Marine Carpentry for Dummies

Clark February 23rd, 2017

To be a true marine carpenter is to live in the high country of the craft, because boats are curved every which way. There is seldom a right angle, seldom even a simple beveled angle, because all those intersecting curves mean that every place two pieces of material join together is a compound angle. To put a finer point on it, terrestrial carpenters can frame a four-bedroom house in a day or two. A team of talented marine carpenters can frame a 40-foot wooden boat in a couple of months? A couple of years?

I am not a marine carpenter, but I often get into marine carpentry projects, or more accurately marine joinery, like building new electrical panels out of teak, rebuilding consoles, and of course endless work on my own boat. I have many more tricks to learn, but here are a few rules I’ve picked up:

Thou Shalt Measure Angles

To make a piece with a compound angle, a tape measure is only going to get you so far. You need some way of measuring angles accurately, then you later replicate these angles to your cuts. I haven’t found a great product for measuring angles in tight spaces, but this protractor is what I’ve got, and I can always make it work by turning it one way or another:


The important thing is to be able to measure accurately down to the degree, because if you’re off my more than a degree in finished joinery it’ll stand out like a sore thumb and reveal that you are a hack.

Thou Shalt Draw Diagrams

All the angles and measurements you take will only lead to confusion unless you document them and get them to the cutting area without reversing something. Overcommunicate with yourself: Note top, bottom, inside, outside, port, starboard, forward, aft, athwartships, all the lengths, and all the angles, and you’ll still manage to screw something up:

Thou Shalt Make Templates

There may be master marine carpenters out there who just go take their measurements, then cut perfect finished pieces, but I doubt it. Everyone I’ve seen makes lots of sacrificial templates, these templates go through multiple rounds of tweaks, and end up with hieroglyphics scrawled all over them.

Good quality teak runs $30 to $40 per board foot. A board foot is a foot wide by a foot long by one inch thick. A sheet of 3/4-inch teak-fronted plywood is $220 where I buy it. Ergo, mistakes become very expensive. This piece of trim I’ve installed in a head is over a board foot of teak, and it sure don’t look like much:

For trim pieces I make templates from cheap, usually scrap, plywood of the same thickness:

Simply mock up your measurements and diagrams in cheap plywood, then go try them out. Of these four templates, one ended up perfect and the other three needed tweaks. I purposely make the templates a little short, which means I accidentally made one too long and it ended up perfect…by mistake. By making them a little too short, say by half an inch, you can fit your template in place (if it’s too long it can’t even fit), and ensure that the angles are all right by sliding it from side to side. If not, you can measure much more accurately now that you’ve got something to go from, and make notes on your templates. You can also now get your final length measurements very accurately, since you’ll be increasing the length of your template by some fraction of an inch, rather than relying on overall measurements.
I guess this is just another way of saying I know I’m going to make mistakes, so if I make mistakes on purpose I feel better about myself. There are two other reasons for cutting your templates too short: First of all, those overall length measurements get very confusing with a piece that has compound angles on one or both ends. Do you mean the length at the inside corners, the outside corners, top, or bottom? These will all end up being different length measurements. Ideally you want your length measurements based on where the saw blade will enter the material, rather than where it will exit, as the entry point can be measured and marked very accurately, while the exit point is only known for sure when, well, the blade is finishing the cut.

Second, due to that pesky fact that boats are curved every which way, your piece will probably have some bend induced into it in final installation, and with a template that’s a little short you can bend it into place and see how this bend changes the angles. Unfortunately plywood is more flexible than hardwood, so there may be some surprises in the final installation due to the different properties of the two materials, but these surprises are usually minor.

For larger panels, to be made out of plywood, there are several 4 x 8 foot sheet products, such as hard board and utility panel, that cost less than ten bucks per sheet. Make templates, and your mistakes, on these. Once you’ve got a template for a larger panel, even if it’s way off, it can be made perfect by stapling, taping, or hot gluing extensions here and there, or cutting off excess material with a saw or utility knife. I discuss how to be gentle with veneered plywood here.

These cheap template materials are usually thinner than the final product, and this sometimes leads to some unpleasant surprises too. If you’re making a really complicated piece out of plywood, best to make the template out of the cheapest plywood you can find of the same thickness.

Thou Shalt Have a Good Way of Cutting Compound Angles

If you’re building something like the trim for this instrument cluster, count yourself lucky. It’s all right angles, and the pieces are so small that mistakes aren’t terribly expensive:
I’ve had this simple hand miter saw for years, which makes accurate angled cuts, and the blade has stayed sharp through countless pieces of teak, but it can’t cut compound angles unless I use some cockamamie method with shims:
To cut compound angles you need either a table saw with a crosscut sled (miter attachment), or what is called a compound miter saw or chop saw.
In other words, you need a way to accurately cut angles, and accurately angle the blade while cutting said angles. Of the two, a chop saw is way cheaper. I’ve seen them for as little as $100, but can’t vouch for quality at that price. A chop saw is the better machine for trim work, for pieces less than six or eight inches wide, but to make long, straight cuts a table saw is king. A chop saw can be stowed away on a shelf; a table saw needs its own room.

A handheld circular saw is great too, and can cut both compound angles and long cuts, but it will never be a precise as a chop or table saw.

When preparing to make your final cuts on your final material you can set the angles on both the miter and the blade angle, then cross-check these angles with your protractor and your template. Use a fine-toothed finishing saw blade to avoid splintering, and clamp your material where possible.

Thou Shalt Not Try to Correct Your Mistakes (Too Much) By Sanding

It just seems like you can nip off that extra material with your belt sander and it will fit perfectly, right? It won’t. It’s nearly impossible to square up an angle by sanding. Sanding always rounds off the edges and leaves the middle too proud. By all means clean up the splinters and rough edges by sanding, but you’ve got to get your angles right with the saw.

Split Your Angles

If you measure a 110-degree angle where you want a miter joint between two pieces of material, each piece needs to be cut at a 55-degree angle. If you make one 35-degrees and the other 75-degrees it won’t work and it’ll look funny.

Shape Your Pieces Before Cutting

Your pieces will undoubtedly be shaped, with rounded corners, or in the extreme quarter-round or half-round material. If you cut your pieces from square or rectangular material first, then shape them afterward, it will be hard to make the miters match. If you shape your whole piece of material first, then cut the miters, it will still be hard to match the miters sometimes, but you’ll be off to a better start.

It’s very satisfying when you get it just right:

Advanced Electrical: Diodes

Clark February 7th, 2017

The most common diodes on boats these days are LEDs, Light Emitting Diodes, which are changing the way we light our boats and use energy. They’re great! There are all kinds of specialty diodes in the electronics world, but the kind of diodes I’ll discuss here are basic, simple old diodes, the kind you could buy at Radio Shack for thirty-five cents, if Radio Shack were still in business. I always keep a few diodes in my box, because they provide a magic solution to some very specific problems.

Diodes are one-way valves for electricity. Place a diode along a wire and electricity will flow one way down the wire, but not the other. If you connect an LED the wrong way it won’t light up; connect it the proper way and voila. Above is the electrical symbol for a diode, and as you might guess, the arrow points in the direction of current flow. Current can’t flow against the arrow.

It’s good to know the symbol, and basic symbols for switches, fuses, and the like, because when considering a diode to solve a problem, diagramming the circuit first really simplifies the matter. An actual diode looks like this, and the silver band is the cathode end, that is, the end the current flows out of, but not into:

There are several common situations when I use a diode on a boat. The first is when I’m installing a light like this:
It’s got a bulb in front, and one in back. When you want it to be an all-around light, or anchor light, you power both; when you want it to just be a steaming light you only power the front bulb. Sounds simple, but it’s not so simple. Since the the two bulbs share a negative wire (three wires, not four, lead into the assembly) you’ll quickly find it’s hard to separate them: Both bulbs will light together when you only want the steaming light.

The simplest way to avoid this is by using a DPDT switch (Double Pole Double Throw), a switch with ON-OFF-ON settings and various terminals for isolating the various loads. Turning this switch to one of the ON positions gives you your all-around light; turning it on in the other gives you your steaming light, maybe along with the nav and stern lights. But sometimes this setup isn’t practical, and many electrical panels come with one switch for an anchor light and one switch for a steaming light. Enter the diode.

By placing a single diode in this circuit you can make your two switches do what you want them to do:

If you follow the circuit you can see that without the diode, unintended current would flow from our steaming light circuit to our anchor light circuit and make the aft bulb light up too. If, in the same circuit, we had nav and stern lights connected to our steaming light switch, then they’d light up when we turned on our anchor light. A second diode would prevent anchor light current from flowing to our nav and stern lights.

Another common use for diodes is for engine alarms. The standard setup is to have a light/buzzer that goes off when you’ve got high water temperature or a drop in oil pressure. Well, which is it? It would be nice to know at a glance whether the alarm is from high temperature or low oil pressure, and to have a separate light for each. Depending on the way the panel is wired, you’ll sometimes get the same problem as with our pole light, both bulbs lighting when you only want one, and a diode can isolate them.

Electricity can be sneaky, especially on engine panels and distribution panels where you’ve got a lot going on in the same place. Sometimes, even in a well-designed and well-built panel you’ll get a sneaky phantom current that makes bulbs glow dimly or buzzers/beepers make irritating noises. Again, simple placement of a diode can solve the problem without completely dissecting your handiwork.

Also found on boats are solar panel blocking diodes: Solar panels “leak” a bit of juice at night, so the blocking diodes prevent this back flow. Solar blocking diodes (indeed all diodes) add some resistance to the circuit, reducing the panel’s output somewhat, so the day/night balance ends up being about a wash.

Basic diodes usually have four different ratings, most of which can be ignored for our purposes. I always use NTE5800 diodes, which are rated for up to 3 Amps of current. I know I’m never going to have more than 3 Amps, because I’m always solving problems like those above, with small bulbs, buzzers and the like, in 12 or 24-Volt DC systems.

The NTE5800 diode takes .9 Volts to “turn on,” that is, to function, and I’m always going to have that in a 12 or 24-Volt system. It’s rated at 200 Amps to break it, that is, the amount of reverse current to make it fail and not block. 200 Amps ain’t gonna happen either. It also has other ratings for the amount of abuse it can take in either direction before it fails, but these aren’t ever going to happen in my applications. I just need to remember it’s good for 3 Amps, and if I ever try to do something exotic I might need a different diode.

In practice I like to install diodes using two heat shrink butt connectors to connect the diode’s two leads to wires. The leads on the diode are live and exposed, so I always then cover the whole thing with heat shrink tubing, both protecting from accidental shorts and waterproofing it (I think they’re waterproof anyway). Then definitely label it on the outside with some kind of label (white heat shrink tubing works well), otherwise it will just look like a mystery blob inside some heat shrink tubing. It’s also very easy to bend the terminals on the diode, insert them into two of the terminals on a screw-down terminal block, then connect your wires to the opposite terminals.

Vendée Globe Nail Biter

Clark January 18th, 2017

If you haven’t been following it, the leaders in Vendée Globe are within a day or two of finishing, to cap one of the greatest games of cat and mouse in sailing history. At the time of writing, after racing for 73 days and over 24,000 miles solo, Alex Thomson is only 34 miles behind Armel Le Cleac’h.

Alex Thompson has slashed the gap by two thirds in the last few days, in part by setting the Vendée single day record. Video here. You will also see in the video that Mr. Thompson is battling multiple equipment failures, but still fighting to the end.

Thompson acknowledges that it would be tough to win at this point (yet he keeps closing the gap!) Full story here. He’s been up for days, and is on the verge of collapse.

At any rate, in the next 48 hours we’re going to see either:

1. Thompson overtakes Le Cleac’h to be the first non-Frenchman to win the Vendée Globe. In this scenario, could the Vendée Globe get into close tactics? Le Cleac’h luffing Thompson up as they turn off the autopilots a go into full close battle mode, when neither have slept in days dodging fishing boats and freighters, hallucinating at the wheel? Unlikely, but would be something for the record books.


2. A very close finish, in which Le Cleac’h crosses the finish line, then just has to wait an hour or two to embrace the man he has battled all the way around the world. The two have thought about each other every moment for 75 days, yet haven’t see each other’s faces since the start. When they finally meet face to face, it will be a moment to remember.

3. Or some crazy thing we never could have foretold…

Ways to watch it are here.

Electrical Fire! (and some lessons learned about starters)

Clark January 2nd, 2017

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Voice Mail: “Hi Clark, it’s (name withheld). I was out sailing today with my daughter and we had an electrical fire on the new starter you installed. Because of the fire we lost the engine and hit the south tower on the Golden Gate Bridge, called the Coast Guard, and had to be towed back to our berth. When I opened the engine compartment there were six inch flames rising from the starter, but I was able to blow them out. I don’t know where that leaves us, but I’d sure like to speak with you.”

Not what a marine electrician wants to hear. After my initial panic, I reflected that this was a basic R&R (remove and replace) of an old starter for a new one. I’d tested it several times, by cranking and starting the engine, and all seemed well. Various scenarios flew through my mind – defective starter, defective solenoid, some sort of shorted wire, stuck solenoid or stuck starter button, or, eh gads, installer error. I called the owner, who was very understanding, and was back on his boat the next day. If you look at the photo above, all the insulation on all the wires leading to the starter is fried, and was burning until he blew it out.

After an initial check, I called the owner and told him that no matter whose fault it was, the damage was probably less than the deductible on his insurance, and that I might as well remove the starter and start the replacement process. He agreed. I pulled the starter and found it well-burnt, and the solenoid completely melted, with both of the studs loose. The main linkage between the solenoid and the starter motor had acted as a fuse, melted through, and ended the fireworks:

I took it back to the starter store, where they were very understanding and agreed to replace it under warranty, but also opined that something had probably got stuck, and that the starter probably wasn’t at fault. They noted some damage to the pinion gear, which I hadn’t noticed.

I installed the (second) new starter and continued my postmortem, finding very quickly that the cranking circuit was closed, as in, if I’d connected it the starter would have started cranking and wouldn’t have stopped. In this instance the boat had a starter button, separate from the key switch that energized the circuit, and the button was stuck:

Blessed sweet mother of God, it wasn’t my fault! I replaced the button, and the burnt wires, tested it all out, and all was well, for the second time. The owner was very understanding, ended up buying my wife and me a nice bottle of wine, and we decided we owed the guys at the starter store a case of beer.

There are some interesting things that happen with a stuck starter, one of which I didn’t know about. I knew about shorts, of course, and 98% of high amperage starter circuits aren’t protected with fuses, so these can be spectacular. And I knew about all kinds of unintended open circuits, as with bad motors, bad solenoids, etc. But I always thought that a stuck starter, as in, a starter that stays engaged after the engine starts, would just burn out its innards or strip its pinion gear.

Nay. A starter that stays engaged after an engine starts gets spun continually, much faster than its intended rotation speed, and actually becomes a generator, sending high current back into the electrical system. In most cases the batteries and cabling can handle the current, but the starter can’t. It gets very hot and finally burns up (from high current, rather than friction, overheated brushes, or whatever). Even in normal use a starter is an intermittent duty motor: With a recalcitrant engine you should only crank it for ten seconds or so at a time, then give it thirty seconds to cool off, and to allow the surface voltage to come back on the battery.

So, it is very important to make sure your starter disengages after your engine starts. In most cases this is obvious, as in your car, where if you held the key in the cranking position, or the starter got stuck this way, you’d hear it. But on many boats it’s not so obvious, since the engine panel might be some distance from the engine, and once started the engine noise can drown everything else out.

This boat happened to be a Catalina, and on Catalinas it’s standard to have a starter indicator light on the instrument panel. This is a good feature, and not common on other boats, but you’ve got to know it’s there:

On this boat it was there and still worked, but the owner didn’t know about it, plus it’s hard to see in daylight, and easy to miss in full combat mode (they were close to the south tower of the Golden Gate Bridge in an outgoing tide, after all). But also on Catalinas, and many other sailboats, the engine panel is exposed to the elements in the cockpit, sometimes gets kicked a lot, and generally takes a beating. In this case the starter button saw constant rain and spray, and eventually corroded and got stuck.

On my boat I’m standing right over the engine when I start it, so I’d hear it in a nanosecond if my starter got stuck, but not so on many boats. If it wouldn’t be obvious to you if your starter got stuck, you should consider an indicator light or buzzer. When you consider that it would result in not only a destroyed starter, but in not being able to start your engine again, and maybe an electrical fire, it’s worth some thought.

Shore Power Cord Economics

Clark December 13th, 2016

Unfortunately, as in the photo above, the connectors on shore power cords often get toasty. It always seems to happen on the neutral connector (white wire in the US system) and I don’t know why. Maybe the electrons get all gummed up and dirty from being on your filthy boat, then get stuck on the way off?

Sometimes it happens on the male side too, and the guts of the shore power inlet have to be replaced:

At any rate, a burned/melted shore power cord is bad, and should be repaired, but therein lies the rub. The new connector for the end runs about $35, but that’s not all. In order to make it like before you also need a new boot, which you can buy with or without the threaded ring, but call it another $15:

So now we’re up to $50 (prices vary, but you get the idea) in parts alone to repair a shore power cord. Fifty foot, 30 Amp shore power cords sell for as little as $80, if you shop around. It’s fairly straightforward to re-terminate a shore power cord, which a do-it-yourselfer can easily do. It takes me about ten minutes, but it’s easy to see that the cost of parts, plus the cost of a marine electrician quickly makes the cost about a wash.

To do it right you’ll want some good wire strippers, a cable stripper (judicious use of a box cutter will suffice), a cutter big enough to lop off the whole fried end cleanly, then it’s nice to have a multimeter or AC tester to check that you haven’t reversed something that will really make things burn. So the task becomes daunting without all the proper tools, and if you don’t have the right tools they’re not cheap.

So what are we to do? It’s terrible that we live in such a throw-away society. I once toured the second largest open pit copper mine in the world, in southern Peru, and it’s no small feat to get copper out of the ground and turn it into copper wire:
Peru 059

So alas, if you just need to replace one end of a 50-foot, 30 Amp cord, repair costs enough less than replacement that you should fight the good fight and do it, if you can do it yourself or your electrician happens to be around working on other things anyway. If you have to replace both ends it’s cheaper to just buy a new one. If the whole cord is looking fairly tired and sun-baked, then definitely replace the whole thing.

If it’s shorter than 50 feet, it’s probably not worth repairing it.

For 50-Amp cords the whole magilla gets much more expensive for either repair or replacement, but the economics are about the same.

Copper wire should always be recycled, but finding where to do this can be a pain. As a marine electrician I take a big box to be recycled every year. Back during the height of the economic crisis people were desperate and copper prices were at an all time high, so shore power theft was common.

New Chainplates

Clark November 30th, 2016

I had to remove a few chainplates for an unrelated project and one of them broke upon removal. I guess I can count myself lucky it happened this way, rather than in full combat mode. Only 49 years old, and it just fell apart in my hand! I plan to write a strongly-worded letter to these Alpha England people about the quality of their product:

I blame the dreaded crevice corrosion:

Years ago I read something about replacing stainless chainplates with titanium, which is stronger, doesn’t corrode, doesn’t crack, and yada yada. I looked into it, and Holy Halyard Slaps! For the price of two simple (meaning flat), small, titanium chainplates I could buy enough 316 stainless bar stock in AND A BRAND NEW DRILL PRESS, which was long overdue:

Upon further reflection, I might have made them out of silicon bronze, but if my 316 stainless chainplates last half as long as the old ones I’ll come out winning. Brion Toss has a good riff on the subject here.

After getting my bar stock from and my new benchtop drill press from good old Sears, I set to work. Cutting was straightforward with an angle grinder with a stainless cutting disc, followed by a grinding wheel.

Drilling holes was also straightforward, using the slowest speed on the drill press, and lots of cutting oil. The old chainplates were countersunk for flat head screws. This would not only be a lot of work, but it seems to me it reduces strength by removing material, and provides a lot of hidey holes for crevice corrosion. My new chainplates will have non-countersunk holes and round head screws, with heads standing proud.

Then comes the hard part: They say the way to prevent corrosion is to polish the chainplates to a mirror finish. I was more or less successful at this, but I started my sanding with a 50-grit disc on an angle grinder, which left some irregular gouges. In the real metal polishing world they have all kinds of wheel sanders for the heavy stuff. I moved up into my higher grits with an orbital sander, then stainless polishing compound on a polishing wheel. All went well, but in the final result I could still see the gouges from my angle grinding. I’d say it’s good enough, and still qualifies as a “mirror finish,” but a mirror finish on some ridges and valleys left by my aggressive angle grinding. I think a belt sander would do a better job, but my belt sander broke.

While I was at it I replaced the backing blocks on the interior with G10. The old backing blocks were teak:

I’m on a kick lately of using butyl rubber, instead of polysulfide, for bedding deck hardware. Which is better? Ask me in twenty years. With butyl rubber it’s a long process of gradually tightening the fasteners over days or a week, as it is stiffer stuff, and takes a long time to squeeze out and find its place:

What Is It?

Clark November 8th, 2016


I was working on a boat in a dry storage area in San Leandro, California, when I saw the boat above. What this strange aperture in its side? On closer inspection the outside of the aperture has fixed vents, made out of plywood:

This outside part does not rotate. In the middle is a galvanized steel pipe, which is designed to rotate, as it is supported by several carrier bearings athwartships:

But on the other side of the boat this axle just sticks out an inch through another hole in the topside, with nothing like the contraption on the starboard side:

I’ve been noodling on it for a few weeks and have absolutely no idea. It wasn’t some thoughtless lark, because the vent thing on the starboard side is very symmetrical, and took a lot of work.

A sideways jet engine? Some sort of revolutionary propulsion system? Something not even meant for water; an unrelated project for which a fiberglass runabout just seemed like the right raw material? I’m stumped.

Advanced Electrical: Galvanic Isolator Case Study

Clark November 4th, 2016

Once I was buying a galvanic isolator in a West Marine store, when a West Marine employee, of all people, was really insistent that I shouldn’t buy it: “Those things are a scam! They don’t do anything. I have it on good authority that they’re a big waste of money!” He had that look in his eye, so rather than get all marine electrician on his ass, I just said, “Well, my customer wants it, so I think I’ll buy it all the same.” There are a lot of misconceptions about the purpose of a galvanic isolator, and what it can and can’t do.

Flash forward to this week when another friend/customer calls me down to his boat, says his zinc anodes are being eaten too quickly and he’s thinking about a galvanic isolator. When I get there he shows me a propeller shaft anode that a diver had replaced just over a week before, and it’s already over a third eaten. To get to that stage should take a few months.

A galvanic isolator will sometimes, but by no means always, solve the anode-eating problem. A galvanic isolator is installed in-line along the safety ground (grounding conductor, green wire) in the shore power connection, so of course if you’re not plugged into shore power at a dock, then you’re barking up the wrong tree.

My customer was plugged into shore power, but being a thorough guy I unplugged him from shore power and did a galvanic survey of all the underwater metal items on his boat using a reference cell, dangling in the water, connected to a digital multi-meter. All the numbers came up about right for a standard fiberglass boat, his bonding system was all intact, and he had the right amount of zinc anodes to protect his underwater metals.

But if we plugged in his shore power cord, his hull potential changed by about 200 millivolts. Aha, problem found, but people want to point to some AC problem, since this is coming from the AC shore power cord. Nay. Galvanic corrosion and stray current corrosion are caused by DC currents.

In fact, I could measure half an Amp of DC current by putting my Amp clamp, on the DC setting, around his shore power cord.

If your boat is bonded properly then all of the major metal parts, above and below water, are bonded together, usually using big green wire. It will also have an AC safety ground, also usually green wire, connecting all the AC outlets and appliances, just like at home. These two systems cross-connect at one, and only one, point. So, when you plug into shore power, your boat is connected, via the safety ground, to the safety ground system on every other boat on the dock, and thus to the bonding system and all the underwater metals, on every other boat on the dock. What could possibly go wrong?

My customer may have been doing everything right, but since his bonding system is connected to his AC safety ground system, and since his neighbors’ boats are the same, and since they’re all connected together via the AC safety ground wires in their shore power cords, his zinc anode was protecting his boat plus the boat next door, or maybe down the way, or maybe all the boats down the row. But even though it’s via the AC shore power cord, it’s galvanic corrosion, which means a DC current.

It could also be stray current current corrosion, that is, corrosion caused by an electrical current, but stray current is still a DC thing. AC current just doesn’t cause or accelerate corrosion in normal circumstances.

Whether his half an Amp of DC current came from pure galvanic action or stray current corrosion is beyond my pay grade. I tend to think the latter, because half an Amp is quite a bit. Maybe there’s no way to tell, but the solution, in any case, is a galvanic isolator.

A galvanic isolator blocks low level DC currents from traveling down the AC safety ground.

It doesn’t do anything about galvanic corrosion within the confines of the boat it’s on, thus the corrosion survey before zeroing in on the galvanic isolator. As a marine electrician, I think I had to go this route to rule out other causes beforehand. If I just slapped a galvanic isolator on there without poking around, I’d have to advise him to have his diver come back in another two weeks to check the anodes, and this would cost more than my additional poking around.

Before the galvanic isolator was installed:

And after:

Voila! But two days before I’d read .5 Amps, instead of .3 Amps. What changed? I don’t know, but .3 is still bad.

As a boat owner who is constantly/often plugged into shore power, should you just slap one on as a matter of course?: Yes

Will it solve your problem with fast anode depletion?: Probably maybe.

But even if you don’t have a problem now, you may in the future, as your fate is tied to all those other boats on the dock, so it’s good insurance. It’s especially good insurance when you compare the couple hundred bucks for the galvanic isolator to the financial ruin of a devoured prop and shaft, keel/keel bolts, outdrives, et al. It’s not just about saving anodes; it’s about saving what gets eaten after the anode is gone.

Likewise, it will not solve a stray current problem within your boat. If you’ve got nasty old exposed bilge pump wires sitting in the bilge water, you might just stray current your keel off.

And a galvanic islolator only protects against low level DC, up to 1.2 or 1.4 Volts, so if there’s some banzai stray current issue in your marina, which creates a voltage higher than that, the isolator won’t do anything, but this would be unusual.

It used to be that a galvanic isolator could fail, not only negating its anti-corrosion purpose, but creating a potentially deadly break in the AC safety ground. So after that they made it so you had to have a monitoring system that would warn you if its function was compromised. Now, galvanic isolators are fail safe, meaning that if they lose their anti-corrosion function they still maintain their AC safety ground function. They are still supposed to be tested annually. If you’ve got an older galvanic isolator, you should replace it with a fail safe.

There is a magic box called an isolation transformer that makes all of this go away, but isolation transformers are big, expensive, and heavy, so not practical for the average sailboat…unless your sailboat is steel or aluminum, in which case you should pony up and make the space.

Teaching Marine Electrical Seminar In Sausalito This Saturday

Clark October 25th, 2016


How many wrong things can you find in this picture?

If you happen to be in the Bay Area this Saturday, October 29th, I’m giving a marine electrical seminar at Spaulding Marine Center in Sausalito, where I will teach electrical excellence, simplicity, and how not to get electrocuted. They suggest a $50 donation and always provide a great lunch. Starts at 10:00AM; goes to about 2:30. Please RSVP. Link here for registration

Electrical Basics: Bus Bars

Clark October 17th, 2016

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Just twenty or thirty years ago the electrical system on the average sailboat was very simple. It had two batteries connected to an OFF-1-2-BOTH battery switch, and all the loads were fed from there:
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On the back of the battery switch were three studs: one for each battery, and one for the common, that is, the terminal that connects to the alternator and all the loads:

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The battery switch for this Catalina 30 is this way. In addition to the connection to each battery, the battery studs on the back of the switch are good places to connect the outputs for the shore power charger, the voltmeter, and the bilge pump, all things we want permanently connected to a battery, and never turned off.

On the common terminal of course is the big cable connected to the engine’s starter, and the feed wire to the main distribution panel, which in this case is just a 10 gauge wire: ah, the days of such simplicity. The back of this switch might be a little crowded, but all of these wires fit.

Today the electrical system on the average sailboat is more robust and complex. With just the aforementioned connections to the battery terminals – voltmeter, charger, bilge pump, maybe the memory wires from a stereo or other electronics – the studs are already too crowded. On the common terminal, forget it. You might have the big cable to the starter, a big cable to an inverter or inverter/charger, big cable to the windlass, and a good-sized cable to feed the main distribution panel, which now supplies a radar, a refrigerator, and a range of modern comforts.

All these cables simply won’t fit, and according to the ABYC standard, you shouldn’t stack more than four ring terminals on a stud anyway.

Enter the bus bar. Give yourself some breathing room!

A bus bar simply expands your single stud into four or more. A large gauge cable, and nothing else, connects to the common stud on the battery switch. The other end connects to the bus bar, where you’ve got a row of big studs for all the other connections. The same could be done for one of the battery connections if you find you’ve got too many cables and wires that need to be connected directly to a battery, without a switch in between. Generally speaking, we want to keep our battery terminals clean. Manufacturers sometimes dictate otherwise, as with some electrical system monitors and chargers, but we should endeavor to have nothing but the supply cables connected to our batteries.
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The bus bar is even more necessary on the negative side, where the negative cables from the batteries, negative ground from the engine, inverter, windlass, corrosion ground (green wire), and feed to main distribution panel, all must connect. Might also note here that bus bar covers are equally important, as they make for a lot of exposed, live metal:
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Many older boats foresaw this scenario, but it was before off-the-shelf bus bars, so they just added distribution studs, or what Blue Sea Systems now calls a Power Post, but one stud just isn’t enough. These are overcrowded and a bus bar would create more room, make circuits easier to trace, and ahem, that thing about no more than four ring terminals to a stud?:
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Now Blue Sea Systems has gone plum crazy with the PowerBar 1000. It’s the Super Jumbo Extra SuperMax GT version of the bus bar. I have yet to find use for one, but when I do I’ll know I’m serious:
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Remember, good wiring is not only electrically sound, but easy to follow. Wherever you find yourself running out of room and trying to cram too many terminals in a tight space, even if it’s electrically sound, it will be difficult to service and trace in the future. A relatively cheap and simple bus bar is often the solution.

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