Hose
The most common bodge -and one of the most dangerous -is the use of ordinary flexible hose in place of proper exhaust hose. Because rubber hose has excellent insulation properties, when everything is working properly it may well be possible to put your hand on the outside of the hose. But the temperature of the inner wall will be far hotter, and if the cooling system is blocked, substandard hose can catch fire in just a few seconds. Always use hose marked Marine Exhaust Hose, with the words 'Lloyds ,Approved' or 'DNV Approved' followed by a certificate number printed along it. In America, exhaust hose carries the marking SAE J2006. Basic rubber exhaust hose complying with the above standards is usually coloured black. While this hose can cope perfectly well with normal, everyday use, it needs to be inspected regularly and replaced at the first sign of deterioration or perishing. It can cope with limited overheating up to 110 deg C.

The next grade up is lined rubber hose, which has an increased overheat tolerance up to 170 deg C. You can expect to pay a bit more for lined hose compared with unlined.

Blue silicon hose is another rung up the quality ladder again, capable of withstanding a temperature of 170 deg C. This is more expensive than lined rubber hose, but gives a greater margin of safety in overheat situations.

The very best exhaust hose is red silicon. Capable of withstanding 250 deg C, it is usually found in military and safety-intensive operations requiring the very best protection against overheating available. Red silicon costs many times that of plain black rubber, and is not normally specified for leisure craft.

Hose clamps
When it comes to joints, any hose is only as good as the clamps holding it in place. These should, of course, be of stainless steel and each joint should be secured with two clamps to ensure sufficient contact area between hose and pipe. Wormdrive clamps, as are commonly found in automotive applications have limited torque capacity and can fail to provide the necessary clamping force -particularly with large diameter hose. The tee-bolt variety must always be used in marine exhaust systems. Check that the nut is of the self-locking type. A note of warning here. Tee-bolt clamps are capable of producing enormous pressures, and if not treated with respect, will cut through the hose and possibly crack the tube. The answer -as always -is to use the right tools and a liberal squirt of common sense. A ratchet handle is fine; a long tee-bar extension is not!

Materials

Hose Clamps