Engine exhaust

ghostlymoron

ghostlymoron

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What are the basic requirements for a yacht exhaust? Does the water trap/muffler need to be a particular level relative to waterline or just a fall from exhaust elbow to trap then straight to exhaust outlet via an anti flooding loop?
 
alahol2 said:
See here for the basics.
Click to expand...

Oh dear.

Much though I admire a lot of Tony Brooks' electrical notes I am afraid I cannot let his diagram "A wet exhaust system showing swan necks and vacuum breakers" pass without comment.


Firstly the should not be an antisyphon valve between the cooling water inlet and the pump. If there is air will be sucked in affecting the pump performance at the least and at worst perhaps resulting in no cooling water flow.
The antisyphon valve should be either in loop in the pump discharge pipe, if there is a suitable pipe, or, as is possibly more common, in the pipe immediately before the water injection into the exhaust.

Secondly it is a water trap that should be at the lowest point in the exhaust pipe. It should be large enough to contain all the water remaining in the system when the engine is stopped. A silencer or muffler may not be necessary in addition to the watertrap but if it is then it should be located somewhere after the watertrap.

Thirdly I have not seen any mention of a requirement anywhere else for an antisyphon valve in the swan neck before the exhaust exit.


I would direct the OP to the Vetus catalog pages 64 onwards for a good explanation of how an exhaust system should be designed

.
 
Thanks guys for pointing me in the right direction. Do you know of any recommendation for the slope of the exhaust back to the water trap? I note that the trap needs to be at the lowest point of the exhaust but not necessarily below the engine which is good for me (obvious really).
 
ghostlymoron said:
Thanks guys for pointing me in the right direction. Do you know of any recommendation for the slope of the exhaust back to the water trap? I note that the trap needs to be at the lowest point of the exhaust but not necessarily below the engine which is good for me (obvious really).
Click to expand...

If the trap is not below the engine (or at least below the exhaust water injection point when the boat is maximally heeled) it is not going to perform the vital function of keeping water out of the engine.
 
KenMcCulloch said:
If the trap is not below the engine (or at least below the exhaust water injection point when the boat is maximally heeled) it is not going to perform the vital function of keeping water out of the engine.
Click to expand...

This is a concern I had and raised in an earlier thread. http://www.ybw.com/forums/showthread.php?t=314655
Although the ever helpful and knowledgeable Tranona pointed out that my waterlock was below the exhaust manifold sufficiently and also hindered back flow towards the manifold, I am not 100% convinced that a problem may not be lurking.

I don't like the idea of a gallon of water slopping about less than a metre from the exhaust manifold and only about 30cms below it. I can envisage steep seas causing some water to find its way into the manifold and thence through an open exhaust valve...
A swan neck (riser) between manifold and waterlock would be the answer but the water injection elbow would have to be on the waterlock side, nothing is available off-the-shelf, and there isn't enough clearance between manifold outlet and cockpit floor so not practical in my case.

My alternative is to fit a solenoid operated drain valve to the waterlock drain which is operated by the oil pressure switch. When the engine is stopped the valve opens until such time as is needed to drain the water lock and switch off the ignition.

Otherwise I'd fit one of the exhaust non return valves sold by ASAP Supplies.
 
ghostlymoron said:
What are the basic requirements for a yacht exhaust? Does the water trap/muffler need to be a particular level relative to waterline or just a fall from exhaust elbow to trap then straight to exhaust outlet via an anti flooding loop?
Click to expand...

Here are some options. Unfortunately I can't seem to post the picture at a readable size. If anyone knows the trick let me know! Or, OP can send me a pm with email address and I'll send the original:
Exhaustoptions.jpg


Some like to put the inlet strainer above the water line, but I've never had that on any of my boats - you just have to turn off the seacock when clearing the strainer.
 
Salty John said:
Here are some options. Unfortunately I can't seem to post the picture at a readable size. If anyone knows the trick let me know!
Click to expand...

Its a funny size but
Assuming you have a decent sized picture to start with upload it to your Photobucket album with a much larger size selected in "Customise your upload options".
I'd suggest 1280x960 or even 1600x1200.

It's always necessary to do this with portrait format pictures.

It does not matter if you make it too large . You can always post it as a clickable thumbnail or reduce it a bit with the edit function in Photobucket.
 
Thanks Vic. It started life at 2257 x 3079; between me and the forum via Photobucket it's become miniaturised!

I've deleted it because I don't think it's interesting enough to invest any more time and effort in publishing.
 
Salty John said:
Here are some options. Unfortunately I can't seem to post the picture at a readable size. If anyone knows the trick let me know! Or, OP can send me a pm with email address and I'll send the original:
Exhaustoptions.jpg


Some like to put the inlet strainer above the water line, but I've never had that on any of my boats - you just have to turn off the seacock when clearing the strainer.
Click to expand...
Salty, thanks for the useful picture. Where did it come from? You say the original was 2m x 3m - that's huge! The labels only go up to no. 11. I can't see item 12 on the diagrams but what is no. 13 called?
Mr Den Ouden was the founder of Vetus I've discovered.
 
To add my tuppence worth.

When I re-engined I moved the water trap from just aft of the engine into the very bottom of the cockpit locker. The original set up meant the water trap was on the centre line of the boat but once I moved it into the locker it was off centre by about one metre.
The consequence of this was water geting back into the cylinder head.
With the boat healed on a Port tack at the same time the engine was switched off I had insufficient fall in the exhaust pipe for all the water to enter the trap. Throw in some swell and it was easy to get a water lock in the cylinder head.
To fix this I had a swan neck riser fabricated by Halyard. This was only about 300mm high but then gave sufficient fall to prevent reoccurence of the problem.
 
ghostlymoron said:
Salty, thanks for the useful picture. Where did it come from? You say the original was 2m x 3m - that's huge! The labels only go up to no. 11. I can't see item 12 on the diagrams but what is no. 13 called?
Mr Den Ouden was the founder of Vetus I've discovered.
Click to expand...

There is no item 12. Item 11 is a 'high-dry' metal exhaust pipe with insulated water injector on down side. Item 13 is a Vetus waterlock muffler.

The picture is by Bruce Bingham from 'Spurr's Boatbook: Upgrading the Cruising Sailboat', first published in 1983. Dan Spurr, an old friend of mine, is a past editor of Cruising World and Practical Sailor magazines amongst other things.
 
ghostlymoron said:
John, have you got any layouts for direct cooled engines?
Click to expand...

Direct cooled does not make any difference downstream of the exhaust injection point. The only difference is that the cooling water comes out of the head and is injected into the exhaust elbow rather than out of a heat exchanger.
 
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