Fluid dynamics?

[keverdmann]

This may sound crazy.

But I just watched an episode of Mythbusters.
They did some tests in fluid dynamics where they were testing if the dimples on a golf ball reduced drag; would they reduce the drag on a car. (and it did by the way?) Check it out on discoverys website

So I got to thinking, if it works on a car. How would it work on the bottom of a boat. It is supposed to reduce drag and wake.

Anyone out there have a sacrificial running boat that they wanna experiment on?

Just a crazy thought?.

 

[fish 4 life]

Re: Fluid dynamics?

I was just watching that episode too. I can't believe, even with the extra weight of the clay, the car still got 11% better gas mileage. I don't see any reason why it would not work for a boat as well.

Unfortunately I have only one boat and I don't plan on sacrificing it for science sake any time soon.

 

[ondarvr]

Re: Fluid dynamics?

There are boats currently being made with dimpled hulls, there were also boats that were made with different types of texture on the hulls. I don't have any info on what worked and what didn't though.

 

[H20Rat]

Re: Fluid dynamics?

one a 100% displacement hull it would make a bigger difference, but on planing hulls you have some different things to deal with.

sort of like waxing. it makes a very small difference, but waxing actually slows a boat down! i've seen the effect personally on a pwc, but it apparently is a big deal in the competition rowing/sailing world.

 

[lowkee]

Re: Fluid dynamics?

Are you saying my horribly orange peeled paint job will actually increase performance?!

Er, yeah, that orange peel is a feature, not a mistake.

 

[Mischief Managed]

Re: Fluid dynamics?

one a 100% displacement hull it would make a bigger difference, but on planing hulls you have some different things to deal with.

sort of like waxing. it makes a very small difference, but waxing actually slows a boat down! i've seen the effect personally on a pwc, but it apparently is a big deal in the competition rowing/sailing world.

Coincidentally, I was watching Time Warp last night and one of the experiments they showed was a pair of cue balls dropped into a fish tank. One ball was plain, was was "waxed" with a microscopic layer of water repellent. The water repellent had the same water beading affect that wax has. When dropped from the seam height, the "waxed" ball created a much bigger splash and decelerated noticibly faster than the plain ball. The water repellent really increased the hydrodynamic drag. I assume wax would as well.

 

[keverdmann]

Re: Fluid dynamics?

Coincidentally, I was watching Time Warp last night and one of the experiments they showed was a pair of cue balls dropped into a fish tank. One ball was plain, was was "waxed" with a microscopic layer of water repellent. The water repellent had the same water beading affect that wax has. When dropped from the seam height, the "waxed" ball created a much bigger splash and decelerated noticibly faster than the plain ball. The water repellent really increased the hydrodynamic drag. I assume wax would as well.

I watched that too. That is so crazy, I would have thoght water repelent would have made it easier to cut through the water.

 

[keverdmann]

Re: Fluid dynamics?

There are boats currently being made with dimpled hulls, there were also boats that were made with different types of texture on the hulls. I don't have any info on what worked and what didn't though.

I would love to know the science behind those dimples.

 

[JB]

Re: Fluid dynamics?

Google up America's Cup.

I recall seeing serious experimentation with texturing hull surfaces and the analogy used was the dimpled golf ball.

I don't recall the outcomes.

 

[BeaufortTJustice]

Re: Fluid dynamics?

Feel free to throw the BS flag on this play...

...but I think I remember back from a college course I took, it has something to do with turbulence. A dimpled golf ball travels through the air with less turbulence then a plain ball. The dimples somehow "organizes" the airflow around the ball. Turbulence behind an object can create a pulling or suction type force that can work against it. Maybe somebody with an aeronautical engineering background can enlighten us.

 

[haulnazz15]

Re: Fluid dynamics?

Well in a similar fashion, many aircraft (especially airliners) have "vortex generators" in strategic places on the wings/rudders/elevators. These are usually an inch or two long and look sort of like shark fins. The point of using them on an otherwise-smooth wing is because at slower speeds it organizes the air stream to keep it from separating from the wing surface, which allows much better control and slow airspeeds.

I'm sure the dimples serve a similar effect on golf balls where it reduces drag by maintaining flow across the surface with little air pcokets in the dimples. The difference in the boating world may come down to the cost of producing a hull with dimples and whether or not you are traveling at a speed fast enough to take advantage of the dimples as pressure zones. It would likely only be usful to dimple the back half of the hull for most boats (back 12" for those crazy bass boats).

 

[Silvertip]

Re: Fluid dynamics?

Ever wonder why fish scales are overlayed toward the rear? Same principle as dimples, vortex generators, and a hail damaged auto. I allows them to slip through the water at faster speeds while expending less energy in the process.

 

[Bob_VT]

Re: Fluid dynamics?

Reggie Fountain (Fountain boats) once tested a hull for a speed record and they pulled the boat and used a drill to dimple portions of the hull to create turbulence which helled the top end.

Look at a shark's skin and there is no doubt about their ability for speed.

 

[metriccrescentwrench]

Re: Fluid dynamics?

I used to have a contact at NASA and had a few email exchanges about this sort of thing with him. 3M used to make an adhesive sheet with small grooves accurately machined in, this technology is call "riblets". These 'grooves' are about 0.001 to 0.005 inches thick. Strategically placed on aircraft it can reduce drag by 4 - 8%.

It's also been used on boats. Stars and Stripes won the America's Cup using this technology in 1987. I heard a while ago that 3M quit making this stuff, it was expensive and not much of a market. Apparently to be effective the machining has to be pretty accurate, not something we could do at home on our hulls.

 

[pmillar]

Re: Fluid dynamics?

I will see if my brother, a naval architect/engineer can provide a helpful link or brief summary of the principles involved. If I remember correctly, a rougher surface may help by creating small eddies or turbulence which actually reduces the impact on the laminar flow of the boundary layers that become "stacked up" by the disturbance created as the hull/wing flows through the fluid in question. A good diagram would truly be worth a thousand words here as I'm not explaining it very well. Of course I am in finance, not engineering.

BTW, my brother works on a pretty cool project, here:http://www.google.com/hostednews/ap/article/ALeqM5gtAdCDYzA8NImWi1iBA8ukiBF08wD9BG3NC83

 

[wa_ssv197]

Re: Fluid dynamics?

I watched that episode as well.

Here is a drift boat with dimpled hull.
Clackacraft

 

[keverdmann]

Re: Fluid dynamics?

Ever wonder why fish scales are overlayed toward the rear? Same principle as dimples, vortex generators, and a hail damaged auto. I allows them to slip through the water at faster speeds while expending less energy in the process.

So what if we use scales on the bottom of a boat instead of dimples?

That would be easier to pull off on a boat. I wonder if it would do the same thing?

Maybe I will ask the mythbusters...

 

[keverdmann]

Re: Fluid dynamics?

So what if we use scales on the bottom of a boat instead of dimples?

That would be easier to pull off on a boat. I wonder if it would do the same thing?

Maybe I will ask the mythbusters...

Its done! I have asked them!
http://community.discovery.com/eve/...67776&m=99519190301&r=99519190301#99519190301
Log on and discuse I want to see it done by them!

 

[Campylobacter]

Re: Fluid dynamics?

It works on people too! Those fancy one piece "sharkskin" swimsuits used in the olympics last year have a rough texture. The swimmers get reproducibly faster times in suits.

I've also hear boat racers sand their hulls, but I have no first hand knowledge of this.

 

[BWR1953]

Re: Fluid dynamics?

Okay, I'll say it... There is a REASON that tin boats use rivets! LOL!