Hard (re)starting list-side engine (ballasted AR240, wake surfing)

[Bruce]

@swatski how about installing a scupper valve or flap on that exhaust.

 

[swatski]

@swatski how about installing a scupper valve or flap on that exhaust.

This is my thinking exactly!
I just didn't want to draw any attention to it for anyone calling it "Swatski's flap". Thanks, @Bruce... not.

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[Bruce]

I think everyone should have a Dr. @swatski Flap!

 

[Cobra Jet Steering LLC]

I do not think a flapper valve will solve the issue here is why, the exhaust is below water and the water pressure on it is greater than the one that is on top so a flapper valve will not reduce the pressure being exerted on the exhaust gases, I doubt it is water entering the water box as much as it is back pressure against the exhaust trying to escape against the water pressing holding back the exiting gases, they are being compressed more than the other engine.
A snorkel would allow the gases to blow out the water and then allow the exhaust gases to exit with no resistance to start, then the snorkel could be pulled off to operate the boat . You could use this to start the engine rather than empty the ballast.
I find it convincing that when the ballast is empty the engine will start, so that in effect has reduced the back pressure by bringing the engine up higher ,it Just sounds logical to me, if it were not for the person behind the boat exhaust extensions would be the answer but since a person would be breathing this I would think just a temp incretion of the snorkel to start the engine and then pull it off so the exhaust goes under the water. If I understand the issue correctly the lower engine is having trouble restarting when it is so far below the water surface the temporary snorkel would be a lot better than emptying and refilling your ballast bag each time.
Another way may be to install a temporary snorkel in the exhaust to bring the top of the snorkel half way up in the water to some place close to where the exhaust is supposed to be when there is no ballast this would apply the same water pressure on your exhaust system as normal operation and keep the exhaust under the water where it would normally be.

Also my potato in the exhaust pipe reference was what people did to keep someone from starting their car it blocked the exhaust gases and the engine could not breath, air not going out will prevent the air from entering also.

 

[Bruce]

So what he needs is a small snorkel to elevate the output of that exhaust.

 

[swatski]

I do not think a flapper valve will solve the issue here is why, the exhaust is below water and the water pressure on it is greater than the one that is on top so a flapper valve will not reduce the pressure being exerted on the exhaust gases, I doubt it is water entering the water box as much as it is back pressure against the exhaust trying to escape against the water pressing holding back the exiting gases, they are being compressed more than the other engine.
A snorkel would allow the gases to blow out the water and then allow the exhaust gases to exit with no resistance to start, then the snorkel could be pulled off to operate the boat . You could use this to start the engine rather than empty the ballast.
I find it convincing that when the ballast is empty the engine will start, so that in effect has reduced the back pressure by bringing the engine up higher ,it Just sounds logical to me, if it were not for the person behind the boat exhaust extensions would be the answer but since a person would be breathing this I would think just a temp incretion of the snorkel to start the engine and then pull it off so the exhaust goes under the water. If I understand the issue correctly the lower engine is having trouble restarting when it is so far below the water surface the temporary snorkel would be a lot better than emptying and refilling your ballast bag each time.
Another way may be to install a temporary snorkel in the exhaust to bring the top of the snorkel half way up in the water to some place close to where the exhaust is supposed to be when there is no ballast this would apply the same water pressure on your exhaust system as normal operation and keep the exhaust under the water where it would normally be.

Also my potato in the exhaust pipe reference was what people did to keep someone from starting their car it blocked the exhaust gases and the engine could not breath, air not going out will prevent the air from entering also.

Jeff, thank you again - I think you put us on the right track here!

A flap that I have in mind would be a hard flap. (I know, I'm totally opening myself up to Bruce's humor, but whatever). It would need to hold the water back from entering the exhaust, or at least slow it down.
I have now experienced this situation during several independent outings, and the commonality is with the "lower"/tilted/listed engine having difficulty starting after approx 15min break.
Both engines are tilted, so that is not an issue per se.
Both ignition keys are ON (I turn the engines OFF and then immediately return the keys to the ON position) - so this is also not an issue, such as pump priming etc, althought it may help to keep the keys OFF - I will start doing it @Rod5's way for sure.

The "lower"/listed engine starts right away after a short break, but not after a longer break - that I think is the key observation. The time difference is not enough to cool the engine, but it is enough for water to enter the exhaust.

In other words, I do not see much of an engine temp difference between a short stop (when the engine fires up fine) and a long stop (when the engine does not want to start and takes a lot of convincing).
From the latter, I surmise that the 15 min maybe enough time for water to migrate into the exhaust and effectively diminish the air volume - making the space less compressible as water replaces the air in the exhaust.

In Jeff's scenario - that is my potato in exhaust effect (due to massively reduced compressible exhaust volume).

@Michael Rasmussen those FAE systems in wake boats are totally different - downward snorkels directing exhaust from the engines that comes out above water line - to release exhaust gasses underwater.

A snorkel that has a built-in loop (like an anti-siphoning loop) could work in my case but it maybe too much.

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[Bruce]

@swatski, I believe Jeff's point is that the deeper you go in the water the greater the pressure due to an increase in density in the water. The engine is effectively a pump moving air from the intake though the exhaust. As the exhaust is lowered into the water the "back pressure" increases. At some depth the engine would not be able to start at all. If the exit of the exhaust is elevated the back pressure will decrease. I am uncertain how much the pressure increases due to inches of change in depth but there must be a reference somewhere. If this is the issue then a flap would not help as the pressure against the flap would increase as the depth increased.

I am hopeful that the issue is not the water pressure but the volume of water in the exhaust which the Dr. @swatski Flap would reduce.

 

[tdonoughue]

I agree with Jeff, to a point. I agree the pressure will be the same with/without Dr. @swatski Flap. However, without the Flap, there will be much greater volume of water for the engine to evacuate from the water box. The engine only puts out a volume X of exhaust at a pressure P. With the Flap, it may only take 1-2 strokes for the engine to build enough P to push X volume of water out to the exit. Without the Flap, it may be that the engine must generate much more volume at pressure P (with each stroke increasing P, which then pushes more to increase X and normalize P, etc.), requiring more strokes (maybe 10-20) in order to evacuate the water box and allow exhaust to get to the exit point.

So I don't think the Flap is necessarily the whole answer, but it may be part of it or enough of it to get you there.

 

[swatski]

@swatski, I believe Jeff's point is that the deeper you go in the water the greater the pressure due to an increase in density in the water. The engine is effectively a pump moving air from the intake though the exhaust. As the exhaust is lowered into the water the "back pressure" increases. At some depth the engine would not be able to start at all. If the exit of the exhaust is elevated the back pressure will decrease. I am uncertain how much the pressure increases due to inches of change in depth but there must be a reference somewhere. If this is the issue then a flap would not help as the pressure against the flap would increase as the depth increased.

I am hopeful that the issue is not the water pressure but the volume of water in the exhaust which the Dr. @swatski Flap would reduce.

Sure. But the depth of engine exhaust does not change between 5-10min (easy start) and 15+ min (very hard start) - of the same engine.

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[Cobra Jet Steering LLC]

Well now you have several things to experiment with, I believe the water entering the water box would do it immediately not over time , next is the rich fuel mixture due to less exhaust breathing and less air intake so due to that, I think the plugs may be getting wet as the combustion chamber cools down adding to the issue is when the fuel system applies more fuel than the engine can use to start because of the increased back pressure . Think of this superchargers add air going IN, larger exhaust systems let air OUT either of those increase the horsepower of engines one two or both.
Another thing to think about, so perhaps a short snorkel upward may be the best solution to the problem and possibly also assist the engine while it is running in that lower position , remember more exhaust resistance due to lower position makes the engine loose horsepower.
So you keep the proper horsepower and solve the starting issue when you wake surf , you can make a removable snorkel for the lower engine

 

[swatski]

next is the rich fuel mixture due to less exhaust breathing and less air intake so due to that, I think the plugs may be getting wet as the combustion chamber cools down adding to the issue is when the fuel system applies more fuel than the engine can use to start because of the increased back pressure .

I do indeed smell gas! At least I think I do, can be hard to tell when on the water. But just like you would in a fuel-flooded motor - immediately reminded me of many a struggle I've had with my old carbureted two strokers.

Okay, so about that snorkel - if it came up from the exhaust and looped above the water line - and then bend down again - to blow exhaust underwater - would that possibly work?

Kind of like a hybrid of fresh air exhaust and anti- siphoning loop.

 

[Wayloncle]

As a joke I was looking for like a tractor flapper..

But the first one that showed up actually looks like something that would work.

 

[Cobra Jet Steering LLC]

I believe if it just went up to the level that would be the normal place it should work, say the engine exhaust is 12 inches lower than it is supposed to be you would probably need to go up 8 to 10 inches to get the water pressure to an acceptable operating pressure even though it is below the water it would have less pressure.
How many square inches is your exhaust opening? water applies .444 pounds of pressure per square inch of surface per foot of depth so 5 sq. inch opening could be receiving say 4.5 pounds of resistance holding in the exhaust and if extra water in the muffler is also contributing to the issue you have less air to compress in the muffler and more pressure resisting the exhaust exiting the muffler so it may be a combination of both. The answer would still be a short snorkel.

 

[haknslash]

Possible fix?

Or this one to trap water ...

 

[seadude]

Doubtful the issue is backpressure - the 1.8l can be hard to start when hot.
Running the blowers seems to help to cool the engine compartment...

 

[Beachbummer]

If its back pressure, consider shifting the human load to sit on the bow, maybe lifting the stern and thus the exhaust? might at least help troubleshoot?

 

[ar240owner]

Doubtful the issue is backpressure - the 1.8l can be hard to start when hot.
Running the blowers seems to help to cool the engine compartment...

Yea what he said !!! Run the blowers this isue was talked about a lot when the 1.8's came out and a lot of people found that when they ran the blower is stoped it , then after they got some hours on the boat it also stoped it

 

[KXCam22]

The engine is under big load with lots of fuel poured possibly making an over rich condition on restart. I would suggest a change to iridium plugs since they fire easier. The electrode temp is better at burning off contaminants. Not really evidence but my 230 has no issues with restarting after a heavy surf. Cam.

 

[swatski]

Doubtful the issue is backpressure - the 1.8l can be hard to start when hot.
Running the blowers seems to help to cool the engine compartment...

Yea what he said !!! Run the blowers this isue was talked about a lot when the 1.8's came out and a lot of people found that when they ran the blower is stoped it , then after they got some hours on the boat it also stoped it

Aside from the fact that I like the idea of running the blowers some extra time, this explanation is not very convincing. I have never had problems starting my engines other than while ballasted for surfing. And then the problem engine is ALWAYS the one on the listed side. Not sure how would the blowers help one engine only in this scenario? What am I missing?

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[KXCam22]

When we surf, no matter how heavily ballasted, our 230 exhaust is always above water. 240 may be different. I don't subscribe to the backpressure idea. Cam.