Exhaust hose clamps

[Divealot]

I am replacing my exhaust hose which connects the exhaust elbow to the fiberglass exhaust tunnel. The exhaust elbow is not in perfect alignment and regular wet exhaust hose seems to put a lot of undue stress on the fiberglass tunnel/pipe. It takes about an18” piece of hose to join the two. Upon inspection it appears there is an old crack in the fiberglass which was repaired earlier in its life but is reestablishing itself. They installed a slightly longer hose to cover the repair. I don’t think they were trying to hide it I think it gave them piece of mind knowing if the repair failed the hose would keep the gases and soot contained.
I am having the crack professionally repaired and I to will be sure my new hose covers the repair. I am installing Trident Silicone hose. I chose it for not only it’s superior life and heat tolerance but for its flexibility. I think it will put a lot less stress on the poorly aligned pieces. The cost of that hose is ridiculously expensive and they don’t sell it by the foot. I had to buy a 5’ piece for a 2nd splice!
My questions to you:
What do you think caused the crack? I think when they were trying to install the new after market elbow they tried to force the fit and or they tightened a clamp too hard. The spot that is cracked has a built in surface imperfection causing a slight dip. I am thinking they originally had a shorter hose and they had trouble sealing that dip and over tightened the clamp. WAG
What do you think about using the silicone hose?

Last and most important. On one of the web sites I found a title of an article written by Tony (I think he is associated with Seaboard Marine). The title reads something like “How to properly clamp an exhaust hose. I have tried numerous times and ways to open that file but can’t. If any of you have that article or know where I can read it I would appreciate it.

I figure the article refers to rubber hose and not silicone. I know to use smooth clamps. Any thing else I should know?

Thanks

 

[Comodave]

I haven’t used silicon hose so I cannot comment on that but I can on the clamps. I used AWAB clamps on my port exhaust and they are a great clamp, but pricey at about $22 each. They don’t have welds to rust and are solid clamps, no slots.

 

[LarryM]

In addition to high quality T-bolt clamps, I would definitely use stainless steel crush sleeves inside the fiberglass exhaust tubes. They are made expressly to prevent the type of tube failure you are experiencing.

 

[Divealot]

Good to know and will keep that one on my list. VOSS clamps were on it when I took it apart. They too are t-bolt clamps but had severely rusted at the welds. Won’t be using them. Thanks again.

 

[Divealot]

That makes a lot of sense. I will google and try to find one. Perhaps I will just cut the tube just behind the crack and install one of these and call it good. Thank you. I had never heard of these but more surprising is whoever made the crack or repair did not use one. I assume some yard made the repair. Thanks again

 

[Ski in NC]

You can get sections of FG pipe and join with short sections of "hump" hose to take care of misalignment. Or cut FG pipe and form an angle and glass the joint together. Lots of ways to do this...

Photos of the plumbing layout would help.

 

[RonR]

I was told the correct way to clamp is 180 from each other with two clamps per side. Meaning one clamp will be on the port side of the pipe with the screw/bolt facing you. The other clamp will be on the starboard side with the screw/bolt away from you. Tighten evenly between the two by hand, not a power tool as they strip out. Run for a day or two, then check them again. I also keep a few spares on the boat.

 

[Slowmo]

I know that over-tightening a clamp can crack a FG pipe. Our PO had done this to our boat and when we replaced the risers we ended having to have a new SS collector made since the FG one was cracked.

I have used Trident Silicon. In our old boat we were getting too much heat on a rubber coupling, you could smell burning rubber after 3-4 hours. I had the yard put in a silicon connector. When the silicon hose overheated it failed catastrophically rather than just smelling like burning rubber. Obviously we had a problem with inadequate mixing of the cooling water into the exhaust so we fixed that. But my take away was that while silicon can take higher temps, if you exceed those it fails without much warning and catastrophically. At least with the rubber we had plenty of warning in the form of odor and it didn't just rip open.

 

[caltexflanc]

Yes, as I have posted here a few times before, I paid a pretty penny to remediate exhausts tubes crushed by over tightened clamps. It proved easier and more thorough to epoxy (and need a special high temp epoxy) new tubes into to the muffles and install crush rings while we were at it. I recall we got them from MESA down in Alabama.

 

[Divealot]

Thank you for all the great feedback. I hate to hear about the silicone hose failing since I have already purchased mine $$. I did discover that there is a huge difference in silicone hose. I selected the Trident hose since the wall is hutch thicker and fits the 5” pipe much snugger than the other.
I have a fiberglass repairman coming today to give me his opinion. I feel much better talking to him armed with everything I have learned from you.
I appreciate the fact that burning hose smell is a good indicator vs silicone just failing. However silicone can handle temps up to 350 - 375. If I am reaching temps that high not only is my hose in jeopardy but my fiberglass and most likely my engine are toast.
Instead of relying on smell I am installing a gear hex temp gauge as well as two exhaust temperature sensors.
I will try to learn how to download pictures and post them.
I also did order the crush tube. So odd that such a simple piece and cheap ($45) that the builder nor PO did not install one.
Thanks again everyone!

 

[psneeld]

If for any reason you lose raw water flow, a normally functioning engine can burn hose and tube....not necessarily toast.

I have had it happen on several vessels and more than just a few times.

 

[Comodave]

We have an alarm that attaches to the exhaust hise immediately after the water injection. It is simple to install. It is made by Borel in California. It is custom made to your specs. Ours has 3 exhaust sensors, 2 high water sensors and 2 WIF (water in fuel) sensors. No affiliation. It will alarm much faster if you loose cooling water than waiting on the engine overtemp alarm.

 

[LarryM]

We have an alarm that attaches to the exhaust hise immediately after the water injection. It is simple to install. It is made by Borel in California. It is custom made to your specs. Ours has 3 exhaust sensors, 2 high water sensors and 2 WIF (water in fuel) sensors. No affiliation. It will alarm much faster if you loose cooling water than waiting on the engine overtemp alarm.

Comodave beat me to the punch. +1 for Borel alarms!

 

[Dougcole]

I replaced the exhaust hoses on my boat a couple of years ago, it was the worst job I've ever done on the boat, so you have my sympathies. My port exhaust runs just above the house battery bank, and the off gassing from a bad bank caused that section of hose to fail much sooner than the rest. To avoid this problem in the future (along with putting the batteries in a better box) I added a section of fiberglass exhaust tubing above the bank. I bought the tubing from a shop that does marine exhausts in Stuart, Fl. They cut the tube for me and put fiberglass crush tubes in each end. Told me they had done crush tests on their work and that they were so strong that you couldn't crush them with any hose clamp, no matter how tight.



Might be worth a look on your FG exhaust instead of the stainless rings, especially since you have a FG guy coming to look at the boat.

 

[Comodave]

Comodave beat me to the punch. +1 for Borel alarms!

I feel good that I was able to beat someone... Usually I am not that quick.

 

[caltexflanc]

Some manufacturers do include crush tubes. In chatting with the guy who supervised my project, he reminded me that he sourced the crush rings from Hatteras, where he used to work. The tubes we got from another local boatmaker and the $pecial epoxy we got from MESA, which in turn we bartered the substantial leftovers in exchange for the tubes. One advantage to living in a boat-building center.

 

[Divealot]

Ordered the AWAB clamps recommended by COMODAVE as well as the crush sleeve. The manufacturer of the clamp states the clamp torque is around 165 inch pounds. What do you torque your exhaust clamps at? I can’t imagine needing that much torque on an open pipe. I would think the clamp’s main functions are to get a proper seal and keep the hose from vibrating off. What torque do you use?

 

[psneeld]

Snug enough that they withstand thermal cycling and minor vibration without you easily pulling the hose off or it leaking. What that equates to in torque on the tightening bolt???? No clue.


Most people overtighten...thus the reason for crush rings.

 

[Comodave]

I didn’t use a torque wrench on mine. I use an allen wrench and brought the clamps as tight as I could with the allen. I figured that was tight enough. So far so good.