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Old 07-10-2017, 06:43   #1
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Designing a simple DC system from scratch.

The forum is such a great resource of information. Lots of you have rewired your boats or designed/updated and wired your system to some extent. And I realize that this is a very generic question. But that is purposeful....... It could get confusing otherwise.

We are in the midst of a new build (Custom Marples 40 trimaran). Just about 90% there and it is time to start wiring the boat. Plan is for a simple, generic, straight up DC system with relatively low demand. Two batteries: start and house. Small diesel with 70 amp alternator. Solar panels will be in the mix at some point. Demand on the house side would be about 40 to 50 amps per day......very roughly.

I have resourced Nigel Calders book and the web......etc. Any and all recommendations would be helpful. "DC electrical systems for dummies perhaps?"

Would you design your system from the load/appliance side of the equation and work your way back to distribution and power source?

Or would you begin at the power source and work your way to distribution and then load/appliance?

Fusing and wire gauge is a big part of the equation. That I know. And ultimately the design and install will be audited.

So the question boils down to ........if this were you with your experience how would you go about the design and install? Any resource or recommendations for diagraming? Words of wisdom and experience?

Thanks in advance.

S
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Old 07-10-2017, 07:29   #2
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Re: Designing a simple DC system from scratch.

The only way that makes any sense, is to figure out what your power demands will be. Then build the system that is necessary to supply those demands, to store sufficient power for those demands, and to allow an adequate margin for growth.

And if you find out that you can't build that system (i.e. no room for the weight it would add) then you have to go back and figure out what you're not going to have on board.
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Old 07-10-2017, 07:32   #3
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Re: Designing a simple DC system from scratch.

Just a couple of thoughts for your big DC project: I would start with a list of all the loads as they really drive everything else. These include the engine starter too, and windlass, lights, electronics, water pump, bilge pumps, macerator pump, and every thing else.

You need to determine the approximate location of all these so you can determine the wire sizes necessary for each run. The best practice is to run all load wires direct back to the DC panel. You would need battery switches of course, with the ability to isolate the start battery when not needed. Don't neglect the DC negative side of the design. And I would strongly recommend you install a DC digital meter if your new panel doesn't have one and install a DC shunt between the one and only one DC cable coming off the house battery to the main DC negative bus. All your big negatives should go here and the DC panel negative. Best practice is to lead most of your load negatives to the DC panel and not to small DC terminal buses scattered about the boat. It makes it easier to troubleshoot problems but uses more wire.

Charging sources have to be determined - to replace the daily average at a minimum. You need to size the batteries (amp hours for the house deep cycle batteries and cranking capability of the start battery). You will need to size the charging system (alternator, AC to DC charger, solar, etc) to give much more than the daily average (on paper) as the batteries and charging will never be close to 100% efficiency. Better to have too much and not need it than too little. Of course, you have constraints on this, like size of alternators you can put and run on your engines, cost, room for solar panels, etc.

I would look at the many sources that describe "good" DC systems. Blue Sea has some good stuff. Nigel Calder too but I am not his biggest fan for this specific question. There are some good books out there.

You will have trade-offs. There isn't one perfect way to do this. If someone says "X" is the only way to do something, back off and get a second opinion. The requirements are all the same based on your situation but the "how to get it done" is not always the same. I have my definite preferences, as do others, but they aren't gospel.

One of the most important issues to deal with is type of batteries to have. They all have pros and cons. And tons of strong opinions on them. The biggest driver is how you will use the boat and how you charge them. In most cases I would recommend 6-volt golf cart form batteries. AGMs are good if you motor a lot or will be on AC most of the time at the dock. They don't do well if not routinely charged to 100% and a lot of cruisers ruin them because the don't. Flooded wet cells work very well for the cost but you have to deal with topping them off, etc. New carbon foam batteries look good now but expensive and in limited sizes. I would recommend lithium for you as they are not for the inexperienced right now.

Definitely plan to use all marine rated gear - wiring, switches, etc. The only way to go. Use the right color for all your circuits if you can. And label both ends of all wires. Maine Sail recommended using a tape labeling machine (like a Brother TZ) and clear heat shrink to make labels. I buy clear heat shrink online and cut to size. It is the longest lasting and cleanest way to label I have seen although it does take longer and you need to have your heat gun at each termination. If you are wiring a boat from scratch it just becomes one extra step as you move from one place to another.

Good luck. There's lots more to this but you can pull it off. And, please, run nice neat bundles of wires that look good and are secured well. Don't cut corners with wires. Use wire ties and tie mounts to secure wires/cables. Size wires right. Don't make it a rats nest. Plan how wires will come in to the back of your panel. I like to put a terminal strip behind the panel to run all my positives to and then run a separate wire to the circuit breakers. Very clean, easy to troubleshoot, and easy to change things as you go.
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Old 07-10-2017, 09:30   #4
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Re: Designing a simple DC system from scratch.

Thank you guys.......very helpful. "Best Practices" is exactly the input we are looking for.

The details like where and when to fuse. 7 inches from the power source or terminal comes to mind. Also when there is a change in wire gauge?? (step down in wire size at a bus for example) Maybe?

I know that it is another topic on the forum.......... Have been looking over the "firefly 31" batteries. Carbon foam design. If the reports on deep cycle are accurate I could probably get away with 300ah on the house side. In the past I used 4 golf cart batts in series/parallel for about 480ah of storage. But that with the intention of depleting to about 50% max. Seems like the jury is still out on the firefly though.

My understanding is that there is only one "correct" way to do this. But there are many ways to execute and design the system. Everyones idea of best practice may differ. So keep them coming.

And thanks again.

S
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Old 07-10-2017, 09:43   #5
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Re: Designing a simple DC system from scratch.

Clarifying my questions ...........

Its not so much figuring out loads and usage and determining charging capabilities and battery size. Most simple DC systems can vary those items on either end to fit the demands.

Its more designing and constructing all that is in the middle of the equation. Best practices and safety. Resources to pull that off.

Not being an electrician, it seems to me that the systems of today have evolved with technology which is normal. So if one were starting from scratch today. Based on your experiences what would be your best ideas and practices?

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Old 08-10-2017, 07:04   #7
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Re: Designing a simple DC system from scratch.

Gord,

Thank you. Most helpful and greatly appreciated.

Thanks to one and all..........

I have a couple of more books on the way and a stack of reference material. It is a good start.

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Old 08-10-2017, 09:27   #8
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Re: Designing a simple DC system from scratch.

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Originally Posted by w32honu View Post
Gord,

Thank you. Most helpful and greatly appreciated.

Thanks to one and all..........

I have a couple of more books on the way and a stack of reference material. It is a good start.

I will add, being about 80% through this process, that you work from a proposed energy budget of X Ah/day, X being 100%

Then, assume you are wrong and that some gadget (global warming affecting ice cube production, lost, awash containers requiring forward-looking sonar all night) will pull more stored energy (X(1.3) Ah/day).

Now, figure out how you are going to replace those Ah per day: alternator when motoring (which is not every day); solar panels (which have perhaps four hours of decent production every day that is sunny...where are you going to be?), wind (noisy and also sporadic), towed "duo-gen" (speed penalty and works best underway) or genset (added cost and complication and weight and fuel draws).

Also figure out where you are going. At the Equator, the panels work great, and you rarely need to kick off a heating system, but there may be a desire to have A/C, which is an energy pig for the most part. Conversely, going around the north of Scotland in June (22 hours of light!) may involve heating the boat underway.

So much is dictated by the energy budget, which can vary on environmental, situational (radar on for busy waters) and lifestyle (am I a lizard?) factors. When you get that eventual energy number, it, too, will be wrong, but it will be less wrong.

On this less wrong number, you have to factor your ability to carry enough batteries (the type decision depends on the nature of the space available) to store effectively the power you can make at every opportunity. More battery capacity is better, because you cycle less deeply a larger bank, although the larger bank takes more space and adds more weight, negatives for many boats. Some use AGMs for this reason: they can be put in narrow or otherwise awkward spaces to be able to absorb sunny day after sunny day while the ice cubes pile up and the watermaker yields sweet showers, but it's all a trade-off given that the average 40 footer has only so much volume and batteries are never small.

And I haven't even got to the cabling, shunts, fuses, charger and monitoring!
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Old 08-10-2017, 12:09   #9
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Re: Designing a simple DC system from scratch.

W32:


Try not to blind yourself with science :-)


Gord May has given you all the “hardcore” stuff you need to know – as you have already acknowledged. MaggieDrum and Alchemy are worth listening to :-)



But you ask explicitly about how “we” would go about wiring a new construction from scratch. So here are some things that I consider essential desiderata. I base them on observations made over half a century in many “production” boats and in several “owner fitted” boats.


Running wires through PVC pipe and placing it behind the furniture in order to conceal it is obviously folly. Do that, and replacement/repair/augmentation will require the use of dynamite to remove the furniture to get at it. Were I fitting out a bare hull, all wiring would be run in wire gutters designed as an integral part of the cabin TRIM, e.g a removable fake “shelf” running along the deckhead/houseside joint.


Provided there is, as there should be, a master switch on the main electrical panel – in the case of TP, at the nav station – there is no reason that ALL below-decks illumination should not be on a “ring circuit” that is live at all (needed) times, "branch circuits" to be provided for by terminal blocks at appropriate locations. Local switches on the lamps will take care of local requirements.


Fittings/electrical devises ex chandlers come with “tails” with bare ends that need to be connected to circuits. “Butt”-connectors are a no-no! For my money, the installation needs to be such that removal/repair/replacement of the fitting may be performed easily. Take, for example, a simple sidelight mounted on the deck house: The “tails” are taken through a grommeted and sealed hole in the house side. Generally, the tails are hardwired within the fitting – which is sensible enuff. On the INSIDE of the house they need IMO to be taken to a TERMINAL BLOCK, so they may be easily disconnected without having to interfere with the permanently installed circuit. In the case of incandescent lights (if any are still used) the polarity is of no consequence, but with LEDs polarity matters. The tails on LEDs are therefore of different colours, commonly red and black, or they are marked with a deeky little label on the positive lead. However, current wiring practice for low voltage (12VDC) is that “return”/”ground”/”negative” should be yellow, and that is therefore what should be used in the permanent circuit(s). In this example, the terminal block should be hidden behind a tastefully designed detachable panel in the ceiling. Both the permanent circuit and the tails from the fitting should be furnished with “captive” (as opposed to "plain") fork terminals. I prefer fork terminals to eye terminals because to disconnent a fork terminal, you don't need to remove the screw completely from the terminal block, risking the loss of it. The means of attaching the terminals to the wires and sealing the joint against moisture and corrosion is described in the material Gordon May provided.


Ideally there should never be any kind of circuit run through the bilge. However, that rule must necessarily be broken in regard to bilge pumps and their “float” switches. The tails provided by the manufacturer of these devices are never long enuff. The proper means of lengthening them is to make a proper SOLDER joint, also described in the material provided by GM. The lengthened wires may then be taken to a terminal block fitted above any level the bilge water could conceivably reach.


In TP I have made a mount for pump and switch so they can be lifted from the bilge as an entity. Complete removal is facilitated by having the wiring taken to a terminal block immediately next to where the mount is held to the floor by studs and wingnuts immediately under the deck sole where. They are easily reached.


The sniffer-element on bilge sniffers will die if it gets wet or in any other way contaminated. As it must of necessity be deep in the bilge to do its job, there is a case to be made for mounting it, also, as I've just described for the bilge pump(s).


As a boat gets older, there WILL come a time when the mast needs to come down. It is sensible, therefore, to make provision at the building stage for taking all wiring leading to mast-mounted devices through the deck in a manner that facilitates this task while at the same time prevents ingress of water through the fitting. As it is utterly impossible to prevent water from getting inside a mast, and as getting inside a mast is an expensive proposition, it is of the utmost importance that any wiring joints within the mast be absolutely above reproach.


At the “business end” of circuits, it is usually obvious what each wire does. That is not so at the “panel end” however. It is essential, IMO, to draw a schematic of the wiring at the panel end, and ALSO to mark all wires so they are readily identifiable. Bits of masking tape with scribbled notations wrapped around the wire just don't cut it! A simple easy way of doing this marking is to use short “rings” of shrink tubing in various colours fitted next to the panel end of each wire. A green wire with the ring combination “red/black/red” might indicate the feed for the cabin lights, for instance, and the combination “red/red/red” on a brown wire might indicate the feed for the bilge pump. With three rings you'll have more permutations than the boat will have circuits. The schematic will, of course, be annotated with the ring combinations, and it will live with the boat's other important documentation.


A practice often seen is to mount the stern light on the “pushpit” (or a “combo”light on the pulpit) leading the wiring through the tubing. IMO that is asking for trouble. Running wire in such a way that replacing it becomes problematic is downright silly, and it is rare that a better placement of the fitting cannot be found, thus giving a more sensible wire-run.


You are already aware, as others have mentioned, that you start your “system design” by establishing a “power budget”, i.e. making a list of the draws of EVERY device you are going to install on the boat. The draw of each device will determine the gauge of wire you need to use for it. GM's material includes a chart for the determination of that. I like to go to the next heavier gauge. As has been said many times, the fuse is there to protect the WIRE, not the device, and should be sized accordingly! The sum total of all draws over a given time is what determines what your generating capacity should be. Your battery capacity should be enough to sustain those total draws for a time long enuff to take you from one charging opportunity to the next. The batteries don't care how the juice is generated as long as they get it. Therefore any combination of generating devices will satisfy the requirements as long as in total they turn out enuff juice to furnish your total draws PLUS an increment to recharge low batteries.


In TP – which has a measly 20HP Beta diesel - I don't distinguish twixt “house” and “starter” batteries. The draw to start such a baby engine is very little indeed, so little in fact that within a few minutes of the engine starting, and the alternator “kicking in” at something like 1,400 RPM, the power used to do it has been replaced! One of our members has written a very excellent treatise on precisely that topic, giving actual test data proving the rectitude of the contention! Obviously TP has a standard “1-2-both-off” switch. To even the load on the batteries I use #1 on odd dates and #2 on even dates for the “hotel” functions when no charging is taking place. For starting, and when charging is available, I use “Both”. That simple!



TP lies afloat all year and plugs into a 30Amp shoreside circuit. She has a 20Amp ProMariner charger. Her Alternator is the 30A machine native to her engine. Her battery capacity is 2 x 27-series deep draw batteries for a total capacity of something like 240A/hrs of which no more than 50% should ever be expended. No fancy stuff at all, because I really don't have any interest in "toys" :-). If, when on the hook, I get "twinges" that the battery in current use for hotel functions may be "getting low", I simply fire 'er up long enuff to satisfy the current needs. The ongoing draws are very little normally. Just LED lights and the odd squirt of water. The solenoid shut-off for the propane is a bit of a hog, but is obviously only active while cooking is happening. Heating is accomplished by means of putting on an extra sweater and the long skivvies with the loden insides:-)! Air-conditioning happens by opening the hatches. Hot water? A kettle on the stove does the job. Showers? Take a dip in the briney!


Oh, speaking of "when on the hook": The capstan, miserable little toy that it is, is a hog. I never run it, up or down, without having the engine at 1,5K or so for the five minutes or so that it's in use, so that the alternator output is more than the capstan consumption. The engine needs to run for reasons of sound seamanship in any event when you are playing with your ground tackle.


I know I'm terribly old-fashioned, but there you have it ;-)!


TP
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Old 08-10-2017, 13:51   #10
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Re: Designing a simple DC system from scratch.

TP has many good points. However I disagree with:

"Ideally there should never be any kind of circuit run through the bilge. However, that rule must necessarily be broken in regard to bilge pumps and their “float” switches. The tails provided by the manufacturer of these devices are never long enuff. The proper means of lengthening them is to make a proper SOLDER joint, also described in the material provided by GM. The lengthened wires may then be taken to a terminal block fitted above any level the bilge water could conceivably reach."

There is no problem running wire through the bilge. It should be high - just under the floor so it does not sit in water and there should never be a splice in the bilge. If you are running duplex wire (recommended) the wire is double insulated and durable. Actually there should never be a splice anywhere in a cable run except where you are attaching the load on the end (light, radio, etc.)

I have owned my boat for 27 years and rewired it completely, using the original circuit breaker panel. I have a bundle of wires about two inches in diameter in the bilge. The worst problem with the run is that it gets dusty over time. Every few years I hose it down to get rid of the dust.

Use good marine rated wire but you don't have to buy into Anchor Wire's marketing BS. 14 gauge wire is 14 gauge wire period. Since you can buy in 500 foot rolls shop around for UL listed marine grade wire. Regardless of load I wouldn't go smaller than 14 AWG wire. Use proper ring terminals and get a good ratcheting crimper - that will save you many headaches in the end.

High load circuits should not go through the main panel. Wire the engine direct to the battery with appropriate overload protection near the battery. If you are installing a windlass the same applies there as well. Keep in mind that the purpose of a fuse/circuit breaker is to protect the wiring, not the device on the end of it. The closer to the power source (in this case the batteries) the better.

Pay attention to wire size. I always use the 5% voltage drop chart.

Also, there has been a lot of discussion about soldering connections. I have come around to the crimp, not solder way of thinking whatever you do use heatshrink tubing over a join - the kind with glue on the inside.

Once done a spray of Boeshield onto your terminal strips and back if main panel will help keep things protected from the salt air.

Of course you will never be completely done since as you own the boat you will find that revisions are needed.
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Old 08-10-2017, 14:01   #11
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Re: Designing a simple DC system from scratch.

Lots of good advice here, but I would like to add the following for consideration. I recently (2 years ago) rewired my boat from scratch. Pulled EVERYTHING out and started again. And because I was uncertain about a few aspects I simply roughed in the wiring and control panels and lived with the rough version for a year or two before I did any of the finished work. Glad I did too. I did not make a lot of changes but the few changes I made would have been difficult to incorporate in a finished control panel or thoroughly bundled wiring trunk.
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Old 09-10-2017, 08:12   #12
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Re: Designing a simple DC system from scratch.

Some really good thoughts above. I would be remiss though in not emphasizing what was mentioned by someone else: diagramming ALL circuits. You start out using diagrams to plan your installation. Then you update them as you actually wire the boat. You will always make changes. And, you will always forget what you did three weeks after you put in the last 20 circuits so you will spend much of your boat life troubleshooting and rediagramming circuits that would have been easy if you had the handy little drawing. Then you put all your diagrams in a notebook you can always find and add more diagrams to.

You don't have to diagram light wiring and that kind of thing, but you certainly should electronics, bilge pump systems, charging systems, inverters, and on and on - especially battery switches. Seems pretty simple and why bother, but do. I often help friends troubleshoot their boats and I find they don't have a clue how their battery switches are wired, and not much else either. Being the simpleton I am, I start off diagramming the system at issue.

Then I leave the diagram sketch with them saying they should never lose it as they will need it again, or I will when they call me back. One particular friend kept losing his battery switch diagram and his were impossible to get to the back of them so I would have to go through the process of identifying which wire connected to which battery post went where. It's easy but a PITA. I quit working on my losing friend's boat. It was irritating especially since I was doing it for beers.

So - you all can tell I am a diagramming fanatic. Guilty as charged! I even use the simple draw function in MS Excel to do permanent diagrams, so I have an electronic copy and can print off new ones when I need them. (sample attached)

I do use butt connectors. In fact I often use them. I have never had a problem with ones I have put on (that I know of), but I have rules when I do. When possible I use heat shrink butts, especially if it is in the middle of a run. I hate to do that but sometimes it is the best thing to do. Sometimes you just don't have access to the entire wire run and replacing it would be a bear. Or you don't have the right wire size and length, or the right color. (I really, really hate to substitute a black wire for a positive wire or to change the color of a wire mid-stream.)

Butts, even heat shrink ones, should be only used in dry locations where possible. Heat shrink ones can be used in a potentially wet location but never the non-heat shrink ones. And the wire insulation should be clean of oil for heat shrink.

Sometimes there just isn't room for a terminal block, or I don't have one, or it would be impossible to get to. (It happens) One issue with terminal blocks is you end up with twice the number of connectors which would potentially go bad or be bad from the start. They are a good idea if you will ever have to replace the device they are connected to but you can also use spade - male and female - push together type terminals there. They are just as reliable if done well as a terminal block. I would only use them for low current circuits though - lights, some small electronics, etc. And - regardless of using a terminal block or not - put in a "service loop" of extra wire so you can replace a bad terminal later or pull a device out far enough you can work on it, or as a "drip loop" so any water getting in will drip down the loop and not into the terminals. I use them everywhere, including at the electrical panels.

And regarding building a new boat and putting in the wiring. One of the biggest complaints from anyone, owners or pros, who has to troubleshoot and repair or upgrade circuits is when the wiring is impossible to get to. Or the use of conduit which always seems to be too small from what you thought would be plenty big. I especially despise the flexible "split loom" tubing. And I hate the little "p" type wiring securing plastic pieces. If you need to replace or add a wire you often have to take them off one at a time by removing the screws. Putting in screws in out of the way places can be a nightmare. OK for the one time you put in the circuit if it will be perfect forever (LOL) or you will never add another wire alongside it (LOL). So I use wire tie mounts.

They require the same amount of work to get that little screw in upside down in the corner where you can't see it, and you can snip and replace the wire ties when you need to without messing with the screws. On my current boat, which I just rewired, I took off any P clips I found and put in wire ties, leaving the wire tie loose so it is a wire organizer for adding new wires and then cinching them down when all wiring is done.

I also use square drive screws. They will stay on the end of your screwdriver bit while you work to get them to the spot you need to start them. And they are tons easier to get out later. And they don't strip nearly as easy as slotted or phillip head screws.

OK - just some pet peeves I have developed working on my own and lots of other boats. Everyone has their preferences. Do what works for you.
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Old 09-10-2017, 08:34   #13
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Re: Designing a simple DC system from scratch.

After you've absorbed what info you can from the reading the technical books, and once you've listed all the specific electrical equipment you think you'll need, and have made a comprehensive wiring diagram of the proposed system, pay a professional to go over it and do a proper engineering job.
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Old 09-10-2017, 12:30   #14
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Re: Designing a simple DC system from scratch.

Some handy reference material

Electrical Systems 101
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Old 10-10-2017, 04:11   #15
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Re: Designing a simple DC system from scratch.

I would make two important changes immediately:

1) Upgrade alternator to 120A minimum. This will allow it to run cooler and
to live longer. It will also allow you to charge your batteries more quickly - especially with modern batteries that have ever higher charge acceptance rates. This reduces engine run time and increases engine life.

2) ditch the engine start battery. Install one battery system only. This will save money, weight, and space. It also makes your entire electrical system simpler, cheaper, and easier to maintain. No 1-2-both switch - just an on-off switch. In the rare event that you have allowed your battery to discharge to the point that it cannot start your engine (in 50+ years of boating, this has never happened to me), you simply pull out the portable lithium battery pack that you keep on board for such emergencies. These things are compact, lightweight, cheaper than a regular starting battery, and are available at most automotive suppliers. (E.g. Canadian Tire, here in Canada). It's also handy for troubleshooting, or taking ashore for picnics, or for charging cell phones, or whatever. You can also use the space and weight saved to increase the size of your battery bank.
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