Throttle refresher course

[TRCM]

The aluminum gearcase housing is the heatsink. It dissipates heat to the air around it. Aluminum will dissipate heat much more heat to the surrounding air than iron will.

Gear set absolutely positively does not turn when the engine is turned off. You can spin that prop shaft in neutral all you want, and the gear set doesn't move. Only the prop shaft and clutch dog spin.

The gearset you mention that we were talking about is on a truck axle under a trailer...NOT a lower unit.

The lower unit will dissipate the heat FASTER because it is aluminum....but it does not dissipate MORE heat than if it was iron,.....both will dissipate the heat generated, one is just faster at doing so.

[TRCM]

Explanation I received from a 30+ year certified Mer/Yammy mechanic. The prop shaft bearings are designed for a "pushing" force as the motor is moving the boat through the water. Not a pulling force you get while it's freewheeling down the road. And yes while in reverse. The difference is you don't run in reverse for hours upon hours at a time like towing. Mercury suggests putting it in gear for this reason. Bottom line tho, you paid for it. Do what you wish, and let others do the same.

At least that makes more sense than the answer I was given.

[TRCM]

Well now ya'll have entertained me but also got me scratchin my noggin. Guess I better go out and take a look at my service manual. I'm talking about a service manual , not an owners manual, big difference.

If my manual says to leave it in gear then I gotta solve the other question. I was always told not to shift the shifter unless the motor is running. Anyone considered this concern ? I haven't seen that brought up in this thread.

Methinks ya can't have it both ways.

Sure ya can....turn it off in gear and leave it.

[hatcreek]

If you inflate a basketball in your jackplate, it'll provide just enough air deflection that prop spinning becomes a non-issue... to say nothing of all the extra lift/floatation it provides... Win-win.

[dean c]

Prop turns in the water when your trolling. Look next time your in clear water.

[getfished]

Sure ya can....turn it off in gear and leave it.

Think it through. Next time you would have to shift it to start it. Like I said ya can't have it both ways.

[bassboy1]

The lower unit will dissipate the heat FASTER because it is aluminum....but it does not dissipate MORE heat than if it was iron,.....both will dissipate the heat generated, one is just faster at doing so.

Where do you get this stuff?

[hugo_stiglitz]

The gearset you mention that we were talking about is on a truck axle under a trailer...NOT a lower unit.

The lower unit will dissipate the heat FASTER because it is aluminum....but it does not dissipate MORE heat than if it was iron,.....both will dissipate the heat generated, one is just faster at doing so.

Moving something faster means moving more in the same amount of time.

1 inch pipe vs 2 inch pipe, same head pressure larger pipe moves more water faster. Exact same function with moving heat faster, aluminum can dissipate more heat in the same amount of time than iron can, because it moves heat faster.

[TRCM]

Think it through. Next time you would have to shift it to start it. Like I said ya can't have it both ways.

true......maybe ya can pull start it with yer trolling motor ??

Where do you get this stuff?

It's called science.

Let's say a heat source has 100,000 btus of energy to give off.

Well, an aluminum heatsink may dissipate that heat in 10 min, where as an iron or steel one may take an hour.

But, they still both dissipated the same 100,000 btus of heat, one just did it a lot faster.

Moving something faster means moving more in the same amount of time.

1 inch pipe vs 2 inch pipe, same head pressure larger pipe moves more water faster. Exact same function with moving heat faster, aluminum can dissipate more heat in the same amount of time than iron can, because it moves heat faster.

Yes and no.

If you have a 50 gal fuel tank in your boat, and you want to drain it, a 2" hose will do it faster than a 1" hose, but they still both only drained 50 gals. One moves more fuel per time, but they both still moved the same total volume of fuel.

Same with heat...if you have a shaft spinning for 1 hr, it only produces so much heat, and the aluminum will get rid of that heat faster, but it can't get rid of heat that isn't generated.

[Perchpro]

all of this! I bet a 4 blade prop spins faster going down the hyway.

[g352nv]

Why not just do what the manual says?

[TRCM]

Yeah, gone way off course..........................

[OkieBud]

Out of gear

[bassboy1]

It's called science.

Let's say a heat source has 100,000 btus of energy to give off.

Well, an aluminum heatsink may dissipate that heat in 10 min, where as an iron or steel one may take an hour.

But, they still both dissipated the same 100,000 btus of heat, one just did it a lot faster.




Yes and no.

If you have a 50 gal fuel tank in your boat, and you want to drain it, a 2" hose will do it faster than a 1" hose, but they still both only drained 50 gals. One moves more fuel per time, but they both still moved the same total volume of fuel.

Same with heat...if you have a shaft spinning for 1 hr, it only produces so much heat, and the aluminum will get rid of that heat faster, but it can't get rid of heat that isn't generated.

Is this common core science?

There is a time aspect to measuring flow. CFS (Cubic Feet per Second). GPH (Gallons Per Hour). Same thing with heat dissipation. BTUs per whatever unit of time you want.

That's like saying a Ranger and an Allison are the same speed, because they both made it back to the ramp by weigh in. Sure, one got an extra 20 minutes of fishing in, but that's irrelevant.

[Lil Mo]

Boat launch is 5 min from the house. Wouldn’t think it would matter much but always in neutral.

[pavi69]

Explanation I received from a 30+ year certified Mer/Yammy mechanic. The prop shaft bearings are designed for a "pushing" force as the motor is moving the boat through the water. Not a pulling force you get while it's freewheeling down the road. And yes while in reverse. The difference is you don't run in reverse for hours upon hours at a time like towing. Mercury suggests putting it in gear for this reason. Bottom line tho, you paid for it. Do what you wish, and let others do the same.

Your mechanic was making us stuff he did not know.

[HiTorq]

Your mechanic was making us stuff he did not know.

Could very well be. But since he was the instructor, on the test I answered, "tow in gear", as per the manual. :)

[kojimep]

true......maybe ya can pull start it with yer trolling motor ??



It's called science.

Let's say a heat source has 100,000 btus of energy to give off.

Well, an aluminum heatsink may dissipate that heat in 10 min, where as an iron or steel one may take an hour.

But, they still both dissipated the same 100,000 btus of heat, one just did it a lot faster.




Yes and no.

If you have a 50 gal fuel tank in your boat, and you want to drain it, a 2" hose will do it faster than a 1" hose, but they still both only drained 50 gals. One moves more fuel per time, but they both still moved the same total volume of fuel.

Same with heat...if you have a shaft spinning for 1 hr, it only produces so much heat, and the aluminum will get rid of that heat faster, but it can't get rid of heat that isn't generated.

this is a very flawed view of how physics works.....

[FlipSide]

My head hurts...

[Fish Whisperer]

In neutral when towing for me.