water tension

[flraptor07]

OK I'll be the Guinea pig, I'm going to use my Q-mono. Same packs, Same prop, Same everything except not sanded and sanded. I'm even going to try to do it the same day so the water conditions are as close to the same as they can be. I'll let you guys know how it goes, I'll even make a prediction. I think we'll see about a 2.5 mph difference.

[Fella1340]

I look forward to seeing it as I am not sold on it yet!

[Fella1340]

If you pour water over the scuffed hull and it sticks to it isn't that actually creating drag? A boat moving at speed and having water stick to it doesn't seem right to me. By scuffing aren't you actually creating a larger surface area that the hull will ride on? Seems I'm the only person on this side of fence but I will continue to be the Devils advocate until shown otherwise. Smooth seems fast to me!

[srislash]

I have done both ways on a mono(a DF 35"), no GPS but it did seem 'looser'.

Jeff, based on your stand a waxed hull should be faster then correct? Pretty sure that old one was proven wrong. Are you familiar with SpeedKote? Same principle.

[ls1fst98]

A really simple test is have the shiny smooth surface, run your finger on it, it tends to stick, if you sand it with say 200 or 300 grit or finer it tends to slip right off. I always said the shark skin thing and people on tho forum jumped all over me stating it's a smooth surface, I defended it. It's a rough surface even unerring a microscope.

[olwarbirds]

Look what surfers and skiers do. Wax then sand...look fwd to test results

[kfxguy]

A really simple test is have the shiny smooth surface, run your finger on it, it tends to stick, if you sand it with say 200 or 300 grit or finer it tends to slip right off. I always said the shark skin thing and people on tho forum jumped all over me stating it's a smooth surface, I defended it. It's a rough surface even unerring a microscope.

Well in my mind the finger test doesn't really prove anything since we aren't running out boats in lakes of fingers....we are running then in lakes of water....right? I keep thinking how if you have a freshly waxed car then you pour water on it, it repels the water....and quickly. Almost like there's a barrier blocking the water....kinda like on an air hockey table, the puck glides across it...take that boundary layer away and it sticks to it. Why would I want water to stick to my hull? Seems like that's what would happen if I sanded it. I dunno...even if it does make a 2mph difference, I'll just add another cell to it to make up the difference.

What's stated above is my opinion. I have no concrete proof. Nor have I seen anyone else have concrete proof....so until someone tests this back to back on the same day....in my mind it will remain unproven.

[Grazacind]

Have a read
http://scitation.aip.org/content/aip...1063/1.4819144

[darryl whitman]

here u go guys-

Superhydrophobic surfaces have attracted much attention lately as they present the possibility of achieving a substantial skin-friction drag reduction in turbulent flows. In this paper, the effects of a superhydrophobic surface, consisting of microgrates aligned in the flow direction, on skin-friction drag in turbulent flows were investigated through direct numerical simulation of turbulent channel flows. The superhydrophobic surface was modeled through a shear-free boundary condition on the air-water interface. Dependence of the effective slip length and resulting skin-friction drag on Reynolds number and surface geometry was examined. In laminar flows, the effective slip length depended on surface geometry only, independent of Reynolds number, consistent with an existing analysis. In turbulent flows, the effective slip length was a function of Reynolds number, indicating its dependence on flow conditions near the surface. The resulting drag reduction was much larger in turbulent flows than in laminar flows, and near-wall turbulence structures were significantly modified, suggesting that indirect effects resulting from modified turbulence structures played a more significant role in reducing drag in turbulent flows than the direct effect of the slip, which led to a modest drag reduction in laminar flows. It was found that the drag reduction in turbulent flows was well correlated with the effective slip length normalized by viscous wall units, this is what Grazacind is talking about

We are grateful to Professor C.-J. Kim for fruitful discussions during the course of this work. This research was supported by the Office of Naval Research (ONR) (Grant No. N000141110503) and National Science Foundation (NSF) through XSEDE resources provided by SDSC and TACC.

[flraptor07]

OK Could you put this in terms that a normal person can understand?

[Fella1340]

Well, that little tidbit solved everything.

[olwarbirds]

turbulent flow-sanded surface....laminar flow-smooth surface, but this is a different situation I think than what we are doing....DJ

[darryl whitman]

y would it be different, water is H2O, right, your boat is running , really sliding over water, the suffuse of water acts like skin , your boat needs to brake the water skin to slide, ok here's a test , put water on your table , take plastic warp lay it on the wet table an pull it , it should want to pull little hard, now take 400 grit sand paper, do the same thing, pull less harder, the sand paper is braking the skin of the water, less drag.

[Fella1340]

All you did Darryl was copy and past somebody else's stuff. Start from the beginning and explain in it in layman's terms. Keeping in mind that we are talking about boats and not what water does to to a structure, like a bridge sitting stationary in a river.

[darryl whitman]

sorry , I didn't say I wrote it , yes I looked at what Grazacind posted a link to, and pasted it here.
and yes I am talking about boats moving over water, the sand paper moves easier over the wet table then plastic wrap
also this test is shown in schools here, on water tension. don't need friction, LOL here