The flat bottom of inflatable boats, often called the flat bottom, is ideal for quiet fishing in shallow water, but has one major drawback: low course stability. When you go on a wave or when you go against the wind, the boat starts to prowl, which forces you to constantly adjust the course and tires the helmsman. keelIt not only stabilizes the movement, but also significantly improves handling at high speeds.
Self-manufactured this element saves a substantial amount of money compared to the purchase of factory counterparts or a finished boat with a keel. In addition, the artisanal method provides a unique opportunity to adapt the shape and size to specific operating conditions, whether it is a fast flowing river or extensive reservoirs. In this article, we will discuss in detail how to design and install. keel-ball Or a rigid element, turning an unstable flat-bottom into a full-fledged vessel.
Before you start purchasing materials, you need to understand that the keel is not just a decorative pad, but an important hydrodynamic element. It works like a fin, crashing into the water and preventing lateral demolition of the body. Properly calculated geometry reduces water resistance and increases the efficiency of the outboard motor, which directly affects fuel consumption and maximum speed.
Selection of design and materials for self-manufacturing
The first step is to determine the type of design you're going to implement, and there are two main approaches: using an additional inflatable balloon that's attached to the bottom, or creating a rigid frame of composite materials. keelIt retains the buoyancy of the boat and does not require complex strength calculations.
The traditional homemade material is PVC fabric with a density of 850 to 1100 g/m2. It is the same material that most high-quality boats are made of. The use of a thinner material is unacceptable, since the keel takes on significant shock loads from waves and underwater obstacles. For rigid inserts, if you choose the combined version, the best fit is plywood FSF or aviation aluminum.
⚠️ Note: Using conventional construction adhesive instead of a specialized polyurethane compound for PVC will cause the seams to disperse at the first serious tension of the fabric under water pressure.
It's also important to define the profile of the keel, which can be triangular, which gives you better course stability, but it's harder to make, or it can be rounded, which resembles an inverted boat, a round profile is easier to build and less susceptible to hooks by algae or driftwood, and the choice depends on your tool skills and the availability of patterns.
Required tools and workplace preparation
It's not just a material that needs to be done, it's also a specialized tool, and without an industrial hair dryer that can produce temperatures up to 600 to 700 degrees, PVC fabric gluing is not possible, and household hair dryers are not suitable because they can't provide the temperature to activate the adhesive layer.
You also need rollers, which are essential for removing air bubbles from the surfaces that are glued together and for ensuring that layers are in close contact. In the home workshop, they are often replaced with rubber rollers for rolling out wallpaper, but a professional tool made of hard rubber or Teflon will do the job much more effectively.
List of necessary equipment and consumables:
- 🛠️ Industrial dryer with temperature control and a narrow nozzle.
- 🧪 Specialized two-component adhesive for PVC (for example, Texacol or its analogues).
- ✂️ Portnow scissors with sharp blades and a cutting knife.
- 📏 Roulette, ruler and markers for fabric (disappearing or permanent).
- 🧹 A solvent (acetone or ethyl acetate) for degreasing surfaces.
- 🪵 Wooden bars or heavy sandbags for pressing gluing.
The workplace should be spacious, dry and well ventilated, the temperature in the room should be maintained in the range from +18 to +25 degrees Celsius, cold air will slow the polymerization of the adhesive, and too hot can cause premature activation of the composition.
☑️ Preparation for gluing
Untie fabrics and create patterns
The process of creating the keel begins with the exact cutting of the material. A mistake in the calculations at this stage can lead to a skewed design, so it is recommended to first create life-size paper patterns. The length of the future keel is usually from 2/3 to 3/4 of the length of the useful space of the boat, so as not to rest on the transom or nose too hard.
The width of the keel at the widest part (middle) varies from 20 to 30 cm, tapering to the nose and stern. This shape ensures smooth flow of water. When you cut, be sure to leave technological tolerances at the seams, usually 3-4 cm on each side. If you make a keel of two symmetrical halves, which then connect, the tolerances must be even larger to form an internal valve.
Use a long ruler or a stretched thread to make the lines perfectly straight. The curves of the nose and stern are conveniently drawn from a pattern of cardboard or flexible slats. All parts should be cut with maximum accuracy, since uneven edges will complicate the gluing process.
The Secret to Perfect Crackdown
Use heavy metal loads (such as a long ruler or profile) to fix the fabric on the table, which will prevent it from shifting and deforming during the cutting process, ensuring that the parts are symmetrical.
After cutting out all the elements, it is recommended to spread them on the floor and visually assess the symmetry. If one side is markedly different from the other, it is better to fix this now than to remake the finished product. Symmetry - a guarantee that the boat will go straight, and not go into circulation.
Technology of gluing of seams and formation of volume
The most important step is to connect the parts, and the glue is applied to both of the glued surfaces in a thin, uniform layer, and after the first layer is applied, you have to let it dry to the stick (usually 10-15 minutes), and then you apply the second layer, and the second layer provides the main strength of the connection.
After the second layer is dry, the surfaces are heated by a hairdryer to the melting point of the glue (the tissue becomes hot to the touch, but does not melt itself). Then the parts are tightly pressed and rolled from center to edges to squeeze out all the air. Pay special attention to the nose and aft parts, where geometry is most complex.
Table of gluing parameters for different temperatures:
| Indoor temperature | Drying time of 1st layer | Drying time of 2nd layer | Time for the seams to cool |
|---|---|---|---|
| +18...+20 °C | 15-20 minutes | 5-7 minutes | 40-60 minutes |
| +21...+24 °C | 10-15 minutes | 3-5 minutes | 30-40 minutes. |
| +25...+28 °C | 5-10 minutes | 2-3 minutes | 20-30 minutes |
It is important not to overheat the fabric, otherwise it will lose its elasticity and strength. If the material begins to shine or bubble, the heating should be stopped immediately.
Mounting the keel on the boat hull
The keel must be carefully marked, the centre of the keel must be closely aligned with the diametrical plane of the boat, and the cord stretched from the centre of the transom to the forehead, and any shifting to the side will lead the boat away from a straight line.
There are two ways of fastening: gluing it all over the area or pointing it in the nose, the stern and the center. The first option is more reliable, but requires perfect bottom levelness. The second option allows for slight irregularities and is easier to perform. Before gluing the surfaces, they must be defatted.
⚠️ Warning: When gluing the keel, make sure that the glue does not get on the sides or other parts of the boat that are not intended for gluing. It is almost impossible to remove the frozen glue from the surface of the cylinder without damaging the protective layer.
The glue process is similar to the keel assembly: two layers of glue, drying, heating, rolling, starting with the stern, gradually moving to the nose, carefully smoothing the fabric so that there are no air pockets under the keel, the air inside can expand into the sun and unstick the structure.
Strengthen the transom and check driving performance
The keel changes the load on the transom, especially when you're sleeve-steeling. If your transom is made of thin plywood, it makes sense to reinforce it with a plate or replace it with a stronger material. The keel takes over some of the load, but the vibration from the motor is transmitted to the entire aft.
The first descent should be in calm weather, and watch the boat's behavior: it should keep its course more confident, stop prowling from side to side, but you may need to adjust the angle of the trim by moving the load or changing the position of the engine.
The key advantages of a properly installed keel:
- 🚀 Increase the maximum speed by reducing the resistance.
- 🎯 Improvement of exchange rate stability on the wave and in side wind.
- 🛡️ Protect the bottom from impacts on underwater obstacles (stones, logs).
- ⛵ The ability to use sailing equipment more efficiently (if applicable).
After the first operation, be sure to check the seams of the keel and its attachment. The absence of detachments and bubbles confirms the correctness of the technology. If there are no defects, your homemade will last for many seasons.
The main result: Self-made keel is a budget way to turn an ordinary flat-bottom into a high-speed and stable vessel, requiring only accuracy and compliance with the temperature regimes of gluing.
Frequently Asked Questions (FAQ)
Can I use a regular rubber glue instead of a special one for PVC?
No, it's not recommended. Rubber glue (based on rubber) doesn't form a chemical bond with PVC. Under pressure and water, this seam will quickly dissipate. Only use polyurethane two-component compounds for boats.
How much will the keel increase the weight of the boat when assembled?
The weight of a homemade keel of fabric with a density of 900-1100 g / m2 is usually from 1.5 to 2.5 kg. This is a slight increase in total weight, which is fully compensated for by improving the performance and safety of the vessel.
Do I need to pump the keel separately from the main boat?
If you make an integrated keel (stick directly to the bottom), it's pumped along with the main cylinder, because it communicates with it or is an extension of it. If it's a separate removable element, it's got its own valve and pressure requirement, usually 0.2 atm.
What to do if the keel caught on the snag at speed?
The inflatable keel has a certain elasticity and often just slips off the obstacle. However, if you hit hard, you can puncture. Always carry a remix. A hard keel is more dangerous in this regard, because it can cause the boat to tip over when you brake sharply.