Continuing with Tom's logic, Pat increased his boat size first 3 feet, and a 27 would be an increase of 2 feet, or 2/3 the initial jump.
Assuming Pat steps up in increments of 2/3 the prior jump:
#4 will be 1.33 feet longer, or 28.33 feet.
#5 will be .89 feet longer (10.7 inches), or 29.22...