Operating an inflatable boat at high speeds often reveals design features that seem insignificant in quiet mode. One of the key elements affecting seaworthiness and handling is bottom rigidity. Standard inflatable tubes and even slate mats do not always provide the necessary hull geometry when sleeved, leading to yaw and increased fuel consumption.
It is to solve this problem that experienced boaters install stringer They work like keels, stabilizing the boat on the wave and improving stability, and making them yourself not only saves a lot of money compared to the factory counterparts, but also perfectly adapts the design to a specific model of the vessel and operating conditions.
In this article, we will take a detailed look at all the steps in making homemade stringers, from the choice of materials to the final installation, learn how to avoid the typical errors that can lead to damage to cylinders, and get proven drawings for independent work.
Purpose and principle of operation of stringers on inflatable boats
The main task of any stringer is to form a clear fracture of the side, which acts as a cheekbone. On rigid housings, the cheekbone is created by the shape of the material itself, but in the case of a squinting rod, the rod is a very large shape. PVC boats The side is a soft cylinder, and when you're moving at speed, the water flows around the side in a chaotic way, creating resistance and causing yaw -- wagging your nose from side to side.
The rigid element is placed along the side, and it forces the hull to form a facet, allowing water to descend in a predictable flow, reducing resistance and improving germination per wave, and having a rigid longitudinal bond significantly increases the overall torsion rigidity of the hull, which is especially important for boats with flat or poorly inflatable bottoms.
It's important to understand the difference between a stringer and a quill. The quillson is a longitudinal beam that sits on the bottom of the cockpit, which protects the inflatable floor from being misused, and the Stringer is attached to the sides, either from the outside or from the inside, to the sides, working with the flow fluid dynamics. The optimal angle of fracture of the side, created by the stringer, is from 15 to 25 degrees.This provides a better balance between stability and softness.
Selection of materials for self-manufacturing
The first and most important step is to select materials, because stringers will be in constant contact with water, subjected to ultraviolet radiation and mechanical stress, the requirements are high. The most popular material for the base is high-density foam or polystyrene foam, it is lightweight, does not absorb water (when properly processed), and is easy to process.
For the outer skin and to create a strong frame, fiberglass is used in combination with epoxy resin. An alternative is carbon fiber, which is stronger and lighter, but much more expensive. As an adhesive for fixing elements between themselves and sealing seams, two-component polyurethane adhesives or specialized formulations for the purpose of fixing the elements among themselves and sealing the seams, the best proven themselves are two-component polyurethane adhes or specialized compounds for the use of the ad. PVC.
- 🛠️ Basis: PSB-C-35/50 foam or extruded polystyrene (XPS) 30-50 mm thick.
- 🧵 Reinforcement: Glass fabric density of 200-300 g / m2 and epoxy resin with hardener.
- 🧴 Clay: Polyurethane adhesive (e.g. Titan, Macroplast) or PVC adhesive with activator.
Some craftsmen try to use a tree soaked in olive oil, but this option only has the right to exist with perfect varnishing, otherwise the tree will quickly gain moisture, become heavy and may begin to rot, damaging the cylinders of the boat. composite They are the uncontested leader in this segment.
Drawings and calculation of profile geometry
Before you pick up a tool, you have to decide on the geometry of the product, and the shape of the stringer depends on the design of your boat: where the balloon is located, what its diameter is, how much it's bloated. There's no universal size, so taking measurements from your boat is a must.
The profile of the stringer is usually a triangular or trapezoidal prism. The width of the base depends on the area of contact with the balloon, and the height and angle of the edge are selected experimentally or by ready-made schemes for specific models. For a standard boat with a length of 320-360 cm, the optimal length of the stringer is about 2/3 of the length of the balloon, starting from the transom.
Typical dimensions for boats 320-360 cm long
Stringer length: 180-220 cm The width of the base (contact with the balloon): 60-80 mm. the height of the profile (creating the edge): 40-60 mm. the angle of the working face: 20-25 degrees. the thickness at the edge (negative): 5-10 mm.
It is important to design smoothly to the nose and stern, and sudden changes in altitude can cause local PVC tissue strain and even punctures, and it is also important to consider the location of the handles for carrying and mounting the cans, so that the stringers do not interfere with their functionality.
Step-by-step instructions for the manufacture of stringers
The manufacturing process can be divided into several technological steps, the following sequence of operations ensures the strength of the product and its durability, and you should not rush to apply the reinforcement layer until the base is ready.
First, the sheet of foam is cut to the removed standards, conveniently using a hot string or a regular stationery knife with a long blade, then glued together (if the thickness of one sheet is insufficient) and given the desired profile using a grinder or coarse-grained sandpaper.
☑️ Checklist for preparation of the framework
The next step is to glue the fiberglass, and the surface of the foam is then ground with an epoxy resin, and then the first layer of tissue is applied, and after polymerization, a second layer is applied, often with the fibers shifted for greater strength, the ends are also thoroughly soaked in resin, and after drying completely, the surface is grinded to smoothness to eliminate the risk of damage to the balloon.
Technology of installation and fastening to cylinders
Installation of stringers is the most important step on which safety depends. There are two main ways of attaching: inflatable and rigid. In the first case, stringers have special pockets or valves where part of the cylinder is refueled; in the second, they are glued directly to the surface of the cylinder or attached to Velcro/belts.
The most reliable method is the combination method using high-quality glue, before gluing the surface of the balloon and the stringer is degreased, the glue is applied to both surfaces, the "stick" time is kept (usually 15-20 minutes), after which the parts are joined and tightly pressed.
To enhance the fixation, you often use a system of belts or Velcro straps that cover the balloon and the stringer, preventing them from shifting when they hit the wave. It is important to make sure that the fasteners do not have sharp edges that can damage the fabric.
| Parameter | Adhesive compound | Mechanical (belts) | Inflatable pocket |
|---|---|---|---|
| Reliability | High. | Medium | High. |
| Difficulty of installation | High. | Low. | Medium |
| Impact on the cylinder | Risk of withdrawal | Friction | Safe. |
| Removability | Immovable. | Removable | Removable |
⚠️ Attention! When using the adhesive method, make sure that the composition chosen is compatible with the material of your boat (PVC or Haipalon). Aggressive solvents can damage the structure of the cylinder tissue, making it unusable.
Structural reinforcement and finishing
After installing the stringers, it is recommended to conduct an audit of the points of contact with the balloon. Often in the area of friction or stress concentration, the fabric of the cylinder becomes thinner. To prevent this, you can glue additional PVC tapes or use special protective linings (liktros) at the points of contact.
If you've used epoxy to make the stringers themselves, make sure the surface is completely smooth. Any roughness will work like an abrasive. If necessary, you can coat the stringers with a thin layer of polyurethane varnish or liquid rubber, which will increase their wear resistance.
To check the quality of the paste, slightly tap on the surface of the finished stringer. A deaf sound may indicate the detachment of the fiberglass or the presence of voids inside, which requires repair.
Finishing also involves painting or pasting with colored film if you want to give the boat an aesthetic look, but remember that dark colors in the sun are heated more, which can lead to local overheating of the balloon at the point of contact.
Operation and typical manufacturing errors
When you're using homemade stringers, you can get design errors, the most common of which is miscalculation of weight, too heavy stringers reduce the payload of the boat and make it roll, which is why choosing lightweight foam and the minimum amount of resin is so important.
Another mistake is symmetry breaking: If the left and right stringers are different in shape or angle, the boat will be constantly led aside, and you will have to constantly adjust your course, which is quickly tiring.
⚠️ Attention! Never use stringers with sharp inner corners facing the cylinder. Under water pressure and when pitching, such a structure can act as a knife, cutting the fabric. All inner corners must be rounded with a radius of at least 10-15 mm.
Regularly check the condition of the adhesive seam. Over time, the glue can lose its properties, especially if the boat is stored assembled or under the influence of temperature changes. Timely repair will prevent the loss of the stringer on the water.
Properly manufactured and installed stringers turn a soft inflatable boat into a serious glittering boat, significantly improving handling and comfort on the wave.
Frequently Asked Questions (FAQ)
Can stringers be used on low-pressure inflatable floor boats (LBPBs)?
Yes, but with caution, on NDND boats, the bottom is hardened by the pressure in the cylinders themselves, and the installation of external stringers can be redundant unless you plan to go high speed, and in these cases, internal quilts are more often used.
What glue is best for gluing stringers to PVC?
Best-proven two-component polyurethane adhesives (e.g. Kleyberg, Titebond Polyurethane) or specialized adhesives for PVC activator (two-component systems) provide an elastic and water-resistant seam that withstands deformation.
How much will the speed of the boat increase after installing the stringers?
Speed gain is not a direct goal of the installation, although it is possible (usually 1-3 km / h), the main goal is to stabilize the course and reduce yaw. The boat becomes more predictable, less "cruising" on the wave, which allows you to keep your course more confident and save fuel due to less engine adjustments.
Do I need to remove stringers when storing a boat?
If the stringers are glued to the dead, then they do not need to be removed, but it is desirable to store the boat in a straightened form or with a minimum number of cracks in the area of the stringers. If a removable mount (Velcro straps, belts) is used, then it is better to remove them for the winter to relieve stress from the fabric of the cylinder.