Quote:Originally Posted by Ad Hoc Y

Quote:
Originally Posted by Ad Hoc
You are mistaken in the understanding. I see you’re from Finland, so perhaps English is not your native language. But you are mistaken in your comprehension of what “whisper spray” is, from reading the papers.
English it not my native language (is it yours?), but I have no problems reading papers in English. I have studied English 14 years at schools and university and all the books we used at the university were in English.

It's not whisper spray, it's whisker spray. The name comes from the look of the spray, which resembles whiskers a cat has.

Quote:
Originally Posted by Ad Hoc
There is no allowance for that sheet of water that is attached to the hull, but is fwd of the stagnation point..that is all it is, nothing fancy at all. So what area is this…how do I calculate it..and what effect does it have on total drag??
That is covered in the paper by Savitsky et. al. from 2007, which I linked earlier (http://www.stevens.edu/ses/cms/filea...Prediction.pdf). I have the whisker spray drag model in my own VPP.

Quote:
Originally Posted by Ad Hoc
I fail to understand how you bring spray rail geometry into this?? As you now seem to equate this whisper spray with spray rail geometry and the amount of radius on them…why?

Spray rail location locations effect the amount of whisper spray, but has nothing to do with the radius etc of the rail.
Spray rails do not effect the amount of whisker spray, they jut separate the whisker spray earlier from the hull and point the spray to a different angle. You may have less visible whisker spray, but the total mass flow is not affected.

The radius of the edge of the rail (not the end) has a big effect on how well the whisker spray is deflected away from the hull and how much energy is wasted to the deflection of the spray.

Quote:
Originally Posted by Ad Hoc
This comes as no surprise when you obverse any planning hull on the water which has no spray rails. However if you add spray rails, what happens, you minimise the effect of whisper spray and on higher Fn boats you can improve the lift/drag ratio of the hull as the hulls ride on the spray rails as their lifting surface rather than the whole hull…that’s what racing power boats do (it increases their L/B ratio)…again, watch any planning hull on the beach it is isn’t rocket science to see why, all you’re doing is minimising that sheet of water, which appears to be called whisper spray by some.. That is what spray rails are supposed to do!. But to put this simple phenomenon into a technical paper, one ends up not seeing the wood for the trees!
Yes there are two functions for the rails, which often run all the way from the bow to the transom. Near the bow (or quite close to transom at very high speeds) they work as spray rails deflecting the whisker spray away from the hull as early as possible. Near the transom the rails work as chines allowing the actual chines come off the water at high speeds and greatly reducing the wetted surface. In some racing boats there are actually no real chines at all. In Finnish these rails are often called "lifting rails".

My VPP takes both of these effects into account and can thus predict accurately resistances at high speeds as well, which is no true for most Savitsky based programs.


There is not much difference whether the rail function as "a replacement chine", a whisker spray reflector or is just under water. It still needs to have a sharp edge to minimise drag.