"under water exhaust" without Butterfly valves and Silent Rider

[cowwboy]

I ove my FAE, but mine is solely for noise reduction. 

When surfing the exhaust note was heading straight at the surfer. It was the best stereo upgrade I have ever had.

I did loose a few MPH but I am thinking it is due to the flow disturbance more then exhaust flow. 

I had mine built as a welded Y and not the adjustable down pipe or I would just spin it backwards and see if you still had the speed loss. 

Edited March 2, 2017 by cowwboy

[formulaben]

16 hours ago, RTS said:

Geez...I've been skiing behind inboard boats for 40 years....fumes were never a problem for me or anyone else in/behind the boat.  No one I know ever died of CO poisoning.

You guys want the 'FAE' type exhaust for noise purposes or whatever, that's cool and I can totally understand.  Go For It.

But if you were to 'advocate' when you 'see the exhaust fumes' in my boat...you'd have a short ride to the dock....

 

 

16 hours ago, RTS said:

Point taken....I have never surfed behind an inboard or any other boat.  

 

Edit:  Still can't help but think that the FAE type systems are a solution in search of a problem.

Geez, pontificate much?

[WAwinegrapes]

3 hours ago, MadMan said:

I agree, the FAE exhaust design is probably the worst you could come up with for exhaust flow.  It's basically blast the left and right sides at each other, then expect it to make an 90 degree bend. 

We have the turn down exhaust tips and they quiet the boat engine noise down significantly.  You still know you have a V8 under the hood, but the tips make conversions easier.  You can talk rather than yell.  Same with music.

Edited March 2, 2017 by WAwinegrapes

[Nitrousbird]

20 hours ago, RTS said:

 Still can't help but think that the FAE type systems are a solution in search of a problem.

People have been hospitalized and died from exhaust fumes at the back of a boat (think teak surfing that is banned in most states).

I noticed that we feel better at the end of the day surfing with the FAE than without it.  Less tired and just a better overall feeling.  I have to attribute that to the FAE.  Sound reduction is nice too, but I already had STE's so it wasn't that big of an impact.

 

16 hours ago, WAwinegrapes said:

it may not be dragging the fae thru the water that is slowing you down.  could be the restrictions of the fae itself. the fae increases the  headloss as the gases escape or are forced out the tip.  restricting those exiting gases may be what is slowing the WOT speed.  Bends and or elbows are very bad  and create mucho headloss.  More restrictions equates to less HP.

I believe it is both.  I lost 5MPH top speed with mine.  I recovered a bit with a prop change but still lost more than I would liked.  IMO, the design that NDawg is creating (which seems to be a pretty close copy to the design FAE has for the 247) is a better design that the one typical for most of their applications (including mine).  The one on your previous Epic looks a lot better than most FAE units as well...of course the better designs are on the boats less frequently seen!

[Woodski]

To add to the speed reduction topic of FAE exhaust:

1.  Exhaust gas flow, to see if the exhaust system is restrictive a couple of things to check.  The outlet area needs to be close and at least slightly larger to the outlet area at the risers, the area for both water and exhaust gas -and- you need to make sure the bends are smooth to minimize pipe loss effects which includes the transition of the two pipes coming together to the pipe going down in the water.  Each bend effectively makes the 'real' diameter effectively smaller so an item to keep in mind.  There are tables available to determine the effect so you can design around the need for the bends, and provides how to calculate losses for types of bends.

2.  From a pipe drag in the water standpoint, a simple experiment to give you an idea of relative force, stick you hand out the window while driving (palm flat to wind direction) then multiply that by 25 (water v air effect) to get a rough idea of the water resistance forces involved.  In other words, there is quite a large force pulling on the pipe so pipe drag is a factor in top speed and indicates the robustness of the design needed.

[WAwinegrapes]

1 hour ago, Woodski said:

To add to the speed reduction topic of FAE exhaust:

1.  Exhaust gas flow, to see if the exhaust system is restrictive a couple of things to check.  The outlet area needs to be close and at least slightly larger to the outlet area at the risers, the area for both water and exhaust gas -and- you need to make sure the bends are smooth to minimize pipe loss effects which includes the transition of the two pipes coming together to the pipe going down in the water.  Each bend effectively makes the 'real' diameter effectively smaller so an item to keep in mind.  There are tables available to determine the effect so you can design around the need for the bends, and provides how to calculate losses for types of bends.

2.  From a pipe drag in the water standpoint, a simple experiment to give you an idea of relative force, stick you hand out the window while driving (palm flat to wind direction) then multiply that by 25 (water v air effect) to get a rough idea of the water resistance forces involved.  In other words, there is quite a large force pulling on the pipe so pipe drag is a factor in top speed and indicates the robustness of the design needed.

Doesn't the drag increase exponentially rather than linear, as the speed (velocity) increases? velocity is always squared.

Just how far down in the water does the fae tip extend?  and if it does, could the tip be shortened? or is there a reason/need for the tip to extend into the water?  Seems to me if it did extend into the water, that would greatly increase back pressure(s).  at least when  the boat is idling (static mode).  Moving would change the dynamics.

it appears that instead of increasing the diameter of each outlet, the cross sectional area is reduced as the 2 outlets transition to the  fae down pipe.  which if correct, could  limit or restrict  laminar flow(s) increasing back pressure and increasing head loss.

If each each exhaust outlet  is 3 inch diam, the down pipe (fae tip)  would have to be approx 4.25 inch diameter so as to not restrict flow (and since that is a 90 degree bend as it transitions from the 2 outlet pipes to the fae tip with no radius, the fae tip  diameter should be even larger).  Is that the case?  That could be where the head loss occurs as the fae tip does not look even close to 4.25 inches in diameter.

[Chia]

17 minutes ago, WAwinegrapes said:

Doesn't the drag increase exponentially rather than linear, as the speed (velocity) increases? velocity is always squared.

Just how far down in the water does the fae tip extend?  and if it does, could the tip be shortened? or is there a reason/need for the tip to extend into the water?  Seems to me if it did extend into the water, that would greatly increase back pressure(s).  at least when  the boat is idling (static mode).  Moving would change the dynamics.

it appears that instead of increasing the diameter of each outlet, the cross sectional area is reduced as the 2 outlets transition to the  fae down pipe.  which if correct, could  limit or restrict  laminar flow(s) increasing back pressure and increasing head loss.

If each each exhaust outlet  is 3 inch diam, the down pipe (fae tip)  would have to be approx 4.25 inch diameter so as to not restrict flow (and since that is a 90 degree bend as it transitions from the 2 outlet pipes to the fae tip with no radius, the fae tip  diameter should be even larger).  Is that the case?  That could be where the head loss occurs as the fae tip does not look even close to 4.25 inches in diameter.

What about a slight extension to the down turn exhaust tips?

[WAwinegrapes]

2 hours ago, Woodski said:

To add to the speed reduction topic of FAE exhaust:

1.  Exhaust gas flow, to see if the exhaust system is restrictive a couple of things to check.  The outlet area needs to be close and at least slightly larger to the outlet area at the risers, the area for both water and exhaust gas -and- you need to make sure the bends are smooth to minimize pipe loss effects which includes the transition of the two pipes coming together to the pipe going down in the water.  Each bend effectively makes the 'real' diameter effectively smaller so an item to keep in mind.  There are tables available to determine the effect so you can design around the need for the bends, and provides how to calculate losses for types of bends.

2.  From a pipe drag in the water standpoint, a simple experiment to give you an idea of relative force, stick you hand out the window while driving (palm flat to wind direction) then multiply that by 25 (water v air effect) to get a rough idea of the water resistance forces involved.  In other words, there is quite a large force pulling on the pipe so pipe drag is a factor in top speed and indicates the robustness of the design needed.

Doesn't the drag increase exponentially rather than linear, as the speed (velocity) increases? velocity is always squared.

Just how far down in the water does the fae tip extend?  and if it does, could the tip be shortened? or is there a reason/need for the tip to extend into the water?  Seems to me if it did extend into the water, that would greatly increase back pressure(s).  at least when  the boat is idling (static mode).  Moving would change the dynamics.

it appears that instead of increasing the diameter of each outlet, the cross sectional area is reduced as the 2 outlets transition to the  fae down pipe.  which if correct, could  limit or restrict  laminar flow(s) increasing back pressure and increasing head loss.

If each each exhaust outlet  is 3 inch diam, the down pipe (fae tip)  would have to be approx 4.25 inch diameter so as to not restrict flow (and since that is a 90 degree bend as it transitions from the 2 outlet pipes to the fae tip with no radius, the fae tip  diameter should be even larger).  Is that the case?  That could be where the head loss occurs as the fae tip does not look even close to 4.25 inches in diameter.

[Monkeybutt]

Here are 2 more pics which may show it a bit better.  As for the top speed there was never a change as the engine alarm goes off as soon as I'm over 5000 rpm and will eventually throttle down to 5000 rpm regardless of what I'm doing (mercury smarttow control).  So speed could only be changed by changing props.

And according to installation manual the bottom tip was supposed to be an inch above the center of the prop. So in sharp turns at slow speeds you could get the FAE to be 'out' of the water - meaning the tip was not fully submerged due to waves but otherwise always under water.

and one more thing: I didn't bolt it thru only used longer screws which went into same holes like the exhaust flange. Well it lasts for 4 seasons but it came off pretty badly - took on more water than I preferred to but gladly live on a small lake so doggies made it home safely.  So bolted the whole thing thru on a Saturday afternoon - was a pain in the rear but should be solid now for the next owner.

Edited March 3, 2017 by Monkeybutt
Missed reply

[oldjeep]

x3, every time I see an fae I wonder why they don't see that they are failing exhaust 101.    I seriously doubt that drag has anything to do with the speed/ power loss

[Monkeybutt]

Anyway I would still like to hear from the OP about the landing at 75mph?  Or did the whole thread become hijacked by my own doing?

[WAwinegrapes]

2 hours ago, Chia said:

What about a slight extension to the down turn exhaust tips?

the down turn exhaust create back pressure or head loss...but it would be minimal due to the short length (approx 6 inches)  there are no bends, elbows which are the biggest culprets.

[Ndawg12]

Are these engines significantly exhausting more than their automotive equivalent?  I don't see many factory 3" exhaust systems and their runs are certainly much longer.  I think you guys are putting too much stock into the bends but I guess that's the TMC way to be now days.  Anyways, should be finished up tonight and polishing this weekend.  If I can't get over 36 mph and my plugs are chalky then I'll come back and eat crow.   

[shawndoggy]

Not sure about ndawg's design, but FAE claims to have negative pressure at speed:

 

[MadMan]

34 minutes ago, Ndawg12 said:

Are these engines significantly exhausting more than their automotive equivalent?  I don't see many factory 3" exhaust systems and their runs are certainly much longer.  I think you guys are putting too much stock into the bends but I guess that's the TMC way to be now days.  Anyways, should be finished up tonight and polishing this weekend.  If I can't get over 36 mph and my plugs are chalky then I'll come back and eat crow.   

These also carry the spent water (and steam) from cooling the engine/exhaust.

[WAwinegrapes]

1 hour ago, Ndawg12 said:

Are these engines significantly exhausting more than their automotive equivalent?  I don't see many factory 3" exhaust systems and their runs are certainly much longer.  I think you guys are putting too much stock into the bends but I guess that's the TMC way to be now days.  Anyways, should be finished up tonight and polishing this weekend.  If I can't get over 36 mph and my plugs are chalky then I'll come back and eat crow.   

Pretty sure they are not exhausting any more or less than their automotive equivalent.   But if your engine is calibrated and designed  for 3 lf of 3 inch exhaust and then venting to the atmosphere, and someone comes along and adds another 3 feet, some bends and ends up venting into water.  You have doubled it and then some.  Now for a car, to double that would take some serious work.

SO it is relative to the existing conditions.   Whether it is significant and changes the calibration of the engine, Indmar might know.

[Nitrousbird]

19 hours ago, WAwinegrapes said:

 

Just how far down in the water does the fae tip extend?  and if it does, could the tip be shortened? or is there a reason/need for the tip to extend into the water?  Seems to me if it did extend into the water, that would greatly increase back pressure(s).  at least when  the boat is idling (static mode).  Moving would change the dynamics.

If it does put the exhaust into the prop wash, it doesn't push the exhaust away from the boat/surfer.

19 hours ago, Chia said:

What about a slight extension to the down turn exhaust tips?

Doesn't put the exhaust into the prop wash.  Might make it quieter but does little for the exhaust fumes.

4 hours ago, Ndawg12 said:

Are these engines significantly exhausting more than their automotive equivalent?  I don't see many factory 3" exhaust systems and their runs are certainly much longer.  I think you guys are putting too much stock into the bends but I guess that's the TMC way to be now days. 

Carrying a water/air mix is the issue...big issue at that.  Think how much volume of water is in there at a heavy engine load.  

[WAwinegrapes]

3 hours ago, Nitrousbird said:

If it does put the exhaust into the prop wash, it doesn't push the exhaust away from the boat/surfer.

Doesn't put the exhaust into the prop wash.  Might make it quieter but does little for the exhaust fumes.

Carrying a water/air mix is the issue...big issue at that.  Think how much volume of water is in there at a heavy engine load.  

Not sure if there is just 1 issue, when looking at topic.  Yes a significant difference when calculating air and or water  being transported from point A to point B thru a pipe.  frictional losses are much different.  And  why I mentioned static vs dynamic conditions.  Maybe I could get some of the curious and inquisitive kids  back at school to look deeper into it.  If nwdawg would volunteer his boat some some "testing", I bet I could round  up some enthusiastic volunteers, as long as all the paperwork  ie idemnification  agreements and non disclosure agreements are signed beforehand.  ha ha

The exhaust tips do attenuate the engine noise.  That is a fact that I can attest to.  And yes there  is an air gap , so the tips do not  direct and or vent the exhaust into the water, more of a bounce off the water.  Since noise is an energy source, any vectoring decreases that energy source.

Edited March 3, 2017 by WAwinegrapes

[Chia]

1 hour ago, Nitrousbird said:

If it does put the exhaust into the prop wash, it doesn't push the exhaust away from the boat/surfer.

Doesn't put the exhaust into the prop wash.  Might make it quieter but does little for the exhaust fumes.

Carrying a water/air mix is the issue...big issue at that.  Think how much volume of water is in there at a heavy engine load.  

quieter is what i want, with cats the CO problem is near zero anyway.

[Woodski]

@WAwinegrapes:  Correct, drag force is a function of velocity squared so not linear and exhaust volume is strictly a function of the air pump (engine) itself regardless of surrounding vehicle.  On the diameter requirement, the restriction will be at the smallest point, the downpipe or possible a poorly designed bend or T.  The required diameter would be that from the riser(s), and if you pop off the downpipe, you will see that the actual outlet diameter (exhaust + water) is smaller than the ID of the rubber attached exhaust hose.  The outlet pipe if designed correctly, will have a draft or suction element to it based on the velocity of the passing water so the total area can be reduced somewhat.  The shape of the downpipe in the water will have a significant effect of water drag also based on shape and frontal area.  I can see several cool experiments for the kids on this one, actually a pretty interesting science project.  I will kind of go out on a limb, but I bet the diameter of the FAE system does not have to be optimized for the maximum power/speed but what is most effective at surf/wakeboard speeds.  I would guess the efficiency is not that good at high RPM and probably not that critical given the usage (you don't see them on slalom / barefoot boats).

@Nitrousbird:  Water flow is related to engine speed, the raw water pump is a positive displacement pump so it does not care what the throttle position is.  Any unneeded water for cooling is also bypassed to the exhaust so the real effect is a change in exhaust water temp due to more/less exhaust gas.  Raw water pumps are close to 10 gpm:1000 RPM, so pretty substantial amount of water flow.

Edited March 6, 2017 by Woodski

[WAwinegrapes]

1 hour ago, Chia said:

quieter is what i want, with cats the CO problem is near zero anyway.

If quieter is what yoou are looking for...then try the down turn extentions.  I think they are called STS?  Pricey, but they quieted the exhaust noise substantially...enough so that you can chat with folks while cruising rather then having to yell!

Edited March 3, 2017 by WAwinegrapes

[WAwinegrapes]

3 minutes ago, Woodski said:

@WAwinegrapes:  Correct, drag force is a function of velocity squared so not linear and exhaust volume is strictly a function of the air pump (engine) itself regardless of surrounding vehicle.  On the diameter requirement, the restriction will be at the smallest point, the downpipe or possible a poorly designed bend or T.  The required diameter would be that from the riser(s), and if you pop off the downpipe, you will see that the actual outlet diameter (exhaust + water) is smaller than the ID of the rubber attached exhaust hose.  The outlet pipe if designed correctly, will have a draft or suction element to it based on the velocity of the passing water so the total area can be reduced somewhat.  The shape of the downpipe in the water will have a significant effect of water drag also based on shape and frontal area.  I can see several cool experiments for the kids on this one, actually a pretty interesting science project.  I will kind of go out on a limb, but I bet the diameter of the FAE system does not have to be optimized for the maximum power/speed but what is most effective at surf/wakeboard speeds.  I would guess the efficiency is not that good at high RPM and probably not that critical given the usage (you don't see them on slalom / barefoot boats).

@Nitrousbird:  Water flow is related to engine speed, the raw water pump is a positive displacement pump so it does not care what the throttle position is.  Any unneeded water for cooling is also bypassed to the exhaust so the real effect is a change in exhaust water temp due to more/less exhaust gas.  Raw water pumps are close to 15 gpm:1000 RPM, so pretty substantial amount of water flow.

YES!!  we are talking the same.  engineering talk!  ha ha

 

Efficiency will never be a strong /selling point with ski boats.  From the wetted surface area, to the inability to trim out the prop, and any number of other issues, the additional 3,4, 5 feet of fae tubing is really insignificant!  As evidenced by the added HP with minimal increases in speed.  Increasing the HP from 410 to 575  (an increase of approx 33%) nets you at most 2-5 mph!  not a big  bang for one's buck!

[cowwboy]

He has some graphs of backpressure on his page. http://www.freshairexhaust.com/about-us/performance-2/

I thought of trying to do some testing with pressure transmitters and a data logger from work. But decided it wasn't worth the time and trouble.

Now if someone wants to help conduct this testing I can come up with all kinds of equipment.

 

[Chia]

On 3/3/2017 at 2:53 PM, WAwinegrapes said:

If quieter is what yoou are looking for...then try the down turn extentions.  I think they are called STS?  Pricey, but they quieted the exhaust noise substantially...enough so that you can chat with folks while cruising rather then having to yell!

i have those, it is really hard getting them off and is the main reason i haven't installed the fae that i have. I haven't really noticed a noise reduction with the STS (edit STE not STS) compared to other boats that i ride in.

this spring i will be removing the silent rider stock muffler that is inside the boat (Larry at fae is not a fan of this product, stated is causes resonance inside the boat) and installing the fae.

Edited March 6, 2017 by Chia

[Michigan boarder]

Just something to add, if anyone has ever seen a go-fast boat, some will have the exhaust come out above the water line on the transom.  I've seen them take off to get up on plane and the water flow out of the exhaust is a LOT....I can only imagine that water splashing into water that is traveling in the opposite direction, then making its way out of the bottom, and definitely a restriction of exhaust gas flow. 

That said - this design works for a lot of people, so if you are not worried about the speed loss and use your boat for surfing, then I think it's the right move.

Got pics of the final product yet?