Gas Strut and Hatch Support Buying Guide

Gas struts also called gas springs or gas props are the pressurised rod-and-cylinder assemblies that hold engine hatches, seat lids, storage compartment covers and other hinged panels open in a controlled position without needing a separate prop rod. A gas strut that's too weak won't hold the panel open; one that's too strong may prevent the panel from closing easily or can slam it open with enough force to cause damage. Choosing the right force rating and length for your application requires understanding a few key factors. This guide covers how to select gas struts for boat applications, what specifications matter most, and what to watch for when replacing worn struts.

How Gas Struts Work

A gas strut contains compressed nitrogen gas and a damping oil within a sealed cylinder. When the panel is opened, the compressed gas in the strut extends the rod, providing a controlled lifting force that holds the panel in the open position. The damping oil controls the speed of extension and retraction a gas strut should open smoothly and hold firmly, not slam open or collapse suddenly. Gas struts have a finite service life the gas pressure gradually decreases as the seals age, and a strut that no longer holds its panel up is typically at end of service life rather than adjustable or repairable.

The Critical Specifications: Force, Extended Length and Compressed Length

Three specifications determine whether a gas strut is suitable for your application:

Force rating (Newtons or kg) the amount of force the strut exerts when fully extended. This needs to be matched to the weight of the panel and the geometry of the installation. An undersized force rating won't hold the panel; an oversized rating prevents easy closing and can put unwanted stress on the hinge and panel. Force calculation depends on the panel weight, the length of the panel, and the mounting position of the strut relative to the hinge. Manufacturer sizing tools or charts, or a calculation provided by the retailer, are the reliable way to determine the correct force don't guess. Check product specifications and, where unsure, contact the supplier.
Extended length (mm) the total length of the strut when fully extended. This determines how far the panel opens. The extended length needs to be matched to the available space and the desired opening angle.
Compressed length (stroke) the length of the strut when fully compressed (panel closed). This needs to be matched to the available space in the closed position. Compressed length = extended length minus stroke.

Replacing Existing Gas Struts

If you're replacing a worn or failed gas strut with the same type on the same application, the simplest approach is to measure the existing strut and match its dimensions and force rating exactly. Measure:

Extended length (end fitting centre to end fitting centre with strut fully extended)
Compressed length (end fitting centre to end fitting centre with strut fully compressed)
Force rating usually stamped on the strut body or printed on a label. A common format is a number followed by "N" (Newtons). If the label is unreadable, contact the boat manufacturer or strut manufacturer with the strut's other dimensions.
End fitting type most marine gas struts use a ball-and-socket end fitting, but the ball diameter and socket type vary. Check the existing end fittings carefully.

Marine Gas Struts vs Automotive Gas Struts

Marine gas struts are manufactured to resist the saltwater, UV and humidity exposure of the marine environment. The cylinder is typically stainless steel or treated steel, the rod is chrome-plated stainless, and the end fittings are marine-grade materials. Automotive gas struts (boot lid props, bonnet props) are designed for a different environment and different force/length configurations they may not be suitable for marine use and may corrode rapidly in saltwater conditions. Choose gas struts intended for marine use where the strut is exposed to saltwater splash or spray.

End Fittings and Mounting

Gas struts connect to the panel and the boat structure via end fittings. The most common type in marine applications is a ball-and-socket fitting a ball stud is mounted on the panel and structure, and the socket end of the strut clips onto the ball. Ball stud size (typically 8mm or 10mm) needs to match the socket in the strut end. Other end fitting types include eyelet fittings and clevis pins. When replacing a strut, confirm the end fitting type matches the existing ball studs or plan to replace the ball studs at the same time.

Number of Struts

Most applications use two struts one on each side of the panel. Using two struts can distribute load more evenly and help reduce panel twisting when opened, and provides redundancy if one strut fails. The force rating for each strut is typically half the total force needed for the application. On very small or light panels (small seat lids, inspection hatches), a single strut may be adequate check the specific application and product guidance.

When to Replace Gas Struts

Replace gas struts when they no longer hold the panel fully open without support, when the rod retracts too quickly (damping failure), when the strut body shows corrosion that may affect seal integrity, or when there's any visible oil leakage (a sign of seal failure). A failed gas strut on an engine hatch is a hazard the panel can fall unexpectedly while you're working on the engine. Replace promptly when failure is detected. Browse boat hatches and portlights for related hardware at Marine Depot.

Why Correct Selection Matters

Gas struts support hatch and locker lids in an open position, and check hatch weight, opening angle, mounting geometry, stroke length, force rating and product specifications carefully before selecting a replacement or new installation. An incorrectly specified strut may not adequately support the hatch it's fitted to, which is a genuine safety consideration given that a hatch unexpectedly closing can cause injury or damage.

Understanding Force Rating

Gas strut force rating needs to suit the specific hatch or lid weight and the leverage created by the mounting geometry, not simply the hatch's raw weight in isolation. A hatch mounted with a long lever arm relative to the strut's mounting point requires a different force rating than the same weight hatch mounted differently. Checking manufacturer sizing guidance, which typically accounts for both weight and mounting geometry, is more reliable than estimating based on weight alone.

Stroke Length and Opening Angle

Stroke length determines how far a strut extends, which needs to match your hatch's required opening angle and travel distance. A strut with insufficient stroke won't allow the hatch to reach its intended open position; one with excessive stroke may not fit the available mounting space or could over-extend the hatch beyond its intended range. Checking your hatch's specific opening geometry against a strut's stroke specification before purchase avoids this mismatch.

Mounting Considerations

Gas struts mount at specific points on both the hatch and the surrounding structure, and the mounting hardware needs to be appropriately rated and securely fitted given the loads involved. Checking manufacturer guidance for recommended mounting brackets and fasteners, and ensuring adequate backing where the mounting point attaches to fibreglass or other panel material, supports a secure, reliable installation.

When Support Failure Creates Risk

Recommend qualified advice where hatch support failure could create risk, particularly for large or heavy hatches, engine bay covers, or any hatch positioned where an unexpected closure could cause injury. This guide provides general background on gas strut selection; for hatches where the consequences of inadequate support are significant, having your specific installation assessed by a qualified marine fitter adds a genuine layer of confidence beyond self-assessment alone.

Replacing Worn or Failing Struts

Gas struts lose their gas charge and supporting force gradually over their working life, and a hatch that no longer stays open reliably, or closes more quickly than it used to, is showing signs of a strut nearing the end of its service life. Checking strut condition periodically, particularly for hatches used regularly or exposed to significant temperature variation, helps you catch this gradual decline before it results in an unsupported hatch.

Struts for Different Hatch Types

Engine bay hatches, storage lockers and cabin hatches each have different typical weights, opening patterns and usage frequency, and considering your specific hatch type when selecting strut specifications rather than applying generic guidance uniformly helps ensure a genuinely appropriate match. Heavier engine bay hatches in particular warrant careful attention to force rating given the consequences of inadequate support in this application.

Multiple Struts for Larger Hatches

Larger or heavier hatches sometimes use two struts working together rather than a single unit, distributing load and providing redundancy if one strut's performance degrades. Checking manufacturer guidance on whether your specific hatch size and weight calls for a dual-strut configuration, rather than assuming a single strut is always adequate, is worth confirming for larger installations.

Temperature Effects on Strut Performance

Gas struts can perform slightly differently across temperature extremes, since the gas charge inside responds to temperature change. For boats in regions with significant temperature variation, checking manufacturer guidance on temperature performance range helps set realistic expectations, particularly if you've noticed a strut feeling different in very hot or cold conditions compared to its typical performance.

Second-Hand Boats and Existing Struts

If you've purchased a boat secondhand, checking existing gas struts for condition and adequate support rather than assuming factory-fitted struts remain fully effective indefinitely is a sensible part of your initial familiarisation with the boat. Struts degrade gradually, and a previous owner may not have noticed or addressed reduced performance before selling.

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Gas Strut and Hatch Support Frequently Asked Questions

How do I know what force rating gas strut to buy?

Force rating depends on the weight of the panel and the geometry of the installation specifically where the strut attaches relative to the hinge. A panel that's heavier or where the strut attaches close to the hinge requires a higher force rating than a lighter panel or one where the strut is mounted further from the hinge. For replacement of an existing strut, matching the force rating stamped on the existing strut is the simplest approach. For a new installation, use the manufacturer's sizing guide or contact the retailer for assistance guessing the force rating can result in a strut that either won't hold the panel or is too stiff to close easily.

My hatch lid gas strut won't hold the lid open anymore can I refill or adjust it?

Gas struts are sealed units they're not designed to be refilled or adjusted in the field. A strut that no longer holds its panel open has lost gas pressure due to seal degradation and is at end of service life. Replace with a strut of matching dimensions and force rating. Attempting to drill, puncture or dismantle a pressurised gas strut is hazardous the gas is under significant pressure.

Are automotive gas struts suitable for use on a boat?

Automotive gas struts (such as tailgate or bonnet props) are designed for a different environment they may not be suitable for saltwater or marine humidity exposure, and their force/length configurations are designed for automotive applications. Marine gas struts use corrosion-resistant materials and marine-appropriate force and length ranges. Choose marine-use struts where saltwater exposure is possible.

How do I measure the length of a gas strut I need to replace?

Measure extended length (end fitting centre to centre with the strut fully extended) and compressed length (end fitting centre to centre with the strut fully compressed). Also note the stroke (extended minus compressed). Measure the existing failed strut if possible a strut that has failed gradually may still be measurable. Also check the end fitting type and ball stud size on the existing installation before ordering a replacement.

Why does my engine hatch not stay open at the correct angle?

If the hatch doesn't hold open at the full angle, the gas struts may have lost pressure (replace them). If the hatch won't open fully even with new struts, the strut extended length may be too short for your installation geometry. If the hatch over-opens or the struts hold it in an unexpected position, the force rating may be too high or the mounting positions may differ from the original design. Check mounting position against the strut manufacturer's specifications for the intended panel weight and opening angle.