If you’re replacing Lewmar deck hatches — or specifying hatches for a refit and comparing options — you’ve probably noticed that Lewmar parts carry a significant price premium. Aqua Marine Storm Hatches are manufactured to the same aperture dimensions, the same bolt patterns, and the same ISO standard as their Lewmar equivalents, which means they fit directly into existing openings with no modification required.

Here’s everything you need to know about choosing the right hatch and fitting it correctly — including the full step-by-step installation process from the official fitting instructions.

What Makes a Hatch “Lewmar-Compatible”?

A Lewmar-compatible hatch shares the same aperture dimensions and bolt pattern as the equivalent Lewmar model. For anyone replacing a worn or cracked hatch on an existing vessel, that means no cutting, no fairing, no structural work — the replacement drops straight into the existing opening.

Cutting a new deck aperture is expensive, time-consuming, and if done poorly, a route to serious structural problems. True compatibility makes the job clean, fast, and permanent.

Aqua Marine Storm Hatches: Built to the Same Standard

Aqua Marine Storm Hatches comply with ISO/DIS 12216.2(E), Design Category “A” — the highest offshore rating, covering vessels operating in Areas IIa, III and IV. This is the same standard applied to Lewmar hatches, and it means the hatch has been tested to withstand the structural loads, water ingress pressures, and operational stresses of genuine offshore use.

For anyone maintaining their vessel’s design category compliance — important for offshore insurance and passage planning — Aqua Marine Storm Hatches keep you fully covered.

Key features at a glance:

• Lewmar-compatible dimensions — drop-in fit into existing apertures, no modification needed
• ISO Design Category A certified — tested and rated for offshore and ocean conditions
• Precision friction lever system — holds the hatch open at any angle without a gas strut
• Locking ventilation position — ventilate below decks without the hatch blowing fully open
• UV-stabilised acrylic lid — maintains optical clarity over years of exposure
• Suits wood, GRP, steel and aluminium alloy decks — compatible with M5 and M6 stainless fittings throughout

Step 1: Prepare the Deck Surface

The lower frame must be fitted to a flat surface with a maximum tolerance of +/- 1mm. Even a slight crown or camber in the deck will prevent a proper seal. Check the installation area carefully before marking out — if the surface needs fairing, address it first.

Also confirm that your deck or hull thickness falls between 25mm and 70mm (flanged version), and allow adequate clearance above the hatch for the lid to open fully — a common oversight on vessels with low coachroof or adjacent fittings.

Step 2: Mark Out and Cut the Aperture

Position the lower frame square on the deck and mark around the inside edge with a pencil. For flanged hatches, use the cut-out template printed on the reverse of the box packaging — it gives you the precise aperture size for a clean, accurate fit.

Cut along the outside of the pencil line using a jigsaw or reciprocating saw. On GRP decks, seal the exposed laminate edges immediately after cutting to prevent water ingress into the core material. On steel or aluminium decks, remove all burrs and sharp edges before proceeding — bare metal will corrode and can damage the bedding compound over time.

Step 3: Bed and Fasten

Before applying any sealant, dry-fit the lower frame one final time. It should sit flat, square, and flush — no rocking, no gaps. This is your last chance to adjust before the compound goes in.

Apply marine-grade silicone sealant to the channel in the lower frame. The compound must be compressible (minimum 3mm thickness) so it can be pulled down evenly as you fasten. Drill two fixing holes in opposite corners first and insert your fasteners to locate the frame, then drill and fasten the remaining holes working from the centre outwards to the edges — this ensures even compression and prevents the frame lifting at corners.

Fastener selection by deck type:

Clean off surplus sealant from around the frame as you work, before it cures. Once complete, check the lid for correct closing and locking action, and even seal pressure all the way around. Any issues are far easier to correct now than after the sealant has fully set.

Adjusting the Friction Levers

The friction lever system holds the hatch open at any angle without a gas strut. Levers are factory-set but may need occasional adjustment — particularly if the hatch starts dropping closed on its own or becomes stiff to open.

Using a 5mm hexagon key, turn the socket head adjusting screws on either side of the lever assembly approximately 1/8th of a turn clockwise to increase holding force. Do this in the fully open or closed position. If your hatch has multiple lever units, adjust all levers equally to maintain balanced operation.

Ventilation and Day-to-Day Use

All Aqua Marine Storm Hatches include a locking ventilation position. Close the handles into the centre slot of the catch block to hold the hatch ajar for airflow without it blowing fully open. This is particularly useful at anchor or in harbour overnight.

A few points to keep in mind in daily use:

• Do not stand on or load the lid when in the ventilation position — this can damage the handle or catch block assembly
• The hatch is not self-supporting beyond the vertical position and will fall fully open if unrestrained — take care when operating in this range
• Keep hands and limbs clear of lever and lid pinch zones when operating or adjusting

Cleaning and Maintenance

Aqua Marine Storm Hatches need minimal maintenance to stay in top condition. Wash the frame with soap, warm water and a soft cloth, and rinse thoroughly with fresh water after saltwater exposure. For the acrylic lid, use soap and water only — abrasive or solvent-based cleaners cause micro-crazing that weakens the acrylic over time, even when the damage isn’t immediately visible.

Check the perimeter seal annually and replace if it shows signs of compression set or cracking. Inspect the bedding compound around the frame base at the same time — any water ingress around the frame indicates the compound has failed and the hatch needs re-bedding.

Frequently Asked Questions