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ivan&alice

Replacing my exhaust and how to choose a hospital silencer?

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After it was suggested to me in another thread, I have been working up the courage to do a DIY exhaust replacement. I had assumed there would be welding involved but I peeled back a bit of the wrapping and it would appear that the pipes just screw together. The outside of the pipes is solid rust.

 

Is there any general advice or tips anyone can offer for this job?


My current silencer is around 6" in diameter and the hole it fits through is just slightly larger than that. I figure if I'm going to go to the trouble I may as well fit a hospital silencer while I'm at it. The smaller it is the smaller the hole I have to cut. The smallest hospital silencer I have found so far is this 10" x 27" one from Midland Chandlers for 255 quid:

https://www.midlandchandlers.co.uk/products/hospital-silencer-10-x-27-lg-1-1-2-bs-ea-019

 

Question is, how do I choose between them? They're all the same price so I'm guessing that larger is more effective?

 

They don't seem to stock anything that they've labelled "exhaust pipe" and I'm going to need 2x 1m lengths of pipe and two 90 degree elbows as well. What specs of pipe should I be looking for and where the heck can I buy it?

I'll need to add lagging as well - a 30m roll here is 47 quid: https://www.midlandchandlers.co.uk/products/exhaust-lagging-30m-roll-e315

 

And I figure metal cable ties would probably be the best thing to do to secure the exhaust.

 

Lastly if I'm adding the silencer I feel like I should also line the engine bay with acoustic foam to try to keep the noise out. Haven't compared but there is this on amazon, for example: https://www.amazon.co.uk/dp/B01MDUB6T6

 

Any advice that you have would be most gratefully received!

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Unfortunately they are at the other end of the canal system but TW Marine sorted my exhaust out for me.  www.twmarine.co.uk

They manufacture silencers and supply pipes and fittings

 

They do sound deadening too. 

They've been endorsed on here a few times.

 

 

 

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You are looking for 1 1/2" BSP steel pipe and appropriate fittings for that silencer. Any decent plumbers merchant should have it or you can buy online.

I'm sure I paid a lot less than £47 for exhaust wrapping - from Ebay.

 

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Another vote for TW. Very helpful. I haven't finished the engine bay yet but my target is around 70 Db as measured on my super accurate phone ap!

Whether I get there or not is a different matter.

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n

14 minutes ago, hawkesmith said:

Another vote for TW. Very helpful. I haven't finished the engine bay yet but my target is around 70 Db as measured on my super accurate phone ap!

Whether I get there or not is a different matter.

TW also do a silencer that is smaller so may fit the space better than a full hospital silencer but still very effective. Many hospital silencers are fitted across the boat and that involves sealing the old exhaust outlet and making a new one on the opposite side. I managed to get my smaller one into an in-line position with a rear exhaust. The rear exhaust made a noise difference as well because the sound did not bounce of hard banks back to my ears.

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Hello, would suggest that you use a flexible pipe in the system to cut down on vibration being transferred to the hull. Don't underestimate how difficult it can be to free up the old screwed joints when working in limited space.

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53 minutes ago, hawkesmith said:

Another vote for TW. Very helpful. I haven't finished the engine bay yet but my target is around 70 Db as measured on my super accurate phone ap!

Whether I get there or not is a different matter.

 

You will easily get down to 70dBA if you move the phone app far enough away from the boat. ?

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1 hour ago, David Mack said:

You are looking for 1 1/2" BSP steel pipe and appropriate fittings for that silencer. Any decent plumbers merchant should have it or you can buy online.

I'm sure I paid a lot less than £47 for exhaust wrapping - from Ebay.

 

I bought a huge reel and still have half of it

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I used 2 in  steel water pipe, from Pipeline Center.  1 1/2 in  should be fine, but have a look at your engine manual for any special requirements   Either rent a pipe threading wrench from a hire shop, or buy a selection of steel barrel nipples when you buy the pipe.  Then cut the nipples in half and weld them on the end of the pipe where you need a male thread.  Welding is less hard physically than cutting a thread, unless you rent an electric machine.   Use swept bends not elbows for going round corners.  You can get weld-together pipe fittings, but threaded ones are easier to assemble in situ.  Whatever sort of fitting you pick, incorporate pipe unions here and there so you can  assemble it all easily and more importantly dismantle it.    Buy or borrow some BIG stilsons- 36 in is about OK for 2 in pipe.  Slather all threaded joints and the mating faces of any pipe unions with a  high-temperature copper grease,  (e.g.  Coppaslip ) or after a few weeks running it will never again come apart.    Fit a flexible section near the engine, and another between the silencer and the outlet.  Consider some sort of sound absorbing mounting for the silencer.

 

 You can get better priced lagging wrap than from MS- Google "exhaust wrap" -  EG: Exhaustwraponline have 30m of  2 in wide  550C tape, with 6 stainless cable ties for £29.99, delivered.     Stainless Jubilee clips are also good for holding the wrap on and are much easier to get really tight than metal cable ties.  Fit one at either end of each section of wrap and overlap the tape really well- about 2/3 overlap is best, half overlap is OK and uses less tape.  With a 50% overlap you need about 2 m of tape for every 300 mm of pipe run.

 

Bigger is better for silencers, but it has to fit, not be too close to anything that will not like getting hot,  not make routine servicing impossible and be get-attable.  

 

N

  • Greenie 1

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As an aside, didn’t someone

mention recently that for private boats the exhaust no longer has to be lagged? I can’t be arsed to go look through the BSS checklist right now. Obviously a better job with it lagged though, and safer. 

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3 hours ago, ivan&alice said:

 

Lastly if I'm adding the silencer I feel like I should also line the engine bay with acoustic foam to try to keep the noise out. Haven't compared but there is this on amazon, for example: https://www.amazon.co.uk/dp/B01MDUB6T6

 

I'd be surprised if that stuff works very well. Closed cell foams will reflect certain higher sound frequencies so that they bounce around inside the engine space, while allowing other lower frequencies to pass straight through. To attenuate and absorb sound energy, open cell foams should be used. Ideally you'd have a lamination of different materials to absorb and reflect different frequencies. Just using that thin layer of closed cell foam won't do very much and certainly won't "soundproof" anything. The term is a misnomer. There's no such thing as soundproofing unless you want metre thick sound insulation and an engine space the size of a matchbox.

Edited by blackrose

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When I had a widebeam fitted with an Isuzu I ran the engine for a while when the boat was out for blacking.  Even with my ear close up to the exhaust outlet the engine was almost silent.

 

However the noise on board was not reduced much.  There are 2 distinct elements to engine noise, and the exhaust noise is only part of it.   Other boaters and gongoozlers will enjoy the comparative silence more than you will. 

  • Greenie 1

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And another vote for TW marine. Nothing in their standard range of hospital silencers could be made to fit sensibly so they custom-made one for me which fits the boat properly (the inlet is centrally at one end of the silencer and the outlet is from the side near the other end) and it works brilliantly.

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10 hours ago, ditchcrawler said:

That’s the stuff :)

 

Specifically this one: 

https://www.asap-supplies.com/soundproofing/soundproofing-sheets

 

I fitted a few sheets to WotEver one weekend - it made a huge difference. 

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12 hours ago, Murflynn said:

When I had a widebeam fitted with an Isuzu I ran the engine for a while when the boat was out for blacking.  Even with my ear close up to the exhaust outlet the engine was almost silent.

 

However the noise on board was not reduced much.  There are 2 distinct elements to engine noise, and the exhaust noise is only part of it.   Other boaters and gongoozlers will enjoy the comparative silence more than you will. 

so true, our Beta 43 has a large hospital silencer and i'm often asked by people on the towpath if its electric as so quiet, half the time I can't hear what they've said as i'm stood directly over it :D

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30 minutes ago, Hudds Lad said:

so true, our Beta 43 has a large hospital silencer and i'm often asked by people on the towpath if its electric as so quiet, half the time I can't hear what they've said as i'm stood directly over it :D

My experience too, with the same set up. People on the towpath will try talking to me at a normal volume and don't understand why I can't hear them. What?

 

Jen

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Thanks for all the responses. I did note that TW Marine was highly regarded in other threads I browsed before starting this one. They don't have an online shop though so I will need some specs to give them when I email to make a reasonable comparison.

 

My engine manual (Beta 38 / BV1505) states that "The exhaust back pressure, measured with the exhaust system connected and the engine running at full speed, must not exceed 80mm Hg".

 

However none of the hospital silencers whose specs I have looked at online state the back pressure they generate. Can this only be measured after installation??

 

My current exhaust system is a 2' long, 2" diameter pipe coming horizontally out of the engine, a 90 degree elbow, a 2' long pipe riser, then my 2' x 5" diameter silencer. So I have space enough for any of the hospital silencers I've seen online. My engine is actually fairly quiet but I am so jealous of the boats with the hospital silencers - ever since the other day I asked the owner of such a boat if his was electric!

 

As for the fact that I can just use 2" steel pipe, and I can cut my own thread using something like this 2" die https://www.ebay.co.uk/itm/292431572067

That really makes the job seem quite surmountable.

 

I can tackle the soundproofing sheets later and perhaps add baffle boxes to my vents. I'll see how it all sounds with the replaced exhaust.

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Have you got a hospital silencer now? Why not do what’s necessary to cure your leak, the cross the silencer bridge in the future?

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27 minutes ago, Richard10002 said:

Have you got a hospital silencer now? Why not do what’s necessary to cure your leak, the cross the silencer bridge in the future?

The leak appears to be from the silencer so it's likely to need replacing. I'd need to remove all the lagging to find out where exactly the leak is coming from. I could just take the wrapping off and use some kind of gunk to plug the hole. Perhaps that would be the easiest. Any recommendations on exhaust friendly gunk?

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Halfords used to sell exhaust paste. Slap some of that on and put the bandage back on. It's only a temporary repair though because of the vibration it is subjected to. 

 

 

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I took the lagging off the silencer now and in my opinion it clearly needs replacing, gunk and tape aren't going to do the trick for long.

Here's some pics to show you guys what I'm talking about.

 

IMG_20190815_130724.jpg.51003bb0f2e54a07c338b2a85640eb7c.jpgIMG_20190815_130711.jpg.37be78b875d897d478f78b8ec5eee35a.jpgIMG_20190815_130703.jpg.f47ff8eb8ce69f8779fb0136b1a75367.jpg

 

There are three big holes and as you can see the whole thing is very rusted and actually spongy around the holes. The lid of the compartment is just a wooden board and is not watertight so rain can get in and drip on the thing. The leak was somewhat contained by the lagging but the worst of it is coming out of the split right at the exhaust end. The compartment actually fills with exhaust fumes and under the piles of rust you can see the compartment is filled with potentially flammable black soot, which is why the BSS examiner was unimpressed.

 

The silencer extends for another 6 inches or so through that bulkhead into the engine bay. Anything larger than it is would involve cutting out a circle, but this shouldn't be too hard to do. If I replace it I may as well upgrade it too.

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20 hours ago, hawkesmith said:

my target is around 70 Db as measured on my super accurate phone ap!

Whether I get there or not is a different matter.

 

Whether it is really 70dB is another matter too.

(decibels not Dekabytes!)

3 hours ago, ivan&alice said:

My engine manual (Beta 38 / BV1505) states that "The exhaust back pressure, measured with the exhaust system connected and the engine running at full speed, must not exceed 80mm Hg".

Probably worth talking to Beta Marine -- that spec might be very easy to meet.

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Hmmm. I'd say that's beyond repair. What does it look like the other side of that bulkhead? At least you won't have too much trouble removing the old one.

 

I went to TW Marine with the idea of having a hospital silencer fitted but they persuaded me it was a bad idea. There wasn't enough space where the existing silencer was situated and putting it in forward of the engine  would have been possible but would have involved some convoluted pipework with the risk of too much back pressure. In the end I bought the largest silencer that would fit in the space. I didn't do before and after sound tests but it did make a significant difference.

 

They're not to good at responding to emails but the chaps at TW Marine will pick up the phone if they aren't on the marina working on a boat. They do have brochures and prices that they can email out and they  have lots of experience. 

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