Lewmar Size 3 Opening Portlight, Smoke Acrylic Lens with Flyscreen

Lewmar's been building ports and hatches since 1946, and the Size 3 opening portlight is one of those parts that quietly does its job for decades. It's an opening port, so it hinges out for real airflow through the cabin, then dogs down tight with a clip handle when the weather turns. If you've got a hot berth or a galley that traps cooking heat, this is the kind of upgrade you notice on the very first muggy night at anchor.

The lens is smoke gray acrylic. That tint does two things. It knocks down glare and cabin heat during the day, and it gives you a bit of privacy at the dock without blacking out the light entirely. The frame is silver anodized aluminum, low-profile and clean against a white cabin side. On the inside you get a white ABS trim ring that finishes the opening off nicely, so you're not staring at a raw cutout edge from your bunk.

Ventilation is the whole point of an opening port, and Lewmar includes a flyscreen so you can leave it cracked at anchor without inviting every mosquito in the anchorage below deck. The screen sits in the interior trim and pops in and out for cleaning.

Let's talk fit, because that's where these live or die. The cut-out is 16-7/8 inches wide by 6-3/4 inches tall. Overall the port measures 17-11/16 inches wide by 7-1/2 inches tall, so the frame gives you a little under an inch of trim all the way around the hole. Before you cut anything, hold the port up to the cabin side and trace it. And measure twice. On a curved cabin side the trick is keeping the cutout from ovaling at the corners, because a port that's forced into a slightly wrong shape will weep at the corners no matter how much sealant you throw at it.

The kit comes with twelve M5 by 25mm screws and the clip handle. We tell every customer the same thing on install: pre-drill your screw holes so you don't strip the aluminum frame, bed the whole port in a good marine sealant, and don't crank the fasteners down like you're torquing a lug nut. Overtightening is the number one reason these start to drip six months later. It bows the frame just enough to break the seal. Snug and even is what you want, and let the sealant do the sealing, not the screw pressure.

One thing to check before you order: if you're mounting into a cored cabin side or deck, you'll want the core properly sealed and a backing arrangement so you're not compressing bare core when you tighten down. It's a standard bit of marine carpentry, but it matters for a part that has to stay watertight for years.

The clip handle is worth a mention. It's a simple, positive latch. You swing the port closed and the clip pulls it in against the gasket for a solid seal. No fiddly knobs to lose overboard, and no tools needed to open or close it from inside. When you're heading out and the forecast turns, you can close every port on the boat in under a minute.

Who's this for? Sailboat and trawler owners replacing a tired, crazed old port, or anyone adding ventilation to a berth, head, or galley that needs air. It's a Size 3, a mid-size port that fits a huge range of production boats. If you're matching it to existing Lewmar ports on the boat, the trim profile stays consistent across the line, so a full set looks like it came from the factory.

Maintenance is easy. Rinse the acrylic with fresh water and a soft cloth, and skip the harsh solvents and ammonia glass cleaners, because those haze acrylic over time. A dedicated plastic polish keeps the lens clear for years. Give the gasket a wipe now and then and a little silicone treatment so it stays supple and keeps sealing. Do that and a Lewmar port will outlast a lot of the boat around it.