Ceramic coatings

I have heard scuttle butt that ceramic coatings (finishes) have been used on bottoms of sailboats to enhance (reduce) drag. I think there is an Opti builder that touts a ceramic treated bottom. Might make sense, but for a few aspects. Any experience out there? Thoughts and comments? Thanks, Chaos

 

"Hydrodynamic drag, also called quadratic or pressure drag, has a quadratic dependence on the velocity of a moving body. Quadratic drag does not depend on the viscosity of the fluid; instead, it depends on the density of the fluid and the cross-sectional area of the body exposed to the flow."

I'm not sure if hydrodynamic drag depends on the roughness or smoothness of the hull.

 

At certain Reynolds numbers, a rough surface may postpone separation earlier and reduce drag. But not likely at the speed of a sailboat and the hull shape inhibits separation.
If you ever find the manufacturer that makes such claims for sail boat, please add it into the thread.

 

One of my previous guys works for a ceramic coatings company in r and d. They are predominantly involved in dod, aerospace and firearms. However he has sent me various things to test over the years, usually things they developed for another industry that didn't work but he thought in testing would have some marine success.

So far I've only applied it to three things, and quite frankly they haven't had enough time on board to prove they are of utility.

Seems like all the good ones need a heat cure, or at least that's been my takeaway. Seems like they certainly have a utility, lord knows he has a pretty neat list of clients. However I'm not positive they are the panacea they have been sold as.

 

Thanks for everyone's reply. This is interesting. I continually re-read Frank Bethwaite's book "High performance sailing". He and his group have performed a lot of testing on hulls, rudders, and keels on dinghies. Invariably, the smoother, the more polished, a wetted surface was, the faster the boat was. I have also recognized that when I refinished the hull of my own boat with the final finish of Pettit's Black Widow, and wet sanded and polished, my boat was incredibly faster. Some of the commentators must not own sailing boats! I am way down the road now, but at one time I studied aero engineering. Aero/hydro, what is the difference? I switched courses, and graduated with a degree in Physics! I appreciate the information by the commentor's, and I very much appreciate the mathematical and physical evaluations, but practical experience in the world says the smoother the bottom, the faster you go.
So, my question is, does ceramic coating (waxing) applied to the wetted surface of a sailboat, improve (reduce) drag?
Thanks,
Chaos

 

If you are referring to the frictional resistance of a hull, it is obvious that the more polished the hull, the less frictional resistance it will offer. The force called "drag", as I understand it, has very litle to do with friction.
As a curiosity, I would like to point out that the great, enormous difference between ships and airplanes is that the former move partially submerged in two different fluids and it is the interface between these fluids that gives rise to waves, which are the ones that generate the greatest resistance to the advance of a ship.

 

OK, if you must, would ceramic coating reduce the FRICTIONAL resistance? Simple question; does ceramic coatings on wetted surfaces of sailboats improve performance or not?

 

To that question the answer is perhaps. It is a function, as Barry said, of Reynolds Number, viscosity, and surface roughness. However, it is subject to fouling, water debris, oiling, whale snot, etc....so like riblets, polishing, and other boundary layer manipulations in ideal conditions they are measurably effective, in the real world...not so much for the added cost and maintenance. You'd get more bang for the buck with new sails every season/race.

 

That is all very interesting, especially the whale snot. But, I still do not have the answer to my question. Chaos

 

The answer for all but the most elite sailors and massively funded campaigns is NO. Ceramic coatings will not make anyone a perfect sailor in perfect wind and water; which is the only place any quantifiable speed enhancement has occurred. They are costly (mainly in time) to maintain and hard to strip. They give little, if any, sailing performance gain outside the lab to the vast majority of sailors and the their vessels. Setting sailing performance aside, there is some benefit to cosmetics above the waterline, and as our President-elect would say..."everyone knows"... that a good looking whatever is ..."obviously"... a "better" whatever. Paint on the pig....

 

Well, finally, I have some input as to "do ceramic coatings on the wetted surface" enhance performance. Thanks, jehardiman. But, please, I think I can decide where my performance enhancement needs are and where they are adequate.

 

Think of it this way, a coating surface effects the last 2.5/10,000" to 5/10,000" of the surface (coatings generally being 1.5 to 2.5 mils thick). That means the hull you put it on must be within 1 to 1.5 mils of ideal 'true' for the coating to have any real effect; so realistically your hull skin needs to be glass smooth with no ripples over its entire surface. The lab tests are done on perfectly flat burnished surfaces and the quantitative differences between two separate, but measurably equal, surfaces can be 25%, and boundary layers on full sized sailing vessels can be 4-5 inches thick. There is too much debate about this region and the data to ever say that a specific method or coating make real quantifiable difference on Cf. See the following thread from several years ago.

Skin-Friction Formulas https://www.boatdesign.net/threads/skin-friction-formulas.31280/

 

Jehardiman, thank you for taking the time to put the information together for me. I can understand your position considering the thread you included. The inconsistencies and variabilities in CF do seem large.
I view the ceramic coating (CC), as I understand it, not really a coating but a group of particles that fill microscopic voids. Hence, the reason CCs do a wonderful job on any painted vehicle to create a beautiful finish. My curiosity here is can CCs do the same for extended length of time on the bottom of boats which would help keep the finishes smoother longer. Would one be able to shorten the bottom prep by not having to sand incrementally down to 1200 grit (or finer)? Could we stop at 600, apply CC and get the same results? And yes, one must try to get the hull "true" to shape to get performance no matter what procedure one uses. And yes, hard to do and requires a lot of elbow grease. But, I think you attempt to get there the best you can. One cannot say "it really does not matter anyway" or you will get so sloppy, your vessel will never perform. How smooth is too smooth? How "true to shape" is close enough? Hell if I know.
Thanks again for the information. Is whale snot the magic bullet?
Chaos
PS: As Comfisherman noted, there are lots of ceramic "coatings" and applications. I have used ceramic coatings on pistons in internal combustion engines., as an example. Here, I am referring to the liquid form with silicon dioxide and/or titanium dioxide the auto finish industry calls nanoparticles.

 

Depending on the location, early start of turbulence can be beneficial. If the vortices are smaller, the drag is less. Flow separation is a given on a boat. It is caused also by pitching, rolling and yawing. The question is over-simplistic. Speed, submerged shape, whether it is a foil or not, etc. all affect the resistance, lift and other forces.

 

As I understand, for small boats, dinghies, laminar flow will extend farther aft. For larger, laminar flow occurs in the fore 1/3 or so and is turbulent farther aft. So, important to have a smooth bottom in that front portion. Your point being, this is very speed dependent, and a multitude of other factors. Understood. Thanks for the response, Gonzo.