There's a certain amount of dampness, especially if you are sailing to the Caribbean - just hang the clothes and the wrinkles will fall out. You can also hang a few items in the bathroom while you shower. For stubborn creases, dampen the area and then hit it with the hairdryer (particularly good for cotton knits).
If you have something that REALLY requires ironing (e.g., anything linen) - seriously consider leaving it home. If you must have it, sent it out to be pressed - only 1/2 the price of cleaning and worth it IMO (spoken as someone who has not owned an ironing board in over 20 years).