A porthole is a window that allows light into your boat. Installing a porthole is not difficult but it must be done carefully because if it is not sealed properly, water could leak into the cabin. Portholes in older boats were made of shatterproof glass but modern manufacturers now make portholes out of plastic or fibreglass. Buy your porthole from a reputable nautical supplier; it should come with comprehensive instructions and everything you need to complete the job.
Choose the best place for the porthole. You need to do this carefully, bearing in mind that the frame of the porthole will need to match the curvature of the hull.
Mark where you are going to need to make the hole for your porthole. If your unit has come with a template you should use that; if not, make your own by laying the porthole on a large sheet of paper and drawing around it.
Cut a hole in the hull of your boat. Choose a saw that is appropriate for your particular boat depending on whether it is made from plastic or wood. You will need to drill a couple of holes on the inside of the area that you are going to cut so that you can fit the saw in and cut out the rest.
Secure the inside part of the porthole frame to the inside of the boat, according to the manufacturer's instructions, and apply sealant all the way around to make sure there are no gaps between the frame and the boat. Put the glass into the frame and apply more sealant to make sure there are no gaps between the glass and the frame. Install the outside part of the frame and seal in the same way. Follow the manufacturer's instructions for the best way to attach the frame. This will again depend on what your boat is made of. Make sure the seal is intact before taking the boat to sea.
Make sure there are no gaps in the sealant between the boat, the frame and the glass.