Operating a boat in difficult water conditions inevitably leads to the risk of a propeller colliding with underwater obstacles. Snags, stones, sand shoals and even accidentally abandoned anchors can turn into a few seconds. propeller Damage to the blades not only leads to financial costs for repairing or buying a new part, but also to vibrations that destroy the lower unit and the oscillators of the engine.
That is why the issue of protection of the screw is before every owner. outboard (outboard motor) be it powerful Yamaha compact TohatsuThere are many myths and technical solutions that often confuse beginners: some rely on the strength of the alloy, others install bulky structures, forgetting about hydrodynamics. In this article, we will explore real ways to minimize risks without turning a boat into a slow-moving barge.
The main task of the protection system is to take a hit or change the trajectory of the boat when touching the bottom. No device gives a 100% guarantee that the screw will remain intact when battering a concrete slab at full speed, but it significantly improves the chances. Competent approach to the choice of protection allows you to save traction and save the budget for maintenance of equipment.
Types of protective devices for screws
The boating market offers several fundamentally different approaches to protection. hydrofoilIt's mounted on an anti-cavitation plate, and it not only keeps the propeller from hitting, but it also improves the boat's performance by reducing yaw, but there are other options, such as safety rings or special linings.
The safety rings are typically a metal hoop, a zoster screw, and they are effective against vertical impacts on rocks, but they create additional resistance to water. vibration And at high speeds, it's going to be devastating for bearings, and these solutions are often found in specialized shallow water motors.
The third option is a variety of plastic pads attached directly to the anti-cavitation stove, which work like a sleigh, sliding through shallow water, which is cheap, but not always effective for side impacts, depending on where you plan to walk: on the clean Lake Ladoga or overgrown grass and driftwood deltas.
Hydrofoil: Double benefit for the engine
Installation hydrofoil The most popular method of protection is the plate that is mounted on top of a standard anti-cavitational plate, and when you hit an obstacle, the first point of contact is the hydrofoil, pulling the shock wave away from the propeller blades, and it also equalizes the flow of water that goes to the propeller.
Owners of PVC boats and small boats often notice that after installing the stabilizer, the boat stops "scouring" from side to side, this is especially true for engines up to 15 hp, where the flow from the screw can be unstable. Mercury and Suzuki Even standard solutions are released, but universal models from third-party manufacturers often turn out to be even more reliable.
⚠️ Attention: When choosing a hydrofoil, make sure it does not cover the water intake holes of the cooling system. Overheating of the engine is a much more serious problem than a bent blade.
The material also matters. Aluminum alloys are stronger, but when hit hard, they can transfer energy to lower unit. Plastic (often reinforced) on a critical impact just breaks down, taking the energy on itself and keeping the motor shaft intact. It's a kind of "fuse" in mechanics.
When installing a hydrofoil, use a threaded sealant, even if the kit includes gaskets. Vibration can weaken the mount over time.
Protective rings and their features
Safety rings are specific to specific tasks, and they are often used on motors that operate in extremely rocky rivers or in soil management (such as pumping water), and the ring creates a physical barrier around the rotor zone. Efficiency of the screw because of the vortices.
If the blades are not evenly aligned with the inner wall of the ring, you will have an imbalance, and at high speeds, you will have a beating that will quickly disable. lower unitSo these systems are rarely put on speedboats, preferring them to slow-moving workboats.
There are composite rings that are easier to mount and solid rings that require removal of the screw for installation, and in any case, the presence of such a element changes the hydrodynamics of the flow after the screw, which can affect the handling of the vessel.
The effect of the ring on speed
Installing a safety ring can reduce the boat's top speed by 5 to 10 percent and increase fuel consumption, a price that pays for increased safety of the propeller in the rocks.
Materials of manufacture: metal or plastic?
The choice of protection material depends on the type of propeller and operating conditions. Aluminum screws are softer and cheaper, so they often choose plastic linings. Steel or stainless screws installed on powerful engines are impact-resistant, but their repair is difficult. Composite materials or special alloys are better suited for them.
Plastic is good because it doesn't rust and it dampens the vibrations, but in the cold, some plastics become brittle. stainless steel Duraluminum, or duraluminum, last longer, but require a check of the fastener after each release to the water.
Comparative table of materials will help to make a choice:
| Materials | Strength | Impact on speed | Price. |
|---|---|---|---|
| Reinforced plastic | Medium | Minimum | Low. |
| aluminum | High. | Average | Medium |
| Stainless steel | Very high. | High (weight) | High. |
| Composite | High. | Minimum | High. |
For aluminum screws, plastic protection is optimal (they break first, saving the screw), for steel - metal or composite analogues.
Instructions for installation of protection
Installation of most protective devices, especially hydrowings, is simple and requires no special skills. However, a violation of the technology can lead to loss of engine warranty or damage to the components. First, you need to dismantle the propeller itself, if the design requires it, or simply clean the surface of the anti-cavitation plate from dirt and algae.
Then you need to install the gasket (if it comes with a kit) and attach protection. It is important not to pull the bolts over so as not to deform the plate or the protection itself. Use the dynamometer key if the instructions indicate specific puff moments.
☑️ Checklist of the protection installation
Once installed, be sure to start the engine on a barrel or in water and make sure that the control hole is a stream of water. If the protection blocked the water intake, the engine will boil in a matter of minutes. Also check for no extraneous noise when working at idle and elevated revs.
⚠️ Attention: Never use conventional bolts from a construction store to mount the protection. Only special stainless steel or zinc galvanic bolts will prevent the electrochemical corrosion of lower unit.
Impact of protection on driving performance
Any interference with the hydrodynamics of the aft part of the boat has consequences. A properly selected hydrofoil, as mentioned, can even improve the planing output by raising the stern. However, too massive protection will create additional resistance, which will lead to loss of speed and increased fuel consumption.
Some aquatic motorists have noted that after the protection is installed, the boat becomes more stable on the course, especially in lateral winds, this is due to an increase in the area of the planes in the stern, but at low speeds, maneuverability can deteriorate slightly due to changes in thrust vectors.
It's important to understand that propeller protection is a compromise, you sacrifice a split second in acceleration to make sure you don't get stuck in the water with a breakdown, and for tourist trips and fishing, that compromise is perfectly justified.
The myth of speed
It is believed that the protection of the propeller always reduces speed. It is not: a well-chosen hydrofoil can add up to 1-2 km / h by improving the angle of the trim.
Maintenance and condition check
The protective device needs to be maintained, and after each navigation in salt water, it needs to be washed with fresh water to avoid corrosion of the fastener, and the plastic elements should be inspected for cracks that can develop from permanent microvibrations.
Check the bolt tightening regularly. Vibration is the main enemy of any joints on the boat. If you use lubricant, use only special compounds that are not washed away with water and do not destroy rubber seals. Graphite lubrication or litol can be washed out, leaving nodes without protection.
If you have a deep scratch or chip on the protection, assess the impact on strength. Small scuffs are not terrible, but the violation of the integrity of the supporting structure requires replacing the element. Do not try to cook cracked aluminum at home without argon - the seam will be weak.
Frequently Asked Questions (FAQ)
Do I need to remove the screw to install the hydrofoil?
In most cases, you don't need to remove the propeller. Hydrowing is mounted on top of the anti-cavitation plate on regular holes or with clamps, but for some models of protective rings, dismantling the propeller is mandatory.
Will my defense help if I hit the rock at full speed?
The protection (especially the hydrofoil) will take the main blow and will most likely save the propeller from failure. However, the inertia of the boat can cause the engine to receive a strong blow, which can damage the lower unit pipe or the trunk of the boat, in such cases, the speed still needs to be reset.
Can I make protection for the screw myself?
You can theoretically make a textolite or aluminum overlay, but it's hard to calculate its hydrodynamic properties. Homemade protection can create dangerous vortices, overheat the engine or fall off on the go. Cheap factory counterparts are safer and safer.
How often should you change the plastic hydrofoil?
Life depends on the operating conditions. If you walk in shallow water often, plastic may need to be replaced every 2-3 seasons. It is a "consumer" taking the blows. Metal protections serve for decades with proper care.