You need to get an LED bulb that matches up with what you are trying to do - a lot of these bulbs are made for automotive backup or turn signals. That won't work for marine use - you need a 1004 type bulb. Look for an bulb with 360 degree LED coverage.
Or you can do like I did and make up your own for a couple bucks. I will try to assemble one this week and post the instructions and pics on this website. If you know which end of a soldering iron is hot, you can probably do it!! No need to spend $100+ for LEDs for your boat.