Choose an opening portlight for any cabin space that needs airflow — galley, head, or a berth without a hatch overhead — and a fixed portlight where you just need light and a sealed, lower-maintenance pane, such as a hull side below a walkway or a spot where ventilation is already handled by a nearby hatch or ventilator. Beyond that base decision, the frame material, acrylic tint, and cutout size determine how a portlight performs and how it looks against your cabin sides.
Portlights at a glance
| Product | Type | Cutout size | Frame / acrylic | Price |
|---|---|---|---|---|
| Lewmar Stainless Steel Portlight Size 0 (LEW393020262) | Opening | 15.6 x 30.3 cm (6 1/8 x 11 15/16 in) | Polished stainless / white acrylic | $295 |
| Lewmar Stainless Steel Portlight Size 8 (LEW393810862) | Fixed | 17.6 x 43.2 cm (6 15/16 x 17 in) | Chrome / chrome-tint acrylic | $330 |
| Lewmar Atlantic Portlight Size 40 (LEW39140070) | Opening | 18 x 46 cm (7 1/16 x 18 1/8 in) | Anodized aluminum / smoke acrylic | $780 |
| Vetus PZ Portlight (VTSPZ621) | Opening, ISO Category AI | 15.5 x 34.4 cm (6 1/8 x 13 9/16 in) | White / opaque acrylic | $365 |
What's the difference between a fixed and an opening portlight?
A fixed portlight is a permanently sealed acrylic pane set in a frame — there is no hinge, handle, or dogging hardware, just a gasket and a bolted or bonded frame. An opening portlight adds a hinge on one edge and a handle with cam or dog latches on the other, so the pane swings inward or outward and can be locked shut. That hardware is also why opening units cost more and need periodic hinge and gasket maintenance that a fixed unit never asks for.
The Lewmar Stainless Steel Portlight line makes this easiest to compare directly, because Lewmar sells the same frame style in both configurations: the Size 0 above is the opening version, and the Size 8 is the fixed version in the same product family, just a larger cutout and a chrome-tint acrylic instead of white.
Which portlight material and finish should I choose?
Frame material is the first fork: stainless steel and chrome-plated bronze frames hold up well in salt air and give a traditional, polished look, while anodized aluminum frames (like the Lewmar Atlantic line) are lighter and more corrosion-resistant at a lower cost, which is why they dominate mid-size production cruisers. Acrylic tint is the second choice — clear acrylic maximizes light below, smoke or grey acrylic cuts glare and UV while still letting in daylight, and opaque acrylic (as used on the Vetus PZ) blocks the view through entirely, which some owners prefer for a head or a quarter berth.
How do I size a portlight for my cabin?
Portlights are sold by a manufacturer-specific cutout size, not a single universal diameter, so the cutout dimensions on the product listing are what you measure against — not the visible glass. The four products above span a working range for a 30-45 ft cruiser: the Lewmar Stainless Size 0 fits a 15.6 x 30.3 cm (6 1/8 x 11 15/16 in) opening, the Vetus PZ a 15.5 x 34.4 cm (6 1/8 x 13 9/16 in) opening, the Lewmar Stainless Size 8 a larger 17.6 x 43.2 cm (6 15/16 x 17 in) opening, and the Lewmar Atlantic Size 40 the largest of the four at 18 x 46 cm (7 1/16 x 18 1/8 in). Always template the existing cutout (or the manufacturer's cutout drawing if you're adding a new one) before ordering — hull curvature limits how large a rectangular portlight can sit flat against the topsides.
Where should fixed vs. opening portlights go on the boat?
Put opening portlights where a cabin genuinely needs airflow and doesn't already have a hatch: heads, galleys, and aft cabins are the usual candidates, and Vetus rates its PZ series by ISO glazing category (the PZ621 above is Category AI) so you can match the unit to how exposed that specific mounting location is. Fixed portlights make sense anywhere ventilation is already covered by a nearby hatch or dorade vent, or wherever you specifically want a sealed, lower-maintenance pane — companionway steps, a quarter berth against the cockpit, or a hull location low enough that opening it underway isn't practical anyway.
Which should I choose?
If the space needs airflow and doesn't have another vent source, choose opening — the Lewmar Stainless Size 0 or the Vetus PZ cover the mid-size range well. If the space is already ventilated elsewhere or you want the lowest-maintenance option, choose fixed, such as the Lewmar Stainless Size 8. Match frame material to what's already on your boat (stainless/chrome vs. anodized aluminum) so the portlights look consistent from the outside, and pick acrylic tint based on how much privacy or glare control that specific cabin needs.
Frequently asked questions
Can I replace a fixed portlight with an opening one in the same cutout?
Only if the manufacturer offers both types in that exact cutout size, as Lewmar does within its Stainless Steel Portlight line. Cutout dimensions are not standardized across brands, so swapping brands usually means a new cutout.
Do opening portlights leak more than fixed ones?
An opening portlight has more places to fail — hinge, gasket, and latch — so it needs periodic inspection, but a properly dogged-down opening portlight from a reputable maker seals as well as a fixed one. Most leaks trace back to a worn gasket or a latch not fully engaged, not the opening mechanism itself.
What does an ISO glazing category like "AI" mean on a portlight?
It's part of the ISO standard manufacturers use to rate a portlight's glazing for a given mounting location and exposure. Vetus publishes a category (AI, AIII, and others across its PZ, PX, and PW ranges) for each portlight so you can match the unit to where on the boat it will be installed.
Should portlight frames match my hatch frames?
It's not required, but matching finishes (stainless, chrome, or anodized aluminum) keeps the cabin sides looking consistent. Many owners stay within one manufacturer's line, such as Lewmar's Atlantic or Stainless Steel series, specifically for that reason.
Can I get a smoke or opaque acrylic pane instead of clear?
Yes — most portlight lines offer clear, smoke/grey, and opaque acrylic options, as shown by the Lewmar Atlantic (smoke) and Vetus PZ (opaque) above. Tint is typically an ordering option on the same cutout, not a different product line.