You've been planning your cruise for months. You've stocked up on sunblock, stowed away your passport and ironed your best Hawaiian shirt. But have you purchased travel insurance?

Travel insurance for cruises may seem like just one more expense, but experienced travelers know insurance is essential to protect their investment.

Here are the three reasons you need to buy cruise insurance for your next cruise vacation.

1. Cruise lines have strict trip cancellation policies.

Think your cruise company will understand when your plans change suddenly and you have to make an emergency trip cancellation? Probably not. They count on having their cabins filled when the ship leaves the dock, so many cruise lines have very strict cancellation policies.

In many cases, no refunds will be issued for trip interruptions, lost tickets, flight delays, no-shows or missing the check-in before departure. Even making a minor change to your travel plans may be considered a trip cancellation.

It's tough, but that's the way it works. That's why cruise lines strongly recommend passengers buy cruise insurance. Consider an insurance policy that covers trip cancellations and trip interruptions.

2. Medical emergencies happen on cruise ships, too.

When you're lounging on the sun deck, it's easy to forget you're hundreds of miles from the nearest hospital. Even if you're in perfect health, you can never predict when you might break an ankle, suffer a heart attack, or come down with the flu.

Ships' doctors are equipped to provide prompt medical care, but for serious health emergencies, passengers may need to be airlifted to the closest medical facility. You don't want to see the bill for that, trust us. Some cruise travel insurance plans include coverage for accidents or medical emergencies.

3. Cruise travel insurance lets you relax.

The whole reason you wanted to go on a cruise vacation was to leave life's worries on shore. But it's tough to relax if you're worried about bad weather, illness, lost luggage, missed flights, theft, international emergencies or that big deadline at work. A good cruise travel insurance policy will offer coverage for the unexpected. Make sure you review your insurance plan carefully before you buy because not all plans offer the same coverage.