Many owners of inflatable floating vehicles sooner or later face the problem when the standard height is not the same. transom The 381 mm (15 in) standard is suitable for most engines, but specific operating conditions or the desire to put a long leg motor require redesign, not just a whim, but often a necessary measure to improve the performance of the vessel.
The extension of the transom board is a process that requires precision and understanding of the physics of boat movement on the water. An improperly executed superstructure can shift the center of gravity, upset the balance, and even lead to the cockpit bay with off-board water. However, with the right approach, you will get a versatile vessel ready to install various types of engines. In this article, we will discuss proven methods of increasing height that will not interfere with the tightness of the cylinders.
Before you start cutting materials, you have to take measurements and weigh the pros and cons. Sometimes it's easier to buy a specialized adapter than to build a complex structure. PVC Keep your hands on the water, stock up on quality materials and tools, and safety on the water depends on the reliability of your vessel.
Why do we need to increase the height of the transom
The main reason for the upgrade is to install a longer, lower unit engine. Standard 15-inch engines may not be suitable for some boat models, especially if you plan to use them as tenders or for specific tasks. Increasing the height of the transom allows you to raise the mounting point of the engine, which changes the way you want to do it. differentiation boat.
In addition, a high transom is often necessary to install additional accessories such as sonars, speed sensors or additional fishing brackets. In some cases, this is a safety issue: a raised motor is less likely to be hit by a wave in a sharp stroke.
It's important to understand that lifting the transom changes the geometry of the screw's interaction with water. cavitationSo the increase in height must be strictly based on the specifications of your motor, and you don't have to chase the maximum height without calculating.
Selection of materials for transom superstructure
The choice of materials for the extension of the transom must be approached with great care, because the design will constantly experience vibration loads and contact with water. plywood The use of conventional construction plywood is unacceptable, as it will quickly layer and lose strength.
To protect the wood from moisture and aggressive environment, special varnishes, epoxy resins or fiberglass are used. sealing It's a guarantee of the durability of your superstructure, and you'll also need stainless steel or galvanized metal fasteners to avoid corrosion at the interconnection points.
- 🌲 Marine plywood (birch or hardwood) of the highest grade.
- 🛡️ Epoxy glue and fiberglass to create a durable shell.
- 🔩 The stainless steel (bolts, nuts, washers).
- 🧴 Polyurethane-based sealants for seams.
⚠️ Warning: Never use aluminum alloys to contact plywood without an insulating pad. In seawater or even fresh water, when salt is present, a galvanic vapor will destroy the metal in one season.
The weight of the superstructure is also critical: a transom will shift the centre of gravity of the stern downwards, which can cause the bow to bury in the wave. Use lightweight but durable composite materials where possible. The ideal combination is a thin but durable plywood and a reinforcement layer of fiberglass.
Dismantling of the standard transcension and preparation of the basis
The process starts with a careful dismantling or site preparation, so if you plan to make a removable add-on, the standard transom stays in place, and the new design is attached on top of it, and if you're going to overhaul, the old transom will have to be removed, which requires you to disconnect the cylinders from the bottom.
Before work begins, you need to thoroughly clean the surface of dirt, grease and old coatings. Any speck of dust can break the adhesion of the glue. Degreasing the surface with acetone or a special solvent is a mandatory step, and only after that you can start marking and cutting the blanks.
☑️ Preparation for installation
When cutting the mold, it is important to observe symmetry, even a few millimeters of skewing will lead to an uneven distribution of load on the cylinders. Use patterns from cardboard before cutting expensive marine plywood. Accuracy at this stage will save you time and nerves in the future.
Technology of building and fastening of superstructure
There are two main ways to increase the height: to create a single superstructure and to build a modular structure. In the first case, you make a new trans board of increased height, which completely replaces the standard one. In the second, you make a "superboard" that is bolted to the existing transom through special eyelets.
The fastening must withstand considerable loads, especially on planing. The vibration of the motor can unwind even well-tightened nuts, so use grovers or carving fixtures. Gasping of rubber or neoprene between the wooden parts will help to extinguish vibrations and prevent rubbing of the material.
Secrets of secure fastening
Use the "through the layer" method, and the bolts not only go through the superstructure, but also grab a part of the balloon through special protective plates, spreading pressure over a large area, which prevents PVC tissue from rupturing in the fasteners.
When assembling the structure, watch the corners. The trunk should be perpendicular to the bottom plane (or have a standard angle of 10-15 degrees, depending on the boat model). Violating this angle will lead to the wrong boat exit for sleeving. Geometry check is better done using the construction level and the coal mine.
Sealing and moisture protection
Wood and water are eternal enemies, so the sealing phase is key to your boat's longevity. Once assembled, all the joints, joints and entry points of the fastener must be thoroughly sealed, and polyurethane sealants are best-proven, which remain elastic after drying.
For maximum protection, plywood is coated with several layers of epoxy resin with fiberglass, which creates a durable shell that does not let water through even when the outer layer is mechanically damaged. Don't skimp on the number of layers of varnish or resin.
| Materials of coating | Resistance to water | Resistance to UV | Difficulty of application |
|---|---|---|---|
| Yacht lacquer | Medium | High. | Low. |
| Epoxy resin | High. | Medium | Medium |
| Fiberglass | Very high. | High. | High. |
| Polyurethane | High. | High. | Low. |
Pay special attention to the places where the bolts are attached. Before inserting the bolt, you should definitely drop a sealant in the hole, which will prevent water from entering the structure of the tree through microcracks around the fastener. Water trapped in the plywood can break the transom when it freezes.
Strength Testing and Test Launch
Once all coatings and sealants have been completely dryed, you need to do a visual inspection and strength check. Try to apply a force to the transom, simulating the load of the motor. The design should not make creaks or cracks. Any doubts about reliability should be eliminated on the shore.
The first exit must be quiet. Don't immediately develop full power. Check if the boat is gaining water near the transom, as the boat behaves at different speeds. Pay attention to the angle of the differential: if the boat's nose is lifted too high, it may be that the transom is raised too high.
Before the first full swim, do a dry test: fasten the engine (no start) and rock the boat, simulating a wave. Check if there are folds or tension of the fabric in the attachment areas of the superstructure.
Regularly inspect the condition of the transom during operation. The appearance of bloating on the varnish, changing the color of the tree or fastener are signals that you need to repair. Timely maintenance will prolong the life of your homemade product for many years.
The quality of sealing and the accuracy of geometry are more important than the thickness of the plywood used, and a lightweight and properly assembled structure will last longer than a massive but poorly protected one.
Can I increase the height of the transom without removing the cylinders?
Yes, this is possible with overhead structures that are attached to the standard transom through special clamps or bolts that pass through existing holes, but this design will be less reliable for powerful motors.
What is the maximum height of a transom can be made?
It is recommended not to exceed the standard height by more than 50-70 mm. Excessive engine lifting disturbs the balance of the boat and increases the risk of cavitation of the screw, which reduces the efficiency of the engine.
Do I need to register changes in the GIMS?
Under current regulations, a small vessel design change that affects its stability or carrying capacity theoretically requires changes to the documents, but in practice, homemade transom superstructures are rarely checked unless they change the dimensions of the vessel drastically.