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wet exhaust replacement or modification?


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My exhaust is a crude steel pipe that goes from engine to hull, it's only around 4-5 inches above waterline with no swan neck. Someone said I could perhaps fit a higher one or put a swan neck in the existing one. I actually have to do a little plating over where the outlet is anyway so is this a good time to redo exhaust?   Are there any better exhaust methods these days other than a steel pipe or is this still the norm? 

 

many thanks  

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If the exhaust is as you say, then the engine must be rigidly mounted. Otherwise, you would suffer bad vibrations and the exhaust, manifold or hull would fail.

 

If this is a steel boat I think I would convert to dry exhaust and do away with the maintenance and complications of the  raw water circuit. you could then use a metal flexible exhaust section.

 

Wet exhaust boats normally use a special exhaust hose to help prevent resonation in a steel tube.

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Thanks for your swift response, never thought about the vibration issue. I'll post a photo tomorrow when this rain stops (hopefully!)

 

The engine has a large bolt at each corner but nothing special I don't think.  I'm quite keen not to have to change the whole cooling system if possible - the damn things cost me enough money already :)

 

 

1 minute ago, Tony Brooks said:

If the exhaust is as you say, then the engine must be rigidly mounted. Otherwise, you would suffer bad vibrations and the exhaust, manifold or hull would fail.

 

If this is a steel boat I think I would convert to dry exhaust and do away with the maintenance and complications of the  raw water circuit. you could then use a metal flexible exhaust section.

 

Wet exhaust boats normally use a special exhaust hose to help prevent resonation in a steel tube.

 

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4 minutes ago, Polishicebreaker said:

Thanks for your swift response, never thought about the vibration issue. I'll post a photo tomorrow when this rain stops (hopefully!)

 

The engine has a large bolt at each corner but nothing special I don't think.  I'm quite keen not to have to change the whole cooling system if possible - the damn things cost me enough money already :)

 

If the bolt is holding the engine foot down onto the engine bed or a length of hard wood then it is rigidly mounted so no need for a photo. If you have never flooded the engine from the exhaust, its probably not worth doing anything to it.

 

If you are worried about water in the exhaust flooding the engine, then you could fit a swan neck and water injection point on the downward slope. You could link the swan neck to the hull fitting with  a length of exhaust hose but its thick and stiff so in a short distance not easy to bend.

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1 minute ago, Tony Brooks said:

 

If the bolt is holding the engine foot down onto the engine bed or a length of hard wood then it is rigidly mounted so no need for a photo. If you have never flooded the engine from the exhaust, its probably not worth doing anything to it.

 

If you are worried about water in the exhaust flooding the engine, then you could fit a swan neck and water injection point on the downward slope. You could link the swan neck to the hull fitting with  a length of exhaust hose but its thick and stiff so in a short distance not easy to bend.

that sounds like a good plan.  I am adding a little plating to the boat so she may be sitting a little lower when I go back in the water, which is part of my concern. 

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 I prefer a wet exhaust so I wouldn't change to a dry one, mine is plastic waterlock  and rubber hose, nothing to rust it doesnt get hot and its quiet compared to most boats.

Whats not to like.

Edited by Loddon
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6 minutes ago, Loddon said:

 I prefer a wet exhaust so I wouldn't change to a dry one, mine is plastic waterlock  and rubber hose, nothing to rust it doesnt get hot and its quiet compared to most boats.

Whats not to like.

until it gets blocked by weed and melts

 

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8 minutes ago, Phoenix_V said:

until it gets blocked by weed and melts

 

Not happened to me in 20 years wiith three different boats.

You would have to be a complete numpty not to notice if the water stopped coming out of the exhaust as it would get really loud  without the waterlock silencer.

Oh and the exhaust on this one is 27 years old, still the original exhaust.

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13 minutes ago, Loddon said:

Not happened to me in 20 years wiith three different boats.

You would have to be a complete numpty not to notice if the water stopped coming out of the exhaust as it would get really loud  without the waterlock silencer.

Oh and the exhaust on this one is 27 years old, still the original exhaust.

the rubber hose tends to give off a burning smell long before serious damage (don't ask me how I know this) but I am suspicious of plastic filters and water traps. There is definitely much more to go wrong on a wet system.

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2 minutes ago, Phoenix_V said:

the rubber hose tends to give off a burning smell long before serious damage (don't ask me how I know this) but I am suspicious of plastic filters and water traps. There is definitely much more to go wrong on a wet system.

To be fair I'm not sure if mine is plastic or GRP, I suspect the latter but its burried at the back of the boat so not easy to view.

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Surprising how many plastic or rubber wet silences you see with obvious overheat damage. I have even known one to get well on the way to sinking the boat where it lost raw water and it burned a hole in the silencer and then the raw water system was cleared.

 

With my dry not quite a hospital silencer I have been asked if the boat was electric, so dry exhausts can be as quiet as a wet exhaust without the extra raw water pump, strainer and pipe work that gives more points of failure.

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5 minutes ago, Phoenix_V said:

the rubber hose tends to give off a burning smell long before serious damage (don't ask me how I know this) but I am suspicious of plastic filters and water traps. There is definitely much more to go wrong on a wet system.

 

Not only that, when it does start to char after a few occasions, the inner lining can bubble down and then split. The exhaust gasses can then get in to the bubble and at high gas flows push it down across the pipe. This results in so much back pressure the raw water pump wings get pushed down so it won't pump.  Then the engine overheats. It can also happen when the mixing elbow furs up. The engine usually idles and works well enough at low speed but as soon as you up the power it starts to overheat. Problem is I have doubts about inland engineers apart from those on rivers, even being aware of the possibility.

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2 hours ago, Phoenix_V said:

until it gets blocked by weed and melts

 

The first sign of blockage is an exhaust note and rise in engine temp. As long as your filter is reasonably accessible, it is a 2 minute job to clear, and a look at it when you stop and grease stern tube is an easy procedure. 32 years on and I would not change. Also, when doing river work cooling is still effective causing no overheating like on some keel cooled craft.

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56 minutes ago, Ex Brummie said:

The first sign of blockage is an exhaust note and rise in engine temp. As long as your filter is reasonably accessible, it is a 2 minute job to clear, and a look at it when you stop and grease stern tube is an easy procedure. 32 years on and I would not change. Also, when doing river work cooling is still effective causing no overheating like on some keel cooled craft.

 

But if you had an underspecified heat exchanger it would overheat, just like boats with undersized skin tanks or keel cooler pipes. You really should not condemn a cooling system because some instances are not properly designed. A PROPERLY designed and installed keel cooler or skin tank system does not need the extra start up checks of the raw water straining system and has far fewer hoses, joints and components to get blocked or fail. I suppose it all depends upon if you value simplicity or complications to get you to the same point.

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2 hours ago, Tony Brooks said:

 

But if you had an underspecified heat exchanger it would overheat, just like boats with undersized skin tanks or keel cooler pipes. You really should not condemn a cooling system because some instances are not properly designed. A PROPERLY designed and installed keel cooler or skin tank system does not need the extra start up checks of the raw water straining system and has far fewer hoses, joints and components to get blocked or fail. I suppose it all depends upon if you value simplicity or complications to get you to the same point.

Only problem is it's almost  impossible to get big enough cooling tanks on the swim of a narrow boat to cool a 50hp Beta when used on rivers. Which is why Loddon was changed from skin tank to indirect cooling as it already had a wet exhaust.

Edited by Loddon
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59 minutes ago, Loddon said:

Only problem is it's almost  impossible to get big enough cooling tanks on the swim of a narrow boat to cool a 50hp Beta when used on rivers. Which is why Loddon was changed from skin tank to indirect cooling as it already had a wet exhaust.

Very interesting - folks often look at my freshwater cooling and ask why i'm not using skin tanks??

FWIW in our hiring days, the only time I had with cooling tanks was on a hire a hire boat which got a bit warm going up the Tideway opposit Fulham FC (it must have been a Chelsea supporter...). I told the Wing Commander (!) - folks may know to whom I refer, and he said rubbish or whatever...

On the ditchy bit of the Thames you really have to push it hard upstream on Yellows + to get any heating at all..  

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The only problem I have had with heat exchanger cooling is weed blocking the intake and that is an increasing problem probably caused by warmer weather and more weed = less traffic = clearer water = more weed. Thing is that by this stage you have to stop every few hundred yards as the propeller is just a spinning ball of weed. Big problem in France but probably coming to a canal near you soon.....

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58 minutes ago, OldGoat said:

Very interesting - folks often look at my freshwater cooling and ask why i'm not using skin tanks??

For a beta 50 you need 12.5 sq ft of skin tank area, with two tanks at 18" tall they need to be over 4ft long.

 

Back to the Rugby ?

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2 hours ago, Loddon said:

Only problem is it's almost  impossible to get big enough cooling tanks on the swim of a narrow boat to cool a 50hp Beta when used on rivers. Which is why Loddon was changed from skin tank to indirect cooling as it already had a wet exhaust.

 

No, the problem is that your boat was built with an insufficient skin tank size. When fitting keel coolers to out Caribbean and similar cruisers the rear most keel cooler connection was 3 to 4 ft in front of the engine so all under the cabin floor. The chloralry of this for a narrowboat is extending the skin tank through the rear bulkhead or fitting another on the other side of the swim. I don't like the latter, but it works. The boat could have been built with cooler pipes  wrapped around the swim which would also work.

 

What you did probably solved the problem in the most cost-effective way for your circumstances, but that can not invalidate the fact that your system has far more failure points and needs more maintenance than a keel cooler or skin tank system.

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It was done before I bought the boat by the original owner. The engine was overspeced  for the skin tank that was fitted not the other way round? 

It would actually need two skin tanks both extending a for a foot or so infront of the rear bulkhead, plus there is no room at the back for a decent dry silencer.

Extra maintenance involves changing the impeller once a year or so?

 

I am happy with the system as it is as it works to perfection despite the naysayers.

 

Can someone point me at a narrow boat that has a 50hp B2203  that doesn't overheat going upstream on a river and uses skin tanks ?

Edited by Loddon
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