Managing submersion for military vehicles | Military vehicle dynamics

Driving your car through deep water is not only unadvisable, it’s also pretty dangerous. In the last five years, the Automobile Association (AA) has been called out to a colossal 23,000 flood rescues and, according to the company’s director of cars, 70 per cent of flood-stranded cars are completely written off by their insurers. For regular passenger vehicles, the advice is clear — don’t drive through water. But, what about specialist vehicles that cannot avoid this terrain?

Here, Cy Wilkinson, managing director of steering column specialist, Pailton Engineering talks about the requirements of military vehicles that need to ensure they can withstand harsh conditions including the potential of wading in water.

Standard passenger vehicles are not designed to be driven through water. Even drivers of higher-riding passenger vehicles, like 4×4’s, are advised against it. If driving through flood water is completely unavoidable, Land Rover advises its drivers to creep into the water at a very low speed, building up momentum to create a bow-wave behind the vehicle as it moves through the water.

This can be an effective way to keep the air intake of the vehicle clear of water. However, it is not a feasible method for vehicles that are regularly subject to wet terrain, or are subject to being partially submerged in water.

‘Semi-amphibious’ is the term used to describe heavy duty vehicles that can manoeuvre through water that is several metres deep — often referred to as deep wading. Many of us will have seen off-road passenger vehicles fitted with a snorkel that is higher than the normal engine air intake, usually level with the top of the cab.

Usually, when these snorkels are fitted to off-road vehicles they are being used by hobbyists or by those with jobs that require them to do a lot of off-road navigation. These vehicles do provide some wading capabilities, but not the level of submersion required for extreme or military applications.

Truly semi-amphibious vehicles are usually armoured military vehicles that can be mostly or almost entirely submerged in water. These vehicles are manufactured with the ability to manoeuvre through wet terrain at the forefront of their design — above the aesthetics, comfort and speed specifications of a regular passenger vehicle or 4×4.

To successfully navigate through water, military vehicles must ensure that all components underneath the vehicle are completely sealed off to external elements — or designed in a way that ensures they are unaffected by exposure. However, it is not just water that military vehicles need to withstand; dust, grit and general rough terrain can also cause problems.

Designing and producing military vehicles is not a cheap exercise, nor is it something to be taken lightly. Consider military steering systems as an example. Many extreme applications expose the steering system to salt, water, grit and mud. Generally, the bevel boxes on steering systems are not designed to handle this exposure, yet many steering systems are standard in design.

By choosing a bevel box that is designed with extreme applications in mind, the manufacturer can ensure it can withstand these conditions, without affecting the durability or agility of the drive itself. Choosing a supplier that can provide proof that the components can withstand these conditions is important, and can help manufacturers to avoid any nasty surprises in the long term.

Military vehicles must be able to withstand tough terrain. So, when purchasing components for a military vehicle, manufacturers should never assume the part has been tested to its limits. Instead, they must choose a supplier with a dedicated testing facility. In the case of military vehicles, the equipment should be adequately tested against the effects of encountering water, mud or grit while driving. Naturally, different types of vehicles require different testing procedures, and this is usually determined by the environment in which the vehicle will operate.

Thorough testing procedures will not only subject the components to different terrains, but will also simulate long distance driving to identify how the system will be affected over time. For example, rotary test machines are a way to check the wear on bearings in universal joints, sliding shafts and other moving parts of a steering system.

It is common sense that most cars on the road are not built to drive safely through flood water. However, for specialist and military vehicles, avoiding wet terrain is not an option, so every little thing that could prevent a breakdown in a dangerous environment has to be designed and tested to keep the vehicle moving.

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