Rewiring of Cape Dory 28

[arecuk]

Guys,
I bought Cape Dory 28 as my first boat. The boat is in a good shape overall but of course I need to fix quite a lot of things. Regarding boat systems I consider myself as amateur and Im trying to figure out how things work.

The first thing I need to do is to rewire the boat. The boat has only 12V system and no shore power. I was looking at the direction of electric cables and found out following:
1) two batteries - engine and house battery
2) those two batteries are connected negative-negative together
3) negative port of one battery is connected to engine body (grounding?)
4) I have 3-way bettery switch:
https://bigorangemarine.files.wordpr...i-dscf0815.jpg
5) positive ports on both batteries led to the switch
6) on the engine is installed alternator
6) negative port from alternator is connected to the swicht

That's how it is now. My questions are as follows:
1) Is that right setup?
2) Im suspisous about wiring of the negative port through engine body and alternator to the switch? Does it mean that the electricity flows through engine body?
3) On the swhich I can choose between engine or house battery only or both batteried to be used. I understand the wiring for single battery in use (one negative to one positive port on the switch) but how does it work when both batteries are used? Is it like that both positive ports are connected to the negative port at the same time?

Thanks a lot for your advices, Tomas

[Stu Jackson]

I urge you to buy a book on boat electrical systems, since there are so many questions you raise. Charlie Wing's book is particularly thorough and understandable.

The engine IS the GROUND for the entire electrical system and all electrical negatives are wired to the engine.

Here are some handy electrical discussions and links, choose away ---

Electrical Systems 101 Electrical Systems 101

[rwidman]

Originally Posted by Stu Jackson

I urge you to buy a book on boat electrical systems, since there are so many questions you raise. Charlie Wing's book is particularly thorough and understandable.

The engine IS the GROUND for the entire electrical system and all electrical negatives are wired to the engine.

Here are some handy electrical discussions and links, choose away ---

Electrical Systems 101 Electrical Systems 101

Definitely. If you don't know what you're doing you can cause a lot of damage.

Why do you think you need to rewire the boat? It was probably wired correctly when it was built.

[arecuk]

Stu, well I will definitely buy a book on that topic, for sure. I was just hoping for some quick tips and advices so I could thing about it and look for additional information.

Basicaly, is the wiring I described basicaly corrent? Mainly the connection of alternator?

Rwidman, you would need to see the current wiring, its a total mess and quite a lot of devices does not work.

My idea is to trace current wires, get rig of old unsed cables and the right ones replace by new cables with silver cover. And in the same time try to understand how its done and look for possibly wrong wired cables.

What about bronze seacocks? Currently they are grounded and that was good practice in the past times. However, I found suggestions that seacocks should not be grounded as in "hot marinas" they may be subject to electrolysis. Instead of grounding its suggested to isolate them. What do you thing?

[rwidman]

If you were just installing a stereo or something like that I would say go ahead and try it.

For what you are suggesting, I think without working knowledge of electrical theory and practice in a marine environment, you are taking on more than you are equipped to do. If the wiring is in that bad shape, you should get professional help.

[arecuk]

yes, thats why I want to do - change cables for stereo, vhp, gps, lights and other small devices ... I dont plan to change battery wiring or alternator wiring ... just want to understand how it is done and whether it is done in a right way ... hence, my original questions

[rwidman]

Originally Posted by arecuk

yes, thats why I want to do - change cables for stereo, vhp, gps, lights and other small devices ... I dont plan to change battery wiring or alternator wiring ... just want to understand how it is done and whether it is done in a right way ... hence, my original questions

I will take one more stab at this and then I'm out.

"Electrician" is a trade. A skilled trade that takes years to learn. You can't ask a few questions on a web forum and expect to come close to being one.

If your stereo has an installation sheet, follow it but without some background you won't know where to tap in for power, where to connect the memory lead and where to connect the ground lead.

You were given a suggestion to buy a book. Buy the book, study it and see if you understand it. If you do, go ahead and install your stereo. If not, study the book again. You will need to understand ampacity, overcurrent protection, resistance, voltage drop, wiring practices and a few other things. You will need some specialized tools and to know how to use them correctly.

I'm not trying to insult you, I'm just trying to keep you from setting your boat on fire or damaging things.

[Ziggy]

1. Definitely buy a book on marine electrics.
2. Are you sure the negative alternator port goes to the switch? Normally it would be the positive (often marked "B" or "B+") going to the switch.
3. Otherwise, the wiring you describe is typical of 1970s and 1980s boats. It's not the best arrangement, but it's simple and it works

[rob67]

Hi
Have to throw my 2 cents in. I agree with all the other posts. If you see a rats nest of wires hire a professional and learn the abyc standards for wiring dc. I bought a old boat for a project and what I found hidden would make you run, I have the back ground to do the job and I ended up with 2 bags of junk wire. tore it all out and rewired to abyc standard (both ac and DC). As you can tell most people won't advise on electrical because it can get quite complicated and potentially dangerous .
good luck

[rob67]

hi
Found this link on another thread download this and start reading

http://www.mojaladja.com/upload/Boat...l_Handbook.pdf

This will answer a lot of questions

[Group9]

Get Nigel Calder's book on boat maintenance and repair. You'll be glad later.

[arecuk]

thanks guys, definitely I will study first before I go deep into re-wiring ... I understand the complexity and knowleadge required

rob, the link provided does not work:
- http://www.mojaladja.com/upload/Boat...l_Handbook.pdf

[arecuk]

one more thing - grounding/bonding seacocks or not? in my CD28 all bronze seaconks are connected to the engine, to the same point as negative port of batteries

see here:
Marine Grounding Systems | West Marine
Bonding and Electrolytic Corrosion Due to Hot Marinas
Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.

[four winds]

The large wire( usually red) from the alternator is the one that goes to the battery switch.

It charges whichever battery is selected from there through the battery cable itself.

The alternator ground wire does not go to the battery switch.

[rob67]

The link I copied is from the liveaboard thread, title is 12 volt bible. I tried the link from there and it downloaded fine so probably when I copied it I screwed it up. Go there and it should download fine.

As for your through hulls things have changed a lot in the last 10 yrs for grounding and bonding rules.
If west marine says isolate then I would isolate.West marine quotes the ABYC standards which are also the USCG standards for pleasure boats , also standard for CCG in Canada for new boat builds. Everyone says to buy this book or that book but if you don't know the proper standards for installation these books are mute. all of your questions can be answered by getting the ABYC standards.

My boat is a 1966 which I bought for a project I have rewired both the AC and DC to ABYC standards. My Insurance company informed me that if I hadn't they would not have insured me. Just by what you described with your boat I would rewire everything including battery to engine wires with marine grade wires. The way your charging system is set up you must alternate between 1 and 2 on your bat switch to charge both batteries.
what year is your boat and where are you located.
I have a copy of the standards if you are interested I could scan and send you a copy just send pm
good luck
Rob