Exhaust hose length

SimonD

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Does exhaust hose have to be a particular length?

On my Westerly Tempest, it comes from the exhaust elbow, down into the bilge below the engine, takes a loop round and comes back up to the water trap which is directly behind the exhaust elbow, about a half a metre behind and below.

The length of the hose is 2m, but if I went direct from the elbow to the water trap, it would be about a metre long.

Because it sits in the bilge, the past 20 years or so of getting wet and a bit oily has literally rotted it away and it now has a sizable hole in it. (I suppose the good news is that I've found out now and not in two weeks time when I'll be half way across Lyme Bay!).

So, does it have to be 2m long - if so, I can raise it up on a couple of blocks to keep it out of the bilge water - or can I take the direct route, saving a bit of cash and making a neater installation?
 
Simon

On my engine - Yanmar 2GM20F - the distance between the exhaust elbow and the water lock is 60cms in a straight line. Can't see any reason why yours is so long.
 
Does exhaust hose have to be a particular length?

On my Westerly Tempest, it comes from the exhaust elbow, down into the bilge below the engine, takes a loop round and comes back up to the water trap which is directly behind the exhaust elbow, about a half a metre behind and below.

The length of the hose is 2m, but if I went direct from the elbow to the water trap, it would be about a metre long.

Because it sits in the bilge, the past 20 years or so of getting wet and a bit oily has literally rotted it away and it now has a sizable hole in it. (I suppose the good news is that I've found out now and not in two weeks time when I'll be half way across Lyme Bay!).

So, does it have to be 2m long - if so, I can raise it up on a couple of blocks to keep it out of the bilge water - or can I take the direct route, saving a bit of cash and making a neater installation?

If it was 1960 and we were talking about tuning a petrol engined car then yes exhaust length and volume matters, but on your tempest the length has no real effect on performance. BUT the volume of the exhaust pipe does matter in terms of how much water it can hold compared with the capacity of the water lock, so shorter is better, you must not be able to overwhelm the waterlock or serious engine damage could result. A muffler somewhere in the system will help quieten the engine down.

So without seeing it I would say yes you can neaten it up.

EDIT: The water lock MUST be as low as possible, and definitley below the exhaust elbow

VETUS have some good resources for boat exhaust design.
 
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Many thanks for that helpful advice. The vetus website says there should be a minimum length of 60cm of hose between the exhaust elbow and the water lock (incidentally, I've got a vetus muffler which is first in line so to speak). There's no maximum length.

The muffler is as low as possible and vertainly below the exhaust outlet.

So, I think you're right: I can tidy it up.
 
the vetus catalogue will give you all the dimensions you need for the optimum distances for your exhaust system, i have just change mine and fitted a waterlock, and there is an optimum distance on total length of hose to waterlock,but shorting it from 2m to 1m shouldnt matter to much, as long as its a downward length.
 
Interesting point: if I shorten it, it will be a downwards run. However, the way it's routed at present has it going down into the bilge and then coming back up a few inches into the muffler/water lock. I would therefore think that the hose always has an amount of water sloshing about in the lowest part of it's length. It doesn't seem right to me but I've always thought those chaps at Westerly must have known something I don't...
 
maybe the 2 metres of hose from the elbow to the waterlock was to take account of some water sloshing around in the hose, and having 2 metres of it before the waterlock would have taken account of being able to distribute it along a longer length than having it direct to the waterlock, and the distance might of been too short for the heat to be cooled to a acceptable amount before it enters the waterlock. therefore killing two birds with one stone, ie temperature and amount of water in hose when engine is off...

The instructions i have for the waterlock was quite detailed in min length of hose from elbow and heights etc, you can find a diagram on page 59 of vetus catalogue.
 
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I don't think it's anything to do with the exhaust cooling before it hits the waterlock.

You've told us about the pipe from the engine to the waterlock, but what about the pipe from the waterlock to the exhaust outlet? Depending on the length of that, is it possible that the volume of water in it might be large enough that it could potentially run back into the engine when the engine is turned off? If so, maybe that's why your boat has the 2m of hose fitted - to provide a reserve volume.
 
I tend to agree with pvb: 2m is way longer than Vetus recommend and I guess that recommendation is based on getting sufficient cooling before hitting the waterlock.

I take the point about water running back and reserve volume. I'd guess that its a bit over 2m from the waterlock to the outlet (unless Westerly put more loops in the hose of course). I'd need to look at the boat again to make sure.

Clearly the safest action is to keep the same length (on the basis that it's not broke if nothing else). That said, it would be worth a couple of blocks to keep it off the bottom of the bilge.

Thanks for the advice.
 
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