Slamming outboard(s) into reverse and hydrolocking the engine(s).

[Philster]

There is some heated discussion going around in other places I won't mention.

Nonetheless, the non-disputed facts go like this:

Outboard-equipped boat running on plane. Debris or other sudden panic-inducing issue causes operator to slam throttle to neutral and then reverse almost immediately, or from forward to reverse. There are documented cases of this causing the engine or engines to hydrolock. In the cases I've read, they are Yamaha o/b engines. Yamaha has even warrantied some engines that have hydrolocked (engines had bent con rods and other damage).

The disputed facts:

Water entered the engine via the exhaust vs. water entered the engine via the intake.

There are two camps that align themselves with one explanation or the other. "There is no way water can come up via the exhaust; not just by slamming it into reverse; it came in via the intake!" vs. "There is no way it can enter the intake; these must be cases of it coming in via the exhaust!"

There is another delusional camp that believes the engine ran in reverse cycle (internals rotating opposite of norm). Since these are four-stroke o/b engines, I prefer to discard this possibility, but would entertain the theory for a moment, if we were talking about 2-strokers, as they can run in reverse (we 2-stroke engine builders call that 'dieseling').

I wanted to get iboaters' takes on this issue. Because owners are relaying the information, there isn't much extra detail (for example, if it happened to me, I'd want to know more about where the water was actually found. Surely, if the engine ingested water via the air intake, I'd expect evidence of that and lack of that evidence might point me to the exhaust).

Please opine. I lean towards water ingestion at the intake, but I also know there are always chances for water reversion at the exhaust.

 

[coastalrichard]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Philster, I am sure that I possess a total volume of engine-related knowledge equal to what you have in your pinky, so I'll tag along for the info. I do enjoy your posts!

 

[haulnazz15]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Well, the problem I would have with the water reversion through the exhaust theory is that you can pull the throttle back to neutral abruptly and have no issues from reversion, so I don't see any reason going to reverse is going to exacerbate the issue. You'd assume the more throttle given in reverse would lessen the likelihood of reversion just due to more exhaust gasses being expelled making it more difficult for water to backtrack through the system. You'd think you could roughly simulate this condition by running in reverse at full speed (whatever that may be for a given boat) to see if reversion happens. Perhaps the water combined with enough rearward speed is enough to over come exhaust gas pressure and any exhaust-flapper mechanism that may exist.

As far as the intake, would we be assuming the move from on plane to reverse happened violently enough as to cause the wash to come up over the rear of the engine hood?! That would seem to be the most likely case, but you'd assume it would be evident under the hood/in the intake tract.

As far as the reverse-cycle is concerned, I assume we are in inferring that the prop is being driven by the water flow while locked in reverse?

 

[Philster]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I would say 'yes'; the violent reversing action is being met with a surge of water that significantly washes over or dunks the cowling, and with significant am't of water on the cowling and an engine turning some serious RPMs (which went on almost non-stop), you've got a screaming engine (which sucks like a vaccuum cleaner) and water, and she is going to ingest water at the intake.

To me, this just isn't much of a stretch. The majority opinion is the exhaust, but I cannot fathom how an engine running at high-rpm and having its high-rpm song blipped for a moment would be able to ingest water.

As for the reverse cycling engine theory camp: There are folks who think the engine itself has reversed, not the trans/gears, so if you think about it, they are saying the operator slammed into reverse gear suddenly, and this somehow reversed the engine's internal combustion cycle into reverse (crank spinning in reverse) which would wind up spinning the prop for forward thrust if you think about it, so I'd rather just let that camp mutter to themselves over there! :facepalm:

 

[H20Rat]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

So my $.02... For a 4 stroke, there is no way slamming into reverse would suck water through the exhaust. Its coming in the intake, period. Doesn't matter what the prop is doing, there is still a cone of vacuum behind the prop due to the forward momentum of the boat which is sucking the exhaust out. That won't collapse until the forward movement has stopped, and by that point, you are just backing up like normal. Engines also have the secondary exhaust holes above the water for a reason. During fast backup operations most of the exhaust is coming out that anyway.


And my other $.01 of the $.02 above. Running the engine in reverse is certainly a possibility for a 2 stroke. Bombardier (aka etec/evinrude) pioneered the modern version of the technology, and its in use on almost all new snowmobiles sold today. The computer slows the engine down until it backfires, and then adjusts the timing to let it spin backwards. And yes, its certainly possible for a 2 stroke not designed to do this to run for a very short time in reverse.

But of course, that part is null and void, as the OP mentioned, it was a 4 stroke.

 

[Ernest T]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I know very little about outboard engine design, and I'm a boating newbie, so take this with a grain of salt. But, as long as the engine is running (regardless of whether you had slammed it from forward to reverse), wouldn't exhaust pressure prevent water intrusion through an open valve? I know that this rule applies to jet ski engines. So, you would have to have much greater than normal water pressure in the cooling system in order to overcome the exhaust pressure to have a failure through this route. It seems that there would be no extra water pressure through the cooling system doing that maneuver...........in fact, it seems that there might be less pressure as the engine rpms suddenly decrease and the flow around the intake ports decrease as the boat slows.

Could it be possible that just going from 6000 rpms to 0 in a fraction of a second, is actually what caused the damage and it had nothing to do with water. Now the engine is locked up, but as the impeller continues to spin for a few seconds water is pushed through a now open exhaust port into the cylinders. A tech. takes the engine apart, finds damage, and water inside, and concludes hydrolock.

 

[Maclin]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I think the intake is the more likely scenario.

If you shut the engines down suddenly back to idle, it takes a second or two for the wave to hit. Now if the engines are off at this point then I suppose it could force back thru the exhaust in some manner peculiar to those engines.

But, if they are running until they hydrolock so to speak, then the exhaust is pushing back against the wave and if the water is splooshing back over the top or near top of the cowlings then my vote is intake.

Like you said Phil, there is a lack of full details available right? like how low the engines are, what type of boat and transom, what speed, sea conditions, does it happen EVERY time, yada yada etc.

 

[Chris1956]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I have never heard of water injestion via gear shifting happening in an outboard. There have been plenty of times when a motor running at near WOT has cut right out, causing the boat to rapidly slow down. I never heard of any water injestion under that circumstance.

Also, OB hoods are made to not allow water to get to intakes. I once had water pouring over the gunwales 4 foot in front of transom. Motor well was under water, motor was running wide open so we wouldn't sink and intakes were nearly underwater, and it still didnt injest water.
I will wait for others to propose the answer to this, as I don't see how it can happen.

 

[Ned L]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Hmm, interesting question. When you say "There are documented cases of this causing the engine or engines to hydrolock. In the cases I've read, they are Yamaha o/b engines. Yamaha has even warrantied some engines that have hydrolocked (engines had bent con rods and other damage).", I would be curious if any water was actually found in the cylinders. if not, it may not be hydrostatic locking. If you think of it, when you throw the engine from forward to reverse at high speed, you are putting some real high stresses on the engine internals for just an instant. Even though the prop & waterflow past it is not much mass, when you reverse the rotation instantaneously at high speed you are looking at some real significant inertia forces. If you put a significant braking force on the crankshaft for just an instant that piston is still going to want to go down, somethings going to give. -- The con rod will bend.
........................ Just a thought.

 

[Philster]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

...

Could it be possible that just going from 6000 rpms to 0 in a fraction of a second, is actually what caused the damage and it had nothing to do with water. Now the engine is locked up, but as the impeller continues to spin for a few seconds water is pushed through a now open exhaust port into the cylinders. A tech. takes the engine apart, finds damage, and water inside, and concludes hydrolock.

That's actually an interesting idea. I am picturing the exhaust being flooded with cooling water that is rushing in but after the engine has momentarily dropped to 500 RPM.

 

[Philster]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Hmm, interesting question. When you say "There are documented cases of this causing the engine or engines to hydrolock. In the cases I've read, they are Yamaha o/b engines. Yamaha has even warrantied some engines that have hydrolocked (engines had bent con rods and other damage).", I would be curious if any water was actually found in the cylinders. if not, it may not be hydrostatic locking. If you think of it, when you throw the engine from forward to reverse at high speed, you are putting some real high stresses on the engine internals for just an instant. Even though the prop & waterflow past it is not much mass, when you reverse the rotation instantaneously at high speed you are looking at some real significant inertia forces. If you put a significant braking force on the crankshaft for just an instant that piston is still going to want to go down, somethings going to give. -- The con rod will bend.

If ones see a bent con rod, one would jump to the conclusion it was hydrolock that did it. But again, lacking visuals, I would love to know what the tech saw. Were the cylinders wet from water or are they so familiar with hydrolock they jump to that conclusion upon seeing the con rod(s)?

 

[rockyrude]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I'm understanding the arguments being put out, but given the design of todays' outboards, I would expect any and all engine damaging stresses would be stopped at the prop. At the worst, the hub should slip unless this is some kind of racing scenario where there is no hub. As was said, there's plenty of cases of an engine stopping/stalling from WOT with no ill effects.

 

[Ned L]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

'Stalling' when wide open is very different than the equivalent jamming the prop with a 2x4 for 1/1000 of a second when wide open.

 

[rockyrude]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Agreed, but my argument still stands, for that 1/1000 of a second the hub should slip not stop the crank.

 

[Home Cookin']

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

If the water got in the engine from the intakes, the operator would know that the motor was completely swamped for a significant period of time. The motors can take dips and there are a lot of baffles between where the air gets in the cowl and then into the carbs. So I don;t see that one except in a total swamping, and that has nothing to do with the gears going in reverse.

Shifting from F to R does not change the rotation of the drive shaft so there's no way the forces would spin the motor backwards. You would have to have the boat in forward and a physical force (like a big ol' wrench) turning the prop in reverse--which I would think would spin the hub first.

Forcing water back up the exhaust in the prop would not occur from the "stern wake" as we call it. If it did, it would be more likely to happen when the motor is stopped or slow--like if you hit bottom at speed adn the motor stops. Now, it might happen if you towed a boat backwards with the motor down really really fast. But if you can't get that to happen just reversing fast, no way going from f on a plane to R is going to get that speed.

I may be wrong but I think the water pump impeller turns, or not, with the drive shaft so if the motor is off, the impeller is off.

If you've ahd a motor stop at forward speed, you know that the prop acts as a brake and gives a rigth hard stop. I don't know, but I doubt the motor continues to turn (as opposed to a car you are roll-starting)

A mechanic told me that if your exhaust baffles are old, they can fail, and allow water back up into the engine. Makes sense to me. That would shut things off, but I don't know that it would "hydrolock" unless you count rusting. maybe the "incident" was a result of a failed baffle instead.

if a guy had to choose between swamping his motor, which is not covered by warranty, and a defect caused hyrolock, which is, which is he going to say it was, once he gets to shore? There perhaps lies the mystery.

 

[Texasmark]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

I'm going to sit by and watch this evolve also. Sounds like fantasia to me.

Mark

 

[Frank Acampora]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Look at the prop from the point of view that it is a torque converter. When rapidly put in neutral at high boat speeds, the water flow will continue to spin the prop at slightly higher RPM than when it was under load. Reverse the gears and it still is moving in the forward direction so very high impulse loads are placed against the gears and the crank which is spinning the opposite direction. Something has to give--I would expect stripped gears but I guess in this case it is poorly designed con-rods. Remember, we are talking about damage that happens in one revolution or less--And in that micro second impulse, the rubber hub will not spin out.

Have you ever tried to spin out a rubber hub? I have, on a 13 inch diameter prop. With the prop shaft chucked in a vise, I needed a 4 foot lever. It turned the prop about 1/4 turn on the hub--the rubber was flexing--and still, the hub did not fail or spin out. While they do provide some measure of cushioning, they are by no means a safety fail point.

Yes, I do things like that, primarily because I am a "nerd" and inquiring minds want to know.

 

[Ned L]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Exactly my thought Frank.

 

[nwcove]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

could the huge amount of cavitation that takes place at wot in reverse, coupled with the inertia of the flywheel cause internal engine damage????

 

[BonairII]

Re: Slamming outboard(s) into reverse and hydrolocking the engine(s).

Sounds like fantasia to me.

Mark

Me, too.

I would guess that when boat owner's ruin their motors(and it's their own fault) they lie about the circumstances ...in hopes that the manufacturer will fix it for free.