Many owners of rowing boats or inflatable PVC vessels with low-power engines sooner or later think about improving the running performance, most often due to the desire to install a more powerful outboard The standard transom, which comes as standard, is often designed for minimal loads and is not suitable for modern engines with a capacity of 5 hp and above.
The modernization process is slow and requires accurate calculations, because the quality of work directly depends on the safety of the crew and the buoyancy of the vessel. An improperly installed engine can lead to deformation of the stern, water entering the hull or even engine separation at full speed. In this article, we will discuss in detail the stages of alteration, the choice of materials and critical points that cannot be ignored when you are self-tuning.
Owners of PVC inflatable boats should consider that the soft transom has its rigidity limitations. Installation of a powerful motor often requires the installation of an additional transmuter board or the complete replacement of the transmuter with a rigid version with amplification. Metal and wooden housings also require a careful approach to strengthening the structure to withstand increased vibration loads and torque of the screw.
Status analysis and selection of materials for reinforcement
The first step should always be a thorough diagnosis of the current state of the stern. If you are talking about an old wooden boat, you need to check the trawler for rot, plywood stratification or corrosion of fasteners. In the case of PVC boats, the wear of the fabric at the place of gluing the stern board and the condition of the slings are evaluated. load-bearing capacity The design is the main parameter that must be determined before the work begins.
For strengthening or replacing transom in metal boats, aluminum is considered the optimal material. AMG5 or AMG6These alloys have high corrosion resistance in seawater and sufficient strength. The use of conventional steel is not recommended due to rapid oxidation, and titanium, although strong, is difficult to work at home. Metal thickness should be at least 3-4 mm for motors up to 15 hp, and 5-6 mm for more powerful units.
For wooden and composite structures, the best choice will be moisture-resistant plywood of increased strength (marks) FSFIt is important that the plywood thickness corresponds to the power of the planned motor: the plywood layers must be glued with phenolformaldehyde glue, which ensures durability even in constant contact with water, the surface must be treated with epoxy resins or special yacht varnishes for complete sealing.
⚠️ Attention: Use of conventional construction plywood or wood that has not undergone special hydrophobic treatment will lead to rapid swelling and loss of strength of the transom already in the first season of operation.
When choosing fasteners, give preference to stainless steel bolts A4 (316)They are resistant to salt water and corrosive environments. Conventional galvanized fasteners will rust over time, which will weaken the connection and can cause leakage. All bolt holes in metal transverses must be cherry-marked and sealed with thiocol or polyurethane sealants.
Calculation of installation height and transom angle
One of the most important parameters in the reworking is determining the correct height of the engine's lower unit installation, which directly affects the efficiency of the propeller and the lack of cavitation. If the engine is installed too low, water resistance increases and maximum speed decreases. Too high a landing will lead to air capture by the propeller blades, which will cause the engine to overheat and lose traction.
The standard transom height for most outboard motors is 381 mm (15 inches) for the long leg and 508 mm (20 inches) for the long leg, but when redesigning an old vessel, these dimensions may differ. The transom angle (different) also plays a key role: the optimal is the tilt of the motor back by 10-15 degrees relative to the perpendicular to the bottom.
Adjusting the angle of inclination often uses transom plates or adjustable mounts, which allows you to experimentally choose the best position for a particular boat and load. The wrong angle of the trim can cause the vessel to yaw on the course or make it difficult to go to the planing. In the design of a new transom, the angle of inclination is laid structurally.
When you put the motor on a transom, it's important to consider not only the height, but also the symmetry of the landing. The engine must be located strictly on the diametrical plane of the vessel. Shifting the engine to the left or right will lead to constant steering to the side, which will require constant operation with the steering wheel or trim, increasing fuel consumption. For precise alignment, laser levels or strained threads from the nose to the stern are used.
Technology of installation of a transom board on a PVC boat
Inflatable boat owners who want to install a more powerful engine often need to replace the standard glued board with a reinforced version. The process begins with carefully dismantling the old transom if it has become obsolete, or preparing a place for the installation of a new one. The surface of the cylinder and the board itself must be perfectly clean, fat-free and dry.
The adhesive technology requires a temperature and aging time, and the adhesive is applied to both glued surfaces in two layers: the first layer is rubbed into the fabric until the stickiness disappears, the second is applied after the first one has been dryed (usually after 15-20 minutes), and the compound is made after the solvent has evaporated, when the adhesive stops sticking to the fingers but retains stickiness. Ride-up The seam is made with a solid roller from the center to the edges to remove air bubbles.
To strengthen the place of attachment of the transom to the cylinder, additional tapes of the same fabric as the boat are often used. The tapes are glued over the main seam with an overlap of at least 3-5 cm. This allows you to distribute the load from the motor over a large area of the cylinder and prevents the transom from being removed by vibration. Particular attention is paid to the corners of the transom board, where the stress concentration is maximum.
☑️ Check before installing the engine
Once the new transom board is installed, the glue must be allowed to fully polymerize. The full load readiness time is usually 24 to 72 hours depending on the air temperature and type of glue used. Early installation of the motor can cause the board to shift and the seam to become leaky. It is recommended that the inflated cylinder be visually inspected and checked under load before the first start.
Metal transmesse reinforcement and sealing
Metal boats, especially Soviet-built or artisanal ones, often have a transom that is not designed for modern high-powered motors. The reinforcement is done by welding extra stiffness ribs or installing a thicker sheet overhead transom. If the standard transom is less than 3 mm thick, welding a new sheet over the old one is the most reliable solution. It is important not to overheat the metal during welding, so as not to let it go and not reduce the strength.
The sealing of the mounting bolts is a critical step in the work: the holes are drilled with a margin of 1-2 mm larger than the bolt diameter, zinced and filled with sealant. The bolt is inserted into a layer of sealant, then applied a second layer on top and tightened the nut. This method, called "wet installation", ensures that water never reaches the metal around the hole.
To protect against corrosion, all welds and the interior of the transom must be treated with anti-corrosion compounds. Epoxy soils and zinc-containing paints are excellent. The outer part of the transmunus in contact with water can be protected with polyurethane enamels or removable plastic linings that will take on screw blows and abrasive effects of sand.
| Engine power (hp) | Min. aluminum thickness (mm) | Diameter of fastening bolts (mm) | Recommended material |
|---|---|---|---|
| up to 5 hp | 3 mm | 8 mm | AMG5, FSF 18mm |
| 6 - 15 hp. | 4 mm | 10 mm | AMG6, FSF 21mm |
| 18-30 hp. | 5 mm | 12 mm | AMG6, FSF 24mm |
| 40+bhp. | 6 mm or more | 14 mm | AMG6, Steel 09G2C |
⚠️ WARNING: When drilling holes in an aluminum transceiver, be sure to use sharp drills and coolant to avoid metal sticking and cracking around the hole.
In some cases, when the standard transom cannot be reinforced due to the design of the boat, a remote transmolant is used, a metal frame that is attached to the sides and bottom of the boat, bringing the engine mounting point outside the normal stern section, which allows you to significantly increase the power of the engine installed without altering the entire aft end.
Installation of transax wheels and additional equipment
As the engine grows, so does its weight, making it difficult to transport a boat along the shore. Installation of transom wheels is one of the most useful additions to remodeling. Wheels can be removable or foldable. Removable structures are easier to manufacture, but require storage space. Foldable wheels mounted on brackets are always on the boat and ready to use.
The brackets for the wheels are attached directly to the transom or to the zygomatic parts of the stern. It is important that the mounting does not interfere with the installation of the motor and does not violate the tightness. For inflatable boats, there are special models of wheels that are attached to slings on a transom board or inserted into special pockets without requiring the cylinder to be drilled.
In addition to wheels, reinforced transoms are often fitted with sounder sensor holders, engine wash water intakes and attachment mounts for attached fuel tanks, all of which must be placed so as not to create additional vortices of water for an outboard motor and not interfere with the control. ergonomics The stern affects the convenience of fishing and safety.
Do I need to lubricate the motor mount bolts?
Yes, threaded joints need to be lubricated periodically with graphite lubricant or compounds like WD-40 to prevent nuts from churning due to galvanic corrosion. However, the plane of the motor's adjoining to the transom cannot be lubricated - there must be a clean metal surface or an antifriction lining.
Finishing and performance check
Once all installation work is complete, a thorough build quality check is required; visual inspection reveals glue leaks, weld irregularities or fastener distortions; a static test is recommended before the first water launch: install the motor, secure the boat on the shore and try to turn a lower unit, simulating the load. No creaks, backlashes and deformations are a good sign.
For wooden transoms, the final step is painting, using wear-resistant paints for decks and underwater, and well-established two-component polyurethane enamels that create a strong, glossy film that is resistant to shocks and ultraviolet light, and the transom color is often matched to PVC tubes or the body of a boat for an aesthetic appearance.
The first water exit should be in a calm mode, you need to check the boat for new leaks, especially in the area of the converted transom, after 15-20 minutes of operation of the engine, and you should also pay attention to the behavior of the boat on the planing: the absence of yaw and stable course indicates the correct choice of transom angle and height of installation.
To protect the threads of the motor mount bolts from acidification, use a Teflon grease spray, and apply it prophylactically at the end of each season before you can preserve the boat.
A well-designed translance extends the life of the boat and allows you to safely operate a more powerful and modern engine. Don't skimp on materials and fasteners, because the cost of error on the water can be too high. Technology and accuracy are the key to successful tuning.
The main secret of the success of transmutation is not so much the power of the new motor as the safety margin of the mounting, which should exceed the design load by at least 1.5-2 times.
Frequently Asked Questions (FAQ)
Can I increase the scalp without completely replacing it?
Yes, you can often do with a reinforcement lining (platinum) made of aluminum or stainless steel over an existing transom, which is true if the main material is intact but cannot withstand the increased loads from fasteners or vibrations. However, if the base is rotten or has cracks, replacement is required.
Which sealant is best used to seal holes?
The best results are shown by polyurethane (for example, Sikaflex) and thiocol sealants: they retain elasticity after drying, are not afraid of ultraviolet light and are perfectly adhesive to metal, wood and plastic. Silicone plumbing sealants are not suitable for this purpose, as they quickly peel off under the influence of vibration.
Do I need to remove the motor in the parking lot?
If the boat is on the water for a long time, the motor is better to remove or use special parking brackets to relieve the load from the transom, also this prevents the defoliation of the lower unit with algae and reduces the risk of electrochemical corrosion if the boat does not have high-quality anti-corrosion protection.
How do you know if the squirrel needs replacement?
The main signs: backlash of the motor in the rods even with a strong puff, visible cracks or stratification of the material, the appearance of rusty flows from the fastener (in metal), a change in the angle of inclination of the motor under load. If the boat does not accelerate when pressing the gas, but "squats" stern and the engine goes under water, the transom is deformed.