I will tell you low 70's with the sun beating down is still quite warm ( I'm in Florida) I mean its a beautiful day and I am thrilled, but the sun is so strong.
I would bring a pair of jeans and a sweater or jacket for the ship. But you will be comfortable in shorts if its a sunny day.
When we have a cold front and its in the 50-60's in the morning here(South Florida), by lunchtime I am usually regretting the sweater.
The Caribbean is about the same as Florida.