Exhaust system in sailboat

[Kalimniosjohn]

Hello all and good day!

So I recently pulled my old perkins 4.236 because the engine bed was made of steel and looked like swiss cheese. Anyway I rebuilt the engine, engine bed and entire mounting system and am now (finally) doing a final reassembly. I have a wet exhaust with a lift muffler and noticed the portion of exhaust hose after the anti siphon loop going overboard is due for replacement. At about $30/ft it's a hard pill to swallow since I'm already waaaay over budget on this haulout. I was wondering if I could use 3" PVC pipe instead? Since its after the muffler and anti siphon loop, will the water and exhaust be cool enough for PVC to handle the job?

Thanks in advance, John.

[Paul L]

Seems like a poor choice

Baseline Temperature/Upper Limit
Standardized reference points for all published PVC dimensions usually apply to a temperature of 73 degrees F. Colder temperatures typically do not affect PVC piping's strength, but as PVC piping gets warmer, it becomes more pliable and less able to hold pressurized fluid. The precise upper temperature limit can vary slightly depending on the exact specifications of the PVC pipe. However, generally speaking, the upper limit of PVC pipes is 140 degrees F; beyond that temperature, the PVC piping is at risk of losing its structural integrity.

[Bellinghamster]

ABYC marine exhaust systems says:
Hose used in wet exhaust systems shall comply
with the performance requirements of SAE 12006 or UL
1129. All other exhaust system components shall meet the
performance requirements ofUL 1129.

It has a table of acceptable materials for diesel wet exhaust (Table 1) that lists a variety of metals, synthetic rubber hose and fiberglass but NOT PVC.

I'd looked up pricing for 3" exhaust hose a few months ago and remember it being around $10/ft. I just looked again (Defender) and it's ~$20/ft. Everything has price-hiked recently , or maybe I'm remembering wrong, but still under $30/ft.

[Cheechako]

In industrial situations I've found PVC to not hold up well with vibration/warm/hot water situations. Even Schedule 80 cracked sometimes.

[Bill O]

Originally Posted by Kalimniosjohn

Hello all and good day!

So I recently pulled my old perkins 4.236 because the engine bed was made of steel and looked like swiss cheese. Anyway I rebuilt the engine, engine bed and entire mounting system and am now (finally) doing a final reassembly. I have a wet exhaust with a lift muffler and noticed the portion of exhaust hose after the anti siphon loop going overboard is due for replacement. At about $30/ft it's a hard pill to swallow since I'm already waaaay over budget on this haulout. I was wondering if I could use 3" PVC pipe instead? Since its after the muffler and anti siphon loop, will the water and exhaust be cool enough for PVC to handle the job?

Thanks in advance, John.

John,
Related question, how is your mixing elbow holding up? Only reason I ask is we had to change ours out last year on our 4.236 and they are not cheap if you go w/the SS tubing versions found online. If you must buy one of these, it could change your exhaust run (from the mixer), then possibly a different amount of 3" exhaust hose. I'll agree, exhaust hose is expensive, so you only want to do this purchase once.

[Cheechako]

3" Fiberglass exhaust tubing is about $20 a foot, not sure how much you need though. You could make your own also if you are in to fiberglass work. I made my own waterlift muffler once.
https://www.westmarine.com/buy/cente...IaAkfXEALw_wcB

[Bill O]

Originally Posted by Cheechako

3" Fiberglass exhaust tubing is about $20 a foot, not sure how much you need though. You could make your own also if you are in to fiberglass work. I made my own waterlift muffler once.
https://www.westmarine.com/buy/cente...IaAkfXEALw_wcB

Centek (or similar) is a good alternative, but I think WM only sells 10' sections (~$200). I saw some shorter sections on ebay and other sites. You'd still need some rubber exhaust hose one each end for attachment to the elbow and water lift muffler.

[Kalimniosjohn]

Thanks for the input everyone. Glad you all told me what I sort of already knew. I guess if defender has it for $20/ft, I'll just pony up and buy exhaust hose. No sense in cheaping out now

Originally Posted by Bill O

John,
Related question, how is your mixing elbow holding up? Only reason I ask is we had to change ours out last year on our 4.236 and they are not cheap if you go w/the SS tubing versions found online. If you must buy one of these, it could change your exhaust run (from the mixer), then possibly a different amount of 3" exhaust hose. I'll agree, exhaust hose is expensive, so you only want to do this purchase once.

Bill, mine seems to be in okay shape, I had it sandblasted with everything else. Here it is with with some high heat paint on it. Still havent wrapped it yet.

[kapnd]

Speaking of hoses...
The exhaust cooling hose off the back of the manifold looks suspect, and the deformed PVC pipe on the left ???
Your engine room deserves whatever it takes to attain “shipshape” condition!
Your insurance company will second this suggestion.

[Kalimniosjohn]

Yeah that hose will get changed. Unfortunately almost every hose will end up being changed. Good for the long term, bad on the bank account.

The bent PVC you see in the picture is one of the cockpit drains. I heated it to take that shape.

[UYA]

Hello Kalimniosjohn,


I hear you. We had a few month ago the same problem. Same old Perking, gas exhaust pipe was leaking and needed renewal. Since we are currently cruising in Mexico we tried ordering the hose from different US suppliers. But we found they are really expensive.


We ended up ordering the tube from Germany:

https://www.svb24.com/en/rubber-exhaust-hose.html
About the same price but 3x the length ;-) (they charge by meters instead of feet).
I am not sure about shipping costs and tax to the US.


Cheers Patrick


PS: I am not affiliated with SVB in any way (just ordered my hose there since it was the cheapest option I found)

[Clivevon]

Just be aware that a leaking exhaust probably also means carbon monoxide inside your boat - thats a potential killer, especially if anyone sleeps at that end of the boat. Economise elsewhere, I would suggest...?

[Compass790]

PVC seems to work fine on our 8hp raw water cooled diesel but I'd suggest it runs a lot cooler than your Perkins. Havent checked exhaust temp but I know the oil temp doesnt go above 60oC on our engine. If you have a plastic muffler I'd give it a go but if its going to void insurance I guess it isnt worth it

Our setup is at least 10 years old.

[chris95040]

Might be misunderstanding the picture, but those cockpit drains seem like a real boat sinker.

I hope there is at least a seacock valve at the base that you can close when that PVC splits open? Depending on how much your cockpit well wiggles with respect to the rest of the hull, it could become a problem fast when you start bouncing around out there.

Also just FYI often those are arranged where the port drain goes to the starboard seacock and vice versa so you don't end up with seawater draining into the cockpit when at a large angle of heel.

Regarding the exhaust piping, understand that it is not uncommon for the raw water cooling circuit to fail (clogged intake, bad impeller, etc.) - likely the engine will run a few minutes before you are made aware of the situation. I'd be worried what might happen in that time to PVC/etc whereas proper marine exhaust hose specs usually explicitly say they tolerate that.

[JOHNMARDALL]

Originally Posted by Kalimniosjohn

Hello all and good day!

So I recently pulled my old perkins 4.236 because the engine bed was made of steel and looked like swiss cheese. Anyway I rebuilt the engine, engine bed and entire mounting system and am now (finally) doing a final reassembly. I have a wet exhaust with a lift muffler and noticed the portion of exhaust hose after the anti siphon loop going overboard is due for replacement. At about $30/ft it's a hard pill to swallow since I'm already waaaay over budget on this haulout. I was wondering if I could use 3" PVC pipe instead? Since its after the muffler and anti siphon loop, will the water and exhaust be cool enough for PVC to handle the job?

Thanks in advance, John.

I don't recommend it, although it happens a lot. The problem is residual heat in the manifold after shutdown. Marine exhaust hose is expensive but it will not kink or collapse when it gets hot. Play it safe.
Good luck
John Mardall