As many of you do long deliveries or long distance offshore races the goal has been to extend battery life without recharging or using a photovoltaic device to keep your batteries topped off. The two choices to make are to purchase more expensive batteries such as glass mat or larger batteries to make them last longer or reduce the amount of current draw on the 12 volt system. I have done the latter on my boat by converting to LED lighting. I have done most of this conversion by trial and error so I wanted to pass on what I have learned. I have been using these bulbs for about a year without problems so I thought it would be appropriate to share my ideas.Its logical
The power consumption of my Northstar GPS is about 12 watts or 1 amp. Each navigation incandescent bulb uses 10 watts each or .83 amps per bulb so if you are sailing at night the power consumption does add up.
With two navigation lights and one stern lights this could add up to 40 watts. The red and green navigation LED's lights draw only .42 watts compared to the 10 watt bulb it replaces. The red and green lenses block about 70 percent of the light of the incandescent! The stern light draws 20 watts but it's LED replacement draws only 2.2 watts. Adding this together one can save over 37 watts in navigation lights alone. The interior LED bulb draws only .36 watts compared to the the 10 watt halogen light. One can see how these numbers can add up to significant power savings. Another reason for replacing your incandescent bulbs is because the LED service life is at least 10 times as long. Finally if an incandescent bulb and an LED bulb have the same type and condition, and the incandescent bulbs take the same amount of power from fresh batteries, the output will probably appear roughly equally bright. But the incandescent one will fade more rapidly when the batteries weaken. The LED one will continue working for many times the amount of time that the incandescent one does. The expected life of a battery is measured in amp hours. A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/2 hour, or 1/3 amp for 3 hours, etc., before dropping to 10.5 volts. If a battery can supply 5 amps for 20 hours then it is called a 100 Amp Hour battery.
Where to find these lamps
The stern light uses a 1157 base with two side tabs and two contacts on the bottom (see illustration above). You can see it is a 90 degree type bulb so the LED's are pointed out.
For the interior lights I have used an Wedge Base bulb (194/168 type) and have bent the wire leads out to match the configuration of the red lens halogen incandescent bulb. This bulb seems to work best since the LED's point into five different directions. I left in the white incandescent bulb in place since I will be most likely be using it with shore power or the engine running.
Fortunately most of the marine bulb bases use standard automotive sizes so it should not be difficult to pick that size fits the application. For those of you that have perhaps another bulb base this is a helpful link that can help determine what it is: http://www.autolumination.com/bases_filaments.html Hopefully this will help many of you get started.