At 0.000039 per inch time 96 inches, and a temperature swing from 30F (easy winter day) to 110F (heatwave) that's about a 0.29" change, but remember that surfaces exposed to direct sunlight often get hotter, i.e. 140-160F so a movement of 1/3" is certainly within the relam of likely.
Any reputable glazing supplier will have engineering diagrams available on the web, showing correct and incorrect installation
schemes to use for their products, allowing for thermal expansion and waterproofing. The bottom line is that the glazing MUST be free to move, and sealed in a way that allows it to move past the seals
, or it will be damaged by ordinary thermal movement and other stresses.
In a boat (or simply a portlight) "built to a price" the builder
may not care if the glazing crazes or leaks
in ten years, by then it is someone else's problem. But the problem, and the answers, are extensively documented.