Hatch & Port-light Installation Check List


Hatches and port-lights should be fitted to a flat surface with maximum tolerance of +/-­ 1 mm. For decks of composite construction (e.g. GRP) it is recommended that the exposed laminate be sealed with the appropriate material prior to fitting the hatch. Openings in metal decks should have all burs and sharp edges removed. It is recommended that the lower frame of the hatch is suitably insulated from the deck if there is a possibility of electrolytic corrosion with the aluminium frame of the hatch. Hatches and port-lights should not be considered as stiffening members and it is recommended that  the deck be adequately stiffened to prevent distortion during heavy weather. Cutting holes in the deck and hull can compromise the structural integrity of the boat. If in doubt, consult a competent yacht designer or surveyor.


Portlights have a maximum and minimum deck thickness to which they may be fitted. Portlights fitted to hulls approaching the maximum deck thickness may have restricted opening. Portlights require different fastenings to suit different deck thicknesses. If the fastenings supplied with the portlight do not suit your hull thickness it will be necessary to order the required fastenings separately.


Hatches should not be opened and closed more than necessary until the lower frame has been securely mounted to the deck. Hatches may be fitted to decks of any thickness. However, on thinner decks the flange in the lower frame may intrude into the cabin. If a Trimkit is being fitted the size of the hole cut out in the boat must be increased by 3 mm. Hatch lids have to be opened past 90º in order to fasten the hatch to the deck. If an obstruction stops the hatch opening this far it will not be possible to fit it. When a hatch is fully open the lid should come to rest so that it is supported near the edge with the handles. If this is not the case, and the lid is supported near the hinges, the leverage on the lid may cause the hatch to be damaged.

Tools/Consumables Checklist for Hatch Installation
  • Bedding compound and application gun (silicone)
  • Fastenings (supplied with portlights)
  • Power drill and set of drill bits
  • Jig saw
  • Screwdrivers, Allen keys, spanners depending on product
  • Compass (for making hatch radii)

Fitting New Lewmar Hatches

When you’re replacing an older Lewmar hatch or port-light and you’d like to find a direct replacement, please note that although the Lewmar standard cutout sizes have remained constant, the corner radius may have changed on certain models.