Charging can be a handful


Tablets, smartphones and small laptop computers can help make life aboard easier and safer. These devices help us stay connected while sailing and they can help us navigate, watch the weather, and even act as anchor alarms. Battery technology has improved as well, but at some point every one of these devices will need a recharge.

Keeping the batteries in all these devices charged while afloat can be a challenge. At first thought it seems fairly straightforward, just plug the device into a car charger right? Anyone who owns a boat, however, knows nothing is ever that simple. Unfortunately this also applies to keeping our portable devices fully charged. Almost all devices are designed to be charged from a 120-volt wall outlet as found in most homes. The problem is that when we are away from shore we do not have that nice, steady 120-volt outlet available and when we do, it may not prove to be the most energy efficient way to charge things up. The simpler solution is to use a 12-volt car charger. The problem is most car chargers are not as efficient as home chargers. Many 12-volt car chargers will not supply the power needed to quickly charge a device, thus drawing out charging times.

A smartphone recharging using an AC adapter.

Before beginning to think about charging options, it helps to understand just what is needed by our devices in order to get and keep them charged. Today’s tablets and smartphones have high-capacity batteries that give long run times; this however can be a double-edged sword in that it can take longer to fully recharge these batteries. Knowing just how much power is needed for your device will help in selecting the best charging solution for use aboard.

Some faster than others

Not all charging sources are equal and some will charge faster than others. We want to keep charging as efficient as possible so as not to waste power while at sea. Most of today’s small electronic devices use a USB-type charger which at first would seem to simplify things. We all know nothing is simple in the world of electronics and boats. Not all devices use the same charge amperage and not all aftermarket chargers are rated the same. Most tablets require 10 watts or 2.1 amps to correctly charge. Smartphones and other smaller devices only require five watts or 1.25 amps. I have heard complaints from some boaters that even after being left on a charger overnight their devices were still not fully charged. Others have complained that when using the device for navigation while plugged into a charger it still lost charge to the point of shutting down. Understanding what charger is best for your device will help avoid disappointing results.

Normally the best option for the fastest charging will be to use the 120-volt wall charger supplied with your device. This works well in the slip with shore power available, but as soon as we leave the dock this approach gets more difficult. There are options for using 12 VDC for charging, but care needs to be used when selecting a 12 VDC charger as not all aftermarket chargers are equal.

A charging outlet on the binnacle allows for handheld recharging in the cockpit.

Before getting too involved in what power source to use for the charger, it helps to understand a bit more about the charger and the needs of the device being charged. As mentioned, most of today’s devices use a USB charger. When the USB standard was first developed it was thought that the power would be supplied from a computer. Because of this the power output was limited so as not to overload the computer’s motherboard. The most common USB standard is USB 2.0 which is set at a maximum charge rate of 0.5 amps. The newer standard of USB 3.0 has a higher charge rate of up to 1.2 amps. This can be important to understand as some devices will “talk” to the charger to determine the USB version of the charger.

Today’s newer, power-hungry devices require more power than what the older USB standards can handle. Many OEM chargers that come with a device will provide the higher output needed to quickly charge the device. Additionally some devices will communicate with the charger to set the best charge rate for the device. This usually only works with the OEM charger supplied with the device. When used with an aftermarket charger, many devices will default to a lower charge rate. Others will take all the power they can get, particularly if there is no data signal detected. When using an aftermarket charger, it can help to replace the data cable supplied with your device with a “charge only” cable. This is a cable that has had the data pins modified or removed to trick the device into accepting as much current as the device can take. This combined with a higher-output charger will often charge your device as quickly and efficiently as possible.


Two types of chargers

Basically there are two types of charger outputs available for charging, five watt and 10 watt or 1.2 amps and 2.4 amps. Most tablet devices require the higher output of 2.4 amps to charge in a reasonable period of time. One has to be careful when selecting a charger as manufacturers seem to go out of their way to confuse the consumer when labeling these products. Many chargers have duel ports so you can charge two devices at the same time, but this can add to the confusion. Many duel port chargers are rated at 2.4 amps, the problem is that, that is the total amount available to both ports. If you have two devices plugged in, the output will only be 1.2 amps per port. Some chargers labeled at 2.4 amps total will only supply 1.2 amps to each port even when just one port is used, while others will allow 2.4 amps on only one used port. Others will allow 2.4 amps for one port and only 1.2 amps for the other. Confused yet?

A USB charging unit.

It gets worse, as many chargers are simply mislabeled. I purchased a charger labeled for 2.4 amps on the package, but when I looked on the charger it had a labeled output of up to 1 amp. Still some others I looked at listed the input power of 2.4 amps, but the output was less than that. To get good results it is important to read and understand the rating of any charger before purchasing.

Now that we understand a bit more about how a device is charged, it is time to look at how this all fits into the best option for charging aboard. We know that the best charger is usually going to be the AC charger that came with your device, but we also know that using an AC charger on a DC system with an inverter may not always be the best way to go.

At first thought it would make sense to get one of the USB chargers designed to plug into a cigarette lighter outlet, or as they are now called “power outlets.” The problem is these devices can vary wildly in their output despite their labeling. Most of these plug-in chargers are often overrated in just what they really supply. This is not a problem with smartphones and smaller devices, but can become a real issue with iPads and tablets that require more power. It is also surprising that different chargers rated at the same output will actually charge at much different rates. In units I have checked there can be as much as 0.5-amp output deference between chargers that are advertised as being the same. Before running down to your local big box store to purchase a plug-in charger, check online reviews of these products and select a charger that has good reviews for the best results.

Permanently installed USB chargers or 12-VDC panel mount chargers are now available as well. Blue Sea and Sea-Dog along with a few other companies, market panel mounted USB chargers that are a good alternative to 12-VDC plug-in chargers. Like the plug-in type these chargers tend to come with dual ports, so care needs to be used when evaluating the advertised power outputs just as with the plug-in chargers. Most will have a total output of the two ports listed. I particularly like the idea of mounting a USB charger near the helm station. If you use a tablet for navigation this would very helpful. Oddly, for some reason, the makers of most panel mount chargers feel the need to add a power indicator light.  This light remains on whether the charger is being used or not. Admittedly these lights do not use much power, but it could add to the overall drain on a boat’s electrical system, so it may help to add a switch to depower the charger when not in use.

Two typical small, low-power inverters.

Generator and inverter

As mentioned above, sometimes using a device’s OEM 120-volt wall charger is often the quickest way to get back to full charge. Away from the dock there are really only two practical ways to use a 120-VAC charger: via a generator or an inverter. For boats equipped with a generator it does not make sense to run the generator for hours on end just to charge one or two small devices. Even if charging a few devices at the same time this would be a waste of fuel and energy for the small amount of power needed. If you are using your generator for other uses like air conditioning then this would not be a problem.

The next best option would be to use an inverter with the 120-VAC charger. Although this may work, once again it may not be the most efficient use of power. A USB charger operates at five volts DC, so it does not really make sense to convert 12 VDC to 120 VAC and back down to five VDC. This is because there is a loss of efficiency with any inverter and this loss is greater the larger the inverter and the smaller the power draw. For inverters to work well they need to be matched to the load. This means you would not want to use a large 2,000-watt inverter just to run a 10-watt charger. If using an inverter just to charge small devices, use the smallest inverter you can find, 100 watts or less would be best and this would be enough to charge two to three devices at a time.

A small, 75-watt inverter useful for charging a single phone or tablet.

Finally it helps to power down your device while charging or at the very least dim the display or place it in sleep mode when not actually using it. It may also help to check the device software settings as some will allow you to change the settings for a higher charge rate. In general if the device’s software is set for “Charging (USB)” this will be a lower charge rate. If it is set for “Charging (AC)” this would allow for a higher charge rate. Select a good quality cable with as heavy gauge wire as you can find and keep the cable as short as possible. This is another good reason to install a charger at the helm station when using a tablet for navigation.

As you can see, charging portable devices can involve some thought. With a little research and careful selection of a charger, however, you will be able to find a solution that best fits your needs. With more standardization in charging protocols a good charging system will work with many of the different devices you and your crew may bring aboard.

Capt. Wayne Canning lives on his Irwin 40 Vayu, in Wilmington, N.C. A marine professional for more than 35 years he is now a full-time marine surveyor, freelance writer, and consultant/project manager on major repairs. Canning also runs websites for those restoring project boats. Visit and for more information.

By Ocean Navigator