What Gas Struts Do
Gas struts help us in many parts of our everyday lives. Our cars, trucks, toolboxes, windows, and even our favorite sandwich shops use gas struts. So what makes them so important on our boats? Many hatches are built to tolerate constant abuse from fishing weights, coolers, and even fish themselves. In the process of being built so strongly, they can get pretty heavy and difficult to lift.
In addition to the heavyweight, some hatches need to be held open. Holding open heavy hatches can pose issues in the best conditions, but in the worst conditions, it can be downright dangerous.
Gas struts can fix all of this. They’re built to provide a certain amount of lifting force that can make hatches feel weightless and hold them open. Because gas shocks exert constant force, they can’t inadvertently slam. This leaves you with both hands for whatever task you have involving your boat’s storage hatches, whether it is maintenance or organizing fishing tackle or sandbar gear.
Gas Struts vs Gas Shocks
Gas struts can go by many names, including gas props, gas lifters, gas lifts, gas springs, gas dampeners, lift struts, and gas shocks just to give you a few. It is important to point out that there could be a difference in function between gas struts and shocks. In technical terms, gas struts are used as lift support, or counter-balance, moving masses.
On the other hand, in technical terms, gas shocks are used to support moving masses while controlling the system’s motion. In simpler terms, gas struts provide lifting assistance, while some may say that these shocks only provide fall dampening. In the case of boating, the terms are pretty interchangeable.
It’s only important to understand when ordering a replacement strut that you know what you’re getting. Here these terms will be used interchangeably.
How Gas Struts Work
Despite their variety of functions, gas struts are incredibly simple. A gas strut is no more than a device for storing energy in the form of compression. Think of the strut as a mechanical spring, but instead of absorbing and storing energy in coils, they store it in the gas of the strut. This similarity to mechanical springs is why they are commonly referred to as gas springs or gas spring struts.
Gas struts consist of a piston, a connecting rod mechanism, and a pressurized gas or oil all contained in a sealed cylinder. The sealed cylinder doesn’t allow any air or oil to escape. By not letting any gas or oil escape, any movement against the connecting rod is compressing gas, raising internal pressure. This compressing gas can slow down an object’s motion, or if strong enough completely stop it.
For example, to compress a strut rated at five pounds means that compressing that gas takes five pounds of force. In most gas struts nitrogen is used as the pressurizing gas. How high or low the gas pressure is within the cylinder is the contributing factor to how high or low the lift force is from the strut.
Gas Struts & Shocks on Boats
Gas struts have many applications within boating due to the wide variety of sizes and forces they come in. Weights from 5 to 90 pounds are available. This weight is a measure of the lifting force the strut will apply at compression. On a lightweight electronics box door, five pounds is an appropriate size. On a thick, heavy fiberglass hatch, 90 pounds might be the appropriate lift force for the gas strut.
Gas Struts also come in a variety of lengths from extra-long gas struts over 26 inches long to very short struts barely over 6 inches. There are two lengths to consider on a gas strut. The first is the compressed length. This is the length from end to end while the strut is compressed. The compressed length is measured while having both ends forced together. The other is the extended length.
This is the length from end to end while the strut is completely extended. Extended length involves the strut extended completely with no forces acting on it at all. Both measurements are taken from the center of one end fitting to the center of the other.
Since they come in so many different shapes and sizes, even hatches that do not come with a factory-installed gas strut can benefit from having one. The lightweight lid of a livewell is not heavy to lift, but having to hold it open is a hassle when you’re rigging baits. A gas strut relieves you of this issue, allowing you to catch and rig baits with both hands.
The T-top electronics box door that always seems to pinch your fingers? It would benefit greatly from a small gas strut or even multiple small gas struts. Not only does the strut allow you to use it hands-free, but it also stops the door from slamming and extends the lifespan of your hardware.
Replacing Worn Out Gas Struts
Now that you have an application in mind, it’s time to mount your strut. Replacing old worn-out struts is not nearly as difficult as mounting new ones. Simply measure the compressed and extended lengths, measuring from the center of one mounting hole to the center of the other mounting hole. Determining the force of an old shock can be more difficult.
You can usually find a part number stamped on the shock, though, which, in most cases, will tell you the force. There are several manufacturers, so part numbers can take some deciphering, but it’s normally not too hard to figure out the force from the part number. Boat Outfitters has a helpful video on the subject.
If you choose to get a strut that provides more lift than the factory original, be sure not to overpower hatches that don’t have secure latches. Overpowering hatches can cause your hatches to open on their own and can put excess strain on brackets, mounting hardware, and mounting surfaces.
Once you get your replacement gas struts it is as simple as pulling the old one off of the mounting bracket ball joint and mounting the new one. Most struts are easiest to install in their open position. This allows you to mount the strut without having to simultaneously compress it.
Installing New Gas Struts
On hatches that didn’t come from the factory with a gas strut, there are a few more steps to the installation process. The first step is getting a rough idea of how the strut will be mounted. There are a few things to consider when deciding how you mount the strut. You need to make sure you have space for the hardware and you need to make sure you consider the angle at which your strut lifts.
The best place is usually halfway between the hinge and the center of the hatch you are lifting. A long gas strut that attaches farther from the hinge will have more leverage, requiring less force. A shorter strut that mounts closer to the hinge will have less leverage, requiring more force. Make sure your strut is clear of any potential interference. Although gas struts are extremely strong, they are not designed to handle any force from the side.
After you find the mounting position, it’s time to find the length. The general rule is that the correct length of a strut is 55 percent of the height of the hatch being lifted, but be sure to measure. After you find the perfect spot for your mounts, it’s time to find out the right lift force for your strut. A very simple method is to just weigh the hatch itself.
However, this method may not be the most accurate since angles, mounting position, and leverage all have a role in the required force. The required force formula is as follows:
- Force Required = weight x length ÷ the distance between the mounting point of the gas strut and the hinge
There are calculators available online, but factor in an additional 10 to 20 percent lift force to be sure you have plenty of lift.
On boats with inboard motors, be careful how close you mount your gas struts to any exhaust or engine components. Gas struts are pressurized units and do have specific operating temperature ranges. Most struts are designed to operate at a much higher temperature than an engine room should contain, but it is an important consideration.
Make sure when you buy gas struts online to check the temperature operating ranges if they’re going to be mounted in an engine room.
Gas Strut Maintenance
Now that you have the perfect strut picked out and installed there are a few things to keep your strut in working order for years to come.
Besides side-loading your strut, the seal is the most likely point where your gas strut will fail. To avoid getting dust or grime on the strut and potentially compromising the seal, always install it as the last part of a project, after sanding or painting.
On the same note, it’s important to keep the spring mounted with the cylinder on top. This allows the small amount of lubricant within the cylinder to keep the seal moist and lubricated.
Be careful when using chemicals near your gas struts; harsh solvents can cause the seal to break down and your gas strut to lose pressure. Most manufacturers even warn against excessive lubrication on your strut, as the seal is designed and manufactured with such fine tolerances that excess oil is not desired.
Avoid any sort of nicks or scratches against your piston rod, as these abrasions can cause the seal to fail prematurely. Lastly, do not cycle your gas strut more than fifteen times per minute, as the components in the cylinder are not meant to cycle at high repetitions per minute.
Gas struts can make certain parts of your boat much more convenient to use. Their simple construction offers years of carefree use with minimal maintenance.
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