Home |
Search |
Today's Posts |
#11
|
|||
|
|||
Wet exhaust sizing.
Wait a minute, something does not add up. This is a 23' hull with an
80HP Nissan diesel getting 7.5 knots? Assuming a full displacement 20' LWL and 6000 lb displacement it should theoretically take only about 23 HP to get 7.5 Kn. As far as the exhaust is concerend what you describe is asking for problems. I assume a relatively short run from the injection point to the transom which works in your favor but if the outlet is level with the exhaust manifold there is defilitely a risk of flooding the engine. You probably don't have to worry about seawater getting in from a following wave but while cranking that engine will probably need to put 3 or 4 gallons of water someplace. That plug of water you see coming out when you start up is what was pumped into the hose during cranking. If the engine is a little slow about waking up and the exhaust is trapped there is a very real danger that the hose will fill up. When you stop cranking to rest the battery at least one exhaust valve will remain open. The water will flow back and fill that cylinder. David Flew wrote: Jim The installation is fairly typical of small wooden boats in my area - at 23 ft this is at the upper end of small. From the exhaust manifold piping angles down. Water injection point is in this downward sloping metal section. At some convenient point the system becomes rubber hose, which then connects to more metal components where the system penetrates the transom. The outlet is "about" the same level as the exhaust manifold, and the centrifugal cooling water pump is directly driven by the engine. A few boats have water lifts or water locks. I've not heard of any backing up problems as you describe, I'd guess that even during extended periods of cranking and failing to start the engine, there is enough air going out of the engine to keep the exhaust from filling with water - and there is little out put from the cooling pump at cranking speeds anyway. I suspect the hose acts a water lock, if it's big enough it certainly acts a crude silencer. I went from 1.75 inch to 2.5 inch hose on a 10 HP diesel in my "old" boat ( hope it will be my "former" boat rather than my "old" boat in a day or two ) and whilst I have no figures, subjectively the engine could be run to much higher revs before it became unpleasant to sit on the stern thwart. In the quieter mode, there seem to be discrete plugs of water ejected from the exhaust, along with continual spray. Once the RPM and exhaust velocity goes up, it's just a gas/water mix. So I suspect that water accumulates in the low points of the hose, and it's a water baffled silencer, if you get my drift. The water locks I've seen advertised suggest this is part of their function - but don't give much data to support the claim. I measured the hose on the "new" boat today - it's 2". I'm really looking forward to replacing it with 3.5". I think minimum bend radius goes up something like the cube of the diameter ... I disagree with Glen, it's not a job for a circus contortionist, but for an animal trainer. I'm really looking forward to taming the new hose. I can see the attraction of just piping the exhaust straight from the engine through the sides - even if you burnt some dangly bits every time you walked past the engine .... This time I'm going to take some noise readings as I go along, also performance details. Although the difference between 7.5 and 7.6 knots at full throttle is not exactly important! Regards David -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
#12
|
|||
|
|||
Wet exhaust sizing.
You're probably fine. As I said, it's a low risk.
Over here, we use fiberglass tubing for serious bends in wet exhausts. It's a whole lot easier than the hose contortions you sometimes get into. For those of you with boats longer than 23', it's cheaper than hose for the long run back to the transom. And, of course, it's much less likely to decide to kink a year from now if you bend a little too much. see http://home.rose.net/~centek/fittings.html -- Jim Woodward www.mvFintry.com .. "David Flew" wrote in message ... Jim The installation is fairly typical of small wooden boats in my area - at 23 ft this is at the upper end of small. From the exhaust manifold piping angles down. Water injection point is in this downward sloping metal section. At some convenient point the system becomes rubber hose, which then connects to more metal components where the system penetrates the transom. The outlet is "about" the same level as the exhaust manifold, and the centrifugal cooling water pump is directly driven by the engine. A few boats have water lifts or water locks. I've not heard of any backing up problems as you describe, I'd guess that even during extended periods of cranking and failing to start the engine, there is enough air going out of the engine to keep the exhaust from filling with water - and there is little out put from the cooling pump at cranking speeds anyway. I suspect the hose acts a water lock, if it's big enough it certainly acts a crude silencer. I went from 1.75 inch to 2.5 inch hose on a 10 HP diesel in my "old" boat ( hope it will be my "former" boat rather than my "old" boat in a day or two ) and whilst I have no figures, subjectively the engine could be run to much higher revs before it became unpleasant to sit on the stern thwart. In the quieter mode, there seem to be discrete plugs of water ejected from the exhaust, along with continual spray. Once the RPM and exhaust velocity goes up, it's just a gas/water mix. So I suspect that water accumulates in the low points of the hose, and it's a water baffled silencer, if you get my drift. The water locks I've seen advertised suggest this is part of their function - but don't give much data to support the claim. I measured the hose on the "new" boat today - it's 2". I'm really looking forward to replacing it with 3.5". I think minimum bend radius goes up something like the cube of the diameter ... I disagree with Glen, it's not a job for a circus contortionist, but for an animal trainer. I'm really looking forward to taming the new hose. I can see the attraction of just piping the exhaust straight from the engine through the sides - even if you burnt some dangly bits every time you walked past the engine .... This time I'm going to take some noise readings as I go along, also performance details. Although the difference between 7.5 and 7.6 knots at full throttle is not exactly important! Regards David "Jim Woodward" jameslwoodward at attbi dot com wrote in message ... Question. You say, "aside from not having a water lock", which concerns me. I assume Glenn and you mean what I call a waterlift -- a pot at a low point from which the exhaust leads out near the bottom so that water in the pot is blown out after the engine starts. The primary function of these is to hold the water that is pumped through the engine before it starts. Something to perform that function is essential unless the engine is mounted high enough so that the exhaust drains by gravity without help. Without it, you run the risk of water backing up through the exhaust valves. If that happens and the engine then starts firing in another cylinder, you may break something in the cylinder with water in it -- certainly it's not good. This may be a low risk event, particularly if the engine and batteries are in good shape and it starts quickly every time, but most of us try to avoid even low risks of putting a rod through the block. -- Jim Woodward www.mvFintry.com . "David Flew" wrote in message ... Glen I was hoping for a response from you - always seem to give a good practical approach. Aside from not having a water lock, I think you are spot on in both the required sizing, the original sizing, and the potential for damage. I suspect that damage was avoided by the previous owner by limiting RPM to 2200 -2500. If 3.5 " is OK for 3500 RPM., then 2.5 " is OK for roughly 2200. Either way the exhaust is clearly too small. As to the "new" engine. It's "new" for this boat. In Australia it's very economical to buy a low mileage second hand Japanese diesel, which is what I have. David "Glenn Ashmore" wrote in message news:lcsqb.7087$62.5549@lakeread04... Acording to the Yanmar JH installation manual the exhaust should be the size of the mixing elbow outlet up to the water lock and then if the run is "long" (they don't say how long long is) to increase by 25%. From the Centrek site a 3.5" exhaust can handle 85 HP max so you might consider using 4" to have a little margin. The exhaust size for the original 80 HP gasoline engine was probably 2.5". If that system is still installed the back pressure is probably doing some damage to your new diesel. David Flew wrote: Can anyone provide sizing info for wet exhausts on diesel engine. My recent purchase originally had 80 HP petrol engine, then 30 HP Lister, now 80 HP converted Nissan diesel. The Nissan is OK up to about 2200 RPM, but over that the exhaust has both a little smoke and what looks like steam to me. And the exhaust if absolutely rocketing out the pipe ! I've seen somewhere that diesels have twice the exhaust volume of similar sized petrol engines, which suggests the exhaust may be half the required area ( I bet it's the original diameter ...) but I'd love either rule of thumb or rigorous methods for sizing exhausts. Thanks David -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
#13
|
|||
|
|||
Wet exhaust sizing.
Glen
I know it doesn't add up - and it's hard to separate the opinions from the facts. I've now found out who made boat ( 1959) and plan to visit them in a few days. Very local and still making boats, but as the former owner put it " with sticks" - please take no offence, it was his prejudice, not mine. The boat was supposedly dies-used for in excess of 10 years prior to the former owner buying it, he had it for about 4 years. The 80 HP V8 petrol engine was seized, he installed a 40 HP lister, but it would not even make way against a stiff breeze and current. So it was converted to a nominal 80 HP truck diesel. The above hearsay. Further inspection this weekend disclosed the remains of a second exhaust, consistent with a V8 installation. But I've no idea if the reputed 80 HP in it 15 years ago was the original, or what the 80 HP represented in terms of boat speed or shaft RPM. Nor do I know if the Lister was in good condition, or how it was matched to the prop. I played around with speed vs. RPM yesterday - the speeds are accurate, GPS based. RPM is numbers from the tacho - just added borrowing a tacho from work and confirming how far the boat tacho is out to the job list .. ( oops - one way speed runs - could be out say +- 0.5 kt for tides.) Add fitting the receiver for the mechanical log and calibrating that too ..... But getting back to your numbers. I found little speed increase between 2000 RPM and 2100; and essentially none over 2200. Given the age of the "new" engine, exhaust system restrictions, losses to drive both the engine and sea water pumps and the alternator, not to mention the gearbox losses ...... if it's putting 23 HP into the shaft I'd say it's doing well. It will be interesting to see if the original maker has any records. All of this has just gone down the priority list a little - making a new engine cover is now No 1. I was going to just re-insulate it with loaded vinyl/foam, but whilst measuring I found it needed some old insulation removed. I'll leave it to you to work out the favoured thermal and fire insulation material in 1959. I'm thinking that adding some lead to the existing engine cover might be a good idea. Just enough so that it sinks. Add a couple of P3 masks and some ear plugs to the stuff to "borrow" from work. Regards David "Glenn Ashmore" wrote in message news:qa6rb.10844$62.5538@lakeread04... Wait a minute, something does not add up. This is a 23' hull with an 80HP Nissan diesel getting 7.5 knots? Assuming a full displacement 20' LWL and 6000 lb displacement it should theoretically take only about 23 HP to get 7.5 Kn. As far as the exhaust is concerend what you describe is asking for problems. I assume a relatively short run from the injection point to the transom which works in your favor but if the outlet is level with the exhaust manifold there is defilitely a risk of flooding the engine. You probably don't have to worry about seawater getting in from a following wave but while cranking that engine will probably need to put 3 or 4 gallons of water someplace. That plug of water you see coming out when you start up is what was pumped into the hose during cranking. If the engine is a little slow about waking up and the exhaust is trapped there is a very real danger that the hose will fill up. When you stop cranking to rest the battery at least one exhaust valve will remain open. The water will flow back and fill that cylinder. David Flew wrote: Jim The installation is fairly typical of small wooden boats in my area - at 23 ft this is at the upper end of small. From the exhaust manifold piping angles down. Water injection point is in this downward sloping metal section. At some convenient point the system becomes rubber hose, which then connects to more metal components where the system penetrates the transom. The outlet is "about" the same level as the exhaust manifold, and the centrifugal cooling water pump is directly driven by the engine. A few boats have water lifts or water locks. I've not heard of any backing up problems as you describe, I'd guess that even during extended periods of cranking and failing to start the engine, there is enough air going out of the engine to keep the exhaust from filling with water - and there is little out put from the cooling pump at cranking speeds anyway. I suspect the hose acts a water lock, if it's big enough it certainly acts a crude silencer. I went from 1.75 inch to 2.5 inch hose on a 10 HP diesel in my "old" boat ( hope it will be my "former" boat rather than my "old" boat in a day or two ) and whilst I have no figures, subjectively the engine could be run to much higher revs before it became unpleasant to sit on the stern thwart. In the quieter mode, there seem to be discrete plugs of water ejected from the exhaust, along with continual spray. Once the RPM and exhaust velocity goes up, it's just a gas/water mix. So I suspect that water accumulates in the low points of the hose, and it's a water baffled silencer, if you get my drift. The water locks I've seen advertised suggest this is part of their function - but don't give much data to support the claim. I measured the hose on the "new" boat today - it's 2". I'm really looking forward to replacing it with 3.5". I think minimum bend radius goes up something like the cube of the diameter ... I disagree with Glen, it's not a job for a circus contortionist, but for an animal trainer. I'm really looking forward to taming the new hose. I can see the attraction of just piping the exhaust straight from the engine through the sides - even if you burnt some dangly bits every time you walked past the engine .... This time I'm going to take some noise readings as I go along, also performance details. Although the difference between 7.5 and 7.6 knots at full throttle is not exactly important! Regards David -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
#14
|
|||
|
|||
Wet exhaust sizing.
One more thing to look at with the numbers you have and the dimensions
of your prop. Take the engine RPM and divide it by the gearbox ratio to get prop RPM. Multiply prop RPM by the pitch in inches to get the theoretical maximum speed with no slip. (inches per minute) Now convert the boat speed in knots to inches per minute by multiplying by 1,216. Divide that number by the theoretical speed and subtract from one to get the propeller slip. The slip for a displacement hull should be somewhere close to 35-40%. For example, let's assume you have a 15" prop and a 2.3:1 gear ratio. At 2100 engine RPM the prop is turning at 913 RPM. Times 15" pitch makes 13,695. Now 7.5 knots times 1,216 gives 9,120. 9,120 divided by 13,695 and subtracted from 1 gives 33% which is pretty good so if my assumptions are correct your hull is a good shape and clean. But we are still not getting full RPM and the mystery gets deeper. OTOH, the natural hull speed for a 20' LWL is only about 6 knots and anything faster requires a lot more horsepower and results in more slip. As your assumed slip is still low, we must assume that the prop diameter is large. Ideally you want the prop dimensions such that the engine will just barely get to its rated maximum RPM and that the boat reach maximum cruising speed at 80-85% of maximum RPM. That is about as far as we can get (maybe to far) without some real numbers and making sure that the engine can actually put out it's rated power. David Flew wrote: Glen I know it doesn't add up - and it's hard to separate the opinions from the facts. I've now found out who made boat ( 1959) and plan to visit them in a few days. Very local and still making boats, but as the former owner put it " with sticks" - please take no offence, it was his prejudice, not mine. The boat was supposedly dies-used for in excess of 10 years prior to the former owner buying it, he had it for about 4 years. The 80 HP V8 petrol engine was seized, he installed a 40 HP lister, but it would not even make way against a stiff breeze and current. So it was converted to a nominal 80 HP truck diesel. The above hearsay. Further inspection this weekend disclosed the remains of a second exhaust, consistent with a V8 installation. But I've no idea if the reputed 80 HP in it 15 years ago was the original, or what the 80 HP represented in terms of boat speed or shaft RPM. Nor do I know if the Lister was in good condition, or how it was matched to the prop. I played around with speed vs. RPM yesterday - the speeds are accurate, GPS based. RPM is numbers from the tacho - just added borrowing a tacho from work and confirming how far the boat tacho is out to the job list .. ( oops - one way speed runs - could be out say +- 0.5 kt for tides.) Add fitting the receiver for the mechanical log and calibrating that too ..... But getting back to your numbers. I found little speed increase between 2000 RPM and 2100; and essentially none over 2200. Given the age of the "new" engine, exhaust system restrictions, losses to drive both the engine and sea water pumps and the alternator, not to mention the gearbox losses ..... if it's putting 23 HP into the shaft I'd say it's doing well. It will be interesting to see if the original maker has any records. All of this has just gone down the priority list a little - making a new engine cover is now No 1. I was going to just re-insulate it with loaded vinyl/foam, but whilst measuring I found it needed some old insulation removed. I'll leave it to you to work out the favoured thermal and fire insulation material in 1959. I'm thinking that adding some lead to the existing engine cover might be a good idea. Just enough so that it sinks. Add a couple of P3 masks and some ear plugs to the stuff to "borrow" from work. Regards David "Glenn Ashmore" wrote in message news:qa6rb.10844$62.5538@lakeread04... Wait a minute, something does not add up. This is a 23' hull with an 80HP Nissan diesel getting 7.5 knots? Assuming a full displacement 20' LWL and 6000 lb displacement it should theoretically take only about 23 HP to get 7.5 Kn. As far as the exhaust is concerend what you describe is asking for problems. I assume a relatively short run from the injection point to the transom which works in your favor but if the outlet is level with the exhaust manifold there is defilitely a risk of flooding the engine. You probably don't have to worry about seawater getting in from a following wave but while cranking that engine will probably need to put 3 or 4 gallons of water someplace. That plug of water you see coming out when you start up is what was pumped into the hose during cranking. If the engine is a little slow about waking up and the exhaust is trapped there is a very real danger that the hose will fill up. When you stop cranking to rest the battery at least one exhaust valve will remain open. The water will flow back and fill that cylinder. David Flew wrote: Jim The installation is fairly typical of small wooden boats in my area - at 23 ft this is at the upper end of small. From the exhaust manifold piping angles down. Water injection point is in this downward sloping metal section. At some convenient point the system becomes rubber hose, which then connects to more metal components where the system penetrates the transom. The outlet is "about" the same level as the exhaust manifold, and the centrifugal cooling water pump is directly driven by the engine. A few boats have water lifts or water locks. I've not heard of any backing up problems as you describe, I'd guess that even during extended periods of cranking and failing to start the engine, there is enough air going out of the engine to keep the exhaust from filling with water - and there is little out put from the cooling pump at cranking speeds anyway. I suspect the hose acts a water lock, if it's big enough it certainly acts a crude silencer. I went from 1.75 inch to 2.5 inch hose on a 10 HP diesel in my "old" boat ( hope it will be my "former" boat rather than my "old" boat in a day or two ) and whilst I have no figures, subjectively the engine could be run to much higher revs before it became unpleasant to sit on the stern thwart. In the quieter mode, there seem to be discrete plugs of water ejected from the exhaust, along with continual spray. Once the RPM and exhaust velocity goes up, it's just a gas/water mix. So I suspect that water accumulates in the low points of the hose, and it's a water baffled silencer, if you get my drift. The water locks I've seen advertised suggest this is part of their function - but don't give much data to support the claim. I measured the hose on the "new" boat today - it's 2". I'm really looking forward to replacing it with 3.5". I think minimum bend radius goes up something like the cube of the diameter ... I disagree with Glen, it's not a job for a circus contortionist, but for an animal trainer. I'm really looking forward to taming the new hose. I can see the attraction of just piping the exhaust straight from the engine through the sides - even if you burnt some dangly bits every time you walked past the engine .... This time I'm going to take some noise readings as I go along, also performance details. Although the difference between 7.5 and 7.6 knots at full throttle is not exactly important! Regards David -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
#15
|
|||
|
|||
Wet exhaust sizing.
Glen
I've just added checking the gearbox ratio and the actual tailshaft RPM vs engine RPM to my list of things to do. When the weather warms a little I can easily jump in and measure the prop dia, but how does one measure the pitch? Boat's not due on the slips for a year. I shall also measure WLL. Looks like this one will be around for a while; I'll advise progress. David "Glenn Ashmore" wrote in message news:hLNrb.13587$62.1025@lakeread04... One more thing to look at with the numbers you have and the dimensions of your prop. Take the engine RPM and divide it by the gearbox ratio to get prop RPM. Multiply prop RPM by the pitch in inches to get the theoretical maximum speed with no slip. (inches per minute) Now convert the boat speed in knots to inches per minute by multiplying by 1,216. Divide that number by the theoretical speed and subtract from one to get the propeller slip. The slip for a displacement hull should be somewhere close to 35-40%. For example, let's assume you have a 15" prop and a 2.3:1 gear ratio. At 2100 engine RPM the prop is turning at 913 RPM. Times 15" pitch makes 13,695. Now 7.5 knots times 1,216 gives 9,120. 9,120 divided by 13,695 and subtracted from 1 gives 33% which is pretty good so if my assumptions are correct your hull is a good shape and clean. But we are still not getting full RPM and the mystery gets deeper. OTOH, the natural hull speed for a 20' LWL is only about 6 knots and anything faster requires a lot more horsepower and results in more slip. As your assumed slip is still low, we must assume that the prop diameter is large. Ideally you want the prop dimensions such that the engine will just barely get to its rated maximum RPM and that the boat reach maximum cruising speed at 80-85% of maximum RPM. That is about as far as we can get (maybe to far) without some real numbers and making sure that the engine can actually put out it's rated power. David Flew wrote: Glen I know it doesn't add up - and it's hard to separate the opinions from the facts. I've now found out who made boat ( 1959) and plan to visit them in a few days. Very local and still making boats, but as the former owner put it " with sticks" - please take no offence, it was his prejudice, not mine. The boat was supposedly dies-used for in excess of 10 years prior to the former owner buying it, he had it for about 4 years. The 80 HP V8 petrol engine was seized, he installed a 40 HP lister, but it would not even make way against a stiff breeze and current. So it was converted to a nominal 80 HP truck diesel. The above hearsay. Further inspection this weekend disclosed the remains of a second exhaust, consistent with a V8 installation. But I've no idea if the reputed 80 HP in it 15 years ago was the original, or what the 80 HP represented in terms of boat speed or shaft RPM. Nor do I know if the Lister was in good condition, or how it was matched to the prop. I played around with speed vs. RPM yesterday - the speeds are accurate, GPS based. RPM is numbers from the tacho - just added borrowing a tacho from work and confirming how far the boat tacho is out to the job list .. ( oops - one way speed runs - could be out say +- 0.5 kt for tides.) Add fitting the receiver for the mechanical log and calibrating that too ...... But getting back to your numbers. I found little speed increase between 2000 RPM and 2100; and essentially none over 2200. Given the age of the "new" engine, exhaust system restrictions, losses to drive both the engine and sea water pumps and the alternator, not to mention the gearbox losses ..... if it's putting 23 HP into the shaft I'd say it's doing well. It will be interesting to see if the original maker has any records. All of this has just gone down the priority list a little - making a new engine cover is now No 1. I was going to just re-insulate it with loaded vinyl/foam, but whilst measuring I found it needed some old insulation removed. I'll leave it to you to work out the favoured thermal and fire insulation material in 1959. I'm thinking that adding some lead to the existing engine cover might be a good idea. Just enough so that it sinks. Add a couple of P3 masks and some ear plugs to the stuff to "borrow" from work. Regards David "Glenn Ashmore" wrote in message news:qa6rb.10844$62.5538@lakeread04... Wait a minute, something does not add up. This is a 23' hull with an 80HP Nissan diesel getting 7.5 knots? Assuming a full displacement 20' LWL and 6000 lb displacement it should theoretically take only about 23 HP to get 7.5 Kn. As far as the exhaust is concerend what you describe is asking for problems. I assume a relatively short run from the injection point to the transom which works in your favor but if the outlet is level with the exhaust manifold there is defilitely a risk of flooding the engine. You probably don't have to worry about seawater getting in from a following wave but while cranking that engine will probably need to put 3 or 4 gallons of water someplace. That plug of water you see coming out when you start up is what was pumped into the hose during cranking. If the engine is a little slow about waking up and the exhaust is trapped there is a very real danger that the hose will fill up. When you stop cranking to rest the battery at least one exhaust valve will remain open. The water will flow back and fill that cylinder. David Flew wrote: Jim The installation is fairly typical of small wooden boats in my area - at 23 ft this is at the upper end of small. From the exhaust manifold piping angles down. Water injection point is in this downward sloping metal section. At some convenient point the system becomes rubber hose, which then connects to more metal components where the system penetrates the transom. The outlet is "about" the same level as the exhaust manifold, and the centrifugal cooling water pump is directly driven by the engine. A few boats have water lifts or water locks. I've not heard of any backing up problems as you describe, I'd guess that even during extended periods of cranking and failing to start the engine, there is enough air going out of the engine to keep the exhaust from filling with water - and there is little out put from the cooling pump at cranking speeds anyway. I suspect the hose acts a water lock, if it's big enough it certainly acts a crude silencer. I went from 1.75 inch to 2.5 inch hose on a 10 HP diesel in my "old" boat ( hope it will be my "former" boat rather than my "old" boat in a day or two ) and whilst I have no figures, subjectively the engine could be run to much higher revs before it became unpleasant to sit on the stern thwart. In the quieter mode, there seem to be discrete plugs of water ejected from the exhaust, along with continual spray. Once the RPM and exhaust velocity goes up, it's just a gas/water mix. So I suspect that water accumulates in the low points of the hose, and it's a water baffled silencer, if you get my drift. The water locks I've seen advertised suggest this is part of their function - but don't give much data to support the claim. I measured the hose on the "new" boat today - it's 2". I'm really looking forward to replacing it with 3.5". I think minimum bend radius goes up something like the cube of the diameter ... I disagree with Glen, it's not a job for a circus contortionist, but for an animal trainer. I'm really looking forward to taming the new hose. I can see the attraction of just piping the exhaust straight from the engine through the sides - even if you burnt some dangly bits every time you walked past the engine .... This time I'm going to take some noise readings as I go along, also performance details. Although the difference between 7.5 and 7.6 knots at full throttle is not exactly important! Regards David -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
#16
|
|||
|
|||
Wet exhaust sizing.
I'd like to know how you put a 3" waterlift 12" below the exhaust elbo in
these small sailboats. Both Yanmar and Westerbeke have gone to larger 3" discharge on 44 and 50 hp models |
#17
|
|||
|
|||
Wet exhaust sizing.
First you practice up handling 3" exhaust hose by wrassling an anaconda.
WestlakeY wrote: I'd like to know how you put a 3" waterlift 12" below the exhaust elbo in these small sailboats. Both Yanmar and Westerbeke have gone to larger 3" discharge on 44 and 50 hp models -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
Reply |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
DIY Exhaust | General | |||
Exhaust conversion to thru-hull | General | |||
Mechanics / Boat Savy: Exhaust Manifold & Thermostat Housing | General | |||
Exhaust question on inboard 1958 Chris Craft | General | |||
Exhaust question on inboard 1958 Chris Craft | Boat Building |