Once you know how much power you need to operate your boat’s equipment, it’s time to plot the path of the wiring that will deliver the goods.
All right, we’ve got a couple of nice deep-cycle batteries, a good marine grade alternator, an external, field adjustable or, better yet, an automatic multistage regulator and a battery isolator/selector switch with provision for alternator field disconnect. So far, so good.
Now we have to lay out a system that will distribute this power to the devices that need it. The system should be easy and quick to expand or to service. We must be able to monitor its performance so we can anticipate and head off potential problems. Finally, we have to develop a wiring diagram, sketch the physical layout of the system and list the materials we will need to install it.
Our perspective is that of a full-time inshore fisherman who can’t afford to spend any more time or money on his electrical system than necessary. Elaborate and expensive electrical systems don’t catch any more fish than less expensive, equally adequate and reliable ones.
The Wiring Layout
The distribution panel is a key element in the system. It’s the “command center,” the basic control element. It’s where you provide for power distribution, protection and monitoring of the system. The positive and negative mains bring power to the distribution panel and from there it is routed through branch circuits to each of the loads, i.e., running lights, cabin lights, electronics, etc. The first thing we have to do is decide where to locate the panel. If we get this right, the rest will be a lot easier. I’m going to assume that we’re talking about a 36′ Jonesport-type working boat.
The distribution panel should be located in a readily accessible, well-ventilated place outside the engine and fuel tank compartments. It should be protected from rain, spray and drips and be easily accessed from front or back. The main positive bus from the common terminal of the battery switch and the main DC ground bus from the boat’s common ground point near the batteries are going to be pretty hefty conductors. They must carry the boat’s maximum current load. We will want to keep them as short as possible. If the distance from the battery terminal to the distribution panel is greater than 6′, measured along the wire, it will have to be fused within 7″ of the battery terminal.
Also, since the conductors for all the loads will originate at the distribution panel, a position on the center line and more or less amidships is probably the optimum location. A position inside the cabin, on the after bulkhead about on the center line and roughly at eye level when sitting down, is an excellent spot. This should put it just about level with the sheer, which is good because most of our fore and aft wire runs will be tucked up under it, probably fastened to the clamp on one side or the other. Cross-vessel runs are also best made at such a bulkhead. Obviously, your boat may not be a 36′ Jonesport, so choose a location that works for you and your vessel.
Before we can go any further, we have to plan the wiring layout — the loads, wire lengths, sizes and routings. Then we can organize them into branch circuits. In terms of system reliability, it would be great to keep each load on its own individual circuit with its own individual fuse or circuit breaker. That’s not always practical and it’s not necessary or cost effective.
The simplest and most useful form for the wiring layout is a plan view of the boat. It doesn’t have to be a precise drawing; a reasonably careful sketch will do. However, this will be very useful later on when you have to troubleshoot the system or want to add something to it, so it’s worth putting a little thought into. Mark on the sketch the location of the distribution panel and each device that will require electrical energy — the loads. You can use symbols, letters or combinations of these to represent these devices. Use any method that works for you but be sure to list them on the sketch, with clear explanatory notes. Otherwise, they may not make much sense to you a year or two from now.
Next to each device, list the current it draws. This information is usually on the device itself or in the literature that came with it. In some cases, this information will be given in watts; simply divide this number by 12 (or by whatever system voltage you are using).
The Fun Begins
Get out your old worn but still readable Stanley tape rule, a clip board, your masterful sketch, a sharp pencil, a big Pink Pearl eraser and a small, flexible, patient and obedient child. Here’s where you get to crawl around inside the boat and decide how to run the wires to and from each device. You could do this the easy way and scale it off the drawings, but I wouldn’t recommend it except for rough estimates.
Take them one at a time, figure out the best routing, measure to the nearest foot distances to and from the device and note them on the drawing. Try to keep them well up in the boat, away from the bilge. Again, up under the sheer along the clamp, up the corner posts in the cabin and along the overhead are usually good routings. They should be accessible. You may have to get at them when the seas are running 8′ to 10′ and breaking.
Continuous runs are best. If you have to connect to more than one device along a run, plan to terminate the wires in a junction box or on a terminal strip and run wires to each device from there. Keep the wires as far away from the compass as possible; 4′ or more is best. If you can’t avoid runs close to the compass, the wires should be twisted together to cancel the magnetic fields generated by the wires. Don’t forget to make allowances for corners, slack for strain relief, vertical runs, mistakes (yes, you), bad connections and uncontrollable fits of temper.
Take the accommodation lighting as an example. Note in Figure 1 we have shown the distribution panel (DP) mounted inside the cabin on the after cabin bulkhead just about on the center line. We have also shown the main cabin overhead light (CL), a light in the forepeak (FPL), a light in the wheelhouse (WHL) and a box labeled “JB/TS,” which stands for junction box or terminal strip. We have chosen to run the wires up the bulkhead (2′). From there, we will run one wire forward to the cabin light (4′) and another to the light in the forepeak (13′). Also, from the junction box/terminal strip, we will run a wire aft to the light in the wheelhouse (8′). Remember, all these lengths will have to be doubled.
We have decided to put the cabin light, the forepeak light and the wheelhouse light all on one branch circuit with one protective device, i.e., a circuit breaker or a fuse. This is all right with lights since they fail open, not shorted, and are wired in parallel so that if one fails, we do not lose the others on this branch circuit. This also applies to running lights. We can locate a junction box on the after bulkhead, near the distribution panel and run separate wires to each navigation light.
Putting more than one device on a fuse or circuit breaker works but is not a good idea with items that can fail short like electronic equipment. In this case, the short takes out the circuit breaker or fuse and you lose the other devices on that circuit until the shorted equipment is fixed or removed. Lamps are one of the few devices which fail open; all other devices should each have their own circuit.
You will want to put the bilge pump on a separate subpanel that has its own switch and protection and is connected to a point in the circuit that does not lose power when the battery isolator/selector switch is turned off.
If we’re going to document the boat, and we’ll have to if it measures over 5 net tons, the Coast Guard teas a couple of requirements that we must comply with. One is for a bilge alarm and the other is for an emergency communications capability–three hours of continuous operation for the radio and the running lights independent of the main battery bank. They’re both good ideas.
There are several bilge alarm systems. They range from about $35 to $165 and more, if you want to tie in some other sensors such as, low oil pressure, engine overheat, etc. The simplest ones consist of a float switch and an audible/visual alarm. The best ones use a 100 dB bell for the audible alarm; that’s pretty loud. You could probably hear that even over the rock music.
Here again, it’s a question of how much you want to spend. In any case, it can be wired just like the bilge pump; it shouldn’t stop working when the battery switch is off, either. Mount the float switch in the bilge, above the float switch for the bilge pump and mount the alarm in the wheelhouse. If more than one compartment must be monitored, wire the float switches in parallel.
As for the second requirement, most boats are just putting a battery in the wheelhouse. The VHF radio and the running lights together will draw about 6 amps, so the smallest deep-cycle battery, about 50 amp-hours, will give you up to eight hours of use if you take it all the way down. You want a deep-cycle battery because you will probably be deep-cycling it unless you have AC aboard and put it on a trickle charger.
These things are no big deal, but you do have to keep the battery charged up, and you’ll have to make up a couple of 12/2 cable pairs. One cable will have captive spade terminals on one end to connect to the terminal block in the running lights branch and battery clips on the other end to connect to the battery. The other cable will have the female half of an in-line plug connector on one end to mate with the one on the VHF and battery clips on the other to connect to the battery. They’ll both be clearly labeled and neatly coiled in the wheelhouse with the battery. And it’s still a good idea whether you document or not.
Continue laying out the wiring runs for each of the loads you will have on the boat. When complete, you will have a reliable wiring layout of your electrical system. From this wiring layout, you can develop the circuit diagram. This is a very useful tool in troubleshooting the system or making changes or additions.
Choosing the Distribution Panel
We wanted a panel that would meet ABYC recommended standards and be economical for a working fisherman who would find it hard to justify spending a lot of money for an unnecessarily sophisticated system. A check of the available panels shows that a top-quality circuit breaker panel from one of the major suppliers can run from $20 to $40 or more per circuit. It depends on the total number of circuits and instrumentation. We could assemble our own circuit breaker panel from catalog parts for something between $15 and $20 per circuit or we could assemble our own fuse and toggle switch panel for about $8 to $10 per circuit. However, a standard, off-the-shelf fuse and switch panel is readily available at less than $25. That’s a cost per circuit of about $4.
Obviously, the quality of the components and the robustness of the design reflect the differences in price. We decided we would use an off-the-shelf fuse panel in our example because it is the least costly, if a dependable source of panels of adequate quality is available. The Sea Dog six-circuit fuse panel is a good example of the off-the-shelf type we want to use. The whole process and the installation procedure is essentially the same. A circuit diagram would look the same except that the fuse and switch symbols would be replaced by the circuit breaker symbol. Fuses and switches are perfectly acceptable and if we use good quality marine-grade products and practices, it will do the job and it will meet the recommended ABYC standards.
A couple of words about the Sea Dog panel. There are several panels out there that look exactly like the Sea Dog, but may not be as reliable. Be sure of what you’re buying and check it before you install it.
You should also be aware that fuses are not resetable. If a fuse blows and we don’t have the right size replacement, we just do the manly thing and put in a larger size, or we short it out. That’s not so bad in itself, if that’s what it takes to get the old girl home. The problem is that we may not get around to making it right. Eventually, the system has been compromised and is without protection. If we’re going to use fuses, we should be sure to keep a little box of each size handy. Right in the enclosure with the panel is the best place.
While we’re talking about fuses, it might be a good idea to clarify a couple of things. The fuses are not there to protect the load; they are there to protect the boat. If a high-current short should occur in a load, say a locked rotor in a pump motor, extremely high currents could flow, overheating the wire, melting the insulation and possibly resulting in fire. Most equipment manufacturers provide protection for their equipment through fuses mounted in the back panel, an in-line fuse holder in the power lead or a thermal circuit breaker internal to the motor. The manufacturer’s recommendations for protection should be followed as well.
Some fuses are designated “AGC” and some are labelled “MDL.” AGCs are conventional fast-response fuses. MDLs are delayed-response or “slow-blow” fuses. MDLs are used for inductive loads, such as motors and transformers. Inductive loads experience an initial current surge when turned on that can be many times higher than the steady state current. This surge lasts for just a few milliseconds; the delayed reaction prevents the fuse from blowing every time the equipment is turned on.
Once we have completed the wiring layout, we can make our final decision. We can call or write to the suppliers listed at the end of this series, ask them to send us their catalogs and applications notes and figure it out for ourselves. Talk to an applications engineer, tell him what we’ve got and work out the best solution at the best cost on the phone. They will put the panel together and send it to us all wired up. If we get in trouble installing it, we can dial their 800 number and they will talk us through the installation and resolve any problems with us. There is a mind-boggling variety of panels available ranging from very basic DC panels with the bare necessities to some very complex and sophisticated AC/DC panels for extended offshore vessels. It’s certainly worth a no-cost phone call to help sort it all out.
The six-circuit panel we have chosen is rated at 15 amps maximum, which is fine for all of our loads except for the pot hauler, which draws 28 amps. This will have to be protected separately. I do not know of a major supplier of marine-grade panel-mounted fuse holders or toggle switches that are rated at more than 25 amps steady-state load. Both Cole-Hersee and Ancor can supply in-line fuse holders rated at 30 amps. But I’m not crazy about in-line fuses, although they are perfectly acceptable.
A solution I like better, although it requires a little more work, is to put the pot hauler on a subpanel with a circuit breaker. We can get a 30-amp circuit breaker at West Marine or Boat/U.S. for about $12. We could go down to our friendly local sheet metal shop and pick up a 2 1/4″ x 3 1/2″ piece of 1/8″ aluminum out of the scrap box for little or no cost. We drill a couple of mounting holes, round off the corners, spray paint it black and we’re in business. Our circuit diagram reflects this approach
It’s important to be able to monitor the condition of the batteries. It’s also useful to be able to monitor the current that is being drawn by the system. This is easily done by the addition of a voltmeter and an ammeter to the electrical system. Keep in mind that the range of the ammeter must be greater than the maximum current drain of the system; 52 amperes for our Jonesport.
The Wire List
Now, in the quiet comfort of the shop, you can spread out your masterful (but now messy) sketch and clean it up so that when you look at it again next season you will be able to make some sense out of it. This is also the time to clear up any questions about the wiring layout, sending the speedy and obedient child out to remeasure, etc. This is also a good time to think about changes or additions you may want to make in the future; GPS,a best fish finder (you can get more information), a change in fishery, whatever. It will be a lot easier to provide for it now than later. When you are satisfied that the sketch is complete, you can get down to figuring out what types and sizes of wire and circuit protection devices, (fuses or circuit breakers) you will-need.
This is an important step and it’s worth considerable thought. To a very large degree, the performance of your system depends on the decisions you will make here. The wrong wire size can not only degrade the performance of the system, it can be downright dangerous. Too small a wire size can cause your electrical equipment to fail to perform as you need it to and it can create dangerous overheating. Adequate or heavy wire sizes would be slightly more costly but it can do nothing but improve system performance and minimize or eliminate hazardous conditions. For this reason we will use the ABYC Wire Size Table for a 3% voltage drop for all circuits (see last month’s installment). Given the amount of the current drain on a circuit, and the length of the wire to the device and back, the table will give you the wire size that should be used. The current rating of fuses or circuit breakers selected for the circuit should not be greater than this current.
Next month we will use this information to make some decisions about wire sizes and types, color coding and identification, cable supports, terminals and other hardware. And we’ll develop the bill of materials we will need to install and troubleshoot the system.
Ev Collier is an electrical engineer (and amateur boatbuilder) who owned a marine electrical-installation business that served commercial and recreational vessels.
Thanks for reading, my name is William. Hopefully with these techniques above of sea fishing, everyone will get the choice fishing areas as well as the best way for your fishing.