How to fight the bow wave
Water entering the engine during off-roading can spell trouble for the car

The term "bow wave" applies to a boat or ship which has to cut a path through water to make progress. Water, because of its hydraulic properties, offers tremendous resistance. It is for this reason the front end of boats or ships are tapered and come to a sharp, knife-like edge to cut through the water. Any other shape and they would create a bow-wave, an almost solid wall to impede progress.

Cars are designed to run on roads and to reduce wind resistance, have sleek and aero-dynamic shapes. The front has to house headlights, radiator grill and bumpers. This necessitates the front end being flat, broad and wide. Not the ideal shape to go through water. With numerous off-road clubs in the area and as many rivers around Chandigarh, one of the joys and challenges of off-roading is to race around on the sandbanks and ford the river.

It is great fun, demanding and a challenge. At the same time, it has its share of dangers. One danger is of water entering the engine compartment. That is bound to happen because as the car moves, it pushes the water ahead and creates a bow-wave. If the water body is deep, the water will flow over the bonnet. When you open the bonnet of the car, immediately behind the grill is the radiator which helps to keep the engine cool. To help in the cooling, there is a fan to suck in fresh air to cool the engine. While in water, the front end has created a bow wave and the fan will suck in water and spray the entire engine.

This will create problems. The new breed of cars have a lot of electronic equipment. Getting them soaked is not recommended. There is also the danger of water entering the air cleaner. This could lead to hydrostatic lock and that costs a lot of money to sort out.

What is hydro-static lock? Under normal circumstances, air has to enter the cylinder via the air cleaner where it will mix with the fuel. The gaseous mixture is compressed by the piston in the combustion chamber, fired by the spark plug, drives the piston down which moves the crank shaft. One of the strokes of a four-cylinder engine is complete. In case of hydro-static lock, water enters the cylinder. Water cannot be compressed. The connecting rod pushes the piston which cannot compress the water. The result is the connecting rod will bend or break, causing massive damage to the engine. If you are a regular off-roader and make it a habit of crossing water bodies, you should get a snorkel fitted to the car. This is a simple extension attached to the air-cleaner system with the intake opening at roof level.

A much simpler way to prevent water entering the engine compartment would be to hang a plastic sheet in font of the radiator. Open the bonnet, drape the plastic sheet, close bonnet, the plastic sheet will be held in place. No danger of water being sucked into the engine. The accompanying photographs show a bow wave created during water crossing (see picture). The lower picture shows how a simple plastic sheet is of great help to prevent water from entering the engine.

You don't have to be crossing a deep water body to suffer hydro-static lock. It can happen on our city roads which can have half a metre of water after a heavy deluge during the monsoon. The only prevention is to drive slow and steady. Happy Motoring !

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