An unreliable electrical system is seldom dangerous but can be a major inconvenience. The good news is that new, affordable technology and good old solid electrical engineering can combine to make a near bulletproof electrical system.

The first step in designing your electrical system is to measure daily consumption. Tally up the loads you want to run and the amount of time you want to run them. For example, running a 5-amp load for two hours a day will take 10 amp-hours of energy. You will likely come up with between 100 and 200 amp-hours in total.

An optimal onboard electrical system starts with a properly sized battery bank in a watertight box. This one has sturdy strapping to keep the batteries secure and three battery switches on top.

Billy Black photo

Size your battery bank to support the loads you want to run. Good battery-bank design conserves 70% of the bank capacity and allows a 20% factor to account for aging. A 150 amp-hour load would require a battery bank with a 540 amp-hour capacity. 

In most cases, the batteries you can fit in the space you have will not support the loads you want to run, so you will need to look for ways to reduce power consumption. A great place to start is with LED lighting. Lighting is a huge power consumer, but LEDs can cut that by a factor of 8 and provide the same light quality. You can likely replace the bulbs in your existing fixtures with new bulbs. The bulbs cost between $15 and $20 each, so you should be able to equip your whole boat for few hundred dollars.

Another good place to cut consumption is with efficient refrigeration. Refrigeration technology has drastically improved in the last 10 years. A small, high-efficiency compressor combined with a keel cooler makes for a great system. The keel cooler gets you all the benefits of water cooling, but with no pumps or plumbing. A modern system will noticeably cut consumption and you will have a really cold icebox.