Whether or not air conditioning is needed is a very subjective topic. The rule of thumb I generally use is if you use air conditioning in your home when it is 80 to 85 degrees outside, you will very definitely want it when aboard a boat.

If you are the type that is comfortable in that temperature with just a fan, then it is not needed.

The type of yacht you will be aboard as well as the airflow inherent to that particular yacht will also make a difference.

I have never used air conditioning in my home. A fan is good enough for me.

Hope this helps.