Golf Ball Fluid Dynamics

[Inquisitor]

I'm sure most of you are familiar with the dibits on a golf ball and that a "smooth" golf ball will not travel near as far as dibit'd ball. Reduced friction has something to do with this. Has anyone ever tried the same thing on a boat hull? For instance... not filling the last layer of fiberglass and leaving it with the cloth's texture.

[h_zwakenberg]

That would leave your laminate open, which would be an invitation for osmosis....

There have been other methods to reduce hull skin friction though: for instance injecting air below the hull. Another method that once was tested - and one you might adopt if you don't care a bit about why the Kyoto Protocol might be important after all - is to increase pollution by injecting certain polymers that reduce the water surface tension. This would also reduce surface drag...

bye
Hans

[Inquisitor]

Thank you for the reply. I meant the last layer was fully epoxied, but just leaving the texture instead of all the rest of the finishing process before painting. I was planning on leaving the tops of my cat hulls this way for grip... and just thought maybe there might be an advantage under the hulls also.

[water addict]

I think the golf ball dimples work because of the spin of the ball- the top of the ball is spinning away from the direction of travel, the bottom toward it. The dimples then increase the circulatory flow compared to a smooth ball, thus producing lift and the ball travels further.

The 12 meter Stars and Stripes in one of the America's Cup campaigns had an applied "shark skin" or "riblets" as they were nicknamed. This was in sheet form and glued to the hull. If I remember right, there were tiny ribs or vortex generators roughly aligned with the flow. These generated micro-vortices which in theory reduce the thickness of the boundary layer, and hence less drag. The jury never decided whether they really did anything, or if it was just a mind-job on the competition. In any event though, this skin treatment is now against the rules in most every handicap class and one-design I can think of.

There is quantified tank-test evidence however, that just leaving a random rough surface on a ship hull increases drag. It is also difficult to keep clean from an anti-fouling standpoint.

From memory - the last olympics - the Aussie swim team had special shark skin bathers - some new material that slips thru the water easier - like shark skin (or modelled on the texture of shark skin), to trap bubbles close to the body and reduce drag etc etc.

As to the Cup yacht with shark skin ribs finnish, wasn't that the race where our Alloy tub split in half and sank?

Hmmm maybe they didn't need shark skin ribs to win - just a boat that would float till AFTER it crossed the finnish line!

Cheers!

According to Frank Bethwaite in High Performance Sailing as smooth as you can get it is best. Now and then you hear stories of how different levels of wet sanding are best but I think Mr. Bethwaite is right.

[cyclops]

Marine Biologists figured out how a near death Salmon can jump so high to clear waterfalls. Just before the Salmon jumps, it releases a super slippery slime out of the skin pores.------------------------------------------ True, the fish have not been re-programed by man yet. We can destroy another marvel if we can just genetically modify the fish somehow.

[rxcomposite]

Originally Posted by Inquisitor

I'm sure most of you are familiar with the dibits on a golf ball and that a "smooth" golf ball will not travel near as far as dibit'd ball. Reduced friction has something to do with this.

Ever heard of a golf ball coated with chapstick? It worked so well it was banned. Nike liftsuit? Same issue, page 47 to 49, Popular Science magazine, June 2002.

Seriously though, all bodies moving through air or water has a turbulent flow moving/clinging near the surface. As it moves, it drags along a second layer called boundary layer. Increasing the thickness of the turbulent flow by air injection or trapping air bubbles, the effect will be very very minimal as it still have to drag the next layer (boundary layer).

[kach22i]

Dimples, nice gimic that sells computer fans?

http://www.sharkoon.com/enghtml/fans_se.htm


Real science:
http://www.aerospaceweb.org/question...cs/q0215.shtml

[rxcomposite]

I'd like to keep the sharkskin where it will do the most good. On the deck as "non skid" surface. Marine growht is enough trouble already to roughen the hull.

[Inquisitor]

Originally Posted by kach22i

Dimples, nice gimic that sells computer fans?

I read through the website you sent and found it both extremely concise and interesting. Mainly, it fully explained to me why not to use it on a hull! To summarize for anyone else mildly curious… for a golf ball, it keeps the un-separated flow attached a “little” longer thus reducing friction. Since a boat hull approaches an airfoil shape, its doing this already. Roughing up the surface would not help at all… and as rxcomposite noted… let’s not give the little beasties something to attach to!

However, it brings up an interesting thought. For non-foil-shaped masts, it should reduce their windage and reduce the length of ineffective sail behind the mast. Any thoughts?

Just one thought..............hmmm Bergalia will like this...

Dimpled shark skin scrotum scratchers patches inside my patented "ball bras"...

Funny where brilliant ideas come from - innit?

Cheers!

[SideshowRob]

Strange, I've just been having this discussion on another site.
My question was this; would a stippled hull allow a boat to move through the water with less drag? Now everyone here has done well to answer this for me. However I have another question.It seems most people are reffering to sailboats (I think?) I am curious about power boats, does the golf ball comparrison apply at any speed, or is there a point at which a greater speed would allow the stippling to actually perform?
This is really just out of curiousity, and a friends strong feelings it works. When I refer to a stippled hull, in my mind I'm thinking of something like Rhino-Lining, which is a spray-on bed liner for truck boxes.
It's getting to the point where I may clean up the hull of my old aluminum, run it, get a GPS reading. Then go Rhino-Line it and do the same run again.
I'm fairly stubborn, but feel free to tell me I'm wasting my time. I might listen.
I'm a little lazy too, so if I can avoid exta work, even better.

[sorenfdk]

Originally Posted by Inquisitor

However, it brings up an interesting thought. For non-foil-shaped masts, it should reduce their windage and reduce the length of ineffective sail behind the mast. Any thoughts?

It's been done years ago on masts of Folkboats. These masts were wooden and for a couple of years it was popular to roll the newly-varnished masts in sand to create a rough surface.
It didn't work, so this practice has stopped.

[tom kane]

A dimpled water surface,that is flat water but many small waves certainly makes my boat feel to go faster but does not show on speedo.Just seems easier to push through the water.I paint my rudders and anti cavitation plates with hammer glaze paint it lasts well and gives a different feel to steering.It has a silicon additive.

On rembering the ocasion when we hit that dimpled water effect the speedo increased from 20 to 23 MPH. My wife and I both noticed extra speed,the fastest it ever went.The boat was an 18 foot 6 inch pushed by a 25 HP Johnson.If a hull bottom was covered in craters about half an inch deep and four to six inches across I would bet extra speed would result.