The Official Magazine of the Bluewater Cruising Association

Chartering: Electrical Considerations

Melissa “Missy” Gervais

As You Wish
Bayliner Avanti 34
October 7th, 2021

Chartering is a great way to see different parts of the world by boat; it is also an excellent opportunity to visit local waters on a larger boat with your extended family.  We work with several chartering companies and, over the years, have put together some things to consider before you let go the lines.

Review The Boat

The check-out is usually done the morning that you arrive at the boat; however, it might be a good idea to have the charter company send you an equipment list a few weeks ahead of time.  This will allow you to familiarize yourself with the electrical and electronic components on board. As with most boats, the largest power draw is the refrigeration.  An average boat fridge draws 50 – 75 amp-hours per day at 12 VDC. If you are motoring every day, then the batteries will have a chance to recharge; however, if you want to anchor or simply sail, then a larger battery bank will be helpful.

Keep your beverages in a separate cooler and not in the fridge.  This will greatly reduce the number of times the fridge door is opened and will cause less power drain on the batteries running the fridge.

Battery Capacity and Charging System – Know Before You Go!

Once you have determined the amount of battery capacity you have on board, it is time to look at how those batteries will be charged. What size charger do you have onboard? Your charger converts AC to DC power and allows the battery to be recharged when there is an AC power source. The charger can either be powered while connected to shore power, or if the onboard generator is running. Knowing the size of the charger and your battery bank capacity will allow you to determine how long the charger has to run to recharge the house batteries.

For instance, if your charter boat has a 40 amp charger, the house batteries are 400 amp-hours (e.g. 4 golf-carts wired for 12 VDC bank), and you don’t discharge the batteries below 50% of capacity, how long will it take to recharge the house batteries? The charger will run at full capacity, i.e. 40 amps, only while in bulk mode. With a lead-acid battery (e.g. flooded, AGM, or gel), the bulk mode is approximately between 0% to 80% of capacity. Considering that your batteries are being recharged at 50% of capacity, you have 30% of capacity to get to 80%. Within this 30% of bulk charging, the 40 amp charger will work at full capacity. Doing a little math, 30% of 400 amp-hours, is 120 amp-hours of batteries to recharge. The 40 amp charger will take at least 3 hours to recharge those batteries to 80%.

Another way to recharge the batteries is with an alternator. What size is the alternator?  Remember that unless the alternator has an external regulator, you will generally get about two-thirds of the rated alternator output as a charge. For instance, a 120 amp alternator with an internal regulator will output about 80 amps at full throttle.  The slower the engine speed, the lower the alternator output. Running the engine at near idle to recharge the engine might only give one-third of maximum rated output. This is why running the engine at idle, while at anchorage, is quite time-consuming as well as being very hard on engine wear and tear.

Familiarize Yourself With All Of The Systems And Ask Questions

Before you leave the dock, there are a number of things to look for. Inspect the shore power cord – are there signs of wear?  Next, take a look at the batteries, is there corrosion on the battery posts, is the wiring organized and labelled.  A quick peek behind the main panel is also a good test – it should be neat and tidy.  These are all good indicators of the care the boat has received.  Familiarize yourself with the operation of the battery monitor, gauges, navigation, anchor lights, and refrigerator.  Turn on the inverter and test a few appliances and outlets.  You will maximize your time away without running a charger or the alternator if you are selective of what is on at the same time and manage your DC power draw.

Ask if the refrigerator is AC, DC or both?  Does it run all the time or just when you are motoring?  Also, is the boat equipped with LED lights or halogen bulbs?  If they are LED then you can afford to leave them on longer.  Where are the spare fuses?  Also, locate the tool chest and open it.  We have spoken to a number of charter clients who go to get tools and they have been misplaced or lost.

When there is a problem, it is quite simple to call the charter company.  However, it may take some time  before they can get to you.  Preparing ahead of time can be the difference between a good vacation and a fantastic vacation.

Cover image: Pixabay license


  1. Cliff Bowering says:

    This is an excellent article. Our last charter was 7 years ago when we chartered a 41 ft Beneteau in the BVI. We had come to sail and we sailed as much as possible every day of our 8-day charter. This meant that we had to endure the sound of a diesel at fast idle for 4 hours every evening in a peaceful tropical anchorage. The engine only had a stock 35-amp alternator and there was no auxiliary generator or solar panels. The two deep cell 100 ah batteries were brand new (at our insistence). Every time we are tempted to charter again, we think of those less-than-peaceful evenings at anchor. A proper 125-amp alternator and a smart charge controller seems to be a rare commodity on a charter boat.

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