When my Catalina 27 is underway, by sail or motor, it tends to squat such that the exhaust outlet on the transom is under water. According to standard sources such as Vetus, Centek, and Nigel Calder, the base of the outlet should be 2-3 inches above the waterline. (I wonder if Catalina designed it that way as a means for low cost, mufflerless sound reduction.) I am completely rerouting the exhaust in an attempt to eliminate the possibility of a following sea filling the engine though the exhaust. I plan to do this by routing the exhaust hose 18 inches above waterline just ahead of the transom, adding a valve to the exhaust in the same area, a flapper at the exit, and a waterlift muffler. The existing system has no muffler, leaky hose, and exits straight out the transom. My question is whether my engine (Universal 5411 11hp diesel) could handle the additional back pressure of a waterlift muffler and longer, more roundabout exhaust hose routing since it already has to deal with the back pressure of the exhaust exiting the hull under water? It would be possible to raise the exhaust exit in the transom by a couple of inches - but not attractive due to all the fibreglass work that would entail. I understand that if I leave the exhaust underwater it would be a good idea to a add a high exhaust temp alarm. My real question is whether I can leave the existing underwater exhaust exit alone while also making the above changes? or do I really need to move the exit up out of the water for excess back pressure or other reasons? Paul Meyer New Brunswick Canada
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That's a very complex question. The answer is
simple. Keep it simple. Back pressure is not a problem with a proper size system. The engines' exhaust exit size should not be decreased. I'm not familiar with your engine. I assume it has wet exhaust. If it doesn't, it needs to be wet. Then cooling water solves all problems. It is inserted at the end of the manifold and cools the rubber hose. Then it enters the water-lift muffler and keeps it cool. It had better, they're plastic. Then as the hose reaches the stern it is formed into a 360 loop. That will block stern waves and further quietens the engine. The disadvantage to this system is that the engine could flood with raw water if it's cranked a long time and fails to start. In such cases it's necessary to close the raw water cooling through-hull. Here' a shot of mine. Note the loop in back. No shut-off either. That's a bad idea. Just asking for disaster. The water-lift system has taken over. Very few other designs being used. Lots of advantages, only one disadvantage. Just don't forget that through-hull. My boat takes about 30 seconds of cranking to flood the engine. It's never hurt it. I would close the through-hull, open the compression releases and crank like crazy to flush water. Finish bleeding or whatever stupid thing I was doing until it was seemingly ready to start. It always did. But that was many years ago when I had lots of engine projects going on. No body really does that anyway.
Good luck, just keep it simple and enjoy the quiet. The link has a good selection of mufflers.
simple. Keep it simple. Back pressure is not a problem with a proper size system. The engines' exhaust exit size should not be decreased. I'm not familiar with your engine. I assume it has wet exhaust. If it doesn't, it needs to be wet. Then cooling water solves all problems. It is inserted at the end of the manifold and cools the rubber hose. Then it enters the water-lift muffler and keeps it cool. It had better, they're plastic. Then as the hose reaches the stern it is formed into a 360 loop. That will block stern waves and further quietens the engine. The disadvantage to this system is that the engine could flood with raw water if it's cranked a long time and fails to start. In such cases it's necessary to close the raw water cooling through-hull. Here' a shot of mine. Note the loop in back. No shut-off either. That's a bad idea. Just asking for disaster. The water-lift system has taken over. Very few other designs being used. Lots of advantages, only one disadvantage. Just don't forget that through-hull. My boat takes about 30 seconds of cranking to flood the engine. It's never hurt it. I would close the through-hull, open the compression releases and crank like crazy to flush water. Finish bleeding or whatever stupid thing I was doing until it was seemingly ready to start. It always did. But that was many years ago when I had lots of engine projects going on. No body really does that anyway.
Good luck, just keep it simple and enjoy the quiet. The link has a good selection of mufflers.
Underwater exhaust exit
It is a wet exhaust system, hose is 1 5/8 inches (40mm)inside diameter. Basicly, I'm wondering whether the engine can push exhaust through water in two places (muffler to be added and transom) without back pressure issues. It currently only pushes exhaust through water at the transom. Paul
It is a wet exhaust system, hose is 1 5/8 inches (40mm)inside diameter. Basicly, I'm wondering whether the engine can push exhaust through water in two places (muffler to be added and transom) without back pressure issues. It currently only pushes exhaust through water at the transom. Paul
Think of it this way.
Turbo diesels generate incredible force to pressurize the incoming air charge. The sky's the limit. That's back pressure. No harm. Then they have to blow the water out of the system. More back pressure. No harm. Just don't stick something in there that can be forgotten like a shutoff valve.
Turbo diesels generate incredible force to pressurize the incoming air charge. The sky's the limit. That's back pressure. No harm. Then they have to blow the water out of the system. More back pressure. No harm. Just don't stick something in there that can be forgotten like a shutoff valve.
Told it wasn't an issue
I have the same issue with my Yanmar 2GM20F (which has a loop and a muffler). This was the response I got from Torresen Marine: "As long as you have a U shape mixing elbow and a good anti syphon you have no worries. Water coming back into the engine is more of a worry than any type of back pressure."
I have the same issue with my Yanmar 2GM20F (which has a loop and a muffler). This was the response I got from Torresen Marine: "As long as you have a U shape mixing elbow and a good anti syphon you have no worries. Water coming back into the engine is more of a worry than any type of back pressure."
Exhaust below water
I think it would be a mistake to change the location of the exhaust on your boat. But, I have a similar question because I've noticed that our boat squats low enough that water covers the exhaust, but only when running at full throttle. It doesn't happen when under sail alone or when the throttle is less than full. The only thing that is annoying about it is that it causes the exhaust to lift along the stern and backdraft into the cockpit. When the exhaust is free to discharge without inteference from water, it is not a problem.
I think it would be a mistake to change the location of the exhaust on your boat. But, I have a similar question because I've noticed that our boat squats low enough that water covers the exhaust, but only when running at full throttle. It doesn't happen when under sail alone or when the throttle is less than full. The only thing that is annoying about it is that it causes the exhaust to lift along the stern and backdraft into the cockpit. When the exhaust is free to discharge without inteference from water, it is not a problem.
Same design, but different annoyance
Yes, my exhaust port is also under the transom but above the water line. My complaint is that when I start the engine, I can’t see if it is really spitting water or not. So I have to walk around to the next slip to peek under the transom. I want to double check to make sure my raw water impeller is working. But looking over the transom from the cockpit, I will just see a bunch of ripples, but the exhaust’s air alone will create the ripples, and I can’t tell how often water actually comes spitting out. No biggie, but annoyed. I envy those boats with the exhaust port in clear and plain view.
Yes, my exhaust port is also under the transom but above the water line. My complaint is that when I start the engine, I can’t see if it is really spitting water or not. So I have to walk around to the next slip to peek under the transom. I want to double check to make sure my raw water impeller is working. But looking over the transom from the cockpit, I will just see a bunch of ripples, but the exhaust’s air alone will create the ripples, and I can’t tell how often water actually comes spitting out. No biggie, but annoyed. I envy those boats with the exhaust port in clear and plain view.
How are Newer Catalina 27's Designed?
How are the newer Catalina 27's designed? I'd suggest just changing what is needed to match the lastest Catalina 27 design and not more (i.e. if it ain't broke, don't fix it). Catalina has done a marvelous job of improving their boats every year, albeit the 27 is no longer made, how was the last of the 27's designed (excluding 'walk-out' transom if any)? Have you reviewed the International Catalina 27 Association's website's 'technical information' and posed the same questions to their tech writer (http://www.catalina27.org/)? Have other Catalina 27 owners 'fixed' the problem the same way? Would not the 'back pressure' issue also be of concern within the 'water lift' muffler since it will experience the 'under water exhaust exit pressure? What does 'water lift' muffler instructions/requirements indicate about the back pressure of an 'underwater' exit? If diesel engines have no problem with 'back pressure', why do all motor vehicles with diesels have much larger exhaust/tail pipes? Are you sure the problem is a design issue and not just a prop/prop alignment/prop shaft length issue? My 1988 Catalina 30 can, with a following sea, when running near full throttle, periodically immerse the exhaust. However, I believe I notice it does it less since I had the prop's blade alignment/pitch checked and re-trued. How bad is your port stern 'walk' in reverse? If it is excessive, the prop pitch could be off, or one or more blades out of 'sync' with each other, causing the 'slapping' effect which caused the port stern-walk, and cavitation. I have also read that if the prop creates lots of 'cavitation', it actually causes the stern to sink down, possibly due to the air bubbles 'hole' created by the cavitation. By the way, on my 30, with a Universal 3 cylinder M25XP, whereas it does have a fiberglass water lift muffler, the rubber exhaust hose does not do a 'loop' on the way to the stern, but it does run high along the port side, just under the rub-rail, on its way to the middle-stern exhaust exit with flap (which is about 5-6 inches above the water when the boat is at rest). I would also echo "JC on Bainbridge's" comment about above the water and visible exhaust exits. I find it very easy on my boat to view the exhaust and verify water is mixing with the exhaust so I then also know my raw water system is working correctly. However, I also installed a neat water flow alarm in my raw water circuit just before the anti-siphon valve, which is just before the mixing elbow and then the water-lift muffler. If my impeller were to fail, of I were to forget to open the thru-hull valve, it sets off my cockpit engine panel alarm (wired it to the 'oil pressure' switch so that either will set-off the panel alarm). It is from Aqua-Alarm and in case your interested, here is the link: http://aqualarm.net/ Hope this helps...
How are the newer Catalina 27's designed? I'd suggest just changing what is needed to match the lastest Catalina 27 design and not more (i.e. if it ain't broke, don't fix it). Catalina has done a marvelous job of improving their boats every year, albeit the 27 is no longer made, how was the last of the 27's designed (excluding 'walk-out' transom if any)? Have you reviewed the International Catalina 27 Association's website's 'technical information' and posed the same questions to their tech writer (http://www.catalina27.org/)? Have other Catalina 27 owners 'fixed' the problem the same way? Would not the 'back pressure' issue also be of concern within the 'water lift' muffler since it will experience the 'under water exhaust exit pressure? What does 'water lift' muffler instructions/requirements indicate about the back pressure of an 'underwater' exit? If diesel engines have no problem with 'back pressure', why do all motor vehicles with diesels have much larger exhaust/tail pipes? Are you sure the problem is a design issue and not just a prop/prop alignment/prop shaft length issue? My 1988 Catalina 30 can, with a following sea, when running near full throttle, periodically immerse the exhaust. However, I believe I notice it does it less since I had the prop's blade alignment/pitch checked and re-trued. How bad is your port stern 'walk' in reverse? If it is excessive, the prop pitch could be off, or one or more blades out of 'sync' with each other, causing the 'slapping' effect which caused the port stern-walk, and cavitation. I have also read that if the prop creates lots of 'cavitation', it actually causes the stern to sink down, possibly due to the air bubbles 'hole' created by the cavitation. By the way, on my 30, with a Universal 3 cylinder M25XP, whereas it does have a fiberglass water lift muffler, the rubber exhaust hose does not do a 'loop' on the way to the stern, but it does run high along the port side, just under the rub-rail, on its way to the middle-stern exhaust exit with flap (which is about 5-6 inches above the water when the boat is at rest). I would also echo "JC on Bainbridge's" comment about above the water and visible exhaust exits. I find it very easy on my boat to view the exhaust and verify water is mixing with the exhaust so I then also know my raw water system is working correctly. However, I also installed a neat water flow alarm in my raw water circuit just before the anti-siphon valve, which is just before the mixing elbow and then the water-lift muffler. If my impeller were to fail, of I were to forget to open the thru-hull valve, it sets off my cockpit engine panel alarm (wired it to the 'oil pressure' switch so that either will set-off the panel alarm). It is from Aqua-Alarm and in case your interested, here is the link: http://aqualarm.net/ Hope this helps...
Is the bilge discharge underwater too?
Is the bilge thru hull also underwater? On my 86 Catalina 27 there is an anti-siphon vented loop for the exhaust but not for the bilge. Well, after last weekend there is a vented loop on both now. Something to think about. Jack
Is the bilge thru hull also underwater? On my 86 Catalina 27 there is an anti-siphon vented loop for the exhaust but not for the bilge. Well, after last weekend there is a vented loop on both now. Something to think about. Jack
Uhh... the bilge thru-hull...
should not be below the waterline. I don't quite understand the reason you can't tell where it comes out. Can't you just follow the hose from your bilge pump and see where goes? If you put a vented loop in it last weekend, weren't you able to see where it came out?
should not be below the waterline. I don't quite understand the reason you can't tell where it comes out. Can't you just follow the hose from your bilge pump and see where goes? If you put a vented loop in it last weekend, weren't you able to see where it came out?
in response to jc
jc At no time did I say I didn't know where the bilge discharge thru hulll is, but, to clarify it to you, I will explain. When my 86 Catalina 27 is at dock the bilge discharge is parallel to the exhaust thru hull, a few inches above the waterline. When motoring, the boat can squat a few inches bringing both thru hulls underwater. Catalina installed a vented loop on the exhaust for the year/model I have. This solved the sihpon problem with the exhaust. The bilge did not have a vented loop. This caused a big problem last week. I explained to Paul{ the author of this article} to check both thru hulls for the siphoning effect, not just the exhaust. Are we straight? Jack
jc At no time did I say I didn't know where the bilge discharge thru hulll is, but, to clarify it to you, I will explain. When my 86 Catalina 27 is at dock the bilge discharge is parallel to the exhaust thru hull, a few inches above the waterline. When motoring, the boat can squat a few inches bringing both thru hulls underwater. Catalina installed a vented loop on the exhaust for the year/model I have. This solved the sihpon problem with the exhaust. The bilge did not have a vented loop. This caused a big problem last week. I explained to Paul{ the author of this article} to check both thru hulls for the siphoning effect, not just the exhaust. Are we straight? Jack
Interesting little device.
Looks like I will need to by both the sensor and a alarm panel. I wonder if I can connect it sensor to some other type of alarm panel. It is time for more research. Thanks.
Looks like I will need to by both the sensor and a alarm panel. I wonder if I can connect it sensor to some other type of alarm panel. It is time for more research. Thanks.
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