Skin your pineapple, then cut it up into bite sized chunks. Place it in your Ninja, food processor or Vitamix and blend until smooth. Set aside.
In a small pot, combine water and sugar and heat just until the sugar melts. Allow mixture to cool.
Add sugar water to your pineapple and blend until smooth.
Taste mixture for sweetness. Depending on how sweet your pineapples were, you may either think the taste is spot on or you may want to add more sugar. If you want to add more sugar, combine equal parts water and sugar (eg, 1/2 cup water and 1/2 cup sugar) and heat just until the sugar melts. Cool and add to mixture until you get the flavor you desire.
For ice cream machine method: Place mixture in your refrigerator for 1 hour. Make sure that your ice cream maker bowl is frozen, then process as much as it will hold for 30 minutes or until nice and slushy. Serve immediately. Freeze leftover in a separate sealed container (never the ice cream maker bowl). When ready to enjoy it again. Allow it to thaw until you can begin scooping the sides and moving it around. You want it to be sort of slushy.
For freezer method: Pour your mixture into a container and place it into the freezer. Every hour give it a good stirring until it is nice and slushy. Serve.
You can also freeze it overnight, take it out and allow it to thaw. It will take about an hour to get to the stage where you can break it up and stir it all around to where it is nice and slushy.
You can also help it along by popping it in the microwave for 30 second bursts, just keep breaking it up and stirring until you get the right consistency.