Which is Faster, Smooth Hulls or Rough?

[thinwater]

Reducing drag is one thing. Maximizing lift on the keel and rudder are another. Air may help on the bottom, but I'm quite sure ventilation is a disaster on the rudder (ask anyone with a >15-knot boat).

If you want a visual demonstration, try the spoon trick under running water with different finishes. Smoother is always better. Don't listen to us--try it.

 

[jviss]

I wonder how many who have replied to this post have actually read the linked article. I have. It seems to me few others have.

 

[jon hansen]

i read it. it seems to say nothing of value. is 2000 grit sanding rough or is a 15 year old pimply faced boy's skin surface rough. and where is the air they talk of coming from. i learned nothing from that article. i need to find a teenager and ask them cause they know everything.

 

[Crazy Dave Condon]

Concur with Jackdaw based on the hundreds of bottom painting and repairs to hulls I worked on as a former dealer and sailing them afterwards.

 

[Jackdaw]

I wonder how many who have replied to this post have actually read the linked article. I have. It seems to me few others have.

Probably. Like I said, people have been looking into this for years, but little makes it out of the lab. Often it works in sterile water, but looses its effectiveness in less that a day in the sea due to marine growth.

Anyway it’s specially prohibited in the Racing Rules of Sailing.

 

[Don S/V ILLusion]

"Dimples on a golf ball create a thin turbulent boundary layer of air that clings to the ball's surface. This allows the smoothly flowing air to follow the ball's surface a little farther around the back side of the ball, thereby decreasing the size of the wake. A dimpled ball thus has about half the drag of a smooth ball."​

https://www.scientificamerican.com/article/how-do-dimples-in-golf-ba/

Itsk not worth digging too deep into the theory on a sailing forum but the article omits the considerationthat most decent golfers impart spin on the ball to enhance flight path and control without which the ball would not travel as fast.

 

[jviss]

Itsk not worth digging too deep into the theory on a sailing forum but the article omits the considerationthat most decent golfers impart spin on the ball to enhance flight path and control without which the ball would not travel as fast.

I agree it's off topic, but in fact, according to my knowledge, spin reduces distance. Here's an article supporting this:
https://www.golftipsmag.com/instruction/quick-tips/reduce-spin-add-distance/

p.s. I play golf, though not nearly as well as I would like!

 

[Don S/V ILLusion]

I agree it's off topic, but in fact, according to my knowledge, spin reduces distance. Here's an article supporting this:
https://www.golftipsmag.com/instruction/quick-tips/reduce-spin-add-distance/

p.s. I play golf, though not nearly as well as I would like!

We'll probably get kicked off the forum for discussing golf...but -
Note that article implies an ideal spin rate below 3000 rpm, not zero. And the spin direction is equally critical.

 

[AlastairLC]

Skin of a sailfish, fastest fish in the world (can do 60 mph).

Not smooth.

 

[Crazy Dave Condon]

This is one thread to discuss at the end of the day over drinking grog

 

[BobbyFunn]

Skin of a sailfish, fastest fish in the world (can do 60 mph).
View attachment 153899
Not smooth.

This falls into the v-shaped protrusion "shark skin" category. Nice rabbit trail. It appears those protrusions offer an evolutionary advantage in biological cases where the surface is under constant replacement like shark teerh.

On a boat the surface would never replace, only fill with crud or be damaged by cleaning. Maybe there will be a paint that can be applied that has the v protrusions as particles. When the paint dries the particles will stack and align. As the paint wears off, new protrusions are exposed.

The air lube model propbably fits the same paradigm as slime on fish scales.

Air lube wont work on sailboats. It takes energy to make the bubbles and pump them in the right locations. The energy will come from what? The wind. Any effort to deflect air under the hull will result in energy taken away from speed. Now, find away to convert heeling into airlube and you might have something.

 

[kloudie1]

Skin of a Hunter 34.. has gone up to 12 knots while surfing some big waves!

 

[shemandr]

I have a book titled The Physics of Sailing. I need to drag it out. There was something in there about hull finish smoothness. The author held that any more smoothest that could be attained with a certain grit of sandpaper was a waste since the physical properties of water prevented the water from "Seeing" the smoothness. I'll see if I can find the book and re-post with a better rendition of the author's argument.

 

[jviss]

It takes energy to make the bubbles and pump them in the right locations. The energy will come from what? The wind. Any effort to deflect air under the hull will result in energy taken away from speed.

You don't know which will have the greatest impact on speed. Maybe wind is better spent on bubbles.

 

[jviss]

I need to drag it out.

Pun intended?

 

[Jackdaw]

Skin of a sailfish, fastest fish in the world (can do 60 mph).
View attachment 153899
Not smooth.

But what precisely does that prove?

 

[Crazy Dave Condon]

I know Gin and tonic is smooth compared to the roughness of pros and cons of this thread. Having a bad hair day reading this thread

 

[BobbyFunn]

any more smoothest that could be attained with a certain grit of sandpaper was a waste since the physical properties of water prevented the water from "Seeing" the smoothness.

I experienced similar results while in high school looking for dates.

 

[AlastairLC]

But what precisely does that prove?

It doesn’t really prove anything, but I think it’s interesting to ponder, as natural selection rewards efficiency, why are the skins of the fastest swimmers bumpy?

 

[BobbyFunn]

It doesn’t really prove anything, but I think it’s interesting to ponder, as natural selection rewards efficiency, why are the skins of the fastest swimmers bumpy?

Dolphins have smooth skin and they can go fast as well. They are new creatures so nature went a differnt tack. No disposable scales but instead have disposable skin cells. Dolphins replace their outer layer every 2 days. Probably the best analogy for boats.

Cool article suggest dolphins could swim faster but cavitation hurts them. Tuna and fish dont feel pain in tails, but do have pitting from the destructive forces of cavitation just like propellers