Electrical System requirements for Bahamas cruising - SailNet Community
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post #1 of 7 Old 12-14-2006 Thread Starter
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Electrical System requirements for Bahamas cruising

I'm currently planning a 6 week trip from Mobile, AL to the Bahamas leaving in early May. The boat is a 47' ketch and we'll have a crew of about 6.

The boat is in good shape for weekend jaunts, but will need some additional outfitting for offshore and long-term cruising. We'd like the boat to be functional and comfortable, but want to minimize outfitting expenses. Once we get back if we're hooked (which I'm sure we will be), we'll take a more long-term approach to outfitting.

The head and galley, fresh water tank, etc. are all in good shape, but the electrical system will be something I'm going to take a serious look at. Here are the things I'm thinking about:

Daily power usage - what should we expect for lights, nav station, nav lights, water pumps, etc.

What about the battery bank size, type, etc.?

We have a very well insulated ice box, but no refrigeration - do we need it, and what should we expect power wise?

What are the best - and most cost-efficient (for the 6 week trip) means for recharging? A gas generator? wind generator? Solar? etc.

If anyone has suggestions on these questions - terrific. Alternatively, are there any good books or articles you recommend reading to get this information? I have the book "World Cruising Essentials" by Cornell, but it doesn't really go into the detail I'm looking for.

Any help would be greatly appreciated.


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post #2 of 7 Old 12-14-2006
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No single answer

Daily pwr usage is a function of the "etc" part of your question. It's pretty easy figure out the stuff you mentioned e.g., lights, but you should do a real energy usage table for everything you have or plan to have on the boat, pwr consumption of each and how many hrs/day usage to calculate total daily consumption.
Obviously, the battery bank size is a function of the above - double the bank capacity you expect to draw between charging as the conventional wisdom is to not use more than 50% capacity without recharge.
Refirgeration typically requires 5-6 AH so in a 24 hr day, you'd draw 50-60 amps - "your mileage may vary".
Re: external charging source for batteries - depends on how much room, sunlight, wind or gasoline you want to fuss with - too individual a choice for anyone to intelligently comment on.
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post #3 of 7 Old 12-14-2006
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I think you'll find many threads already here and in some other internet forums with details. A lot depends on how tech you want to get and what the budget is. More, on how ell you know the boat and whether you have a reliable system and good wiring on it, or kludge jobs from PO's.

Refrigeration is a major project in itself, and the single biggest energy drain on a boat. If you plan to add it--odds are everything will have to be upsized to handle it. Fifty years ago people didn't need it, but poll your crew. See if they can find enough information online and if they can live without fresh meat and ice cubes for a while, or if they'd rather ante up the costs of the reefer system.

The best way to do up an energy budget for your boat, is to actually spend time aboard with a clipboard and pencil. Go aboard after dark, note everythign you turn on, and note how many hours per day it will be in use, i.e. nav lights may be on 12 hours/day in the winter/spring. Also note the wattage or amperage for each device. If that means opening up a fixture to see if it has a 10-20-30 watt bulb, do so, because you'll need to note that for your spares list anyway.
Write 'em all down, do the math, you'll have an estimate in amp- or watt-hours per day when you are done. Then you have to decide how to feed that.
Wet lead batteries (more threads in the lists) can only accept a charging rate of 20% of their rated capacity, and should not be run down below 1/3-1/2 of their rating in order to get good life from them. So, if you burn 30AH per day with all the toys, and your battery bank provides 200AH, you might want to run something to recharge it every third day. If the battery bank is half that size, you'd need to charge every day. And sticking in the bigger alternator can't speed up charging, once the rate gets to 20% of the battery's rated capacity. It only boils electrolyte when it gets above that.

Take a good look at the wiring while you are at it. Does it look reliable? Was it tinned copper, neatly fitted? Or plain copper, now blackened, with taped splices? Never too soon to replace what you might want to, while you're still in port.

For one six-week trip, as a one-shot, simply buying the fuel to run the main engine for the extra hours--and use the motor so there's a proper load on it. A genset might be the next most effective, if you remember to manage monoxide problems, location, noise, and stowing gasoline. Solar is going to mean a higher dollar committment, which you might not want to make until you're sure you're going to do this again.
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post #4 of 7 Old 12-14-2006
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Aren't you the 1,2,3 guy?? Sorry...just couldn't resist.

There are lots of ways to go, but to meet your stated goals of: (a) outfitting the boat for the upcoming 6-week trip; and (b) minimizing costs at this time, with the possibility/likelihood of making more investments later on....

I'd suggest the following.

1. install an Adler-Barbour cold machine, air cooled, for refrigeration. It runs off 12v, is bulletproof, simple, easy to install, and costs less than $1,500.

2. upgrade your house battery bank to at least 400AH capacity. 600-700AH capacity would be even better if you have the room and the bucks. The most cost-effective system would be to use Trojan T-105 flooded 6V golf-cart batteries in a series/parallel configuration, combining them to make one large house bank.

3. be sure you have a completely separate engine starting battery. Keep this charged with a small device like an EchoCharger, which senses a charge on the house batteries and bleeds off up to about 15 amps as necessary to keep the starting battery fully charged. It needs no maintenance.

4. be sure you have a high-capacity alternator on the engine, with a smart multi-stage regulator to keep the batteries charged efficiently. This is an important item. Automotive-type stuff just won't do the trick, and will have you running your engine all the time to try to keep up with battery charging needs.

5. carry aboard a high-quality digital multimeter for all manner of electrical testing, including checking your battery system. Fluke makes several models which would do the trick, at a reasonable cost (under $100).

6. if you don't have it already, pick up a copy of Calder's "Boat Owners Electrical and Mechanical Manual", latest edition. It's the bible, and you're gonna need some "religion" out there.

7. be sure that all your electrical connections are clean and tight. This is especially important with the battery connections, alternator cables, starting cables, etc.

8. be sure that you use adequate size wiring, especially in the battery circuits and the charging circuits. Don't skimp on this, even though the price of good wire (marine, tinned copper, stranded) has recently gone thru the roof.

9. while you can get by OK for this trip without solar, wind generator, or other generator power, it's nice to have a means to charge your batteries that is completely independent of your engine's alternator. An inexpensive, very easy, and very workable solution for the short run would be a small Honda gasoline generator, like their 2,000 watt model.

10. be sure you have a large enough smart charger to quickly charge your batteries when at dockside or with a generator running. I'd suggest a minimum of 50-75 amp capacity, multistage smart charger. A very good one which works well with generators and which has an excellent design and build quality is the Iota, with an IQ-4 smart charge plug-in. You can find these on eBay, or JackRabbit Marine. If you're going to go this route, consider the 75A model for your needs, both short and longer-term.

This list isn't exhaustive, but I hope it helps a bit.

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post #5 of 7 Old 12-14-2006
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Functional & comfortable but minimizing outfitting expenses... that is a paradox, I am afraid. Now stand back boys, pull out the check book, and let's talk turkey!!:

1) Daily power usage: About 140 AH/day conservative with no watermaker, 160 - 180 with. I think Cam (and my boat, a Catalina 400 with two kids, wife and worthless old dog) use the later pretty religously.

Offshore you will use the high end of that scale (or beyond) and will likely run the Genny a lot (if you do not have one). Otherwise, you will be running the main a whole lot. I think the radar pulls about 5ah, and chart 4-5. Autopilot, assuming you are in calm seas, about the same. If you get in a storm, a whole lot more. Check you books for more info on that.

2) Battery type, size, etc: THis is a very debated subject on this forum. No one is alltogether wrong or alltogether right (well, except me of course, I am perfect). So, here is my philosophy: Bloody batteries are your lifeline (no pun intended). DOn't skimp. With that large of a boat, I would have close to 1000 AH and a seperate start battery. 4-4D's or 8'D's would give you about 500 AH useable. That is about 2-2 1/2 days between recharging, assuming no outside power sources and everyone remembers to turn off the lights. Not all batteries are created equal... especially (ESPECIALLY) AGM's and gells. I have had outstanding service with Lifeline AGM's. There are some advantages to buying wet cells, but I really don't care to name them because I think an AGM far outweighs them (the exception maybe being a really high end wet... maybe like a ROlls or other commercial batt... but if you don't like the prices of AGMS, you really won't like the prices of those). SO, buy your batteries once, and buy the good ones. Go Lifeline AGM.

3) Refrigeration. Do you need it? I sure do. But you know what, the sailors of old traveled the seas with salted meat and ate month old apples. Didn't use toilet paper either. So ask yourself, do you fall into the "No-toilet paper" category or do you fall into the "I think I will have some level of civilization and comfort on my boat" category. I have two boys and a wife I love. I want to keep them. Thus, I chose the later.

As far as draw, about 50ah/day. That was included in the budget I gave you earlier.

4) Best means of recharging? All of them have a place on a boat with the budget. I am NOOOO fan of the portable gas generators. Used one once. Then realized I would prefer to have it as an anchor versus litening to that piece of crap all night (not to mention having to fill it up with gas, hauling it up on the boat, looking like a camping trailor on the water, etc). I bought a good diesel genny. I have used Matervolt and Fisher Panda. They are both good, but the Master seems the best at this point.

AH/Day - How much diesel do you have?

Solar. I use 4-Kyocera 130's and a Outback MPPT Charge Controller. THere are others. I wont regurgetate everything that has been said on many other threads (including one that is active right now on Gear and Maintenance), but don't skimp and buy cheap ones. You will hate them and they won't work right. If you go solar, do it right. ICP and Kyocera seem to have the market.

AH/Day. With 4 Kyoceras and the Outback, over 100, less than 200. Depends on the clouds, temperature, etc.

Wind. I bought a Air-X. Some people love them, some hate them. It is without a doubt the cheapest source for power, but it obviously is going to be worthless on light air days.

AH/Day - Who knows... depends on the wind. ABout 7-10 Kts minimum. If it blew all day, over 100 but less than 200.

A high-output Alternator (100-120 minimum with 4-D's) with a multicharge controller. Balmar seems to have this market. If you have a cheap alternator, pull it off and stick it in the hold (as a back-up) and go buy a good one with a Multistep Charge Controller.

5) Book reccomendations. Ahh, you want details? Let me point you to Nigel Calder's book on Mechanical and Electrical Systems. It will give you more details than your brain can absorb. That book has a place on every boat, along with a DVD of Captain Ron and a little Marley/Buffet.


1) Diesel Genreator: About $15,000. This probably does not include install. DO it yourself.

2) Solar: You can get out for less than $4500-$5000 if you already have the arch. No arch? Tack on another 3-4 grand.

3) Wind: About $1,000.

4) High Output Alternator and Charge Controller. ABout $1,000.

5) Nigel Calder's book. About $30.

6) The hospital bill after you read this thread: Priceless.
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post #6 of 7 Old 12-14-2006
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Pelham... The refrigeration/food issue is also dependent on where you'll be and how you will be living aboard on this jaunt. Canned goods get old on a crew quickly...there is just so much DintyMoore one can swallow!! If you are gonna pull in nightly somewhere and dinghy in to a restaurant or tie up at a marina then you don't really need a fridge...or the batteries and charging system needed to support it. If you are going to the Abacos...you can have fresh meat and veggies from the supermarkets there...not so in the Exmumas or in the out islands so where you cruise can also affect this issue.
If this truly is an "experimental cruise" then you would probably be better off financially with the stop and stock method than investing in a fridge and all the other stuff. On the other hand...if the admiral isn't convinced about the cruising life...the more you make it like a camping trip...the less she will like it! (Yeah...I know...probably a sexist comment...but also true in the majority of cases! )
I second the suggestion of getting a Honda 2K ...if you don't like cruising...you can use it at home when the power goes out!!
Now let's move on to a discussion of the anchors and rode you will need, followed by a selection of a dinghy....
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post #7 of 7 Old 12-18-2006 Thread Starter
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Thanks to everyone for the good suggestions.

Nigel Calder's book is now on the way, and should be here by Christmas and I'll be taking a look into the batteries and different charging options.

Solar is probably out of the budget this time around given the high initial cost (I know it would probably pay for itself in the long run). I'll need to consider all the options, but I'm thinking for just 6 weeks, we'll probably end up with the small Honda generator so we can avoid just starting up the diesel for charging batteries.

Thanks again!

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