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Old 02-17-2013, 12:49 PM   #1
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Wet Exhaust Questions

Looking at the exhaust on my Gulf Star 36 Trawler with twin 4-154 Perkins (60 hp). The exhaust manifold/water injection elbow is 2" diameter and about 9-10" above water line. Attached to the elbow is 4" diameter hose running along the chine of the hull aft to the mufflers and out through the transom. The mufflers are not water lift units and they are mounted about 4-6" above the lowest point of the exhaust hose. My concern is that when I disconnected the hose from the manifold the standing water level in the hose was only about 12" from the exhaust manifold. Although I haven't had a problem it seems a little close for comfort. I've been thinking of raising the height of the injection point. My questions are:

Ideas for sourcing injection elbows?

Is the 4" hose & muffler overkill for this engine? My Perkins guy says the exhaust should be 2" all the way to the transom. The 2" would be easier to route but I don't want to create a backpressure problem.

Does anyone know the size and configuration Gulf Star used?


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Old 02-17-2013, 02:51 PM   #2
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Rocks,

I had National Marine Exhaust in Marysville Washington State build one for me w SS and I'm very happy w it. $750.

I'd probably go for lift mufflers.
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Old 02-17-2013, 03:08 PM   #3
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I believe Buck Algonquin and Osco or Barr makes those elbows....

Water Cooled Exhaust Elbows on Buck Algonquin

I have a pair of Perkins 6.354's that had to have the wet manifolds and wet elbows replaced...got them made of stainless steel by MESA in Alabama...

I don't think I would reduce the size if the existing exhaust is working fine and the hose is all in good condition as well as the elbows....but you might want to add something like a Vetus waterlift muffler to prevent backflow if you are worried about it....
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Old 02-17-2013, 03:14 PM   #4
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If you decide to add waterlift mufflers get them made of fiberglass. They will last the life of the boat and are superior even to stainless.

And whatever kind you get make sure they have a drain fitting at the bottom so you can drain them of water in the event you have to crank the engine a bunch of times for some reason. If you can't drain the muffler it can fill up with water and backfill up into the manifold. Ideally the entire setup--- elbow, connection, and muffler, should be well below the back of the exhaust manifold.

Our Lehman 120s have exhaust runs to the transom that are at least 4" in diameter. I would think a 2" hose would be far too small but this is not my area of expertise.
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Old 02-17-2013, 04:05 PM   #5
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Normally, performance wise, the exhaust can't be too large in diameter. However in a boat, standing water in the exhaust can roll into the engine when the boat pitches as when anchored in a seaway. In this respect, smaller is better because it will contain less water. 3" is fine for your engine and 2" if manufacturer allows.

The hose should slope down all the way to transom then there should be no standing water in the exhaust when stopped and no chance for it to roll into the engine.

So why, if 9-10" above the waterline do you see any water when you remove the hose? Are the mufflers holding it? There are mufflers available that don't hold water. Is the lowest spot not at the transom as it should be?

If the exhaust hose can be rearanged (or elbows raised) so it slopes continuously down to the transom, and the mufflers do not hold water, you are fine with 9-10" drop. If not, a waterlift muffler in the engine space, as shown in a previous post, may be the answer but waterlifts have their own criteria for installation. They must be able to hold all of the accumulated water in the system aft of them for one. They also can fill with water and overflow into the engine under certain conditions.

I would favor correcting the system without taller jacketed elbows because they are expensive and when they leak internally, water will go right into the engine. Your existing elbows could be raised using dry pipe fittings but would have to be wrapped (lagged) for fire safety.

In looking at your photos again, it seems that the installer used up all the drop (and then some) right in the engine space creating a low spot right there. N/G
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Old 02-17-2013, 05:11 PM   #6
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The recommendation from the gurus at boatdiesel is for the lowest part of the exhaust elbow be 12" above the water line. See the following picture. You don't seem to have anywhere near that much.

There are a couple of solutions. The best is to make up a high rise dry exhaust riser that will add about 6-8" to the height of your installation. You can do it with 2" stainless steel pipe fittings: a short nipple from the exhaust port, an elbow, a 6" nipple and another elbow. The last fitting is your existing injection elbow. You will have to lengthen your exhaust hose and maybe the raw water hose and insulate the dry riser.

Another, but not as good solution, is to replace your muffler with a water lift muffler and then from there make a high loop in the exhaust hose before it goes out the transom. It isn't as good a solution because if heavy seas force water over the top of the loop, eventually the muffler will fill with water and then back up to the exhaust port. Almost all sailboats use this design however and it seems to work.

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Old 02-17-2013, 05:56 PM   #7
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So you know....I have found on our GS44...when I replaced the exhaust hoses on both sides...the last person to install them allowed them to droop...there were no supports mounted at intervals... When I put the new manifolds, elbows, and hoses in....I elevated the mid sections to continue a "drop to the stern"...which eliminated any mid section droop that could hold water.. Additionally, if you are concerned about backwash from waves, following seas, bad weather, etc....You might want to install a flapper on each of the exhausts that will block water attempting to enter the exhaust hoses...
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Old 02-17-2013, 05:59 PM   #8
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Norther Lights PDF on wet exhaust

Please donít drown me is a Northern Lights pdf file about installing a wet exhaust for a gen set,

The basic rules are pretty universal - propulsion or gen.

Nicely illustrated.

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Old 02-17-2013, 08:05 PM   #9
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I question 2" size as adequate. I note the exhaust elbow for a 60 hp Perkins needs a 2 1/2" ID hose and the 80 hp a 3". Suggest you double check with some install drawings or Perkins manual. Ask your Perkins guy to show his source of information.
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Old 02-18-2013, 06:16 AM   #10
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A look in any 60's era Yachting Mag will show a stern exhaust fitting by WC.

This has a closing flap in it to serve two purposes.

It might stop water from backing up the exhaust in a following sea , but more important it will help delay changes of air in the exhaust system.

The fresh damp air blowing in thru the exhaust is a cause of cylinder rusting , esp in seldom used boats.
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Old 02-18-2013, 11:28 AM   #11
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Quote:
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A look in any 60's era Yachting Mag will show a stern exhaust fitting by WC.

This has a closing flap in it to serve two purposes.

It might stop water from backing up the exhaust in a following sea , but more important it will help delay changes of air in the exhaust system.

The fresh damp air blowing in thru the exhaust is a cause of cylinder rusting , esp in seldom used boats.

I don't believe this is a problem if one has a water lift muffler.
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Old 02-19-2013, 07:20 AM   #12
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I don't believe this is a problem if one has a water lift muffler.


No the water lift muffler problem is either a "no start" condition where multiple crank attempts with no exhaust pressure fills the lify can , the hose , the exhaust manifold and the engine.

The muffler must also be winterized or drained as required .

And of course the engine cylinders "see" water at all times in the exhaust , perhaps accelerating cylinder rusting after shutdown.
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Old 02-19-2013, 10:04 AM   #13
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On the Rocks,

Here's my SS National Marine Exhaust riser/mixer w heat shield. I use this with a FG lift muffler.
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Old 02-19-2013, 01:58 PM   #14
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Thanks all. I do have a low spot between the muffler(s) and the injection elbow. Because I have an aft cabin there isn't a great place to route the hose to allow a proper slope between the injection elbow and the transom. Still scratching my head trying to figure out if I can do it without a water lift muffler. The exhaust line is so long and so big (4") that I think I would need pretty large water lift mufflers to hold all that water (which is why I was asking if smaller hose would be ok). I really appreciate the discussion and have gotten a couple of ideas to look at.
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Old 02-19-2013, 02:25 PM   #15
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By the way I was not correct on the size of my exhaust flange on the manifold of my perkins 4-154s, it is 2.5" not 2". So I was looking to reduce the hose size from 4" to 2.5".
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Old 02-19-2013, 05:11 PM   #16
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Quote:
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Thanks all. I do have a low spot between the muffler(s) and the injection elbow. Because I have an aft cabin there isn't a great place to route the hose to allow a proper slope between the injection elbow and the transom. Still scratching my head trying to figure out if I can do it without a water lift muffler. The exhaust line is so long and so big (4") that I think I would need pretty large water lift mufflers to hold all that water (which is why I was asking if smaller hose would be ok). I really appreciate the discussion and have gotten a couple of ideas to look at.
I think 3" hose would be fine and maybe 2-1/2", I could look it up. But will either size allow you to get rid of the low spot in the engine space? If it will, I think that is the best answer.
Remember, even with a waterlift fitted, if the trip to the transom is uphill, water entering while moored/anchored will still roll down into the waterlift and after filling it, you are back where you started. But, and this is the good part, with a waterlift you can have a gooseneck at the transom to prevent water from entering in the first place which, without the waterlift you can not have.
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Old 02-24-2013, 12:53 AM   #17
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Tony's Tips - Marine Articles & Boat Politics

Go to the link above. It will show numerous info pieces. Scroll down to the Marine Exhaust Sytems articles and have a good look. There is some info there that you may be able to use.
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Old 02-24-2013, 12:27 PM   #18
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I can't imagine why they put 4" exhaust hose on those engines! My 6.354's use 3", and all the other 6.354's I have seen do as well... The PO must have gotten a really sweet deal on the 4" hose!

If you downsize it with a reducer, which might be needed if the elbow connection is 4", you can do it with fiberglass reducers, or if you prefer...stainless steel...about 2' down the hose....then run the smaller hose of 2.5" to the stern...which will allow you to adjust the position of the hose so that there is a constant downhill run to the exhaust outlet....

Fiberglass elbows/reducers: Centek Industries - Products

Stainless reducers/elbows: 4

Considering the price difference between 4" and 2.5"....the reducers cost would be negligible....and you would not have to change your existing wet elbows if they are still serviceable.
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Old 02-24-2013, 03:31 PM   #19
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I can't imagine why they put 4" exhaust hose on those engines! My 6.354's use 3", and all the other 6.354's I have seen do as well... The PO must have gotten a really sweet deal on the 4" hose!

If you downsize it with a reducer, which might be needed if the elbow connection is 4", you can do it with fiberglass reducers, or if you prefer...stainless steel...about 2' down the hose....then run the smaller hose of 2.5" to the stern...which will allow you to adjust the position of the hose so that there is a constant downhill run to the exhaust outlet....

Fiberglass elbows/reducers: Centek Industries - Products

Stainless reducers/elbows: 4

Considering the price difference between 4" and 2.5"....the reducers cost would be negligible....and you would not have to change your existing wet elbows if they are still serviceable.
What he said....
Don't use a waterlift if you don't have to, sloping to the transom by using smaller hose is the way to go if you can.
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Old 02-25-2013, 07:27 AM   #20
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"Don't use a waterlift if you don't have to,"

I would install a waterlift on any engine for the huge advantages.

IF a water lift can be fitted of proper diameter it will reduce the noise immensly, to tghe comfort of all aboard and nearby.

Too small a lift muffler will raise back pressure too high.
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