Diesel exaust problem

Seagreen

Seagreen

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Welcome to my cockpit. Yes, its being refurbished, but here's my question. As you can see from the picture, I want to re-route the exhaust from its present course, to the one run by the red line, rejoining the pipe as arrowed.

This means raising the waterlock about two feet higher than at present, and the final run of the pipe will be under the side deck rather than up under the floor of the cockpit. Does raing the pipe and waterlock like this cause any problems, or should I find a plan B?
 
You should leave the waterlock where it is and not lift it. You might have to fit a larger one but don t lift it as that introduces a problem between the high waterlock and the engine.
 
I think you may have a prob, in that there will be a possibility of to much water left in the exaust after the w/lock, (when the engine stops), for it, the w/lock) to absorb/accomodate. I have a similar problem, i.e. the exaust runs via a dry steel pipe, to a cast iron mixer/water injection point high under the cockpit coaming. The dry section is looking "sad", I have been trying to figure out how to run it wet/rubber from the engine. Some very good ideas from forurites, I will be following your enquiery with vested interest. Bill
 
My aim is to move the waterlock and as much of the exhaust pipe out from under the floor of the cocpit as I need as much space as possible for a new diesel tank. I'm trying to get as much space between the new (not yet) tank and the exhaust. I this separation necessary, though? The old run of the exhaust ran along a similar path to the red line past a rusty tank (still there) with no obvious ill effects. Can this be done now?
 
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you can not have the water lock above the point where it injects in to the exhaust unless you use a one way valve

[/ QUOTE ] That's right.
In fact the water lock must be the lowest point in the system. I would think that it is vital that the section from the engine exhaust manifold MUST drain into the waterlock. Otherwise the section between the two will drain back into the engine!
I cannot think what type of one way valve one could use to prevent that happening.

After the waterlock, which must be large enough to hold all of the water left in exhaust system when the engine is shut down, the pipe can safely be run at a higher level.
 
[ QUOTE ]
After the waterlock, which must be large enough to hold all of the water left in exhaust system when the engine is shut down, the pipe can safely be run at a higher level.

[/ QUOTE ]
So would a larger waterlock - with more capacity- solve this and how much volume should I allow per metre for a 2" pipe? I calculate a max run of about 3m to the port at the counter from the lock. Would "back pressure" be an issue?
 
Another problem would be with the large amount of backpressure caused the head of water to a raised waterlock.

Why not just turn you waterlock through 90 degrees at the same height as present and re- route the existing exhaust up to the bottom of the stbd locker, reusing the existing pipe and skin fittings.

If you are going to put a new tank down there you will still need access to the prop shaft connections.
 
If the present sized waterlock does the job of a) silencing the exhaust to an acceptable level and b) providing enough volume of water to remove the heat before exiting the boat I would not mess about with it.
You are quite right to be concerned about increasing the back pressure if you increase the size of the watertrap. The vital dimension is the vertical height from the waterlevel in the water trap to the top of the swan-neck in your exhaust system. The bigger that distance the less chance of having water come back into your engine.
 
Well, the 90 deg. rotation seems favorite so far. I've allowed enough space to inspect the coupling, and I'll have to see where I can run the pipe and still have the space I need. I suppose there is insulation available to lag an exhaust pipe laying next to a steel tank?
 
I would have thought your biggest problem would be the tight bends you'll need to turn the waterlock. Alcco used to do 90 & 45 deg bends in sched 40 50mm 318 ss that you just jubilee clip into the exhaust pipe.

The only other concern I would have would be chafing, but properly clipped it should be ok.

Why worry about insulating the exhaust if its up against the steel, its against timber at the moment and steel isn't going to catch fire if timber insn't. I wouldn't think there would be enough heat transfer from any sections touching the new tank to raise the temp of fuel inside the tank by a significant amount if at all.
 
[ QUOTE ]
So would a larger waterlock - with more capacity- solve this

[/ QUOTE ] It wont solve the issue of the position of the waterlock. It must be the lowest point. It must not be above the exhaust outlet from the engine or you'll get water draining back into the engine when you stop it.

3m of 51mm diam pipe will have capacity of over 6 litres but obviously that wont all be water. I cant find any guidelines, or any waterlock capacity figures for that matter, as they just seem to be sized according to pipe diameter.

Contrary to what has been said elsewhere I don't think back pressure is an issue because the exhaust pipe should rise anyway to a point as high as possible inside the transom before falling to the outlet fitting. That's the "swan neck"
 
It is a mistake to ignore the implications of increasing the back pressure. Increased back pressure will cause an engine to loose power and make starting harder.
The factor that affects this is the distance from the lowest point in the waterlock to the height of the exhaust outlet. I have seen installations where small engines are trying to force exhaust gases through water traps which are far too big causing very poor performance.
 
Alan006 - that is an interesting observation. Is there a way to calculate the size water trap needed? I would have thought that along with the distance the water has to be lifted, the volume of water that has to be exhausted would have an effect. Essentially the volume and height would not change with a bigger waterlock. The volume is not determined by the size of the waterlock but by the amount pumped through the cooling system.
 
I agree with everything said (especially the posts by Vic) but looking at your picture I guess what you are trying to do is get the waterlock out of the way of your new engine. It looks as if you can still move it to where you want it or thereabouts and still have it well below the manifold outlet of the engine. As Vic says it should be the lowest point in the system (I would add on either tack when sailing and because of that the centreline is best) but as long as you achieve this you can raise it up a bit. You can also reduce the need to increase the size of the waterlock by coming straight up out of the WL and sloping down to your skin fitting if that's possible. Its only the rising section that will dump back into the WL then. Don't forget an anti-syphon bleed either! Usually a good place is at the side of the engine. When you have installed it there is usually space on the opposite side to the manifold allowing a sweep around and down which is ideal.
 
I do not know how to calculate the ideal size of the water trap. I expect someone here will know more about this than me.
The volume of water will change with the size and positioning of the waterlock as once the engine starts running the water will fill up the waterlock till equilibrium level is reached. It is not dependant on the rate of flow as if the flow rate is low it will just take slightly longer to fill up the water trap. In practice the way to affect this is the height the bottom of the waterlock is below the exhaust outlet (this assumes the outlet is above the waterline), by lowering the unit more water is retained and it will cool and silence the exhaust better.
 
Boatmike has hit the nail on the head. Get the pipe as high as possible as soon as possible after the waterlock, and then run downhill to the skin fitting. That will minimise the amount of water the waterlock has to accommodate, and also reduce any backpressure - there won't be any after the highest point because the exhaust will just be chasing water that is running downhill anyway.

In fact with the simplest system you don't always need a waterlock at all, just a sufficient loop of pipe to accommodate water from the rising sections. Remember the pipe is largely full of exhaust gas, not water. You don't have to accommodate ten feet of solid water, just a small quantity spluttered along by the exhaust.
 
[ QUOTE ]
Get the pipe as high as possible as soon as possible after the waterlock, and then run downhill to the skin fitting

[/ QUOTE ] The more usual arrangement is for the pipe to run at a low level and rise to a maximum by way of a swan neck immediately before the final exit point. However what you are suggesting is perhaps a sensible alternative which will, as you say, reduce the volume of water that has to be accommodated by the waterlock.

I would therefore suggest that the pipe should rise as a swan neck as soon as possible after the water lock and then have a gentle fall to the outlet although normally the swan neck would be close to the transom to minimise the volume of pipe that could become flooded by a following sea.

There are some diagrams in the Vetus catalogue, of which I have an oldish printed version, at www.vetus.com
Maybe you'll have more luck than me at getting the online catalogue to "play ball"
 
Have a look at p144 onwards of the Vetus catalogue which has good guidance on designing wet systems. The NLP type waterlock will enable you to turn the exhaust thru 90 degrees to take it into your locker where you fit the gooseneck if it is above the waterline and then run the hose to the outlet on the transom. Should be no need to insulate as the gases and water are cool once they get past the waterlock.
 
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