Keep the Bugs Out: 3D-Printed Insect Screens for Hatches, Portlights and the Companionway
Anchored in a quiet bay on a warm evening is what most of us bought the boat for. Then the sun goes down, the hatches are open for air, and within twenty minutes the cabin belongs to the mosquitoes. Off-the-shelf boat screens exist, but they cover a handful of popular hatch sizes, cost more than they should, and almost never fit the odd-shaped portlight or the companionway on your particular boat. A 3D printer turns this into a solved problem: a screen is just a frame, a mesh and a way of holding the frame in the opening, and all three are easy to print sized to your boat.
This guide covers the three openings that matter most, hatches, opening portlights and the companionway, and the frame designs, mesh choices and materials that work in practice. If you have never printed a boat part before, start with your first 3D-printed boat part and come back.
Measure the opening, not the hatch
Most deck hatches have a moulded inner liner or trim ring with a small lip, and that lip is where a screen frame sits. Measure the inside of the liner at both ends and in the middle (liners are rarely square), note the corner radius, and measure the depth from the liner face to the underside of the closed lid: the frame must be thinner than that or the hatch will not shut over it, which matters if you want to leave screens in and close up in a squall.
Opening portlights are easier: almost all have a flat-faced rectangular or elliptical inner frame, and the screen only needs to cover that face. For the companionway, measure the slot width between the washboard channels, the height from sill to sliding hatch, and the thickness of the washboards, because the best companionway screen is simply a screen-filled washboard that slides into the existing channels.
Frame designs that work
There are three frame styles worth printing, and the right one depends on the opening.
Push-fit lip frame for hatches
A flat rectangular frame, 6–10 mm tall and 12–15 mm wide, sized 0.5–1 mm under the liner opening so it drops in and sits on the lip. Give it a slightly compliant outer edge, a thin fin or a TPU bumper strip, and the frame holds itself in with friction: no fasteners, no adhesive, nothing to leave a mark. Add two finger tabs underneath so it comes out without tools. Frames larger than your bed are printed as corner sections and joined with dovetails or splice plates; see splitting and joining large 3D-printed boat parts.
Magnetic frame for portlights
Portlight screens go in and out constantly, so magnets are worth the extra work. Print pockets for 8×3 mm or 10×3 mm neodymium discs into the frame, press them in with a drop of epoxy, and print matching keeper plates with magnets to stick or screw to the portlight trim (a steel portlight frame needs no keepers). Pockets should be 0.2 mm over the magnet diameter and closed on the outer face so the magnet stays captive even if the glue lets go.
Screen washboard for the companionway
This is the one that transforms cabin life at anchor. Print a frame the same thickness as your washboards, in two or three horizontal sections that stack in the channel like the original boards, each with its own mesh panel so a damaged one is swapped in ten minutes. Add a tongue-and-groove between sections, a lip on the top section to meet the sliding hatch, and a cut-out handle so it lifts out when someone wants to come below.
Fixing the mesh
Mesh is the one thing you will not print. Fibreglass insect mesh from any hardware store is cheap, UV-stable and cuts with scissors. Buy the noseeum grade (roughly 20×20 strands per inch, sold for tents) if your cruising ground has the tiny biting midges that walk straight through standard 18×16 mosquito mesh.
The neatest way to hold it is a spline groove, exactly as on a house window screen: print a 4–5 mm wide, 5 mm deep channel around the frame, lay the mesh over it and press 4.5 mm rubber screen spline into the groove with a spline roller. The mesh pulls taut as you go and is replaceable without tools. A two-part frame that traps the mesh between an inner and outer ring works well for small portlights but doubles the print time on a big hatch. Avoid gluing mesh directly to the frame: it looks fine for a season and then peels at one corner.
Material and print settings
Hatch screens sit under a lid that is open most of the day, so they get real sun. Print ASA for anything in direct light, PETG for mostly shaded portlight frames, and TPU for bumper strips and anything that flexes into a liner. Our materials guide applies unchanged, and if a PETG frame is going to live under an open hatch all summer, the coatings in making 3D prints UV-resistant are worth the extra hour.
| Part | Material | Walls | Infill | Notes |
|---|---|---|---|---|
| Hatch push-fit frame | ASA | 3 | 25% gyroid | Print flat; frame face down for a clean visible side |
| Portlight magnetic frame | PETG or ASA | 3 | 20% | Pause print to drop in magnets, or press-fit afterwards |
| Companionway sections | ASA | 4 | 30% | Print on edge if your bed is tall enough for a flatter face |
| Bumper strip / gasket | TPU 95A | 2 | 100% | Fits a printed groove; see the gasket generator below |
Print frames flat on the bed with a brim: a long thin loop of ASA will warp if the corners lift. If corners crack when you flex a frame out of a liner, the fix is one more wall and a small internal radius at each corner rather than more infill; the rules in print orientation and strength apply.
Sizing tricks from the catalogue
You do not have to model these from scratch. Our custom-size flat plate makes a rounded-corner plate to any dimension and is a quick blank for a portlight keeper plate or spline frame. The parametric gasket generator produces a rectangular TPU ring that doubles as the bumper on a push-fit hatch frame. For hatches that stay closed but still need to breathe, the parametric vent grille with a mesh pocket behind it becomes a ventilating insect-proof cover. All of these live in the Interior & Cabin collection.
A few practical notes
- Print one frame first and live with it for a week before printing the set. The changes you want, a deeper lip, a tab on the other side, a finer mesh, will be obvious by then.
- Give every frame a stowage plan. Loose screens in a locker get crushed; a printed wall clip or a slot behind the companionway steps keeps them flat and findable.
- Do not screen vents that feed a gas or diesel appliance without checking the maker's minimum free-air requirement; mesh cuts airflow more than you would expect.
- If you leave screens in and close the hatch, check the dogs still seat fully. A frame that stops the lid a millimetre short lets water in at the first wave.
Safety note: 3D-printed parts are not certified marine equipment. A screen frame is low-risk, but a companionway board is also part of your boat's ability to close up in heavy weather: keep the original washboards aboard and fit them, not the screens, when conditions build. Check material suitability and fit before relying on any printed part, especially for anything structural, below the waterline or in a critical system.
Questions about sizing a frame for an awkward opening? Write to us at info@marinelab3d.com with the dimensions and a photo of the liner, and we will point you to the right parametric file.
