Relation between skin friction and speed

I have a new idea but I'm not telling

 

Jenny Giles: you have by far the best response yet. I love Aussie humor....or do you spell it humour? LMAO

 

Again, no reply to any questions (of course he's under no obligation either, though he did start this thread) all of which were reasonable and easily could conceal the product secrets. How about telling us how it was tested. How were the tests setup, what scale, how was "slipperiness" determined, how far off the surface of the test object was the test(s) conducted? I can think of a few dozen, quite innocuous questions that would help support your notions and product without compromise, but yet you have found it necessary to run away, with what I would classify as mild banter. If this is all it takes . . .

If you are this sensitive to debate about your product, you are clearly the wrong person for the job of presentation and explanation.

I'll tell you what, I'll bow out and let you have this thread all to yourself. How's that sound? I will not make another post here on this thread without your express permission. We'll see how long it takes, before someone else smells what I (which easily could be mistakenly) have a whiff of.

Someone can send you an email telling you of this grand event, your evil nemesis has left the thread.

 

I don't like marketing with secret research that is quoted but not substantiated. It has the hallmarks of a dodgy marketing campaign.

Look at all the coatings that have been sold for propellers over the decades, low friction high efficiency and there are some quite refined products now.

This product is probably a spray on low energy water repellent surface and sounds like just another wax coating.

There are some coatings which are expensive to apply which work very well. The problem is keeping them adhered to the hull and in seawater the surface must also resist fouling. So far the cost benefit ratio makes them inapplicable for most applications. The next best approach is a smooth surface with a low micron finish.

Some hydro canals have had their flow rates increased considerably by the application of specialist low friction coatings, based on high density Poly's and Teflon type products which adhere to concrete. In test section s of Hydro canals here there was a very noticeable drop/increase in flow height/velocity. It stimulated interest amongst some NA’s but the conclusion was that you’d have to coat your hull with something like cement before the paint would stick. But the future may be in coating a hull in HDP's of some description for reduction in friction and more importantly self cleaning reduction in resistance.

 

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When I was sixteen I saw a material called "Super Glide" written up in Popular Science or Popular Mechanics. Used on an outboard they claimed a 10% increase in speed. The stuff had molybdenum disulfide powder in it. Anyway, I had a big race coming-the 65 or 66 Southeastern Districts in Montgomery,Alabama so I could not resist ordering some of the stuff. It was incredibly slick to the touch. My brother and I both used the very thin gray paint on our boats and practiced and practiced in the lead up to the Districts.
I won 5 out of 5 races by large leads and I was a candidate for a lot of vitriol after the race. What saved me was that my brother got 3rd place instead of second. I was out of racing for about 5 years and never heard of "Super Glide" again...Was that what you were referring to, Tom?
Looking back on it I'd have to say that the stuff......didn't hurt me any! I might buy it if I could find it-can't help myself......

my boat in 67-singlehanded w/o the jib:

 

Doug,

I may have spoken to quickly. The stuff may not have survived several moves and storage rearrangements over 40 years. Anyway, I could not locate it. If I remember correctly (not a sure thing), it was called something like "Poly go" and was discussed in the main sail racing magazine of the time, "One Design and Offshore Racing". That magazine morphed into "Sailing World", I think.

I coated the bottom, daggerboard and rudder of my Windmill before trailing to Lake Norman for a Championship regatta. It rained on the 100 mile trip and the boat arrived with a lot of road grit coating the bottom. I washed most of the stuff off in cleaning the bottom prior to the races. Between races we were all anchored for a while waiting on wind and one of my main competitors swam over and grabbed at the rudder. I thought he would have a heart attack when his hands could not grip the rudder because it was so slick. My wife crew also pulled the DB up and laid it down wet in hull bottom. That made the bottom so slick that it had to be cleaned before it was safe to move about in.

I can imagine what a capsized boat might be like and never used any of that stuff again..

Anyway the theory still says that flow velocity at a surface in fluid is zero. That needs to either be accepted or proven false before any coating that does not improve surface smoothness can reduce surface friction.

 

Ad Hoc: agree entirely: I thought I excluded planing boats from my discussion.

Henrik: I didn’t receive your PM, however good luck with this no matter where it leads you! I don’t know much about the Tech. University of Munich but I know that they work with the Max Planke Institute in Munich, where I have spoken once or twice, and that is World Class so I have no doubt about its quality. On another topic, I’ve learned not to take forum comments too personally and to never reply in kind. If you read PAR’s comments in post #12 and mine, they are essentially both stating that a lot of patient analysis is required, and that it is your job. If you need help with proceeding with those, just ask!

Tom, MoS2 was called Molyslip long ago in the UK at least.

 

My supervisor says that I owe the original poster an apology.

"If massive boundary layer separation is induced on the aft half of the hull, the shear stress drops to zero, and therefore the skin-friction is zero over that region. In other words, the skin friction could be halved."

He also said he will endorse the product and/or service if some minor difficulties to do with form drag can be overcome.

 

Jenny
Drag reduction through base flow separation is not the aim of his coating. It would delay separation and keep the flow attached but laminar. I suspect it's just another wax product in his case.

Sometimes when attached laminar flows separate they create their own problems and an attached turbulent flow might actually be a better option.

 

Yes, but it would controlled by the pressure distribution around the body (in other words, by the hullform), the coating would serve only to ensure a smooth surface finish - so any smooth coating or varnish would do the job.

 

My supervisor was joking! He just wanted to show that it's possible to reduce the skin friction by half, not that it was practical or sensible.
The actual product is nothing more than snake-oil at this stage.

 

No he was not (or maybe he did, but just a little bit).
He was talking about the Stratford pressure recovery criterion, used in airfoil and submarine design. It is controled by the body shape, as I said in the previous post.
Not very usable in hull design for surface vessels (apart rudders, keels and bulbs for racing sailboats), because a resulting hull shape would have an odd and unfavourable volume distribution (with probable balance/trim problems and increased wave drag).

 

Hi Ad Hoc,

I actually did not want to reply anymore as the spirit in this forum is totally out of my wishes. I just wanted competent response to my basic question.

There is a full 32 page report from the Munich University and of course I can not share that.

All the best - Henrik

 

If you cannot share this, then there is little point anyone commenting upon a "claim" and little point you suggesting how "wonderful" the product is, since there is no evidence other than your post claiming it to be so.

I have published many technical papers in international journals etc. All go before peer review before publishing. Without this mechanism, anything i say, its just an opine. Ergo, without you publishing the 32 page report publicly, you will get nowhere fast.

 

Just another example of a perfect introduction to the cruel world of bd.net.

Claims, and the desire to get a preconception confirmed, if that does not happen, we are all unacceptable.

Every week again................