Choosing the right or making a stand for the storage of an outboard motor is not just a matter of convenience, but a critical step in extending the life of your outboard motor. lower unitMany boat owners make the fatal mistake of putting the motor upright for long winters without thinking about the possibility of oil or water in the crankcase, which is why the size and angle of the stand play a crucial role in the preservation of technology.
The size of the rack is directly dependent on the power of the unit and the length of its lower unit. Standard height varies widely, but for most civilian models there are averaged norms. Two-stroke and four-stroke The engines have different mounting geometries, which should also be considered when designing or buying a support, and improperly chosen height can lead to deformation of the ramp or even to the fall of the heavy machinery.
In this article, we will discuss in detail what dimensions are optimal for different power classes, how to calculate the dimensions for a particular model and what to look for when assembling a structure yourself, you will learn why the width of the base is more important than height and how to avoid common errors when fixing the engine.
Criteria for the selection of dimensions of the support structure
The first thing to decide before purchasing materials or searching for a ready-made solution is loading capacity The outboard motors are much heavier than it might seem, especially the four-stroke models with an integrated generator and starter. The metal frame must withstand a weight margin of at least 30-40% to eliminate the risk of collapse in the event of accidental touch or vibration.
The second key parameter is lower unitThe length of the lower unit determines how high the strut or bolts will be, and if you make the strut too low, you'll have to tilt the motor too hard, which will put an excessive strain on the simulator transom, and if you put it too high, it will make the structure unstable and uncomfortable to maintain.
⚠️ Note: When calculating the height of the rack, take into account not only the length of the lower unit, but also the height of the engine rod itself. The gap between the lower edge of the lower unit and the floor should be at least 15-20 cm for free drainage of condensate.
The third aspect is base-stabilityThe width of the support section should be proportional to the height of the center of gravity of the motor. A narrow high rack under a heavy motor is a guaranteed fall. For motors over 15 hp, it is recommended to make the base wider than the motor itself by one and a half to two times.
Finally, the material of the execution is important: wood is cheaper and easier to process, but it is afraid of moisture and can rot, changing its shape. size Metal (profile pipe or corner) is more durable, but requires high-quality anti-corrosion treatment, especially if the rack will be in an unheated garage or outdoors.
Standard sizes for motors of different power
The marine engine industry has standards that allow motors to be classified by the length of a lower unit, which is the starting point for calculating the height of the vertical part of the rack. The short lower unit (S – Short) is about 381 mm (15 inches) long, which is typical for low-power motors.
For medium- and high-power engines, long-dried (L-Long) days are used, which are approximately 508 mm (20 inches) long, and there are also models with ultra-long lower unit (XL - Extra Long), but they rarely require specific racks, as they are often stored in specialized conditions or on a boat.
Use the marking of lower unit (S, L, XL) when searching for drawings on the Internet - this will significantly narrow the range of suitable designs and save time on fitting the dimensions.
Below is a table showing the recommended dimensions of the rack depending on the power class and type of lower unit, these dimensions will ensure the correct position of the motor at an angle of 10-15 degrees from the vertical, which is optimal for draining oil and water.
| Engine power (hp) | The kind of lower unit | Recommended height of the rack (mm) | Base width (mm) | Max. load (kg) |
|---|---|---|---|---|
| 2 - 6 | Short (S) | 450 - 500 | 300 - 350 | 30 |
| 8 - 15 | Short / Long | 550 - 650 | 400 - 450 | 50 |
| 20 - 40 | Long (L) | 650 - 750 | 500 - 600 | 90 |
| 50 - 90 | Long (L) | 750 - 850 | 600 - 700 | 140 |
| 90+ | Long / XL | 850 - 950 | 700+ | 200+ |
It's important to understand that these altitudes are approximate. The final size depends on the model. Yamaha, Mercury, Tohatsu Or any other brand, because the shape of the lower unit and the location of the mounting holes may differ, always take measurements of your unit before you start work.
Geometry calculation for homemade rack
If you want to make a rack yourself, you need to have a precise geometry calculation. The basic principle is to create a rigid triangle. The vertical rack on which the motor is attached, and the inclined strut connecting the vertical to the base, form a bearing circuit. The angle of inclination of the vertical part relative to the floor should be approximately 75-80 degrees (or 10-15 degrees deviation from the vertical backward).
To calculate the length of a profile pipe, use the Pythagorean theorem if you're planning a complex structure, or simple trigonometry to determine the height of the mounting point. It's critical to correctly calculate the distance between the mounting holes on the rack, and it should exactly match the distance between the holes on the rod of your motor.
☑️ Rack material calculation
When calculating the cross width on which the motor rests, note that it should not be too narrow. The optimal width of the shelf is 100-150 mm. This will prevent the breaking of the lower unit and ensure an even distribution of the load. For heavy motors (> 30 hp), it is recommended to use two parallel crossbars or a wide metal plate.
Don't forget. centre-upThe center of gravity of the motor should be approximately on the axis of the vertical pillar or slightly shifted towards the base for stability. If the motor is strongly forward, the pillar can be turned over even with a small external impact.
Materials and tools for manufacturing
The choice of materials determines the durability of your design. For a frame, a profile tube of square or rectangular section is best suited. The optimal profile size is 40x40 mm or 50x25 mm with a wall thickness of at least 2 mm. The use of thin-walled pipes or fittings is unacceptable, as they may not withstand dynamic load.
As fasteners, use bolts of strength class not lower than 8.8. Conventional "store" fasteners can burst under the weight of the motor, especially in winter, when the metal becomes brittle. Welding is preferable to connect the elements of the frame, but if this is not possible, use powerful bolt connections with coiled washers.
⚠️ Warning: When using wood (100x100 mm timber), be sure to treat it with antiseptics and oliphate. The tree "breathes" and changes sizes from humidity, which can lead to loosening of the engine mounts.
To protect against corrosion, which is inevitable in the storage of boat equipment, use rust primers and enamel paints. Well-proven hammer paints that hide small defects in welding and create a durable coating. In the areas of contact of the motor metal with the metal of the rack (on the shelf), it is advisable to stick a strip of rubber or linoleum to avoid scratching lower unit.
Do I need a painting inside my profile?
The inside of the profile pipe is not necessary if you use quality soil. However, if the pipe is not galvanized, it is recommended to pour inside a little anticoric or waste oil before assembly to prevent rusting from the inside.
Step-by-step instruction for assembling the support
The assembly process starts with cutting the workpieces according to your calculations. First, we assemble the base, which is the frame that will lie on the floor. It should be as rigid as possible. Then weld or screw the vertical rack. At this stage, it is important to strictly maintain the angle of inclination. Use the building level and the transporter for control.
The next step is to mount the crossbar to install the motor, and you have to drill holes that correspond to the mounting holes of your motor, and the standard distance between the holes is often 100-110 mm, but it is better to measure individually, the bolts must pass through the rack shelf and be fixed on the back side or inserted from the bottom.
The final touch is to put stops or stops that will keep the engine from slipping sideways, and you can also weld small hooks for suspension of fuel hoses or keys. After assembly, be sure to perform a load test: install the engine, rock the structure, make sure that there are no backlashes and cod.
A well-assembled rack should not be staggered under the weight of the motor. If there is a backlash, you need to add scarves (triangular reinforcements) to the welded joints.
Features of storage and conservation on the rack
Putting the motor on the rack is only half the battle. Proper storage requires following certain rules. As mentioned earlier, the motor must be tilted to keep the water and oil from flowing out of the lower unit. For two-stroke motors, it is especially important that the piston rings do not sour.
It is recommended to periodically (once a month) turn. crankshaft It's a starter (if you have an electric starter) or a flap, and it'll push the oil through the knots and prevent the buildup of bullies on the first run after the winter, and for a manual starter, you just need to make a few jerks.
- 🛡️ Be sure to cover the motor with a cover or a dense cloth to protect it from dust and rodents who like to build nests in carburetors.
- 💧 Before installation on the rack completely drain the fuel from the float chamber, if you do not use fuel stabilizers.
- 🔋 Remove the battery and store it separately in a warm room if you have an electric-start model.
If you keep the motor outside under a canopy, make sure the rack is securely attached to the wall or has a very wide base so that wind gusts can't overwhelm the structure.
Frequently Asked Questions (FAQ)
Can the motor be kept horizontally?
It is strongly recommended not to store the motor lying on the side or back for a long time. In this position, the oil from the crankcase can enter the cylinder (hydraulic shock at start) or leak through the sapoon. Horizontal position is permissible only during transportation and for a very short time.
What angle is considered ideal for draining water?
The optimal angle of deviation from the vertical is considered to be within 10-15 degrees. At a lower angle, water can stagnate at the lower points of the lower unit, with more - an excess load is created on the fastening units of the strubbine and the center of gravity of the entire structure changes.
Do I need to take the engine off the boat for the winter?
Yes, keeping the motor separate from the boat on a special rack is an option, which takes the load off the trunk of the boat (especially if it is PVC), prevents deformation of the transax board and allows you to properly preserve the engine itself in convenient conditions.
Will the wooden rack withstand the engine 30 hp?
Yes, if you use a timber section of at least 100x100 mm and quality hardwood (oak, larch) or well-dried pine. However, the tree requires constant care and protection from moisture, so for heavy motors, the metal profile is still more reliable.