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Chas H 10-14-2016 06:20 PM

Riblets
 
Shark skin is covered with microscopic patterns called dentricles, which help reduce drag and keep microorganisms from hitching free rides. NASA scientists copied the patterns to create drag-reducing patterns they call riblets. They worked with 3M to adapt the riblets to a thin film used to coat the hull of the sailboat Stars & Stripes, before the riblets were banned in 1987. Apparently the America's Cup race has since reinstated them.

I'd like to hear of any personal experiences with riblets. I'm sure the film is expensive, but wonder what it would cost to cover a 24.
- CH

bobperry 10-14-2016 06:32 PM

Re: Riblets
 
Riblets were tried on AC boats about 35 years ago and were thought to be helpful. I have not heard anything about them since. I suspect not.

overbored 10-14-2016 08:49 PM

Re: Riblets
 
whats the point. if they are legalized on race boats then everyone would have them and then there would be no advantage, except to the riblet salesman. when I was in college we tested them on a Rowing Shell and they do work and they were made illegal to use in a race. decreased 2000 meter times from 6 min. to 5min. 48 seconds. about 10 to 12 seconds for 2000 meter race. Putting them on 24' boat would increase your speed from 5 Kts to 5.001 Kts. if you want to go faster spend your money on new sails.

midwesterner 10-14-2016 11:09 PM

11 Attachment(s)
Quote:

Originally Posted by Chas H (Post 3698922)
..
. called dentricles, which help reduce drag and keep microorganisms from hitching free rides.

But what about the other part of the question. That could be worth it if it works.

RichH 10-14-2016 11:23 PM

Re: Riblets
 
Quote:

Originally Posted by overbored (Post 3699186)
Putting them on 24' boat would increase your speed from 5 Kts to 5.001 Kts. if you want to go faster spend your money on new sails.

Thats nice; but, if you win a race by a mere 16.75" over your nearest and otherwise equal competitor, you still WIN the race.

The same prohibitions have long ago been issued against the emissions of detergents and other surfactants that reduce the surface tension (hence friction) of the water to hull boundary layer interface. Those that did 'soap their hulls' also won races; but, with a wee bit of sudsy wakes.
Tunnel-hulled boats that trap air under the hull are a bit faster than flat bottomed hulls, too.
For years, I used Holly Speed Wax .. a wax fortified with PTFE/teflon and probably won a lot pewter because I was 'inches' faster.

Sailboat racing is a game of constantly and consistently gaining inches.

Stumble 10-15-2016 02:06 PM

Re: Riblets
 
They were banned because of the huge cost, not because they didn't work. It's been a long time, but first they required the boat to be dry sailed since any growth at all on the film (even algee) made them worse than bottom paint. And as I remember it the dry sailed boats had to replace it every couple of days too.

No one wanted this to become part of the lexicon, it was just too expensive, and the gain was enough that it really mattered. Basically it added $1,000/day to racing, and those who could afford it got a massive gain, but even the people who couldn't afford it didn't want to pay that much

Ulladh 10-15-2016 04:15 PM

Re: Riblets
 
Would it be possible to apply a textured surface using a hard bottom coat with a "riblet" textured roller if such a thing existed?

RichH 10-15-2016 09:07 PM

Re: Riblets
 
You'd need a more finely design than a textured roller, as riblets are vee grooves just a few thousandths of an inch deep. Most disclosed data from the time of '87 AC race was that riblets could possibly decrease overall drag/resistance (theoretically) by up to 8%; and, the bulk of the drag reduction was probably occurring at the first 30% of a hull/foil's length.

So without a 'textured roller', you could probably approach the form and shape of riblets simply with an '(very) open-coat' ~100-120 grit sandpaper ... IF you could maintain a constant pattern in a single pass of the paper and correctly aligned parallel with the flow of water along the hull/keel.

BUSINESS TECHNOLOGY - ADVANCES - 3M Coating Aids Yacht In Cup Effort - NYTimes.com

FWIW - Back in the late 80s, I tried the 100 grit open-coat paper on a burnished smooth teflon bottom paint (on a Melges-20 scow); and, found no noticeable difference (but one doesnt get much wake nor turbulence from a tunnel-hulled 'skimming-dish' scow, anyway). These scratches did promote faster fouling if the boat wasn't dry hauled.


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