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Thread: Low friction underneath hull?

  1. #1
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    Default Low friction underneath hull?

    Hello to all, Is it possible to use some sort of tape or paint on our rc hydroplane hulls that makes it have lower friction on the water. Not sure what they use in H1 but I am curious? But in photo you see some kind of coating in black underneath.

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    The hydrodynamic science says a rougher surface on the bottom is faster. It induces the formation of micro bubbles in the water, which act like ball bearings and thus lowering surface tension between the hull and water. A smooth surface can actually create suction and therby increasing drag. Now, the degree to which this will actually affect a scale RC boat is up for debate to some degree. The physics behind it is solid, enough so that many will scuff the riding surfaces with sandpaper on a bias direction to the water flow across the hull and recommend against polishing or waxing the underside of a hull.
    Vac-U-Tug Jr (13mph)

  3. #3
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    Maybe it was something like this? I guess it was a popular speed coat for hull bottoms but fairly toxic. Funny the ad even mentions r/c boats. I bought a spray can of it and tried it on the bottom of a Sport 40 about 10 years ago, it dries matt black with sort of a graphite feel.
    http://www.westcoastoffshore.ca/Lubr...1Q-P11920.aspx


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    Regarding fweasel's comment, many years ago now, I added ride pads to a sport hydro. Just for fun, I dripped some thin CA into the unfinished wood. The result was a very rough surface that felt very much like sandpaper. During testing, I couldn't point to any difference, even when swapped for smooth, finished ride pads. AOA, width, etc. was all the same between the two. I guess it might make a difference if it was on a lighter rigger. However, when setup correctly, there's so little surface in contact with the water, I can't imagine that it would make but so much of a difference.

    I did witness a larger mono with some 'slick' spray on the bottom. At SAW speeds and no other changes, once the 'slick' spray was applied, the model would blow-over. I've never tried any slick additive, so I couldn't say conclusively one way or the other.
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  5. #5
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    Cool

    “Speed coats” have been used on FE boats for many years. The JAGs team used them on some of their earlier record-setting SAW boats. I did some testing on my own SAW boats years ago and found a small speed advantage - 5% on a 45 mph 5 volt boat - by painting sponsom bottoms with a epoxy/colloidal graphite mix. But the advantage may have been due more to the excessive sanding and blueprinting I had to do to the coated sponsons than the coating itself. I don’t know the effect on a hull with more wetted surface like a mono or cat.

    And while it is true that at speed very little of a hydro is in the water at speed, all model boats are wetted down in turns. This is where an effective speed coat would do the most good.


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    Thank you so much for all your input, truly appreciated it.

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  7. #7
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    On the full size Miss Bud we used a graphite impregnated paint on all the running surfaces but it really never proved to be a of a significance benefit
    Screen Shot 2018-04-05 at 10.25.47 AM.jpg

    On my Scale hulls I just paint those surfaces black for appearance sake

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    At my local marina they use some stuff called sharkskin. I'm not sure if it works but maybe it's worth taking a look.

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    Quote Originally Posted by Moonie View Post
    At my local marina they use some stuff called sharkskin. I'm not sure if it works but maybe it's worth taking a look.
    The biggest thing. You can do reduce drag is make sure that all the breaks in running surfaces ,sponson backs, hull steps, transom ect. have nice sharp edges. Any radius-ed edges will cause the water to roll off not break cleanly causing the hull to suck down in the water increasing drag

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    Quote Originally Posted by Tom G View Post
    The biggest thing. You can do reduce drag is make sure that all the breaks in running surfaces ,sponson backs, hull steps, transom ect. have nice sharp edges. Any radius-ed edges will cause the water to roll off not break cleanly causing the hull to suck down in the water increasing drag
    Tom I agree with what your saying 100% and it's the same method I use.

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    I was thinking about scuffing the bottom of a mono I have to test this theory. So let me ask you guys this. Would it be an accurate enough test if I ran the boat, checked the speed gps. Then bring the boat in. Top the batteries back off right then and there. Scuffed the bottom. Threw it back in and attempted to duplicate the same direction run as the first run. I can’t think of any other way to do it more accurate. Anyone interested?
    32" carbon rivercat single 4s 102mph, 27” mini Rivercat 92mph, kbb34 91mph, jessej micro cat(too fast) was

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    Sounds like a good A-B test to me. But I think that “shark skin” talked about earlier would be a more consistent texture. Scuffing them up will produce a rather random surface, don’t you think?

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    Quote Originally Posted by CraigP View Post
    Sounds like a good A-B test to me. But I think that “shark skin” talked about earlier would be a more consistent texture. Scuffing them up will produce a rather random surface, don’t you think?
    Well I was gonna use my Cnc scratcher. Just kidding. This is such on a small scale I’m not sure it matters
    32" carbon rivercat single 4s 102mph, 27” mini Rivercat 92mph, kbb34 91mph, jessej micro cat(too fast) was

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    I have noticed a difference on monos but never really tested it on cats. And the mono was just ‘seat of pants’ judgement on any benefit.
    Try it out Travis. Lots swear by using the 400 grit on the bottom.

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    Quote Originally Posted by srislash View Post
    I have noticed a difference on monos but never really tested it on cats. And the mono was just ‘seat of pants’ judgement on any benefit.
    Try it out Travis. Lots swear by using the 400 grit on the bottom.
    I feel like it helped my fast mono I had and my Rivercat. All my fastest boats have been scuffed.
    32" carbon rivercat single 4s 102mph, 27” mini Rivercat 92mph, kbb34 91mph, jessej micro cat(too fast) was

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    Quote Originally Posted by kfxguy View Post
    I feel like it helped my fast mono I had and my Rivercat. All my fastest boats have been scuffed.
    Yup, pretty much just ‘something I do’. A little scuff is part of the FighterCat’s regime.

  17. #17
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    Teflon treatment? Nothing sticks to Teflon very slippery, treat both top and under side, slippery on top for better air flow, water slides smoothly under hull.
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    One of our Club Members here in the Carolinas uses Rain-X religiously on the underside, and we know it works on the windshield. My two cents.

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    Just the 1 rear-most ride pad, or the one after that one as well?

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    Hyspeedkote

    This is what a lot of the big boats (Mono,s and Cat.s) use.

    Larry
    Past NAMBA- P Mono -1 Mile Race Record holder
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  21. #21
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    Quote Originally Posted by TRUCKPULL View Post
    Hyspeedkote

    This is what a lot of the big boats (Mono,s and Cat.s) use.

    Larry
    I’ve been wanting to try SpeeKote for a heck of a long time. I have a bigger mono build coming up. Maybe I’ll try it on that for a before and after. As I recall Larry, we can’t get it in Canada.

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    Quote Originally Posted by srislash View Post
    I’ve been wanting to try SpeeKote for a heck of a long time. I have a bigger mono build coming up. Maybe I’ll try it on that for a before and after. As I recall Larry, we can’t get it in Canada.
    https://www.google.ca/search?q=hyspe...jV7IaxW2gTeRM:

    I have a 1.5oz spray can that I bought years ago here in Canada.

    Larry
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    Past NAMBA- P Sport -1 Mile Race Record holder
    Bump & Grind Racing Props -We Like Em Smooth & Wet

  23. #23
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    What matters a lot is getting the hydro-prop to work as it is supposed to be .... i.e. not IN the water, but slightly above. That means you have to raise the transom, by e.g. catching some pocket of air underneath the transom. Need some evidence?


  24. #24
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    This isn’t evidence. The thread is not about prop position, but about reducing friction between the hull and the water. Hydros have very small contact area when at full song, but in corners they do wet down. Monos wet down a lot. What has proven to work is eliminating the glossy surface contacting the water by scuffing the bottom with sand paper. The surface should not bead water but instead be thoroughly wetted. Wax is certainly not the answer.


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  25. #25
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    Quote Originally Posted by Fluid View Post
    The thread is not about prop position, but about reducing friction between the hull and the water. Hydros have very small contact area when at full song, but in corners they do wet down.
    Reducing friction between hull and the water is all about getting some air underneath the hull and especially the transom. No contact of hull-surfaces with water reduces way more friction (sum water/ air) than eliminating the glossy surface.

    Then there is another important aspect often overlooked... of course, the hull scratches the water, but very often props are dragged through the water too. You can spend hours "eliminating the glossy surface", but this will bring you little to nothing if the prop is still being dragged through the water!

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