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TollyLucia 03-01-2016 11:34 PM

Help me design an electrical system for a "Wanna-Be Trawler"
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Hello everyone, I've been reading this forum for a while now among others on the internet. Although I know my boat isn't exactly a trawler, you guys seem to know your stuff and I believe would have the closest (compared to say, center console forums, etc) advice I can find to what I want to do. Also please forgive my ignorance, I am asking, no begging for help here.

Well, without much more, here's my boat. A 1979 Tollycraft 26. She's got twin gas 3.8L GM V6's. No generator or air conditioning. Batteries completely shot. I should have mentioned, I am doing a complete restoration.. so almost anything is possible (within reason). Many of my projects on the restoration are started (engine's rebuilding, new fuel tanks, interior, etc). I have started to contemplate my electrical system, now would be a good time to start as the boat is pretty much apart.

Goals for my boat:
1. NOT living aboard
2. Stored on a trailer
3. Will be used for 1 to 3 week trips. These will be mostly spent anchored out. But several nights of a 3 week trip would be in a marine, on shore power.

Goals for my electrical system:

1. Small air conditioner, 8 to 15 amp/hour range
2. Small refrigerator
3. Anchor windlass, small
4. Interior and Exterior lights
5. Electrical equipment - Radios, GPS, small computer, etc
6. Bilge Pumps

Operational modes needed:
1. Underway - two engines, I can have two alternators.. hopefully large enough to power everything above by themselves?
2. Shore power - Hopefully all systems could be powered via shore power?
3. Not underway - Generator. I know the AC draw will be the hardest to manage. I need help here.

Here is what I am thinking, and PLEASE, correct me if I am just flat wrong.


1. Properly sized inverter connected to 1 or 2 250+ AH batteries.
2. Couple high AMP alts on the engines to charge the batteries underway.
3. Battery charger to charge batteries from shore power when connected.
4. Generator to charge batteries when at anchor.
5. Run all AC loads always off inverter / battery(s) always. (Big Question here)
6. DC loads off batteries.
7. Myriad of switches or auto switches to accomplish this.
8. Start batteries for engines thrown in somewhere..

Help needed. I'm ready for a thrashing. :hide:

dhmeissner 03-02-2016 01:21 AM

Welcome aboard,

Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems by Nigel Calder | 9780071432382 | Hardcover | Barnes & Noble

Boatowner's Illustrated Electrical Handbook / Edition 2 by Charlie Wing | 9780071446440 | Hardcover | Barnes & Noble

Boatowner's Illustrated Electrical Handbook / Edition 2 by Charlie Wing | 9780071446440 | Hardcover | Barnes & Noble

The 12-Volt Bible for Boats by Miner Brotherton, Edwin Sherman, Charlie Wing | | 9780071392334 | Paperback | Barnes & Noble

caltexflanc 03-02-2016 06:04 AM

Read the first few chapters of the Calder book linked above, then come back here if you till have any questions. Otherwise you will end up more confused than ever. Some of us may seem to know our stuff, but Calder actually does know his stuff

O C Diver 03-02-2016 06:45 AM

Welcome to the forum! Best of luck with your project!


TollyLucia 03-02-2016 07:05 AM

Thanks for the info guys. I have ordered two of the above mentioned books. Thanks! Any input would still be appreciated. Glad to be here.

FF 03-02-2016 07:34 AM

For a trailer boat , weight is a dirty word.

And I just read on the Trojan battery site that they consider their batts to loose 4% per week.

I would think the overpriced AGM might be best for a trailer sailor where it might be a while before plugging in.

kulas44 03-02-2016 08:00 AM

X2 on the books, Calder especially. Keep in mind that 12 volt DC used for AC loads (inverter) is not terribly efficient, cabling is large and loads are large. Connections can become a source of problems. 24 volt would be better but usually doesnt coinside with whats there. 48 volt would be ok, alternators are available as are inverters. Amperage would be much less on the DC side. Inverters are more efficient at 48 volts. You would need to step it down for 12 volt loads. Easily doable.

koliver 03-02-2016 10:26 AM

Why put in AC power at all? Your systems don't need it, unless you are boating where Air Conditioning is absolutely a must have.

Our first cruising boat was about that size, a 30' sailboat, and we cruised it 11 years without any shore power/generator. Simply didn't bring aboard anything with a power cord. That included winter cruising, so I added a Dickinsen diesel heater. Battery charging was handled by the engine alternator. Keeps weight down too.

Portage_Bay 03-02-2016 10:36 AM


I'm currently re-wiring the AC side of a '71 Tolly tri-cabin. I started with what I need the final system to do, studied the books mentioned above then tore out the old stuff.

I knew I wanted to use Blue Sea Systems There are other good systems but Blue Sea is good quality and in common use in my area. Their catalog can be downloaded and is a great resource.

When I have my "perfect" system design roughed out I will have an experienced marine electrician look over my boat and plan. I'll then pull the new wires, mount the new hardware, label everything where it goes and bring the electrician back in for a final approval before I hook it all up.

DC is another time, it's a complete disaster and will need much more thought and effort.

kulas44 03-02-2016 12:19 PM

I have to agree, if you dont need air conditioning AC power is not neccessary, or even desirable. Gas (propane) for cooking, engine for hot water, everything else can be dc. As an aside, even the aircon could be configured to run off the engine (s). The 3.8 chevy engine comes with the neccessary brackets in automotive form. IIRC it uses a Sanden compressor. All of the neccessary items can be sources easily and cheaply at about any automotive recycling center (junk yard). One major benifit being the newer serpentine belt arrangement. The biggest problem with this is that you need to run a big engine to do it. Not so great at anchor, and inefficient to boot unless your cruising.

Portage_Bay 03-02-2016 01:00 PM

Please, do think carefully about using automotive electrical components in a gas powered boat's engine compartment.

I'm no automotive AC tech, but I do know there are electric components used in controlling the AC system.

Difference between "marine" parts and common automotive parts - BoatTECH - BoatUS

FlyWright 03-02-2016 10:37 PM

With gassers, you need to be extremely careful to ALWAYS install components that are compatible with operating in a marine gasoline powered ER. That should always be Rule #1 with gasoline engines.

kulas44 03-03-2016 08:13 AM

I assume the starter is a "marine" unit. The alternators can easily be specced as "marine" if thats what you want, they are the same case anyway . I was just pointing out that it would be cheap and easy to convert the 3.8 v6 to the serpentine belt system. Personally, I would convert the entire engine to Vortek, new heads and complete injection system, if its not now. I dont recall if the V6 was offered with the marine injection system (external injectors) but the standard automotive system is very good.

Phil Fill 03-03-2016 09:42 AM

So what is wrong with the existing wiring? Tollycraft already has dc and limited ac wiring. You might have to install additional bigger house batteries and a portable gen that you plug the shore power cord into. Change modify what is there already, :confused:

FF 03-03-2016 02:28 PM

Using a gas engine as a noisemaker to run Air cond on rare occasions should not be a problem.

Gas does not suffer as a diesel does from underloading , and 1000RPM or so is usually very smooth and quiet.

With a service life close to 4.000 hours a couple of days of ideling should not be a bother.

prairieoyster 03-04-2016 08:57 PM

Hey!! Im in the same boat!!
This thread will be perfect... you guys can help out 2 at once. I too am in the process of restoring a 1981 Tolleycraft 26'.
Mine has a detroit diesel 8.2L and V-drive. I have that sorted out I think....

but electrical is going to be an issue.


FlyWright 03-04-2016 09:00 PM

Different components in the ER when considering gas vs diesel. Also, it's a different system with a single vs a twin, unless you have dual alternators on that Detroit.

Do you have a generator?

prairieoyster 03-04-2016 09:09 PM

Calder's book is available on my kindle for 55 bucks Canadian. Woot!!

prairieoyster 03-04-2016 09:13 PM

I'm trying to decide how big an alternator to get for the DD. how big a battery? 2-12volts and a seperate bank for cabin?
No generator...but considering building in a small Honda for power.

kulas44 03-04-2016 10:19 PM

Get the real book, nothing beats turning a paper page. Nothing beats digging out the "book" and looking up the info you need. Nothing beats sitting on the boat reading the "book" on paper, the feel of it in your hand and they way it smells after having been there awhile. The oil and grease stains and maybe, if its lucky, some electrical burns. Old service manuals come to mind, heavily thumbed, dog eared pages, Toombs of knowledge, especially if they have been "notated" by previous users.

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