Dimpled speed

[Neil Gordon]

How about if we sell advertising space on our hulls?

You're thinking below the waterline, yes? So the ads would only be visible when the opposing rail is buried. Hmmm... I'm thinking that given the prevailing winds, stbd side ad space would sell at a premium to the port side.

[Neil Gordon]

Both air and water are fluids, so why shouldn't dimples in your bottom paint be just as efficient as dimples on a golf ball?

Why am I thinking that having a tiller vs. a wheel will somehow work its way into this discussion?

[Parfait's Provider]

Maybe the velocity has something to do with it? The viscosity? Maybe we should try driving wet golf balls? Could be a secret weapon to use against an opponent, but I can't quite figure out how to wet his and not mine. Maybe we could drive the balls further under water? Do balls drive longer in the rain? In high humidity? In the desert? At high temps or low?


So many questions, so little information.

[tartansailor]

Far be it from me to burst any person's preconceived notions, but for an authoritative treatise on bottom finish for speed, may I direct your attention to: SAILING SMART Winning Techniques, Tactics, and Strategies By Buddy Melges (The guy that won the America's Cup a while back) and Charles Mason. Henry Holt Co. NY 1983 p.52 "Preparing the Hull".

Cedat Fortuna Peritas

Dick

[John Vigor]

John,

By George, I think I've got it!

Your upcoming title must be: Nautical Myths and the Sailors Who Will Die Defending Them.

Yes?

But David, David, excuse me but this is not a myth. It's absolute fact that a rough-skinned golf ball produces less drag than a smooth-skinned golf ball. There's no myth about that. That's why a dimpled ball goes faster, farther, and higher.

If you take the hull of a boat as half a golf ball, a not unreasonable inference, why shouldn't a rough bottom provide equal benefits to the speed and windward ability of a Cape Dory?

To wit: why spend time and money trying to smooth your bottom paint?

I recognize that some people scoff at my theories, and that's their right and misfortune. Nevertheless, I was greatly hurt by the rejection by many of my theory that a fixed propeller creates less drag than a spinning propeller. (Sniff!). Excuse me. The tears still spurt. But I soldier on bravely, shouldering life's little setbacks with quiet equanimity and a steady grinding of teeth.

If I may be permitted a brief revisit of the propeller theory, I'd like to mention a beautifully simple way to prove it. I believe it was done by a British boating magazine. You simply moor a boat to a buoy in a moving stream. You insert a small household scale in the rode near the bow, and watch how many pounds of drag are produced when the prop is allowed to spin, and how that number drops when it is locked in place.

But all that is in the past. Let us reflect on it no longer. Let us concentrate on our bottoms, some of which (the rougher ones) are very interesting. I don't care what Buddy Melges said about smooth bottoms helping to win races. He never had the guts to try winning a race with a rough bottom. He might have been very surprised.

What we're about here is pioneering; daring to be the first to try out a new principle.

This is the kind of gutsy innovation that made our country great.

This is the American way.

This why our enemies fear us and why our allies swoon with mute admiration.

So roughen your bottom and go for it! I'm right, and you know it.

Cheers,

John Vigor

[Len]

When I asked for a discussion on increasing speed I had no idea it would segway to golf balls. Nonetheless , lets consider the acme of speed- the race car. Who is faster the car with slicks that slip on turns or the that scuffs up its tires before racing.( Assuming a varied and unpredictable track surface-wet/dry,smooth/rough,straight/curvy.

[Lee Kaufman]

I do some whitewater paddling in kayaks. One of the innovations in kayak design is to dimple the bottom which is supposed to make the boat slide more readily through the water. Could the same apply to our CDs?

[David van den Burgh]

John,

By George, I think I've got it!

Your upcoming title must be: Nautical Myths and the Sailors Who Will Die Defending Them.

Yes?

But David, David, excuse me but this is not a myth.
Cheers,

John Vigor

But John, John, excuse me but I did not specify which was the myth and which was fact. I'll leave it to far wiser and more intelligent minds to sort out that one.

Cheers,

David

[M. R. Bober]

[quote="John Vigor"
...
I have certainly been passed by sister boats whose bottoms, I know for sure, were as rough as a goat's backside.

Both air and water are fluids, so why shouldn't dimples in your bottom paint be just as efficient as dimples on a golf ball?


John Vigor[/quote]

John,
It's a bit like a helicopter.

Every best wish,
Mitchell Bober
Sunny Lancaster (where smooth is a way of life) VA

[John Vigor]

Why am I thinking that having a tiller vs. a wheel will somehow work its way into this discussion?

Because you're a cynic who's been around the block a couple of times, that's why, Neil,

But now that you mention it, a boat controlled by a tiller will be easier to steer and keep under control. If the rudder is dimpled, as I presume it would be if the hull is, then it will be more effective. It will provide more lift for equal boat speed.

This will make the steering apparatus far more sensitive, and those of you with wheel steering will find yourselves over-steering without knowing the reason why. We all know how little feed-back there is from a wretched wheel. You'll be out of control and crashing into everything. Panic will be rife.

On the other hand, a tiller than can moved with a mere flick of a finger will give an immediate assessment of the boat's balance, and the extra sensitivity of the helm will be compensated for automatically.

I'm not against wheel steering per se, you understand. It's just that I feel compelled to point out the truth.

Cheers,

John Vigor
-----------------------------------
Prune juice shall set ye free

[tartansailor]

With All Due Respect!

Dennis has it right when he said that dimples are incorporated to promote laminar flow to lessen the drag on the aft surface of the sphere.

The aft submerged surface of a sailboat is canoe shaped. There is no turbulent flow!

For a rough surface, any micro component less than 180° will disturb the flow; that means drag.

But you are still absolutely correct in your locked wheel thesis, and I will defend you in that with all my might.

Cedat Fortuna Peritas

Dick

[Neil Gordon]

Because you're a cynic who's been around the block a couple of times, that's why, Neil,

I'll admit to being a cynician.

It's not having been around the block though; it's having been around these threads. There was also, of course, the thread about the block that I was around.

[Ed Haley]

Another school of thought comes from the DaySailer Class Racing Rules. The class will not allow a rough bottom that takes advantage of the lesser drag during racing.

"5.2 A yacht shall not have a specially textured hull surface, the intention or result of which is to reduce drag in the water. The underwater surfaces of the hull may be sanded, filled and faired and or painted."

I'd like to see how the determination was made. Maybe some elegant testing on a mooring ball.

[tartansailor]

Ed,
You are comparing pumpkins to mustard seeds.
Yes, the latest Americas Cup boats have a "sharkskin" (for want of a better term) texture that is in micro dimensions, [and of a uniform pattern] which is orders of magnitude apart from a rough paint finish
in a random pattern.
Respectfully,
Dick

[hebert01]

On golf ball dimples, here's a good article that explains the aerodynamics and the dimples contribution to ball flight in layman's terms.

http://www.titleist.com/technology/details.asp?id=19