Can someone explain this?

[zenoahphobic]

I think it agreed this is a bit of BS.

At such high speed a shift into reverse will do a "bit" of damage and I doubt the LU will be fit to rotate the engine in any direction!

And if it were possible for there to be enough water pressure on the propellor to rotate the engine backwards (me thinks more BS), thee sudden reversal would blow things to Smithreen.

I think the writer may have meant a sudden deceleration can create sufficient "vacuum pulses" that can introduce water back into the exhaust. Very feasible in two strokes. A four stroke does not necessarily automatically work in reverse - the piston just continues to move up and down not knowing the engine rotation. However I suspect a four stroke outboard would not act kindly pushed in reverse, so water ingestion would be the least of your worries!

[ausnoelm]

I think the biggest issue here is why the motor would stall if shifted into reverse at any speed, the load is the same on the motor, it does know, or care what happened after the drive shaft, it might not do some components good though.

[ausnoelm]

Just to add to this, I once heard that a boat was started by towing it, in gear at high speed, and the ignition was then switched on, true or not?? no idea, but it made for interesting reading.

[pstephens46]

It's hard to imagine forcing a stalled large 4 stroke engine to reverse. Based on the water flow over prop My first thought was the 175-180 psi compression. Now a smaller motor or 2 stroke...at any rate an interesting topic.

I am not willing to water test this one. Maybe Fairdeal would consider?

[99yam40]

Question for Boscoe,
was that guy that had 2 power heads destroyed and replaced running a single motor or multiple on the boat?

as far as push starting an automatic trans automobile,
My 64 Ford Galexie 500 had one of the last transmissions that had a rear pump that could be pushed started.
I could be running down the road,turn the key off for a little bit and then back on to light off the gas build up in the exhaust system just like you could in a manual trans car.
You really needed to have cherry bomb mufflers that did not have seams to rip open tho.
after that with no pump on output shaft there was no way to build any pressure so that the transmission could do anything.

as far as an outboard being push/towed started, it would have to have enough electrical power (12 volts) depending of the ignition system and fuel pumps to allow that to work, and enough torque on the prop to spin the motor against the compression of the cylinders fast enough.
I guess on some motors it could be done, but not many of them

[dray0151]

Sounds to me like Mr. Experiemental Fairdeal needs to hook up an old ruined counter rotation engine to his boat, put the engine down prop in the water move the engine into reverse and take off to speed, come back and see if water got sucked up into the old ruined engine? Guess you could use a standard rotation also as this would apply to boats with three engines also.

[boscoe99]

Just to add to this, I once heard that a boat was started by towing it, in gear at high speed, and the ignition was then switched on, true or not?? no idea, but it made for interesting reading.

I had a long time Yamaha (ex OMC) guy tell me it was true. That he had actually done it. He reported that they towed the motor at high speed and then, with the ignition on, shifted it into forward gear. It was a two stroke with not much compression. Relatively easy for the propeller to turn the motor.

Now if the motor were to be shifted into reverse gear while being towed forward it would rotate backwards. A two stroke might very well start and run backwards. Mercury motors used to run in one direction for forward and the opposite direction for reverse. A four stroke, not so much.

[boscoe99]

Question for Boscoe,
was that guy that had 2 power heads destroyed and replaced running a single motor or multiple on the boat?

as far as push starting an automatic trans automobile,
My 64 Ford Galexie 500 had one of the last transmissions that had a rear pump that could be pushed started.
I could be running down the road,turn the key off for a little bit and then back on to light off the gas build up in the exhaust system just like you could in a manual trans car.
You really needed to have cherry bomb mufflers that did not have seams to rip open tho.
after that with no pump on output shaft there was no way to build any pressure so that the transmission could do anything.

as far as an outboard being push/towed started, it would have to have enough electrical power (12 volts) depending of the ignition system and fuel pumps to allow that to work, and enough torque on the prop to spin the motor against the compression of the cylinders fast enough.
I guess on some motors it could be done, but not many of them

As I recall he had a single. Both times he inadvertently shifted from forward to reverse by mistake while traveling forward at a good clip. He admitted that he did it. Being honest is what got him a replacement power plant the second time.

[TownsendsFJR1300]

Just to re-iterate, whether in forward gear or reverse, the engine will ALWAYS SPIN in the same direction (not manually spinning the flywheel by hand backwards).

Prop direction change is con*****ed in the LU by the dog clutch.

Also, for a prop (in gear) to spin over an engine, think about it.
How much torque is needed from the starter to a large flywheel
to spin the engine over fast enough to start?

Can you pull start a F100 or larger engine? Ain't gonna happen..

Trying to spin over a stopped engine with a prop, BY WATER PRESSURE
IMO, would be impossible (too much slippage)



.

[boscoe99]

as far as an outboard being push/towed started, it would have to have enough electrical power (12 volts) depending of the ignition system and fuel pumps to allow that to work, and enough torque on the prop to spin the motor against the compression of the cylinders fast enough.
I guess on some motors it could be done, but not many of them

Yamaha recognizes the problem. So much so that in the digitally con*****ed models the engine will recognize if and when it is being rotated backwards, in which case the ECU will command the electronic shift mechanism to put the motor in neutral. Trying to prevent damage from the motor being turned backwards. Nonetheless, some of the digitally con*****ed models have been known to suffer damage when the motor turns in reverse. Perhaps the sense system is not as quick as it needs to be.

Here is snippet from the first DEC model, the F250B.

[boscoe99]

Sounds to me like Mr. Experiemental Fairdeal needs to hook up an old ruined counter rotation engine to his boat, put the engine down prop in the water move the engine into reverse and take off to speed, come back and see if water got sucked up into the old ruined engine? Guess you could use a standard rotation also as this would apply to boats with three engines also.

All that is needed is for someone to have a lower unit removed. With the lower unit being in reverse gear. If the propeller is rotated the way that water flow over the propeller would cause it to turn, the drive shaft will turn opposite to its normal rotation. If coupled to the crank shaft, and given enough torque being applied to the crank shaft, in pound feet, the crank shaft will turn opposite its normal rotation.

Exhaust becomes the intake. Intake becomes the exhaust.

[dray0151]

I just thought it would be much more exciting if Fairdeal took it out for a real world test situation, you know under load!!!!!

I'm happy my icons are back and I can bold.

[TownsendsFJR1300]

All that is needed is for someone to have a lower unit removed. With the lower unit being in reverse gear. If the propeller is rotated the way that water flow over the propeller would cause it to turn, the drive shaft will turn opposite to its normal rotation. If coupled to the crank shaft, and given enough torque being applied to the crank shaft, in pound feet, the crank shaft will turn opposite its normal rotation.

Exhaust becomes the intake. Intake becomes the exhaust.

The bolded above, ^^^ is a VERY BIG IF.

We're talking about an engine IN the water (water intrusion).

In the water, perhaps with say a three engine OB equipped boat.

Put one engine in reverse (turned off), in the water, trimmed down and run the other two up to max rpms/speed. If the prop hub doesn't shear / fail, I suspect your may be able turn the engine backwards (and suck water into the combustion chamber-with water pressure alone helping get water up into the power head).

[TownsendsFJR1300]

To add, I many years ago, was looking at jet ski's to purchase (Yamaha of course).

Should you tow this particular one (and the one's I looked at), you have to pinch off a water line (under the hood) or YOU WILL push water up into the engine.

I don't remember if it was a two or four stroke engine, but I suspect water would probably be pushed up the exhaust.

[99yam40]

I just thought it would be much more exciting if Fairdeal took it out for a real world test situation, you know under load!!!!!

I'm happy my icons are back and I can bold.

we all are
we can all have a Merry Christmas and a Happy New Year now