Super-hydrophobic shell coating

[Alistair]

I know there are rules against this. But there seem to have been big
advances in (super)hydrophobic materials in the past few years.

I'm thinking of the one which are essentially lots of teeny-tiny hairs.
Youtube "superhydrophobic" for some impressive demonstrations.

Anyway, anyone care to hazard a guess to whether a boat would benefit
from this stuff?

[Kit Davies]

Just for reference, here is a thread on this topic from 2011
https://groups.google.com/forum/?hl=en#!topic/rec.sport.rowing/NsZ1fbct1X4

[Alistair]

Kit Davies wrote:

>> Anyway, anyone care to hazard a guess to whether a boat would benefit
>> from this stuff?
>
> Just for reference, here is a thread on this topic from 2011
> https://groups.google.com/forum/?hl=en#!topic/rec.sport.rowing/NsZ1fbct1X4
>
>

Thanks, but I think that may have been riblets or something similar: the
theory behind them is to make the water stick to the boat longer before
breaking up. Or something.

Anyway, if you can feel it like sandpaper it's not the same thing -
superhydrophbic materials feel really smooth, although microscopically
they're not.

[tcyr...@gmail.com]

A number of years ago my wife's tennis partner was a physicist who had helped develop the paint for US fighter jets. It's important property was microscopic spheres in the coatings which cause the vortices that reduce drag. He claimed that it would also work on boats (perhaps the Navy uses something similar). At that time, (the 1990's,) it cost $800 per US gallon. Not sure if it's banned today or not.

[thomas....@googlemail.com]

this article talks about ultra very dry on boats

http://www.pocock.com/wp-content/uploads/2013/08/pocock-floating-on-air.pdf

[Alistair]

thomas....@googlemail.com wrote:
> this article talks about ultra very dry on boats
>
> http://www.pocock.com/wp-content/uploads/2013/08/pocock-floating-on-air.pdf
>

Yeah, I'd sort of figured most of that out when I had time to think
about it. However, there are some useful side-effects of using a
hydrophobic coating elsewhere on the boat:

* the water that slops up onto your canvas would instantly roll off.
* if you used the coating inside the shell, any water coming in would be
much easier to mop up with a sponge or something
* when you turn the shell upside-down to empty it out, it would all leap
out in a most satisfactory way
* it would be useful to have on rowing kit, which (in a cold climate
where you're wearing a few layers and leggings) is probably a few kilos
heavier after a wet/rainy outing for each rower.

But, I also wondered about putting it on oars and shafts (afaik this
isn't banned). Not because it would make the oar-water interaction more
effective with regard to lift generation, but because when you recover
the blade there is an appreciable viscosity that might be reduced. It
wouldn't be much, but if you watch a blade extraction in slo-mo an awful
lot of water sticks to the blade/shaft.

Like here - look carefully at bow's left oar shaft -
http://ydtalk.com/jdispatch/wp-content/uploads/2012/07/London-Olympics-Rowin_Simc1.jpg

[Carl]

On 10/01/2014 14:21, Alistair wrote:
> thomas....@googlemail.com wrote:
>> this article talks about ultra very dry on boats

<snip>

>
> But, I also wondered about putting it on oars and shafts (afaik this
> isn't banned). Not because it would make the oar-water interaction more
> effective with regard to lift generation, but because when you recover
> the blade there is an appreciable viscosity that might be reduced. It
> wouldn't be much, but if you watch a blade extraction in slo-mo an awful
> lot of water sticks to the blade/shaft.
>
> Like here - look carefully at bow's left oar shaft -
> http://ydtalk.com/jdispatch/wp-content/uploads/2012/07/London-Olympics-Rowin_Simc1.jpg
>
>

Is that an adhesion or a dynamic effect you see there?

What I do like is those finishes, already feathering during extraction.

Cheers -
Carl


--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: tinyurl.com/2tqujf
Email: ca...@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells

[Alistair]

Carl wrote:

>>
>
> Is that an adhesion or a dynamic effect you see there?
>
> What I do like is those finishes, already feathering during extraction.
>
> Cheers -
> Carl

Dunno, what's dynamic effect?

According to rsr orthodoxy, a few ms before this photo was taken water
is flowing down the shaft onwards past the blade tip (apparent by
looking at what is happening to the water on bow's right hand
shaft/blade - you can see it whizzing off the blade tip.) As he pushes
down there's quite a lot of water adhering to the shaft and what you see
here is it falling off.

My point is that on the release any water you take with you is a waste
of effort. So, if you made the material less 'sticky' then you might
gain an advantage.

[hunt...@plu.edu]

I'm the guy who wrote the article posted up above (thanks for the link, thomas). Alistair, I think you're right on with regard to the 'side effects' of a hydrophobic coating on a boat, and I've often wondered about the same things - as we know, a clean boat is a fast boat! However, I just wonder if it would be worth the extra weight added in applying the coatings (bottom and top coats), rather than just cleaning the boat manually.

I am curious about the usefulness of the hydrophobic coating on an oar shaft, but I'm not sure the benefit would be very noticeable (not that I've studied it or even thought about it in any great detail, you understand). Also, while I'm not entirely familiar with the blade/water interaction, I don't think that the lift-generation of the oar will be affected. I'd have to go back and look into it more to be sure.

And as far as I know, these sprayable hydrophobic coatings (like ultra ever dry) are NOT recommended for clothes, as skin contact can irritation (reportedly), although they do advertise it for use with boots on their website. User discretion required, I think!

Best,

Jacob Huntington
Research and Development
Pocock Racing Shells
1-888-POCOCK1 ext. 15
ja...@pocock.com

(I have to use my old school email to reply to google group threads, but feel free to contact me at my work email).

[Carl]

And that was an excellent article, Jake.

My question to Alistair concerned what is induced to move by the fluid
dynamics immediately preceding that photo & what could be said to have
been adhering. My proposal is that, as Alistair says, just before that
photo was taken the water flying off the shaft had indeed been flowing
somewhat along it. It apparent adhesion to the shaft is the consequence
of its entrainment around the shaft along which it was flowing - which
would occur, I think, whether or not there was a hydrophobic surface.
Surface hydrophobicity would doubtless help the water to bead once the
remaining surface film was sufficiently thinned & slowed WRT the surface
of the shaft for its surface tension, drawing it into droplets, to
become more significant than other processes to which it is subject, the
rest of the water having first begun streaming off the shaft under
inertial & other effects.

But, a most interesting question. I'd like to know what others think.

[RunDMC]

Apropos to this discussion, I volunteered to test an epoxy/silicone coating marketed by Wearlon Corp here on the USA as an anti fouling hull coating that they believe also reduces drag. Note that this is a hydrophobic but not super hydrophobic coating.
The test protocol consisted of a series of about 20 ten-stroke pieces from a flying start (6 strokes to build) at max pressure and fixed stroke rate of 30 with several minutes rest between pieces. All were done on days with little or no wind, and alternating direction to ameliorate any effect from wind or current. Speed Boss was used to record data from impeller. Water temperature was recorded but not controlled, and changed quite a bit from day to day. The slowest and fastest pieces were discarded, mean and standard deviation calculated from the rest.

I used my old Van Dusen with freshly sanded gel-coat for one session, then had their technician spray coat with their Super FM-1 coating and redid the tests about 4 weeks later. Results were, as you might anticipate from limitations of the study design, inconclusive. The results suggested an increase in hull speed of up to 0.9%, but some or all of that may have been related to changing water temperature and increasing fitness of the sculler over a month. The study was also unblinded and there was certainly motivation to believe that my newly coated boat was faster than before.
I have since sold the boat and heard no further from the manufacturer.

[gsl...@gmail.com]

One has to wonder about the competence of any engineer or scientist that would expect to learn anything from that test. There is no chance that you would get conclusive results from a protocol like that.

To do this you should really have two identical boats except for the coating and swap between them. Best if you have two people seat racing each other, and the rowers change boats between each piece. Best if no knows which boat is which.

[Carl]

Better still, tow a properly loaded shell, out on a long beam, ahead of
& to the side of a launch, running in flat water & with a force gauge in
the towing link. Not too hard to arrange.

But, failing that, I'd have thought Dan's experiment had value since a
sizeable benefit from the coating would probably have shone through
deficiencies in the protocol. I don't say that 0.9%, were it to be
confirmed, was insignificant since if reproducible it would suggest a
2-length advantage.

[RunDMC]

I agree the test protocol was poorly designed, but consider the context: the salesman was an acquaintance who hoped to create demand for one of his employer's products. I was the typical sculler looking for an edge who had looked into super hydrophobic materials but had neither the time nor resources to carry out a proper test program. I had one single scull with worn gel coat that was in need of a refresh anyway. I figured I had little to lose. This coating apparently has been used by speedboat racing enthusiasts with unverified improvement in results.
Since the tests were somewhat biased in favor of the coating, I think it is safe to conclude that, for this one non-super hydrophobic coating, the effect on drag is small or nil. It did, however, have some of the salutary effects on shell water/dirt shedding referenced in earlier posts.

My personal bias is that there is more promise in altering the microstructure of the hull surface than in altering the physicochemical properties, although both may play a role. The economic impact of success in reducing hull drag and military implications should continue to drive research. I don't expect the sport of rowing to play a major role here.

[hunt...@plu.edu]

Carl is on the right track here - any product that could actually produce a consistent two length advantage would be gobbled up by the top crews (and most likely summarily banned by FISA)

Also, RunDMC, consider that your older gelcoat would have exhibited considerable surface texture, and a new gelcoat, provided it was properly applied, would have done a lot to reduce some of that surface texture, thus reducing drag. Of course, I can't say that would lead to a 0.9% reduction in drag. An anti-fouling paint (or any paint, for that matter) can certainly reduce drag if once applied it leads to a smoother surface.

I think it will be a serious challenge to produce a super hydrophobic coating with the correct microtexture spacing to produce (and preserve) the desired air pockets in between those geometries and induce slip on a 57ft long racing eight.

[gsl...@gmail.com]

On Tuesday, January 14, 2014 4:39:34 AM UTC-8, Carl wrote:

>
> But, failing that, I'd have thought Dan's experiment had value since a
> sizeable benefit from the coating would probably have shone through
> deficiencies in the protocol.

But if you did have very sizable benefit you would have never known if it was from the coating or from something else. You just don't have the controls to conclude anything.

[RunDMC]

I have to agree that the project was doomed to be inconclusive, as there were too many uncontrolled variables and not enough test data. I tried to minimize the drag of the old gel coat by wet sanding to 600 grit prior to testing, but for all I know that is a poor surface compared to a fresh gel coat. Well, I've shared my data, now it's on one of you to do it properly and report back, what say you ?
Dan

[ja...@sylphidetechnologies.com]

Certainly with Carl on testing procedure.

Great topic
Just another angle on this,


Quote:


"...My point is that on the release any water you take with you is a waste of effort. So, if you made the material less 'sticky' then you might
gain an advantage..."

I agree 100% that water lifted above the relative waterline around the shell, but cleaver blade shape (compared to the old Mancoons) is having the handle/pin force leveraged from the blades position; and some stage towards the later part of the stroke ( maybe 30%?? Different for all boats etc) the back of the blade face is being held in place by the low-pressure body of water. I remember when we switched to cleavers, we really modified holding the finishes. As always, just my take on it, would be keen to hear other thoughts down this path.
Best
James