Author Topic: Re: Reasons To Be Grumpy thread  (Read 342837 times)

Icarus

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Re: Reasons To Be Grumpy thread
« Reply #3660 on: January 27, 2020, 02:54:33 AM »
Siz, the interupted surface concept works on high velocity golf balls but not on relatively low speed boats.  There is the matter of Reynolds numbers that play into the turbulent separation of water or other fluids. ( air and other gasses are considered fluids when the physics of the matter are under scrutiny)

Reynolds numbers are functions of velocity and distance along a fixed body.  A boat of 14 feet or so will develop a turbulent boundary layer well before the mid point of the run along the surface.  The low velocity trick is to delay boundary layer separation as far as possible.  That is a function of velocity  and  is also positively influenced by the smoothness of the surface on which the fluid impinges.

The closest part of the boundary layer sticks to the surface and adheres there, The adjacent layers move along the surface in ever increasing equality to the velocity of the moving body.  That can be interpreted, in the practical sense, as the surface friction of the moving body.  This is well proven principals of physics.  Advantage of roughened surfaces of a sailboat is plain bullshit that should be dismissed without delay. Why in hell does the cruising boat sailor pay so much attention to the barnacle or scum accumulation on his bottom?  I repeat! Rough surface advantage is out and out bullshit expounded by sailors or others who do not , or choose  not, to believe in  the irrefutable rules of physics.

Heeling the boat does not necessarily increase or decrease the weather or lee helm of the boat.  The deal is to relocate the center of lateral resistance in such a way as to neutralize helm.  All you have to do is to relocate the center of lateral resistance so as to neutralize the helm. That is a simple operation with a dinghy.  Move your weight  fore or aft so that the rudder input is neutral or nearly so. Tilting the board is often enough to affect the desired result.  If your dagger board is cut straight on the leading edge, the part that is housed in the board trunk,  then cut off a wedge of the leading or trailing edge so as to be able to tilt the board fore or aft.....not the surface below the boat bottom.  That moves the CLR to whatever advantage.  Long, deep boards are particularly effective with this ploy.

Some of the most ferocious competitive sailors, the world around, are Sunfish sailors.  It is common to see them, pre- race , to carefully wash their bottoms with soap or other cleanser to remove even the slighest trace of contaminatiom.  Enough said. 

 

 

Siz

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Re: Reasons To Be Grumpy thread
« Reply #3661 on: January 27, 2020, 09:31:36 AM »
Siz, the interupted surface concept works on high velocity golf balls but not on relatively low speed boats.  There is the matter of Reynolds numbers that play into the turbulent separation of water or other fluids. ( air and other gasses are considered fluids when the physics of the matter are under scrutiny)

Reynolds numbers are functions of velocity and distance along a fixed body.  A boat of 14 feet or so will develop a turbulent boundary layer well before the mid point of the run along the surface.  The low velocity trick is to delay boundary layer separation as far as possible.  That is a function of velocity  and  is also positively influenced by the smoothness of the surface on which the fluid impinges.

The closest part of the boundary layer sticks to the surface and adheres there, The adjacent layers move along the surface in ever increasing equality to the velocity of the moving body.  That can be interpreted, in the practical sense, as the surface friction of the moving body.  This is well proven principals of physics.  Advantage of roughened surfaces of a sailboat is plain bullshit that should be dismissed without delay. Why in hell does the cruising boat sailor pay so much attention to the barnacle or scum accumulation on his bottom?  I repeat! Rough surface advantage is out and out bullshit expounded by sailors or others who do not , or choose  not, to believe in  the irrefutable rules of physics. 

The phenomenon that bizzy posted a link to was something named Superhydrophobicity - quite different from what you describe above.
Quote from: UCLA
In theory this means that the surfaces can trap air bubbles, creating a hydrodynamic cushion... [snip]
...The researchers modeled both laminar and turbulent flows, and unexpectedly found that the drag-reduction was larger in turbulent conditions. The irregular fluctuations and swirling vortices in turbulent flows on smooth surfaces generally increase drag, Kim explained. However, the air cushion created by the superhydrophobic ridges altered the turbulent patterns near the surface, reducing their effect.
It's worth a read - https://www.sciencedaily.com/releases/2014/01/140117153637.htm

Heeling the boat does not necessarily increase or decrease the weather or lee helm of the boat.
I'm afraid it really does (there are some exceptions). Where the water contact area is asymmetrical (as in a heeled hull) there will be a turning force. That's why rudderless steering works.

The deal is to relocate the center of lateral resistance in such a way as to neutralize helm.  All you have to do is to relocate the center of lateral resistance so as to neutralize the helm. That is a simple operation with a dinghy.  Move your weight  fore or aft so that the rudder input is neutral or nearly so. Tilting the board is often enough to affect the desired result.  If your dagger board is cut straight on the leading edge, the part that is housed in the board trunk,  then cut off a wedge of the leading or trailing edge so as to be able to tilt the board fore or aft.....not the surface below the boat bottom.  That moves the CLR to whatever advantage.  Long, deep boards are particularly effective with this ploy.
Centreboard shape is set by class rules, as it is in most classes. I can tilt it (it's on a pivot, as you mention), which does change the CLR (fore/aft), and this is certainly one of the settings that need adjusting depending on point of sail, but you're thereby introducing other imbalances. I want the centreboard in a position where it can best fulfil its primary purpose of keeping the boat moving in a straight line. That is typically fully extended on a beat [point of sail] where you're most likely to be heeling.
A more simple solution to lee/weather helm [turning force] is to just keep the boat flat.

Some of the most ferocious competitive sailors, the world around, are Sunfish sailors.  It is common to see them, pre- race , to carefully wash their bottoms with soap or other cleanser to remove even the slighest trace of contaminatiom.  Enough said.
Yes, not confined to that class. I see the 'Topper Dads' (a term I use with complete contempt) doing the same to the bottom of Little Tarquin's brand new Topper before events at our club.

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Re: Reasons To Be Grumpy thread
« Reply #3663 on: January 27, 2020, 02:06:52 PM »
all thiz is super interesting

nothing is simple with this stuff

https://www.google.com/amp/s/www.latimes.com/science/sciencenow/la-sci-sn-shark-skin-riblet-denticle-drag-bioinspired-20160314-story.html%3f_amp=true

Yeah, who knows with evolution...???

The Superhydrophobicity mentioned previously requires a hull's access to air which (for all intent and purpose) shark skin does not have (assuming, as I think is correct, that sharks rarely break surface). So I don't see a reason why Superhydrophobicity as a friction reducer mightn't still be applicable for boats.

When one sleeps on the floor one need not worry about falling out of bed - Anton LaVey

The universe is a cold, uncaring void. The key to happiness isn't a search for meaning, it's to just keep yourself busy with unimportant nonsense, and eventually you'll be dead!

hermes2015

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Re: Reasons To Be Grumpy thread
« Reply #3664 on: January 27, 2020, 02:13:54 PM »
all thiz is super interesting

nothing is simple with this stuff

https://www.google.com/amp/s/www.latimes.com/science/sciencenow/la-sci-sn-shark-skin-riblet-denticle-drag-bioinspired-20160314-story.html%3f_amp=true

Yeah, who knows with evolution...???

The Superhydrophobicity mentioned previously requires a hull's access to air which (for all intent and purpose) shark skin does not have (assuming, as I think is correct, that sharks rearely break surface). So I don't see a reason why Superhydrophobicity as a friction reducer mightn't still be applicable for boats.

Shark skin, known as shagreen in the design world, was used by people like Jean-Michel Frank in some very beautiful furniture designs. These fetch high auction prices today.
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Re: Re: Reasons To Be Grumpy thread
« Reply #3665 on: January 27, 2020, 03:02:54 PM »
I'm sitting here, waiting for a tabletop my mother bought for her school to be delivered. It was supposed to arrive this morning but it's midday and still nothing.
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Re: Re: Reasons To Be Grumpy thread
« Reply #3666 on: January 30, 2020, 01:41:19 PM »
Looks like I'll be spending the entire weekend in the lab again. :sad sigh:
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Re: Re: Reasons To Be Grumpy thread
« Reply #3667 on: January 30, 2020, 01:52:29 PM »
Looks like I'll be spending the entire weekend in the lab again. :sad sigh:

Does that mean you'll talk to us a lot?
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Re: Re: Reasons To Be Grumpy thread
« Reply #3668 on: January 30, 2020, 02:02:20 PM »
Looks like I'll be spending the entire weekend in the lab again. :sad sigh:

Does that mean you'll talk to us a lot?

Probably when I return home in the evening. :blahblah:
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Bad Penny II

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Re: Re: Reasons To Be Grumpy thread
« Reply #3669 on: January 30, 2020, 02:51:02 PM »
Looks like I'll be spending the entire weekend in the lab again. :sad sigh:

Does that mean you'll talk to us a lot?

Probably when I return home in the evening. :blahblah:

OK, got it, lab time is time when Phinx doesn't talk to us and hence bad.
God bless those mods who toil so we can tosh.

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Re: Re: Reasons To Be Grumpy thread
« Reply #3670 on: January 30, 2020, 05:57:43 PM »
Looks like I'll be spending the entire weekend in the lab again. :sad sigh:

Does that mean you'll talk to us a lot?

Probably when I return home in the evening. :blahblah:

OK, got it, lab time is time when Phinx doesn't talk to us and hence bad.

 :blush:
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Kusa

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Re: Reasons To Be Grumpy thread
« Reply #3671 on: January 30, 2020, 11:11:35 PM »
Being alive is sufficient reason for being grumpy.

Bad Penny II

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Re: Reasons To Be Grumpy thread
« Reply #3672 on: January 31, 2020, 12:37:13 AM »
Being alive is sufficient reason for being grumpy.

Only some days.
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billy rubin

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Re: Reasons To Be Grumpy thread
« Reply #3673 on: February 08, 2020, 12:15:42 AM »
damn

seven days ago it was 65 F around here, and the ground flora is still showing green.

this morning it was just below freezing, and by midday there was over a foot of snow on my road for me to go home through. i live in the middle of nowhere, so we don't get the road ploughed. we have to use the hit-it-as-hard-as-you-can technique, which works on fresh snow up to about three feet for very short distances, and two feet for most of the bad section between here and the macadam.

two of the three four-wheel-drives are dead at the moment, so the number two daughter gets the three quartr ton to go to school, the wife gets the front wheel drive minivan, and i hit the hills and the drifts as fast as i can in a little two wheel drive pickup



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Re: Re: Reasons To Be Grumpy thread
« Reply #3674 on: February 08, 2020, 12:27:41 AM »
My magical never-ending lobster tank is still on the fritz!