Not that heavy
Plastic hatch boards will certainly weigh a lot more than plywood, but they still aren't going to be very heavy.Here are some options you might think about.1) Make the hatch boards out of 1/4 inch plexiglass and put a teak frame around them that slides into your grooves. Saves weight and cost and gives it a unique look. Requires some wood working skills to make a picture frame around your hatch boards.2) Use the 1/2 inch plexiglass and cut them into 3 equal hatch boards rather than the two you currently have. Cuts the weight down for each piece, but you have to handle 3 pieces. Bigger boats have three3) If you use plexiglass, make sure you bevel or rabbet the edges where the two hatches fit together so you have some sort of overlap. Otherwise they will leak into the cabin during a rain.Good luckWard