plastic tank/exhaust distance

[smithy]

I have just fitted a vetus plastic diesel tank. The exhaust swan neck is now almost touching the tank is this potential dangerous? This is well after the waterlock. I dont know how hot this would get if the water pump failed. Anyone know if there a recommended clearance?

 

[White Horse]

Wrap some exhaust lagging round the pipe. The sort used on the exhaust of the diesel heaters. Comes in 50mm wide and you can get it from most chandlery's. Few layers round the pipe will help keep it clear and stop it warming up the diesel. It's not going to go bang. Watched a guy welding a plate on a diesel tank that was leaking and the tank was full of diesel.

 

[gavin_lacey]

look up the small boat safety scheme. available online. not compulsory for sea going boats but an indication of good practice. I am pretty sure that it includes a minimum exhaust/tank distance.

 

[gavin_lacey]

just looked it up. petrol tanks must be 4 inches from any general heat source, 10 inches from dry exhaust. Diesel not mentioned. If closer then fireproof baffle to be fitted as well as lagging on dry exhaust. I think common sense is needed. In normal running a wet exhaust does not get much more than hand hot. however water pumps do fail. if you have to worry not just about buggering up your engine but also a catstrophic fire then motoring might not be relaxing. A baffle plate in the area where the exhaust passes the tank might be a good idea.

 

[smithy]

Thanks for the replies, should be able to get some insulation/plate between the two.

 

[rob2]

Actually, although lagging the pipe is a good idea, you should think this through. If the water pump fails, the hose on the injection elbow will get the full brunt of the exhaust flame and will melt. I've also been told that the Vetus and similar waterlocks are prone to melting if the water flow stops. So the chances are that the problem will manifest itself well before it gets to the tank. There is a bigger risk of carbon monoxide poisoning in most installations.

Another useful addition would be to fit an automatic extinguisher in the engine bay - one of the Halon replacement types. If the exhaust melts, the hot exhaust gases will trigger it and the engine will stop as it is smothered. I know this, I've had it happen. The down side is that you cannot run the engine again as the lack of back pressure will probably stop it, but that's going to happen anyway.

I would also consider fitting a no-valve type syphon break with its outlet into a cockpit drain, so you can see at a glance whether the cooling water is flowing.

Rob.

 

[Stemar]

As mentioned above, a correctly cooled exhaust shouldn't be much more than hand hot, far too cool to worry a plastic tank.

The issue then is what happens if the cooling water stops. Surely money & effort would be better spent on something to warn if this does happen - an exhaust temperature gauge or low flow alarm. Not only do you protect the tank, but you could save your engine, or at the least a length of expensive exhaust hose and a swan-neck.

 

[Billjratt]

+1

Thermal switch to the buzzer.