Operation of the inflatable floating craft begins long before the water, even at the stage of preparation for descent. Pressure in cylinders It's a critical parameter that's critical to driving performance, wave stability and, most importantly, crew safety. PVC boats make a fatal mistake, pumping the boat "by the eye" or relying on the hardness of the side, which often leads to deformation of the bottom or, conversely, to rupture of the seams in the heat.
For boats with keel The internal pressure requirements are significantly higher than those of simple rowing models, under-filling turns the bottom into a bubble that creates tremendous resistance to water and makes the vessel’s handling unpredictable, while over-pressure when ambient temperatures change can lead to an emergency where the material simply cannot withstand the internal stress.
In this article we will analyze the physical principles of inflatable structures, give accurate tables of values in the PSI And we'll look at the effects of temperature changes, and we'll learn why you can't leave a fully pumped boat in the sun, and how to use it properly. gauge to monitor the condition of the boat before each exit.
Physics of the process: why the exact value of the PSI is important
Materials PVC The structure that makes modern boats is a composite fabric with a reinforcement cord, which provides strength, but also sets rigid limits on elasticity, and when you pump the cylinders, the air inside creates pressure on the walls. PSI (pounds per square inch) too low, the fabric sags, the geometry of the hull is lost, and the boat begins to "scour" along the course, reacting poorly to the relay. steering-bar.
The keel, in inflatable models, has to be a keel, which is like a keel, which has to be hard like a log to be stable, and if the keel is lower than the cylinders, when you set speed, it will collapse, and the boat will start to throw from side to side. Aerodynamics The hydrodynamics of the body work only when all the elements are inflated to a state of elasticity.
⚠️ Warning: Never test pressure with your finger or by pressing. The human sense of "hardness" is subjective and depends on the temperature of the hands and the time of day. Use only a calibrated gauge.
And the right pressure also distributes the load to the seams. When you don't pump, the main loads are on the internal partitions and the gluing places, which accelerates wear and tear, and pumping stretches the material beyond measure, making it vulnerable to punctures and tears when hit by a wave or obstacle. Balance is the key word for long-term service of your body. boat.
Standard pressure standards for different elements of the boat
Manufacturers PVC boats, such as Flinc, Badger or YamaranHowever, there are general industry standards that should be followed if documentation is lost. For cylinders with a diameter of more than 30 cm, the optimal range is from 0.2 to 0.25 atmospheres.
Special attention is required keelSince it carries the main load on the formation of the bottom, its pressure should be maximum for the structure, usually 0.25-0.3 atmosphere. The deck (if inflatable) is pumped to lower values to ensure comfort of the legs and not create unnecessary stress in the places of attachment to the cylinders.
Always start pumping with cylinders, then move to the keel, and only at the end do the deck, which will avoid distortions of the structure.
Below is a table that organizes the data by the boat's elements. Note the translation of units of measurement, as pump scales may vary.
| Element of the boat | Pressure (atm) | Pressure (PSI) | Pressure (kPa) |
|---|---|---|---|
| Cylinders (main) | 0.20 - 0.25 | 2.9 - 3.6 | 20 - 25 |
| Inflatable keel | 0.25 - 0.30 | 3.6 - 4.3 | 25 - 30 |
| Inflatable deck | 0.15 - 0.20 | 2.1 - 2.9 | 15 - 20 |
| transom pad | 0.15 - 0.20 | 2.1 - 2.9 | 15 - 20 |
It's important to understand that the values in the table are working. When transporting or storing in a warm room, the pressure can rise. So if you pump a boat in a garage at +20 ° C, and you plan to launch at +30 ° C, you should focus on the lower limit of the range or blow some of the air before you leave.
Effect of temperature on cylinder pressure
Gay-Lussac's law says that at a constant volume, the pressure of a gas is directly proportional to its temperature. PVC Imagine a situation where you pumped up the boat in the morning when the air was cool (+15°C) and left it on the shore in the scorching sun.
Within a couple of hours, the temperature inside the cylinders can jump to 40°C or higher. pressure And if you're going to pump the boat to the point, the heat will cause the tissue to become overstretched and the seams to rupture. PVC When heated, it becomes softer and more vulnerable.
Formula for calculating pressure change
For an approximate calculation, use the ratio: P2 = P1* (T2 / T1), where T is the temperature in Kelvin. A temperature rise from 288K (15 ° C) to 313K (40 ° C) will give an increase in pressure of about 8.7%.
The reverse happens in the fall or when you go out of the water from a cold room. If you pump the boat in warm water and then lower it into cold water (+10 ° C), the pressure will drop. The boat will become soft, lose shape, and you will have to pump it already on the water. This is a normal process that does not indicate injury or puncture.
⚠️ Warning: Never leave a fully pumped boat in direct sunlight unattended, and if this is not avoided, be sure to blow some air or cover the boat with a light awning/blanket.
Step by step: how to properly pump the boat
The process of preparing a vessel for water requires consistency and the use of the right equipment. The use of automotive compressors without pressure control is strongly discouraged, as they overheat quickly and do not give accurate readings. pump for PVC with a built-in pressure gauge.
First, open the boat on a flat surface, clear the sand and debris. Open all the valves to straighten the folds. Start pumping the cylinders to a state of light elasticity (about 0.1 atm), then get the installation done. pyeol (if the floor is hard) or by straightening the inflatable floor, and only after the construction is assembled, the cylinders are pumped to the working pressure.
☑️ Pumping procedure
When pumping the keel, use a pump with high performance, as the volume of the keel can be significant. gauge Once the arrow has reached the right mark, stop the air supply. You can use a separate, more accurate gauge for the final check, because standard instruments on cheap pumps often have a higher margin of error.
Typical errors and risks of transfer
The most common mistake of newcomers is to make the board stone, and owners rock the boat until the fabric stops wobbling at all, a gross violation of the technology of operation. Pumping leads to the fact that at the slightest impact on a wave or log, a rupture occurs, which is often impossible to seal qualitatively in the field.
Another mistake is ignoring temperature expansion, and people forget that the sun not only warms the air outside, but also the dark material of the boat, which acts as a heat collector, and as a result, the internal pressure grows uncontrollably, and it's also dangerous to use compressors from trucks that can create an instantaneous overpressure that can cause a hazard to the body. valve.
The golden rule is that the side of a pumped boat should be elastic, but when you press your thumb hard, you should feel minimal cushioning. Absolute hardness is a sign of danger.
If you notice that the boat has become too hard in the sun, don't expect the consequences. Immediately open the valve (better through the adapter or carefully with your finger) and put the excess to the standard values. It is better to miss the boat by 10% than to pump 5%, since the defect can be compensated on the water, and the seam rupture is not.
Maintenance and control of pressure during operation
PVC material tends to slowly release air, especially in new boats or after long storage, so checking the pressure should be a ritual before each step on the water. tightness valves that may be contaminated with sand or salt.
During long periods of water stay, especially on a hot day, it is recommended to check the hardness of the cylinders periodically (every 2-3 hours). If you plan to leave the boat on the water overnight, be sure to blow some of the air so that the morning sun does not tear the boat apart. This is especially true for boats of dark colors that heat up faster.
To store the boat, on the contrary, you have to blow it completely or leave minimal pressure so that the folds do not break. Regular care of the pressure gauge and the pump is also important: sand trapped in the pressure gauge mechanism will knock its calibration, and you will receive false data, risking the integrity of your pressure gauge. boat.
How do you keep a pressure gauge?
Keep the pressure gauge in a protective case, away from direct sunlight and dust, periodically check its readings on a reference device or compare it with another working pressure gauge.
Can I swing a boat with a car compressor?
You can use an automobile compressor, but only with great care and necessarily in pairs with an external accurate pressure gauge. Standard pressure gauges on compressors are often lying, and high performance can quickly create excessive pressure, dangerous for PVC seams. It is better to use specialized pressure limiter pumps.
Why does the boat become soft after descending into the water?
This is the physical effect of cooling the gas. If you pumped the boat in a warm room or on hot sand and then lowered it into cool water, the air temperature inside the cylinders dropped, which led to a decrease in pressure. That's OK. You just need to pump the boat to work, whether it's afloat or off the coast.
What pressure is critical for a joint to break?
Excess pressure of 30-40% or more is considered critical, but the strength of the seam depends on the quality of the gluing and the condition of the fabric. Old boats or articles with defects can burst even at a lower exceedance. The safe limit is usually specified by the manufacturer, but it is better not to exceed 0.35-0.4 atm in any of the cylinders.
Do I need to blow the air before transporting it to the roof?
Yes, if you're driving a boat on the roof of a car in hot weather, be sure to blow some of the air out. At speed and under the sun, the pressure inside rises rapidly. If you can't blow the air out (for example, a boat in a bag), try to minimize the time of transportation in the heat and do not pump it before the trip "before the bell."