Exhaust hose sag?

[TrawlerTed]

While rebuilding the rear stateroom I uncovered the exhaust hoses. These hoses sag down between the two bulkheads on either side of the room as seen in these pics (sorry for the quality), between the muffler in the ER and their exit out the transom. In fact, the port side hose is particularly long and snakes around on the floor a bit before it exits. Is there some reason that these hoses need to sag down like this before they exit (perhaps for a water pocket)? Or could they be raised up so that they're essentially level? I was thinking I would at least need to lift them up and drain in order to winterize... otherwise they would take a lot of antifreeze! Thanks for any comments.
- Ted

 

[ScottC]

Interesting question, Trawler Ted!

I will jump in on this thread with a comment relevant to your installation and also with a hope to see responses on my somewhat related situation.

My comment is this:
I have a "sag" in my exhaust hose between the engine and the muffler (See picture below). The boat came from the factory 10 years ago with this sag and I never thought anything of it. Didn't even notice, really. Fast forward 10 years and the yard storing my boat while it is in France said it's not good this way and should be raised. Apparently, they feel, the trapped water can lead to extra moisture traveling back into the engine, speeding up corrosion. Maybe, Trawler Ted, this would not be of concern for you, as your sag is after the muffler??

And here is my question for TF discussion:
I ran this situation by my home boat yard who services my boat when it's in Sweden and they think it's nothing I should worry about. Their recommendation: do nothing.

One other item of note - my exhaust outlet is actually under water - on the bottom of the boat.

So, what say you, TF??

(Apologies, Trawler Ted - I am not trying to hi-jack your thread, but I think my contribution and question will help extract a full pros & cons discussion on this topic from TF members. My guess, anyway...)


CLICK ON PICTURE TO ENLARGE.

 

[twistedtree]

I think my preference would be for the hoses to have a continuous downward slope and be self draining. But I'm not an expert. My reasoning is two fold.


First, the fewer places where water can collect, the less opportunity there is for that water to get sloshed or splashed back into the engine. This is almost never a problem in "normal" operation, but when you get into some odd situation, trouble can occur.


Second is general maintenance, including winterization. Pockets of water are just one more thing to freeze, fester, or otherwise cause problems.


I've just had too many cases of water collecting in low spots in hoses to think there is anything but trouble to come from it. I haven't had to deal with this with an exhaust run, but I have with a variety of drains and other water lines. If at all possible, sloped and self draining is preferred. I actually wrote this into my build contract as a requirement for all hoses and pipes that aren't meant to always be full of liquid.



BTW, you might consider fiberglass exhaust tubes for those long runs. They won't sag like a hose, and will be much easier to support sufficiently, I expect.

 

[stubones99]

If he switched to fiberglass tubes for the hose runs, he would still need to support them along the way, since most fiberglass tubes are not that structurally strong to support the weight of the tube and exhaust cooling water. Fiberglass tubing would be a longer lasting solution to the problem.
He could fiberglass a trough for the exhaust hose. Make sure the hose has no delaminations on the inside to help you decide. If you will have to replace the hose, now you have a hose vs tubing decision. Use borescope to see what the existing hose looks like inside.

 

[twistedtree]

If he switched to fiberglass tubes for the hose runs, he would still need to support them along the way, since most fiberglass tubes are not that structurally strong to support the weight of the tube and exhaust cooling water. Fiberglass tubing would be a longer lasting solution to the problem.
He could fiberglass a trough for the exhaust hose. Make sure the hose has no delaminations on the inside to help you decide. If you will have to replace the hose, now you have a hose vs tubing decision. Use borescope to see what the existing hose looks like inside.

Agreed. My thinking was that it would take fewer support points to get a straight run with and FRP tube vs with a hose. And that if you are considering glassing in a support trough, why not glass in a tube instead.

 

[bayview]

Since you have water lift muffler is suspect there is always water in the exhaust system so getting the hoses to drain probably doesn't matter from that stand point.

Raising the hose require some careful thinking as it is heavy and needs to flex and not put strain on either end. It loos like the forward section is as high as the hull outlet so raising the hose appeals to my sensibilities.

The hose in the lower pix looks like it is supported?

 

[RT Firefly]

Greetings,
Mr. TT. Ooh Boy. I recognize THAT scenario (the cabin gut, not the hose). I would replace the snakey hose on the port side with a length of FRP tubing, as suggested. You shouldn't need but 2, possibly 3 supports. You then will have a nice gentle slope to the transom. Starboard side simply needs a couple of support blocks "glued" to the hull to keep the hose somewhat in place with the same gentle slope.


Looking good, so far. Seems like you've got her cleaned out fairly well. The bull work is done. When I did ours, I took the opportunity to paint the hull sides before re-installing all the "stuff". I know, I know...nobody will ever see that again but I'm anal (just a bit) that way. Didn't cost much, just time.

 

[TrawlerTed]

The hose in the lower pix looks like it is supported?

No support except at the bulkheads. However the run on the starbound side is shorter... about 6.5' versus port side snake of a hose where there is about a 9.5' run.

Sorry for my lack of knowledge here, but these FRP tubes being mentioned... premade? Or do you fiberglass around a tube, and if so what do you use for the inner tube material? Thanks for all the thoughts/comments.

 

[Alaskaflyer]

No support except at the bulkheads. However the run on the starbound side is shorter... about 6.5' versus port side snake of a hose where there is about a 9.5' run.

Sorry for my lack of knowledge here, but these FRP tubes being mentioned... premade? Or do you fiberglass around a tube, and if so what do you use for the inner tube material? Thanks for all the thoughts/comments.

Google "vernatube" as one brand line. There are others, most marine supply houses carry one brand or another.

 

[stubones99]

https://fiberglasstubingsupply.com/

There are a few companies that make fiberglass tubing of various sizes and lengths.

 

[Comodave]

I agree that less water sitting in the exhaust hose is better. As to winterization, we actually measure the exhaust with a refractometer as the water and antifreeze exit the boat so any sitting in the hose will be treated with antifreeze also.

I would paint the area too. Even if you can’t see the area I would know that it looks like crap and it would bother me if I didn’t paint it.

 

[Sabre602]

I agree that it would likely be preferable to have the hose run level or slightly downward as it runs to the transom, but I would not be concerned about freezing damage during winter layup. You're in Oak Harbor? My bilge spaces have never gotten anywhere close to freezing here in western Washington, never mind below freezing temps cold enough to freeze salt water. If the boat is on the hard for the winter, it's more of a concern, but who would lay up over the winter without a heater or at least a few light bulbs going?

 

[Comodave]

I would not use a space heater. Look at Boat/US about fires and space heaters.

 

[TrawlerTed]

I agree that it would likely be preferable to have the hose run level or slightly downward as it runs to the transom, but I would not be concerned about freezing damage during winter layup. You're in Oak Harbor? My bilge spaces have never gotten anywhere close to freezing here in western Washington, never mind below freezing temps cold enough to freeze salt water. If the boat is on the hard for the winter, it's more of a concern, but who would lay up over the winter without a heater or at least a few light bulbs going?

Boat is on the hard right now in Anacortes.

 

[BruceK]

Our port engine has a longer exhaust run incl. a fibreglass pipe section. It had a support underneath but had fractured near the support, more than once I think, before my time. We repaired it, kept the support, and added a strap support/hanger secured above. Flexible hose can be supported with bracket/hangers if there is a good attachment point.

 

[twistedtree]

Here's an example of a glassed in FRP exhaust tube. This one is 8" diameter.

 

[sunchaser]

No doubt FRP will work but a well laid out quality rubber hose will too. Rubber sound attenuates much better than FRP, takes vibration better and can accept a few bends and directional moves without cracking.

The worry about freezing is much less with rubber as it won't crack like FRP. In the Anacortes area freezing of exhaust runs is easily dealt with and a non issue if your boat is stored in the water.

The death of any exhaust run is an overheat, poorly designed exhaust shower head and poor supports. There are several good yards in Anacortes and Bellingham that could offer relevant experience and advice. A discussion with local builders like American Tug and Nordic Tug likewise.

As mentioned, painting the area and providing access for down the road exhaust run maintenance are greatly facilitated with everything wide open.