as part of another project I am looking to add a transducer to my Garmin 3210 and was torn between Airmars tilted element or adding a high speed fairing block. The boat cruises at about 15kts? I do mostly cruising with a little fishing on the side so it will be used
mostly for depth readings at cruise and fish finding at slower speeds. Limited space is an issue for the fairing block and the simplicity of the tilted element is attractive. Will I draw too much turbulence without the fairing block?
Thanks for your time and an excellent web site.
Eric

Ok, so let's sort through this step by step.

First of all, if your zincs (anodes) aren't being consumed in a Saltwater environment, you should be concerned. Since Eric is located in Salem, MA I know he's in saltwater. Is his anode consumption excessive based on what he is telling us here. Nope, it sounds like things are just right. The idea is to install enough anode mass to last the boating season. If he were using up his anodes sooner, then he would need to add another shaft zinc perhaps, or the transom zinc he mentions. Now, based on what he is telling us the rudder and post were not connected to his boat's bonding system over the last boating season. This deminishes slightly the amount of anode mass that is needed to provide protection for all the underwater metal. So, by re-connecting the rudder, which is of course the correct approach, he will be altering what is known as the anode to cathode surface area relationship a little. This means that he may need to add another anode to the equation this season to make sure he gets a full season's service from his anodes. This is because he is effectively connecting in more metal to the bonding system that needs protection. Another way to do this is to install another disk anode to the rudder itself, similar to the trim tab anodes, or zincs as Eric describes them. (Not all anodes are made of zinc.)

As for Eric's Dyna-plate, understand that it really has nothing to do with corrosion mitigation. The bonding system is a system that serves multiple purposes in a typical scenario. It is also the connecting system for the boat's grounding system. I'll talk about that in another post here later in the week.

As for the transducer Eric wants to install, my general advice is always going to be that if you can avoid using a fairing block of any type it is a better approach than using one. Airmar's newer tilted element transducers do a great job of making this an easy thing to accomplish.

Well, my Say Yes to Seacock Labels post  ( http://www.edsboattips.com/maintenance-a-diy/193-say-yes-to-sea-cock-labels )  earlier this week got an almost immediate response from one of our readers. Karl wrote:

"Looking at that photo, there are three (or, possibly four) seacocks with their own thru-hulls...all within inches of each other.

I would think best-practice would be a single thru-hull, terminating with a seacock manifold. Why have so many hull penetrations within inches of each other, when all have the potential to fail? I'm naturally paranoid of below-waterline hull penetrations, and believe they should be consolidated. Just my opinion, but what do I know?

Labels are the least of the problem." So here's another photo that might help to explain my answer to Karl, at least in part.

What is being shown above are two through-hull fittings that supply a marine head system. Now you will notice that at least in part the builder applied some of Karl's thinking here. The through-hull fitting on the right is supplying two water inlets, as I recall feeding two marine head systems. The larger diameter hose on the left is an outlet from a marine holding tank to facilitate overboard discharge in an offshore scenario where it would be legal. The point I'm making is that designers can't apply Karl's single fitting approach as easily as he may think. We have inlets and outlets that simply must be separated.

Back to Karl's thoughts though, could we have all the inlets fed by one seacock and all the overboard discharges taken care of from just one more seacock? Perhaps with a manifold for inlets and one for outlets. I'm certain we could design such a configuration but I suspect that since boat builders are trying to use off-the- shelf, readily available components for these systems to minimize cost, it is unlikely that we'll see a set-up like Karl wants on production boats any time soon.

I'm of the thinking that just getting the builders to "bundle" all of the seacocks into one area, much like the big boat "sea chest" arrangement where all the seacocks and through-hull fittings are in one box or place on board is a major step forward. This approach by the way, adds cost due to the additional hose required to route everything to one place. I'm sticking to my thoughts in my earlier post, labels are nice. 

A few days ago I received an email asking about the use of the new LED replacement bulbs in navigation light fixtures. The query came in from the general manager of a high-end, full service boatyard on Chesapeake Bay. This manager was concerned that there may be a problem with the use of these bulbs as it might have the potential to alter the characteristics of the navigation lights. You see, navigation lights are required under Federal law to meet established criteria for color, range of visibility and arc of visibility. The querie came in over the weekend and I was busy at the Miami Boat show so I didn't get to answer the question immediately. One of my colleagues at the ABYC did however and I have to share as well as supplement his answer because it is important information that needs to get out to everyone.

The bulbs in question are available from a few different sources and are direct replacements for either the socket type or bayonet type bulbs commonly used. They look like the photo you see here, the socket type is shown.

Now the quirk here is that these bulbs are cataloged as being direct replacements for the light bulbs in the navigation light fixtures. But, and this is an important but, the catalog also contains a disclaimer that few probably read that can have serious legal implications in the event of an accident where use of poper navigation lights may be a question. My colleague Dante from the ABYC technical department provided a solid explanation here:

"An LED array with the base of a bulb designed for retrofit into an existing light fixture has filtrated the automotive and marine industries. The bottom line is the optics in the existing lamp assembly were not intended for the LED’s unique light pattern. Even if the retrofitted LED physically fits and illuminates, it may put too much light (or not enough light) where it is needed for a navigation light to work properly. Or create blotchy light pattern that may appear have a flashing effect at distance as the boat rotates relative to the viewer. The retrofitted LED and existing lamp assembly were not color tested together, something that is specified in detail in ABYC Standard A16. Nor were they heat tested, which is concern for LEDs as their light output and life decrease with heat. The retrofitted LED into a incandescent housing has more points of failure than the simple bulb or a properly designed LED system."

Several years ago I was involved as a professional examiner to inspect a boat that had been crashed into and one of the folks on board had been killed as a result of the accident. The question being asked centered around whether or not the stern light on the vessel was operational at the time of the accident, one in which a following boatload of July 4th revelers had run right into and up onto the deck of the lead boat. The claim was that the boat that ran into the one I inspected had not seen the lead boat because the stern light was not operational. I determined that the stern light could not have been operational due to the way it had been wired.

The boat with no stern light lost out on their claim for damages, even though one of the members of that party died.

 You get the idea here. In spite of the overwhelming benefits of using LED's, low current draw and long life, they MUST be purchased as a light assembly that has been tested as a unit. That means replacing the whole fixture, not just the bulb.