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PostPosted: 14 Jul 2016, 10:17 
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onthewater102 wrote:
...so, returning from left field...let me simplify my question - how fast does water flow to fill a void? I've found calculators for flow rate in a pipe - but not on open water.


Or to answer it another way....makes no difference as none of us are good enough to take advantage of it! If you follow the procedures above it will solve itself.


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PostPosted: 14 Jul 2016, 11:15 
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Joined: 15 Mar 2014, 16:57
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DaleH wrote:
onthewater102 wrote:
... so, returning from left field - how fast does water flow to fill a void?

You do realize that water, fluid mechanics or hydrodynamica calculations are some of the toughest to predict, never mind solve?

If truly laminar, you could project a consistent flow, with same expectations if turbulent flow only. You'll have a mix, as vortexes form to fill the resultant 'hole in the water', which results in nonlinearity in the filling, where oscillation from the inflow will likely create the largest nonlinear disparity. That's all I recall from my physics and mechanics (theory, not wrench turning ones ... lol!) classes.

But that's a long way around of saying ... I have no freakin' clue :roll: !



Thank you! A step in the direction to what I was looking for and should be enough for me to try & get to what I'm looking for.

For a small planing style hull with a flat bottom I would think the turbulence would be strongest along the edges of the transom and simplify the flow calculation to just the void behind the center portion of the transom. The turbulence caused by the propeller will be aft-ward of the area I'm concerned with and I have no choice but to hope it has a minimal impact on the flow. It will be a non-linear inflow for sure - as I'm trying to calculate the net upward flow of water immediately behind the boat due to the atmospheric pressure acting on the surface of the water - but this is really the only flow I'm trying to account for and the source of pressure I was overlooking when I asked this question in the first place - so thank you!!! I realize this won't be perfect as apart from turbulence, momentum diffusion from the forward movement of the boat hull will create a pressure differential due to the variations in the laminar flow directly beneath the boat - but I should be able to calculate that too if nothing else but to see if it is material to the pressure differential between the void and the water (gut instinct is that it won't matter).


All I want to achieve at the end of this is to get a better idea of what height to put my range of adjustment relative to the bottom of the boat, I know it will still require trial and error to tune it, but I don't want to go through $50 worth of aluminum making 6 different height configurations and all the time installing/removing the motor before I get it right when I could play around in a spreadsheet for a while & get a reasonable idea of where to start & have ~1"~1.5" worth of adjustment range to work within.



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PostPosted: 15 Jul 2016, 19:39 
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May be easier to just buy an adjustable jack plate with more adjustment than what you are talking about..................

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