Gear Ratio Debate 1.62 vs 1.75

[LakeFever]

My farmer brain says the math in 25 is spot on. There is no torque multiplication in gear sets, they are simple lever boxes not actuated devices like a torque converter in a car which slips and multiplies torque until hydraulic lock neutralizes the multiplier as close to 1:1 as possible given the fluid properties so the multiplication examples do not add up to any advantage in a mechanical lever box which is what a lower unit primarily is. There is an argument to be made about which ratio functions with less resistance at given RPM due to tooth contact, engine dynamics such as pulse and harmonics distributing load preferences towards one or the other and my guess is any mechanical differences in feel will fall into this very small black hole of function harmony.

The prop load, speed, slip, and water volume involved with each turn is a WHOLE lot more variable and where all the change happens imo. If different lever boxes manifest into tangible performance differences its the prop and water relationship that make the differences, not the gear ratio. The gear ration may only provide more or less favorable conditions for a given prop to work. Even then, I would wager my boat that two prop masters working one identical prop save for pitch following post 25 equalization math allowing them to modify the prop for best results will become a coin toss who ends up faster or quicker and neither lower unit ratio will factor into the end result.

[FMP]

It's whether you want to take more little steps or larger strides with every engine rev to get the travel.Even so both examples would intersect on a graph at some point in the rpm acceleration. If the travel can truly be equalled the testing on a hull may change the results , one example may favor the water off the hull bottom over the other. In a controlled lab it could be different. If surface running , which are really just paddle tip blading. Smaller more frequent inputs or longer less frequent , what will the liquid resist, hold more efficiently.

[LakeFever]

Yes granted where I said "following post 25" I should have inserted same boat, same motor, same day in the model criteria

[FMP]

It would seem to be next to impossible to distinguish the differences but examples of testing have be mentioned which describe the differences. Hull effects and mass likely, through the graph if you can imagine one.

[engineermike]

.... Keyboard results do not understand the more revolutions the input shaft turns to get one output revolution.

I'm not sure exactly what you mean by this, but I can assure you I am quite capable of calculating torque multiplication and speed reduction in a gear unit. It's a big piece of what I do and I can design the gears as well.

The easier it is to turn. If your chain hoist lifted your outboard 1 inch for each input revolution. It would be much harder to turn the input pulley vs it taking 5 input turns to lift your outboard 1 inch.

Ok, so what you are saying is that more input turns on a chain hoist for the same amount of hoist lift (5:1 vs 1:1), means that it will be easier to pull, correct? I totally agree. Therefore, the same number of turns on the chain hoist means it will be the same effort to pull (1:1 vs 1:1), correct? Totally agree. Fortunately, you just demonstrated perfectly the point I made in post 39. Whether you are using 1.75/35" prop or 1.62/32" prop, they both result in the same inches of boat movement forward for the same number of crankshaft revolutions. Viola! There is no difference from a basic mechanical advantage standpoint. If we can all agree on that, then we can move on to other more interesting pieces of the discussion.

Also, I can't help but notice you folks seem to slip snarky insults directed towards me in each one of your retorts. I have not insulted any of you and I would appreciate it if we could act like adults.

[FORBESAUTO]

Any heavy equipment mechanic that has ever used 4-1 torgue multiplier, which is simply a planetary gear set, will beg to differ that there is no torgue multiplcation in a gear set. You take a bolt that has to torqued to 500 ft lbs, try and torque it with 6 ft cheater bar then with the gear reduction and tell me it’s only leverage. A little runt can do it with the “torque mutilplier” and it’ll still take a man with cheater bar. If there is no torque multiplication when tightening a bolt to 400 ft lbs with a 4-1 multiplier, why do you set the torque wrench to 100 ft lbs?

[LakeFever]

Torque multiplier is a fixed concept within a lever box. A torque converter literally multiplies torque until stall speed has been achieved. Lever boxes which lower units are can only multip-ly torque at a fixed rate it is not variable. Prop pitch and load determine movement which are also scaled in rates of multiplication BUT are forced to operate within liquid that is never truly fixxed. The behavior in the fluid is far more variable and offers performance advantage if you can capitalize upon this. If you happen to find the better functioning result with a given ratio be it 1.5:1 or 2:1 the lever box only serves to translate RPM limits vs prop load and offers no performance advantage or disadvantage. Its more a tool in the box rather than a component of chaos to tame

[Captaincj]

Torque multiplier is a fixed concept within a lever box. A torque converter literally multiplies torque until stall speed has been achieved. Lever boxes which lower units are can only multip-ly torque at a fixed rate it is not variable. Prop pitch and load determine movement which are also scaled in rates of multiplication BUT are forced to operate within liquid that is never truly fixxed. The behavior in the fluid is far more variable and offers performance advantage if you can capitalize upon this. If you happen to find the better functioning result with a given ratio be it 1.5:1 or 2:1 the lever box only serves to translate RPM limits vs prop load and offers no performance advantage or disadvantage. Its more a tool in the box rather than a component of chaos to tame

REALLY enjoying your posts and Engineer Mike's. Agree.

[LakeFever]

This is a good thread, because as I said before this site is awesome. Theres some great thinkers here, I had lurked a while before joining

I love a good think thread

[HStream1]

This is all I have to say on this matter from now on. WHAT HAS A CARS THIRD MEMBER GEAR RATIO AND TIRE SIZE GOT TO DO WITH THE ORIGINAL QUESTION??????? Again I say Its like trying to compare apples to pomegranates. The two cant be compared at all. Running on H2O vs asphalt, Drag Coefficient etc??? A TFH has achieved a 3.43/274.92 mph pass while a TF Dragster has achieved a 3.8/336.15 mph. Both in 1000 ft. Break that one down for me fellow engineers

[Captaincj]

This is a good thread, because as I said before this site is awesome. Theres some great thinkers here, I had lurked a while before joining

I love a good think thread

I think even the guys on the other side of the debate are partially correct, right up to the propshaft. They just don't see how the changes in the prop pitch neutralize the gear ratio difference.

[LakeFever]

Thats precisely what makes a discussion like this so fruitful. There really isn't a lot of wrong, more of a focus on where the gains are to be had. In reality there is also cost vs. Not many folks have the time to spend or the money to buy and try literally every combo possible to achieve a desired outcome. This is why racing is so interesting because if you dont show up with something to race you have nothing. If you do show up and manage to produce a competitive product its far more likely that you have built a better machine with more money, or more experience which took a lot of time and time is measured in money so it also took a lot of money. Experience and know how are then handicapped within rules so in this grey is where mechanical advantage is the difference between first and last place and those differences are very slight.

Now apply above to this thread and everyone in here is looking for mechanical gains, we all share that end goal. Its the why/how/where to focus thats unique to each and we are supporting our positions accordingly as best we can. None wrong, but all thinking "hmmm this should work" and I really enjoy being proven wrong because thats where I get to learn. This is why threads like this are so much fun, they make you dig and think and consider that maybe there is a better solution than I first thought.

[FMP]

This is all I have to say on this matter from now on. WHAT HAS A CARS THIRD MEMBER GEAR RATIO AND TIRE SIZE GOT TO DO WITH THE ORIGINAL QUESTION??????? Again I say Its like trying to compare apples to pomegranates. The two cant be compared at all. Running on H2O vs asphalt, Drag Coefficient etc??? A TFH has achieved a 3.43/274.92 mph pass while a TF Dragster has achieved a 3.8/336.15 mph. Both in 1000 ft. Break that one down for me fellow engineers

What's to break down, the H achieved top speed in shorter time traveling the 1000 with a higher average speed.

Let's start with a 1:1 and 18 pitch, in increments reduce the ratio to 2:1 and increase the pitch accordingly to match the travel per engine rev. Same outcome at the end on paper. But it's a liquid and plenty of variables on props through the range but if all could be equalled how far off would the results be?

[HStream1]

You sure about that statement? or did I read it wrong?

What's to break down, the H achieved top speed in shorter time traveling the 1000 with a higher average speed.

[Captaincj]

Assuming equal slip and equal prop efficiency, I see the propeller (the two different pitches that neutralize the gear ratio difference) as the final gear in the system.

Imagine a boat on a 4 wheel trailer and on a test track. Imagine the prop replaced with a pinion gear and a fixed gear rack on the ground along the track. Test it once with 1:62 gears and again with 1:75 gears but change the pinion teeth count to equal the same final ratio. Would one be any different than the other?

If you assumed equal slip and prop efficiency would that not be the same?