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Old 08-11-2007, 11:39   #1
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OK to splice Genset Exhaust?

While on STBD tack we always got a wet spot on the carpet in the aft cabin. Water seeps out from underneath the hanging locker. I always assumed it was due to a blind pocket in the bilge... but I was not so lucky.

Further inspection reveals that the genset exhaust hose is weeping about 2 feet inboard from the through-hull which sits about 3 inches above the waterline. When we heel far enough water seeps through the hose and under the berth. Then makes its way forward to the hanging locker.

Of course I plan to replace the entire hose - later. In the meantime is it OK to cut back the hose to a "good" point, then use a galv pipe insert to splice on a new section that I will then run to the through-hull? We're about 6 feet from the engine room at the point of failure, and about 14 feet hose-length from the water-lift (due to the length of the anti-siphon loop).

Suggestions?

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Old 08-11-2007, 12:49   #2
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Yes you could do that, but I would bet that it would leak a bit any way.

If you can locate some hose barbs, The fittings that hook into hoses they might actually work better.

They real key is to use Tee clamps, rather than hose clamps.

I have used tee clamps and threaded nipples and had good service holding radiator fluids in.
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Old 08-11-2007, 13:10   #3
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No problem at all doing what you plan. You don't need barb fittings or anything fancy. Pressure on an exhaust hose is minimal. Make sure you have a snug fit, double clamp and have at least 1.5 inches of hose pushed onto the pipe. I use fiberglass hose connectors to avoid any issues of metal in a salt water/exhaust environment. Check your local chandlery. I would, however, recommend replacing the entire hose since its integrity is in question. R U sure the problem isn't with the thru hull?

Brett
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Old 08-11-2007, 13:25   #4
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My concern was not with pressure, but achieving a good seal on the partially deteriorated hose where he will likely be clamping.

Also if something falls over on the hose will the hose clamps have enough friction to keep the thing together.

Of course this all depends on how tight a fit he can find between the hose ID and the pipe OD.
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Old 08-11-2007, 16:15   #5
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I would also pick up some exhaust silicone for the areas that are not quite 100% together to fill in the little gaps so you are not sucking fumes.
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Old 09-11-2007, 07:05   #6
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Quote:
Originally Posted by LtBrett View Post
No problem at all doing what you plan. You don't need barb fittings or anything fancy. Pressure on an exhaust hose is minimal. Make sure you have a snug fit, double clamp and have at least 1.5 inches of hose pushed onto the pipe. I use fiberglass hose connectors to avoid any issues of metal in a salt water/exhaust environment. Check your local chandlery. I would, however, recommend replacing the entire hose since its integrity is in question. R U sure the problem isn't with the thru hull?

Brett
I've verified where the leak is, and it's not the through-hull (thankfully).

I was concerned about temperature and using fiberglass inserts. But as I think about it, it's water-cooled and pretty far from the engine anyway. That approach sounds better than the old galvanized pipe trick.

Thanks all.
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Old 09-11-2007, 08:35   #7
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I suppose the question becomes, "how temporary is this repair?" If you are just looking to get by for a couple of months until you can replace the entire hose, you could consider iron pipe. Forget the galvanized stuff, as the first thing to go will be the zinc coating. You could make a permanent coupling if that makes your life easier by installing fiberglass fittings. I don't remember the manufacturer, but if you ask for exhaust-rated fiberglass fittings in the diameter of your hose, you'll get what you need. They are, however, a little more expensive than iron pipe. I'm still scratching my head on why you don't replace the entire hose now. If the hose was leaking and the problem was not due to some localized abrasion, you have a major safety concern.

Brett
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Old 09-11-2007, 09:21   #8
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Fiberglass Marine Wet Exhaust Connectors/Couplings;
Goto: Trident Marine: Wet Exhaust Tube Connectors
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Old 09-11-2007, 09:24   #9
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Tee Clamps

Trident Marine: Wet Exhaust
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Old 09-11-2007, 09:40   #10
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I'd try to leave the repair in as short as possible. This will increase back pressure on the gens engine and after many hours could cause premature failure.
I do see a problem using galvanized. Try to find a fiberglass piece. The galv will be exposed to warm salt water and will corrode over time.
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Old 09-11-2007, 15:19   #11
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Thanks guys!
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Old 09-11-2007, 17:33   #12
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For a wet exhaust after the water lift muffler another alternative is to use common old schedule 40 PVC pressure water pipe. Very easy to use and a lot of fittings available, including plastic clips for securing it to supports.

Our main engine exhaust from water lift muffler to the transom discharge is all done in PVC pipe (2 inch) in a run of around 10 feet. The connector to the muffler and to the transom fitting is rubber hose and the PVC pipe is a perfect slide fit into that in our case. This was installed by a very good boatbuilder when the boat was built for us and I suspect that he knew what he was doing.

Been like that for 11 years and I cut recently into it to reroute part of it and was like new inside.
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Old 09-11-2007, 22:37   #13
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I really don't want to counter anyone but PVC is much too brittle to be relied upon for something which has the potential for sinking a boat. PVC becomes more brittle over time. The USCG bans it on inspected vessels for bilge systems or any other systems which could potentially sink a vessel. If you are going to consider some sort of cheap plastic then go with ABS plastic...its not brittle at all.

In your situation I would go ahead and replace the entire hose. Splices in hoses just increase the chances of a leak or a break.
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Old 10-11-2007, 04:12   #14
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I think that you will find that you are being unduly pessimistic regarding the use of uPVC pressure pipe given that it has a service life of at least 50 years (typically 100 years is quoted for it before rehabilitation in water and waste pressure pipework). On land PVC is used in much more onerous services such as for gas pipework. You mention it as being a cheap plastic - in my experience uPVC pressure pipe and its fittings are not cheap. Perhaps you are thinking of the like of uPVC domestic waste pipe and fittings which are cheap?

In the case of a yacht main engine or generator below the waterline as long as it is protected on the raw water suction side by an anti siphon loop and the exhaust discharge is overboard then the only possibility of flooding is from the engines own raw water pumping, not from back flooding from the sea.

I would suggest that the likely risks of that are higher from failure of pipework, joints, seals on or about the engine, including the water injection elbow and riser to the water lift muffler, or from failure of exhaust rubber hose (whether used for joints or runs) or water lift mufflers such as or similar to the Vetus ones commonly fitted which have a reputation for failure (the likes of Centek excepted) than it is from a properly installed uPVC pressure pipe wet exhaust.

Also, the materials commonly used in exhaust systems all have their problems including the hose that you recommend. As an example, I recently project managed the build of two big power boats for a client and which were designed and built to Lloyds rules (SSC). The main engine risers and exhausts (exhausts approx 8 inch) were 904L ss pipe to aluminium overboard penetrations - I can guarantee the life of that high quality solution will be much less due to corrosion and fatigue than that of smaller diameter uPVC pressure pipe properly installed in a small pleasure vessel.

In the case of the generator exhaust in the original posters question, if it were my problem I would take the exhaust from the through hull (which is only 3 inches above the water line and is also subject to flooding during heeling so cannot be classed as an overboard discharge on either count) from a valve at the penetration, which it not being able to be classed as an overboard discharge it should be fitted with, to 300mm above the maximum heeled waterline in ss or grp pipe, in reality probably to the top of the anti siphon loop mentioned. I would not use a lesser material such as rubber hose (nor uPVC) for this section as back flooding is possible if it fails even though I would expect the likelihood of failure here due to raw water cooling loss would be low because of the long run from the muffler.

Personally, and only personally given my experience with it, for the rest I would use uPVC pressure pipe but grp would be preferable - however, given the long length I would not like to be the one paying for running it all in grp. I would rate both those, properly installed, as being significantly more reliable than approved rubber hose which I would personally never use in an exhaust for anything other than flexible joints.
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Old 10-11-2007, 04:55   #15
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As MidlandOne suugests a uPVC or cPVC sleeve should suffice as a TEMPORARY exhaust repair.

In general, inorganic materials, acids and alkalis have no effect on PVC. The groups of materials that can have an effect are:
a) The highly aromatic hydrocarbons.
b) The heavily chlorinated hydrocarbons.
c) The ketones.

The rate of hydrocarbon attack is very slow – for instance it takes months of continuous contact with gasoline to soften PVC.

The recommended maximum continuous operational temperature for uPVC pipes is about 60 degrees C (140 F).
The recommended maximum continuous operational temperature for cPVC pipes is about 105 degrees C (220 F).

This limitation refers to the complete pipe wall being at 60 deg. C (or 105 deg. C for CPVC) and would apply for constant discharge at 60 deg. C.
For discontinuous flow, such as in an exhaust system,,discharge temperatures can exceed the continuous maximums.
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