To remove and install a sailboat hatch or portlight, lift the old lower frame free by gently prying it off the deck, cut the bedding compound, clean out the old sealant and fixing holes, then bed the new unit onto a flat surface (+/- 1 mm) with fresh sealant and through-bolt the hinge points. Careful cut-out marking, jigsaw work, and generous bedding compound are what separate a dry, long-lasting installation from a leaky one.
Hatch and portlight installation at a glance
| Step | Hatches | Portlights |
|---|---|---|
| Mounting surface | Flat, +/- 1 mm tolerance | Flat, +/- 1 mm tolerance |
| Deck thickness | Any thickness (flange may intrude on thin decks) | Has a min and max deck thickness limit |
| How it clamps | Lower frame fastened to deck; hinges through-bolted | Outer frame clamped to inner frame from inside the boat |
| Fastenings | Through-bolt hinges, self-tap the rest | Match fastenings to deck thickness (order separately if needed) |
| Sealing | Generous bedding compound bead around frame | Generous bedding compound bead around frame |
What do I need to know before cutting the deck?
Hatches and portlights should be fitted to a flat surface with a maximum tolerance of +/- 1 mm. On composite decks, seal the exposed laminate with the appropriate material before fitting. On metal decks, remove all burrs and sharp edges, and insulate the lower frame from the deck where there is a possibility of electrolytic corrosion with the hatch's aluminum frame.
Remember that hatches and portlights are not stiffening members. Cutting holes in the deck or hull can compromise the structural integrity of the boat, so stiffen the deck adequately to prevent distortion in heavy weather. If in doubt, consult a competent yacht designer or surveyor.
How do I remove an existing hatch without damaging the deck?
Great care during removal prevents delamination and deck damage. Make a bridge of wood over a corner of the hatch frame, protecting the deck with cardboard or carpet under the feet. Place a second piece of wood under the boat's inside hatch frame across the same corner (a miter joint helps it contact only the lower frame), then use a G-clamp to pull that piece upward toward the bridge. As soon as the frame lifts a few millimeters, cut the bedding compound with a sharp, thin-bladed knife. Before fitting the new hatch, remove all old sealant and fill the old fastening holes.
How do I install a new hatch?
Do not open and close the lid more than necessary until the lower frame is securely mounted. Confirm the surface is flat (+/- 1 mm), then mark the cut-out dimensions on the deck — if a Trimkit is being fitted, increase the aperture length and width by 4 mm and the corner radius by 2 mm, per Lewmar Trimkit fitting instructions. Offer the hatch up to the marks to check accuracy.
Avoiding any power cables, gas pipes, or other services, drill a hole for the jigsaw blade on the waste side of the cut line and cut the aperture with a jigsaw (a hole cutter matching the corner radii can cut the corners; you may need to trim the headlining). Test-fit the hatch before applying sealant, mark the lower-frame fixing holes, remove the hatch, and drill all fastening holes. Bed down with a generous bead of compound around the frame, seal both sides of the fastening holes, refit, and fasten — through-bolt the hinge areas and use self-tapping screws for the remainder of the lower frame. Clean up the excess compound to finish.
How is installing a portlight different?
Portlights have both a minimum and a maximum deck thickness. Units fitted to hulls near the maximum thickness may have restricted opening, and they need different fastenings for different deck thicknesses — if the supplied fastenings don't suit your hull, order the correct ones separately. Use the supplied template to mark the cut line on a flat surface, drill and jigsaw the aperture, then test-fit the portlight and clamp ring before sealing. A portlight is fixed by clamping its outer frame against the deck using the inner frame inside the boat. Apply a generous bead of bedding compound, refit, clamp the frames together with the greased fixings, and clean up the excess.
Which tools do I need?
- Bedding compound and application gun (silicone)
- Fastenings (supplied with portlights)
- Power drill and set of drill bits
- Jigsaw
- Screwdrivers, Allen keys, and spanners depending on the product
- Compass (for marking hatch radii)
- Felt-tip pen and ruler
Frequently asked questions
How flat does the mounting surface need to be?
Both hatches and portlights must be fitted to a flat surface with a maximum tolerance of +/- 1 mm. An out-of-flat mounting will distort the frame and cause leaks.
Do I need to increase the cut-out for a Trimkit?
Yes. If a Trimkit is being fitted, the cut-out length and width must be increased by 4 mm and the corner radius increased by 2 mm, per Lewmar Trimkit fitting instructions.
Which fastenings should be through-bolted?
The hinge areas of a hatch should always be through-bolted, while self-tapping screws can be used for the remainder of the lower frame.
Why won't my hatch fit even though the hole is correct?
Hatch lids must open past 90 degrees to fasten the frame to the deck. If an obstruction stops the lid opening that far, the hatch cannot be installed in that location.
Can I fit a portlight to any deck thickness?
No. Portlights have a minimum and a maximum deck thickness, and units near the maximum may have restricted opening. Match the fastenings to your deck thickness, ordering them separately if the supplied ones don't fit.
How do I keep the installation from leaking?
Bed the frame down on a generous bead of bedding compound so a small amount squeezes out all the way around, seal both sides of the fastening holes, and fill any old fixing holes with sealant before refitting.