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Deck

Repairing deck hatches and companionways — sealing

A practical guide to repairing leaking hatches and companionways: replacing seals, re-bedding the frame and protecting the deck.

The sailing catamaran Madras

A leaking hatch is one of the most common causes of a damp interior and, in the longer run, of a soaked deck core. Water gets in by two routes: through a worn seal between the frame and the pane, and from under the hatch frame bedded on the deck. Start the diagnosis by identifying which route it leaks by — hose the hatch down while watching from inside, or close the hatch onto a sheet of paper and see whether it can be pulled out (a seal compression test). Only then decide the scope of the repair.

Author: Maciej Baniewicz · Boat & Yard editorial team

Methodology: The material was prepared from the sources given and from practical service rules; the parameters have to be confirmed in the manual for the specific manufacturer or model.

Replacing the seal is the simplest case. Old rubber (usually EPDM) loses its elasticity, hardens and cracks. Take the old seal out of the groove, clean and degrease the channel thoroughly, and cut the new profile to length with a slight excess, butting the ends together at the middle of the top edge and bonding them with cyanoacrylate. For hatches from established makes such as Lewmar or Gebo, it is best to buy the original seal profile in the right section — universal rubber rarely gives even compression.

If it leaks from under the frame, re-bedding is needed. Undo the fixing screws, lever the frame with a thin tool to cut through the old sealant, and lift the hatch out. Clean all the surfaces — deck and underside of the frame — thoroughly of old sealant and degrease them. This is the moment to check the state of the screw holes: if the deck has a balsa or foam core, the holes should be sealed with resin so that water cannot soak the core.

For bedding we use a flexible sealant — most often polyurethane or an MS polymer (from the Sika family, for example). Important: do NOT use classic polyurethanes or solvent-based sealants on acrylic and polycarbonate panes, because they can cause stress crazing in the plastic. Lay the compound in a continuous bead around the whole perimeter and around every hole, and tighten the screws only lightly at first, leaving a thin layer of compound to cure.

The key mistake is tightening the screws fully straight after applying the compound — that squeezes the sealant out from under the frame and creates metal-to-deck contact with no seal. Correctly: tighten lightly, wait for the compound to partly cure (a few hours) and only then tighten fully. The excess squeezed out is removed once it has partly cured, by paring it off with a knife; fresh MS polymer can be wiped off with a cloth and a little soapy water.

Check that the mechanisms work too: hinges, locking arms and clamping knobs. Corroded or worn hardware will not compress the seal evenly, so even new rubber will leak in a corner. Clean the moving parts and grease them with a water-resistant grease, and write off cracked acrylic panes for replacement — scratched or crazed acrylic loses strength and lets water through when a wave loads it.

After the repair, repeat the water test only once the sealant has fully cured (usually 24–48 hours, depending on the product and the temperature). It is good practice to note down which compound and seal were used, so the next service goes faster. Checking the compression and the cleanliness of the seal groove every season extends the hatch's life and saves the deck from an expensive soaked-core repair.

Material prices — products and options

Indicative prices in EUR (incl. VAT), as of July 2026. Products widely available in Europe; prices depend on the shop, the pack size and consumption. The links lead to example shops that ship across the EU. Dollar amounts are converted at 1 EUR = 1.1622 USD (ECB, 7 September 2026) and rounded — treat them as a rough guide, not a price in a US shop. Imperial values in brackets are conversions of the metric figure.

EPDM seal profiles
Flexible sealants (bedding frames)
  • Sika — Sikaflex 291i
    all-purpose marine polyurethane adhesive sealant, 70 / 300 ml (10 fl oz) — the classic for fittings    €8–18 (≈$9–21)
  • Sika — Sikaflex 295 UV
    bonding and sealing plastic windows, UV resistant, 300 ml (10 fl oz) — premium option    €26–35 (≈$30–41)
  • Tec7 — MS polymer
    MS polymer, solvent-free adhesive sealant, safe for plastics, 310 ml (10 fl oz)    €12–20 (≈$14–23)
  • Bostik — Simson MSR / Den Braven MS
    MS polymer, version safe for acrylic and polycarbonate, 290 ml (10 fl oz)    €10–18 (≈$12–21)
Cyanoacrylate adhesives (joining the ends of the seal)
Degreasers and scrapers
  • Sika — Remover / Aktivator-205
    cleaning and activating the surface before a PU sealant, 250 ml (8 fl oz)    €15–25 (≈$17–29)
  • Isopropanol (IPA) degreaser
    isopropyl alcohol for degreasing the groove and frames, 0.5–1 L (0.1 US gal–0.3 US gal) — budget option    €6–14 (≈$7–16)
  • Plastic scrapers (set)
    plastic scrapers that will not scratch gelcoat or varnish, for removing old sealant    €5–12 (≈$6–14)
Stainless screws and tools
Epoxy resin (sealing the core)
Waterproof greases
Finishing the beads
Complete hatches (premium)

Price sources: svb24.com, compass24.com, sika.com, lewmar.com. Prices may vary depending on the shop and the pack size.

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