I saw something weird on an outdrive, what was it for?

[HT32BSX115]

Re: I saw something weird on an outdrive, what was it for?

So what is the value of an aerator on a Go Fast Outdrive, or any outdrive for that matter,,,

Drag reduction......... "bubbly" produces less drag than pure liquid!

 

[Knightgang]

Re: I saw something weird on an outdrive, what was it for?

Drag reduction......... "bubbly" produces less drag than pure liquid!

That may be, but wouldn't that also be a weaker force to push against, providing less forward thrust and not more? I am asking because I do not understand the logic behind it.

A prop takes water that is in front of it and pushes it against the water behind it providing foward thrust. If you "thin" the water (by bubbling) going through the prop to reduce the friction of the prop, my logic tells me that you will have a weaker (less dense water) comming form the prop and pushing against solid water, therfore compressing the "bubbled" water and creating a less effecient thrust...

Please explain my errors and the why/how these work...

 

[JustJason]

Re: I saw something weird on an outdrive, what was it for?

In a stern drive there is *some* oil flow top to bottom/bottom to top from gear rotation.

Eagh... there really is no flow of oil. There is a passageway that's like 3/16ths of an inch in diameter. The passageway is just to simplify filling, and thats it. The oil doesn't circulate. First, its much to thick to circulate. 2nd, if it really was intended to flow, then there would be 2 passageways much bigger in diameter instead of just the 1. On older drives there was no passageway, and you had to fill the uppers and lowers seperately.

Under normal operation, The top is cooled from heat transfer to the bottom via some oil flow

Again... there is no flow.

If you guys want to take this to the sub-atomic scale, thats fine by me. I'll just bow out and let you guys have at it. I was trying to keep this simple.

I understand that the "concept" of heat is energy, and not matter.

But the engery of heat causes matter to become less dense, and any kind of matter that is less dense succumbs less to the laws of gravity (or bouyancy) than their denser counterparts do.

All I know is this... Cold air balloons do not rise. 2nd floor fires usually contain themselves to the 2nd floor unless flaming debris falls. And the top of my radiator is considerably hotter than the bottom of my radiator.

 

[Knightgang]

Re: I saw something weird on an outdrive, what was it for?

Jason, I thought you were going to tell us about the aerator, not continue the heat transfer talks...

Eitherway, good reading...

 

[JustJason]

Re: I saw something weird on an outdrive, what was it for?

So what is the value of an aerator on a Go Fast Outdrive, or any outdrive for that matter,,,

It causes the prop to ventilate. When the prop ventilates engine rpms increase due to the lack of "resistance" on the prop. Hi performance engines make their peak power in the last 10% of the rpm range. The idea is to get the engine to full power first by slipping the prop, and let the prop play catch up while the boat is under way.

An easier analogy would be dumping the clutch. You launch a car a lot faster off the line when you peg the gas, bouce the engine off its rev limiter, and dump the clutch.
Sure you spin the tires, but when those tires catch the RPM is still a lot higher (and hence closer to peak power) than it would be than if you just rolled the car out in first gear and then pegged the gas. Think of the prop as those spinning tires.

 

[HT32BSX115]

Re: I saw something weird on an outdrive, what was it for?

I suspect that you wouldn't want the aeration to be in front of the prop. Maybe above and below it, lest you cause cavitation too!

Here's a "prop" aerator...From Teague Custom Marine.

The above link describes what they claim it does.

While aerating the water under a boat and in the area of the drive *would* reduce over all drag, that is not what this one does. This one allows a VERY HIGH pitch to be used for low speed maneuvering.

btw, they love to talk about this stuff over on Offshoreonly.com.

 

[JustJason]

Re: I saw something weird on an outdrive, what was it for?

(which is why you need to rebuild the whole drive when you get damage in a "lower" or an "upper")

Eagh.... If you blow the lower, typically the upper is fine. Heavy metal particales do not float up the passageway and destroy the upper.

If you blow the upper. Most of the particles stay in the upper. A few make there way to the lower naturally. But when you go and drain the oil (because you can not drain the upper sepperately). any particles that are in the upper obviously gets dragged down to the lower with the oil.

So if you blow just the upper or the lower then why are both "rebuilt"?

1. money, its more for the shop and more for me.
2. if it's not done, the mechanic, the shop, all look like arses should the drive grenade shortly after the "rebuild"
3. safety, a customer wants to have confidence in his equipment. If he takes his boat 10 miles off shore and the drive grenades because only the upper or the lower was serviced, well heck, nobody wants that.

Rebuilding a drive is a judgement call by the mechanic on every gear, every bearing, every seal etc, as to what parts stay, and what parts get replaced.

If you toast your lower, I don't "rebuild" the upper because "i think" it's got contaiminated (metal shavings) oil. I'm fairly confident that it doesn't actually. But I will tear the upper apart and inspect everything, take care of that leaky yoke seal, and anything else in "my judgement" that "I don't like".
Typically you replace all the oil seals in a "rebuild" because they all have the same amount of hours on them. Even if the upper didn't leak at the time and I'm putting a gearset in the lower. The upper gets new seals. If the drive has 300 hours on it total and you just do the lower. Well then you have a lower with new seals and an upper with 300 hours on the seals... that doesn't make much sense.

Wether you rebuild the upper or the lower it doesn't matter, the final product has to work as a combined set for it to function properly.

Its like having a house wired for electricity but not having any power from the street. It doesn't matter how pretty your chandeliers are if they aren't working.

 

[Knightgang]

Re: I saw something weird on an outdrive, what was it for?

So, I am guessing that the prop sucks the air down through the tube basically by a force of vacuum.

I can understand the Clutch dumping theory and i supposed I can even buy the low speed maneuvering claim for large boats around docks. But to think that one product can work in such a universal way for these applications is pretty mind blowing. Also, if it works so well, why are they not installed more often, especially on say 25' I/Os and larger...

I just think these are a bit odd and the website has its claims, but no explaination in science...

 

[JustJason]

Re: I saw something weird on an outdrive, what was it for?

But to think that one product can work in such a universal way

It's not universal, it's the world of "go fasts". Alot of has to do with the boat owner and what he expectes out of it. A 496 engine will last many thousands of hours in the hands of a casual boater in your average cruiser. Its very common however, to see that same 496 in the back of a Fountain completely smoked with only 200 hours on it. The 496 in the back of the Fountain has seen 1 hour at idle speeds and 199 hours at 5200 RPMS banging off of wave after wave. Big difference.
Theres all sorts of gimmicks with props. Some work well, some not so much. If you have an old prop laying around drill 3 1/2inch holes in it. 1 in between each of the vanes, about halfway up the outer hub. Install it and punch the gas.... The motor will rev like crazy and you'll slowly start picking up speed. But when you hit a certain speed the water pressure will overcome the exhaust comming out your drilled holes, prop ventilation will stop, and the boat will take off like a rocket.

 

[bruceb58]

Re: I saw something weird on an outdrive, what was it for?

And the top of my radiator is considerably hotter than the bottom of my radiator.

That's because the water exits the engine into the top of the radiator.

We are engineers and studied this stuff in school. Why are you debating this still?

 

[Knightgang]

Re: I saw something weird on an outdrive, what was it for?

Jason, not that I have a prop to try it, but I am starting to see where it makes sense... I thought the product website was also stating that it was applicable for any large boat maneuvering around docks, etc... I can see where the go-fast application is a plus now...

Thanks...

 

[HT32BSX115]

Re: I saw something weird on an outdrive, what was it for?

If you toast your lower, I don't "rebuild" the upper

Boy, this is getting off the original thread subject I suppose.....

If I had a "Toasted" upper or lower I would completely disassemble to inspect it all since there is a slight flow from lower to upper, upper to lower etc....

And you're right. If a shop didn't look at both, They'd be liable!

 

[JustJason]

Re: I saw something weird on an outdrive, what was it for?

Boy, this is getting off the original thread subject I suppose.....

Wicked off subject... But the conversation is civil and interesting.

That's because the water exits the engine into the top of the radiator.

Not in every car. GM to my Soobie is apples to oranges but on mine its a bottom mounted water pump and it pushes water up the radiator into the engine. It's a PITA to bleed

 

[HT32BSX115]

Re: I saw something weird on an outdrive, what was it for?

Wicked off subject... But the conversation is civil and interesting.

Well, yeah....and this is ok I think!