There are a few things to consider when determining how tall your navigation lights need to be on your boat. First, you'll need to know the height of your mast. The taller your mast, the taller your navigation lights will need to be. Second, you'll need to know the length of your boat. The longer your boat, the taller your navigation lights will need to be. Finally, you'll need to know the width of your boat. The wider your boat, the taller your navigation lights will need to be.
Assuming you have a standard size sailboat, most likely around 30 feet long and with a mast that is around 50 feet tall, then your navigation lights should be around 2 feet tall. But again, it really depends on the specific dimensions of your boat. So if you're unsure, it's always best to consult with a professional or look up the specific regulations for navigation lights in your area.