Relation between skin friction and speed

can it be bought in gallon cans?

 

or is it some sort of shark skin tape?

 

Hi there, I thought this forum was to enable folks to draw on one another experience? Clearly not. Bye bye from here

 

BYE

 

So many people claim so many things.
Very few actually do what the claim ....

 

Henrik,

For a guy who's not going to post any more, you sure post a lot!

I wish you well on your adventure my friend.

Kind regards,

-Tom

 

No, this Forum is mainly to express our own biased opinions. Not to back up yours.

One must understand that most of us are mentally instable, physically already halfways gone, and educationally second graders. Many don´t even manage to leave home without adults assistance, hence our massive presence here.

Therefore, there is not much to draw from us, especially not experience.

But our wives enjoy that we play with the computer instead of criticising their housework.

And we prefer your nagging over theirs!

So, everything is good, except your assumption.

Regards
Richard

with the assistance of my 26 year old granddaughter who can already read and write

 

ROTFL !!!

 

No answer to the challenge

Although this discussion early on took an unfortunate turn, the really interesting thing is, to me, that NO ONE has been able (or willing) to suggest a mathematical relation between friction and speed.

If I had started out saying that my product would reduce friction by 3% maybe the discussion would have been more fruitful.....

Henrik

 

Have you all notice that certain people around here never sleep. Some have never been on a boat, and some never leave. As for me I log in at least twice a day to see what new scheme Questor or some other nut/dreamer is think about. I am hoping that this time they really got a good idea and see if Apex finally loses his temper. rofl...

 

If you had a question about mathematical relation between friction and speed you should have just asked for help with out a "product" coming into the equation.

Do your research, gather the information you want then when you mention your product be ready for bashing and be ready to justify your finding with knowledge data and statistics.

If i had a product like yours i would not be hiding in the shadow pointing fingers i would be grinding through stone to prove what its worth. Life aint easy and cutting it needs a whole lot of hard grinding work,

My 3.3534 cents ...

 

what I question is if the product was tested at a university, how was it tested without know the answer to his question?

 

Geez, Richard, why didn’t someone tell me that before? Only 2 out of 3: no wonder I have a problem fitting in around here ...

Henrik, we keep telling you the relationship cannot be expressed mathematically. What you need to do is select a hull, input its lines into a computer application for hull design with hydrodynamic analysis capability, run the resistance subroutine and look at the results in graph form. When you do this, note that the friction component predominates at low speed and rises more or less linearly. A given speed you can determine the friction reduction from using your product. Then see how much the speed can increase if the total resistance is increased by the same amount. At the speeds that most boat folk are interested in, the total resistance will be rising much more sharply than the friction alone, so a small reduction of friction will return only a small increase in speed.

Here is a worked example for my canoe design currently in development, which is an adaption a classic canoe dating back to 1893:

Total resistance at 4 k: 4.6 lb
friction component: 2.5 lb
3% reduction 0.075 lb
Slope of total resistance at 4 K: 5 lb/k
Increased speed 0.075 / 5 = 0.015 k = 0.375%

The percentage speed improvement is less than the percentage friction reduction because the slope of the friction component is less than the slope of the total resistance at the 4 k speed. 4 k is about 80% of the hull speed for this boat: at higher speeds the improvement will be even lower.

Constrast that with the speed improvement at 2 k; at that speed it will be about 2.7%, which will illustrate how non-linear the relationship is. This relationship will not hold true for any other hull design. This hull has the same underwater form as the classic boat which inspired it, stretched by 11%. That seemingly insignificant increase in length is sufficient to change the relationship significantly.

Please stop complaining about the advice you are getting; you may care to note that it is consistent in all posts that trouble to take your claim seriously, which should be an indication to you that we are giving you the best information that we can. It is not personal, we are not the enemy, the enemy is hydrodynamics.

I am trying to tell you that there is a lot of work involved, it is not our job, it is yours. You seem not to know how to proceed: the above example tells you how. Note that, while the amount of time to input lines data into an suitable computer application is not excessive, it does involve a fair amount of learning time to master the application.

Again, good luck. Now it is time for YOU to do the hard work! One caveat: the computer applications are only approximations; for accurate results you will need to perform actual tests ...

 

It's all very well described and no mystery. You can look up the mathematics involved to model the systems. But they are systems of PDE's

It all depends of the Reynolds number, below around Re 4000 the surface roughness isn't so important, above this it has a significant effect and the shear energy within the fluid layers and is related directly to surface roughness.

There's books galore in basic hydrodynamics that explain all this.

Any bonofide lab test would show the Reynolds numbers and the resistance and you simply have a family of curves for different surface roughness.

In this case one for the applied product and one without.

From those curves you can deduce your own mathematical constants for the relationships if you know the surface roughness.

Without publishing those curves no-one will take the product seriously.

 

wow the magic skin coating !!
Skin friction is a major for hi-speed race boats and its why tunnel boats work so well because they ride on a cushion of air that lifts the almost completely hull clear of the waters surface