Sometimes a boat project seems simple, but it’s not. Other times a project can seem difficult, and it turns out to be easy. When I decided to add a gas spring to a hatch on my Pathfinder 2700 Open, the job turned out to be a bit of both.
The hatch on the large cooler forward of the console came mounted on friction hinges that quickly lost their ability to hold it open, probably because of the hatch’s weight. The cooler also serves as seating when the cushion is snapped into place. The risk of the hatch slamming shut on someone’s fingers prompted a fix, and rather than replace the hinges I decided to install a gas spring.
Gas springs are self-contained, nitrogen-driven units that provide a uniform lifting force to a hinged moving object to reduce or negate the effort needed to lift it. They come in a wide range of lengths and force ratings to cover a myriad of installation criteria. They are commonly used on boat hatches. You can find them at marine stores, but those are stocked to replace existing springs that have weakened over time. Replacing a gas spring is simple; just measure the old one, check the force rating (indicated in pounds), get the appropriate replacement, and pop it onto the existing mounting brackets. However, determining the proper gas spring and how to fit it on a hatch that has never had one is a different thing altogether.
A few calls led me to Richard Blum. He’s a consultant for LaVanture Products, a major supplier of high-quality gas springs, and an engineer with 35 years of experience in gas spring design, manufacture and application. He works with boat, RV, bus and aircraft manufacturers. He explained that the job was not a typical do-it-yourself project. Determining the proper gas spring length, force, mounting hardware and mounting locations leaves a lot of room for error without an engineer’s guidance. Doing one-off applications like this one is simply too time-consuming for most manufacturers to consider. Yet with some prodding he agreed to set me on the right path, to see if I could come up with a formula to simplify the process for the most common gas spring usage on boats, a horizontal hatch.
I started by taking the following measurements per his suggestion (see graphic at top right): Accurate weight of the hatch lid (W); opening angle (A); distance from the pivot point of the hinge to the top edge of the lid (L); distance from the pivot point of the hinge to the center of gravity of the lid (C); approximate depth of the gas spring’s fixed mounting position below the edge of the box (G).
These measurements are required to determine the gas spring needed for the job and the relative position of the mounting hardware. An engineer would enter that information, along with other data points, into a rather complicated formula to determine the requirements for the application. Since my last name isn’t Euclid and I don’t have an engineering degree I asked myself, “Well, what would MacGyver do?”
I looked at similar gas spring installations on boats and determined that I would ideally like to place the fixed mount approximately 3 inches forward and 3 inches below the pivot point (G) in the thick fiberglass lip inside the cooler box. I wanted the upper mount to be located about half the distance between the center of gravity and the top of the lid when open and came up with a length of approximately 20 inches. The further the top mounting point is from the center of gravity, the greater the force needed to lift the mass, so I simply matched the force of a gas spring on a similarly large hatch on the boat’s casting deck at 60 pounds.
I went to the LaVanture website and thumbed down the list of available stainless-steel units until I found one that had an extended length of 20 inches and a 60-pound force rating. It’s important to know both the extended and compressed lengths of the spring for determining placement of the mounting hardware. This 20-inch unit had a compressed length of 12 inches. Both measurements are taken from the center of one ball mount to the center of the other. Then it was back to the boat for more measuring. I determined where I wanted the fixed mount to be and put a piece of masking tape in that position and marked where the ball center would be with pencil. With the hatch opened 90-degrees I measured up 20 inches and marked it with tape the same way.
The moment of truth came when I closed the hatch and measured the distance between the two tape marks and it came out to just under 13 inches, enough to close the hatch without bottoming out the gas spring, which would prevent it from fully closing. The hard part was done.
I ordered the spring and the appropriate hardware for the job, including the fixed mount, and upper mount. All it took to install the mounts was six #10 stainless steel panhead self-tapping screws, an electric drill and bits, and a Phillips screwdriver. Total installation time, including measuring everything extra carefully, was 20 minutes.
The spring works like a charm. When I unlatch the hatch, it gently lifts all by itself, even with the seat cushion in place, and remains open until I push it closed with little effort required. Tip: Always install the spring with the nitrogen-filled body at the top when the hatch is open. I have to thank Blum for his help, and MacGyver for the inspiration.
This article was originally published in the January 2024 issue.
