"Glenn Ashmore" writes:

It has something to do with the texture and flexibility. It is apparently a
thick coating that has a microscopic surface pattern that slime spores and
barnacles have a hard time binding to. It also flexes slightly under
varying water pressure so the barnacle cement pops off. A side benefit is
that those little bumps improve laminar flow reducing wetted surface drag.
Sort of like the dimples on a golf ball.

It is the other way around actually. The dimples of golf balls are
there to trip the boundary layer to make sure you get rid of the
laminar boundary layer.

--
Martin Schöön "Problems worthy of attack
show their worth by hitting back."
Piet Hein

On Sun, 17 Aug 2008 00:21:36 +0200, (Martin
Schöön) wrote:

"Glenn Ashmore" writes:

It has something to do with the texture and flexibility. It is apparently a
thick coating that has a microscopic surface pattern that slime spores and
barnacles have a hard time binding to. It also flexes slightly under
varying water pressure so the barnacle cement pops off. A side benefit is
that those little bumps improve laminar flow reducing wetted surface drag.
Sort of like the dimples on a golf ball.

It is the other way around actually. The dimples of golf balls are
there to trip the boundary layer to make sure you get rid of the
laminar boundary layer.

This is true.
When you hit a golf ball the loft [slope] of the clubface puts
backspin on the ball. This sucks air off the top and piles it up under
the ball. This pressure difference holds the ball up and makes it fly
farther. The dimples get a better grip on the air, so this Magnus
Effect works better. A smooth ball will go about half as far.

Casady

3M product was "riblets", used in Perth. Works and was banned. The
application of a Swedish concoction sloughed-off and left the riblets
clean. Had to be washed off and re-applied every night. Sometimes
America Cup technology does not trickle down. Them's the rules from
'86. Dry sailing is required.

On Aug 16, 6:21*pm, (Martin Schöön) wrote:
"Glenn Ashmore" writes:


It is the other way around actually. The dimples of golf balls are
there to trip the boundary layer to make sure you get rid of the
laminar boundary layer.

--
If you google riblets you will find the 3M product as an adhesive application. These were banned by the AC and the accompanying "go-fast" solution. This was in the days of "national origin" of equipment

Just reading up on golf ball dimples They evidently create a thin layer of
turbulence that keeps the laminar flow from breaking away longer reducing
the turbulent area behind the ball. Discounting the Magnus effect because
a hull does not (normally) spin, the result is less drag.

That said, it seems to follow that dimples on the mast would hold the air
flow around it further aft reducing the turbulence on the luff of the main.
Probably not much but then the big racers cut their toothbrushes in half...
:-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

wrote in message
...
On Aug 16, 6:21 pm, (Martin Schöön) wrote:
"Glenn Ashmore" writes:


It is the other way around actually. The dimples of golf balls are
there to trip the boundary layer to make sure you get rid of the
laminar boundary layer.

--
If you google riblets you will find the 3M product as an adhesive
application. These were banned by the AC and the accompanying "go-fast"
solution. This was in the days of "national origin" of equipment

On Sun, 17 Aug 2008 14:50:12 -0400, "Glenn Ashmore"
wrote:

Just reading up on golf ball dimples They evidently create a thin layer of
turbulence that keeps the laminar flow from breaking away longer reducing
the turbulent area behind the ball. Discounting the Magnus effect because
a hull does not (normally) spin, the result is less drag.

That said, it seems to follow that dimples on the mast would hold the air
flow around it further aft reducing the turbulence on the luff of the main.
Probably not much but then the big racers cut their toothbrushes in half...
:-)


The guy in the next slip to me is a serious racer, and pretty
successful at it. He talks about "seconds per mile" and I assume that
if a "golf ball" finnish would actually increase speed he would be
spending every Sunday punching dings in his hull.

Since he isn;t I suspect that dimples probably don;t effect the speed
of a boat hull.

However, boats, particularly submarines, operate in very similar
conditions as a competitive swimmer and if the new suits give them a
5% decrease in drag then why not boats? Or perhaps, why them and not
boats?


Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

Bruce in Bangkok wrote in
:

On Sun, 17 Aug 2008 14:50:12 -0400, "Glenn Ashmore"
wrote:

Just reading up on golf ball dimples They evidently create a thin
layer of turbulence that keeps the laminar flow from breaking away
longer reducing the turbulent area behind the ball. Discounting the
Magnus effect because a hull does not (normally) spin, the result is
less drag.

That said, it seems to follow that dimples on the mast would hold the
air flow around it further aft reducing the turbulence on the luff of
the main. Probably not much but then the big racers cut their
toothbrushes in half...
:-)


The guy in the next slip to me is a serious racer, and pretty
successful at it. He talks about "seconds per mile" and I assume that
if a "golf ball" finnish would actually increase speed he would be
spending every Sunday punching dings in his hull.

Since he isn;t I suspect that dimples probably don;t effect the speed
of a boat hull.

However, boats, particularly submarines, operate in very similar
conditions as a competitive swimmer and if the new suits give them a
5% decrease in drag then why not boats? Or perhaps, why them and not
boats?


Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)


Do you think the suits came before the subs - or the subs came before the
suits?

"Glenn Ashmore" writes:

Just reading up on golf ball dimples They evidently create a thin layer of
turbulence that keeps the laminar flow from breaking away longer reducing
the turbulent area behind the ball. Discounting the Magnus effect because
a hull does not (normally) spin, the result is less drag.

That said, it seems to follow that dimples on the mast would hold the air
flow around it further aft reducing the turbulence on the luff of the main.
Probably not much but then the big racers cut their toothbrushes in half...
:-)

Alu spars for monohulls used (I haven't checked this in a while) to
have a few riblets about one fourth down-stream on each side to trip
the boundary layer to stop von Karman vortices from forming. This reduces
the separation bubble on the suction side of the sail and reduces
the risk of spar oscillation in harbour.

Another approach is of course to make sure the spar contribute
to drive rather than to drag: a rotating wing-shaped spar.

--
Martin Schöön

"Problems worthy of attack
prove their worth by hitting back"
Piet Hein

I’ve been using this technique on my boats bottom for years. The
doubting Thomases in the boat yard assumed that it was because I was
just too bone idle to prepare the surface properly and that my
painting technique was lousy. But I knew better. Still haven’t got it
quite right though, a few more lumps this year and she should go like
greased lightning.

Mike.


I wonder whether this phenomena applies to boats? Should we be
attaching shark skin to our boats?

I have seen the dinghy sailors polishing the underwater surfaces of
their dinghys with 2,000 grit sandpaper and wonder whether this might
actually be the wrong thing to do.

Is there any empirical information regarding the application of this
technology to boats?

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

On Sat, 16 Aug 2008 12:38:29 +0700, in message

Bruce in Bangkok wrote:

I wonder whether this phenomena applies to boats? Should we be
attaching shark skin to our boats?

I have seen the dinghy sailors polishing the underwater surfaces of
their dinghys with 2,000 grit sandpaper and wonder whether this might
actually be the wrong thing to do.

Is there any empirical information regarding the application of this
technology to boats?

The orientation of the surface is very important in determining
whether drag is reduced or increased, thus the effect is much easier
to manage on submerged bodies like sharks or aircraft, rather than
surface craft like sailboats that are subject to varying flow
directions due to wave action, heel angle, etc.

The effect is real. The major problem in application so far has been
that the surfaces are fragile and easily damaged by things like
slings, collision with minor debris, etc. It's not worth it outside
racing, and the RRS prohibit it.

Ryk