waxing hull...or sanding?

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waxing hull...or sanding? - 9/2/2009 2:45 AM

FredNitroJunk

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hi guys, i'm not much into boating ( but its on my wish list

) so i need help from you hull expert. one of my friend just jump into RC by buying a super vee 27 brushless. he ask me for couple of tip on RCing so i talk about batterie, charger, esc and on and on..... and then i say the only tip i know about boat is that you should wax the hull. but he reply: no, i read somewere that is better too lightly sand the hull with a green pad or somethong similar, just to do some 'micro sratch' on the hull. that create bubble that make the boat slide easier.

i told him that he shouldn't take for granted something just because he read it on the net, and he don't even remember the source. is a kind off one track mind so i didn't argue with him and just say ' oh well dude, go ahead, scratch your hull'.

so what you guys thinking? 13 layers of nu finish or go nuts with the sand blast machine????

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RE: waxing hull...or sanding? - 9/2/2009 3:03 AM

srw1960

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Sand blasting would be way over the top ..but no your friend isnt nuts..wax will roll off the bottom of the hull LIGHTLY wet sanding the bottom of the hull will give you the best results so im told by several good folks on here whos advice I highly respect its part of a process called blue printing the hull I am just learning about it myself

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RE: waxing hull...or sanding? - 9/2/2009 3:06 AM

FredNitroJunk

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so wet sanding with like a 800 or 1000 grain should do? or the green pad is the best option?

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RE: waxing hull...or sanding? - 9/2/2009 5:10 AM

rebuilder

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Here we go again...................sanding or waxing........................thats getting to be kinda like "paper or plastic" at the market.

I dont think there will ever be a "final" decision on this issue...............but its fun to keep re-cycling it.

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RE: waxing hull...or sanding? - 9/2/2009 6:31 AM 1 votes

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Justaddwata

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Evidence suggests sanding delivers the best results as it breaks the surface tension between the water and the hull (similarly to the reasoning as to why golf balls are dimpled). Looking at the running surfaces of such performance hulls as the Miss Budweiser it is clear that they too are of the same belief. Remember - you only need to scuff the wetted running surfaces - not the whole bottom of the hull.

And this will not add much in the way of measurable MPH gains to most boats - but it may mean the difference between crossing the line first or second (a second a lap or so). So if your just having fun on the pond then you can just as easly overlook it - it is a speed tip but not necessarly going to give dramatic results.

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RE: waxing hull...or sanding? - 9/2/2009 7:19 PM

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I have challenged both options and can not clearly state one is better than the other. So I don't bother with either as I have not yet proven to myself there is a difference.

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RE: waxing hull...or sanding? - 9/2/2009 8:59 PM

FredNitroJunk

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so what i understand here is for a guy who run in figure 8 in a pond, that don't seem to mather. and i gess that keeping the hull well wax is probably easier then have it sand the right way ( for a newbie ). OK then, i'll send him a e-mail copy-paste of everything here and he will do what best by is own judgment. anyway i planing to by my first electric boat next summer and it will probably be the same boat that he got, i'll wax it and maybe we will get an anser!!

thx everyone

PS where is the spell corrector?? when do they took it off? i'M dooooom

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RE: waxing hull...or sanding? - 9/2/2009 9:02 PM

FredNitroJunk

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quote:

ORIGINAL: rebuilder

Here we go again...................sanding or waxing........................thats getting to be kinda like ''paper or plastic'' at the market. I dont think there will ever be a ''final'' decision on this issue...............but its fun to keep re-cycling it.

well, i gess it will be back each time someone will buy his first boat, maybe we need a good tread about this and have it sticky

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RE: waxing hull...or sanding? - 9/4/2009 6:20 PM

Ron Olson

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For the Average Joe Boater it's no big deal if you want to just leave it as is, wax or sand the bottom. For those that are trying to get every 1/10 MPH out of their boat then you can work on it as you're not going to see any significant improvement in speed. The non-racer isn't going to tune everything to the nth degree anyway.

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RE: waxing hull...or sanding? - 10/27/2009 5:26 PM

Dockman

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I have mentioned it many times here on RCU. Speed Coat the running surface of the boat and be done with it. Here is a link to it http://shopping.rexmar.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=lubrabonda&gclid=CLbUuoDS3Z0CFRPyDAodXFK_OA

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RE: waxing hull...or sanding? - 10/27/2009 6:31 PM

Dreamin Hemi

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Yeah, another thread beating a dead horse. But since it's here......I'll leave my $.02.

Think about this. Most information that is passed through this site comes from heresay, and not actual testing within a controlled environment. Parasitic drag is caused by moving a solid object through a fluid medium, in this case water (air is also a fluid medium). Once you even dull the surface or even worse, scratch that solid object, you have significantly increased the parasitic drag of that object. In simpler terms, a waxed car has LESS parasitic drag than a car that is full of rust. So my sanding (or scuffing) you INCREASE drag! Another point....look at a finish on a car (or boat) that is shiny, and waxed up....the wax (or polish) REPELS water...it dosen't want it on it's surface so woulden't it make sence to have the bottom of your hull to repel water? One last thing.....anything that skims across water that creates little pockets of air or air bubbles is loaded parasitic drag. Again, these are just my educated opinions so take it however you like. I teach this stuff at the college level and am fairly sure I know what I'm talking about.

Main thing is here if scuffing the running area speeds up a boat, it is so miniscule no one would hardly notice. Unless someone has scientific proof that it works and I'm not talking about gps speeds (very inconsistant) or lap times since conditions for repeated attempts are never exactly alike, I'll continue running with my mirror finish and waxed hulls.

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RE: waxing hull...or sanding? - 10/27/2009 9:05 PM

Nosedragger

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I have to agree with Dreamin Hemi. We are running PLANING hulls, planing hulls need the boundary layer to work efficiently. What hydro-planes easier on the highway? a bald tire or a treaded one?

The sanding idea works because it removes minute high and low spots that reduce PLANING efficiency.The surface texture does nothing.

The golf ball analogy is a bad example because its flowing through a 3 dimensional medium, a boat planing on the water is working in 2 dimensions.

Every skip a stone on a pond? what skips better? flat smooth stones or rough rippled or cratered stones?

DISPLACEMENT hulls on the other hand do benefit from surface texture treatment.

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RE: waxing hull...or sanding? - 10/27/2009 10:13 PM

Justaddwata

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quote:

ORIGINAL: Dreamin Hemi

Yeah, another thread beating a dead horse. But since it's here......I'll leave my $.02.

Think about this. Most information that is passed through this site comes from heresay, and not actual testing within a controlled environment. Parasitic drag is caused by moving a solid object through a fluid medium, in this case water (air is also a fluid medium). Once you even dull the surface or even worse, scratch that solid object, you have significantly increased the parasitic drag of that object. In simpler terms, a waxed car has LESS parasitic drag than a car that is full of rust. So my sanding (or scuffing) you INCREASE drag! Another point....look at a finish on a car (or boat) that is shiny, and waxed up....the wax (or polish) REPELS water...it dosen't want it on it's surface so woulden't it make sence to have the bottom of your hull to repel water? One last thing.....anything that skims across water that creates little pockets of air or air bubbles is loaded parasitic drag. Again, these are just my educated opinions so take it however you like. I teach this stuff at the college level and am fairly sure I know what I'm talking about.

Main thing is here if scuffing the running area speeds up a boat, it is so miniscule no one would hardly notice. Unless someone has scientific proof that it works and I'm not talking about gps speeds (very inconsistant) or lap times since conditions for repeated attempts are never exactly alike, I'll continue running with my mirror finish and waxed hulls.

http://www.meguiarsonline.com/forums/showthread.php?t=22135 Might be helpful

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quote:

Re: Waxing the running surface of your boat?

HI Don,

According to an owner/driver I recently met at a hydroplane boat race, you should never wax the bottom of a boat. The reason is the wax does not allow the water to stick to the bottom surface and therefore only creates more friction during forward motion.

Here is how it works. When the bottom of a boat is either painted or left unwaxed the water is allowed to stick to the surface. Since water is now attached to the bottom surface, the water actually acts as slippery medium between the moving boat and the water that is basically standing still. According to what I was told, water against water creates a lot less friction, compared to water against wax.

I am not making this up. This information is coming directly from someone who understands the dynamics involved. Definitely something to consider before waxing below the waterline.
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I have always heard it referred to as breaking the surface tension of the wetted surface. I ran my hand over the ride pads on the Miss Bud and it was textured - not polished. Breaking the surface tension is key - look at a hull with steps vs one without.

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RE: waxing hull...or sanding? - 10/27/2009 11:47 PM

jetpack

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In model boats, I would have to say block sanding the bottom would have more impact than a sanded surface can provide.

RTR boats that are molded I would guess could all benifit from at least checking with a block sander.

If I was going to sand my hull I would take that one step past just a scuff pad and do it up right with blocks.

Wood hulls naturally go through this step when they are built.

One trick that stock outboard racers have used in the past is to run down the rear third of the bottom with an orbital sander over the varnish to develop a swirl pattern. Picture fish scales going the wrong way. The pattern left behind (the trick also involves setting up the right sheet of sandpaper) helped promote a little ball bearing surface of air and water slurry farther back than just being gloss.

The swirls help carry air back to the next swirl sort of effect. The trick is to have just a few large, sharp grit pieces standing up so when you push the sander it will leave sort of a hook and loop pattern to help create streaming bubbles, lots of them. You're trying to create foam, but not drag. The goal was to get nice sharp valleys that air could follow and mix.

You have probably seen this pattern with an orbital sander if it forms a "digger" in the pad. This I guess you could call a more refined mistake.

< Message edited by jetpack -- 10/28/2009 12:20 AM >

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RE: waxing hull...or sanding? - 10/28/2009 2:11 AM

Dreamin Hemi

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Thanks for the link Matt. Definately makes sence, and I certantly am not saying that my ideas were absolutely correct.........just my own thinking. I would really like to see research on this. More testing in a controlled environment to see what the differences would be.

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RE: waxing hull...or sanding? - 10/28/2009 9:32 AM

Justaddwata

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Scott - it certainly stands to reason that a polished finish should be "slicker" than one that has been scuffed.

On a related subject - I guess we could consider the finish of props as they contact a considerable amount more water in their travels than the hull does. Advice I have always read is the thrust surface is polished (for better bite) and the back of the prop (surface facing the front of the boat) is scuffed to reduce surface tension. One thing I have always heard with props - Never wax them (for as much as I would love to keep them from tarnishing).

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RE: waxing hull...or sanding? - 10/28/2009 10:46 AM

Dreamin Hemi

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Again thanks Matt. You would need to hire an assistant to keep up with all the polishing/waxing of your props!

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RE: waxing hull...or sanding? - 10/28/2009 6:48 PM

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I've done a bit of reading on reducing hydrodynamic drag over the last year.

For what it is worth, it appears that small shallow grooves DO help reduce drag (vs a plain flat surface) and this has been tested and proven since 1948. Here is an article from the British Maritime Technology that calls these grooves "riblets:

http://www.springerlink.com/content/p8746pq28732p1t5/

Here are some more related links to abstarcts from MIT and Harvard:

http://oe.mit.edu/index.php?option=com_content&task=view&id=14&Itemid=140
http://adsabs.harvard.edu/abs/1989nasa.reptR....R

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RE: waxing hull...or sanding? - 10/28/2009 7:10 PM

Dreamin Hemi

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Great articles, thanks for posting!

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RE: waxing hull...or sanding? - 10/28/2009 7:56 PM

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Here is my 4 cents.................WW II ELCO 70' PTB
Standard speed was 42 knots with a 33 ton boat .
They installed 6 steps to the bottom & sides. Speed jumped to 56 knots and cornered better................Very large dimples??
Boats travel fastest when completly in air. Only the prop & rudder need to be in the water to qualify as a " real boat ".

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RE: waxing hull...or sanding? - 10/28/2009 8:16 PM

TCHedOff

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Funny you should mention dimpling, another drag reducing topic I've researched. What I've learned is 1) dimpling is only really effective on curved surfaces (not flat surfaces) - (I've been thinking about trying them on the top-nose of my rigger tub and also on the top of the sponsons) and 2) round-shaped dimples are less effective than dimples w/sharp edges (EG a square, star, polygon etc etc) - Rod Geraghty would laugh about this.

< Message edited by TCHedOff -- 11/7/2009 3:03 AM >

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RE: waxing hull...or sanding? - 10/29/2009 3:00 AM

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In the 60's ?? The USAF took a jet & drilled THOUSANDS of tiny holes on the top & bottom and blew air out of them. Result was more speed with less power from the engine.

How many ways are there to skin a poor cat ??????????????

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RE: waxing hull...or sanding? - 11/7/2009 3:13 AM

TCHedOff

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Cyclops, that technique is also interesting (I've read a number of articles of similar ways to reduce drag in boats, but most involved pushing a fluid out the skin of the hull to reduce drag). Quite number of patents applied for on various ways to di this.... but for a RC boats, all seemed impractical to be worth trying.

I AM going to test using Teflon tape over the winter. Of the 6 types of Du Pont Telfon, PTFE has the lowest co-efficient of drag (was like .04-.07).... I scored some $60/roll PTFE tape for free from a local suppler who had it in their "reject bin"; I plan to build some channeled wooden ramps: 1 with epoxied/sanded surface and 1 w/teflon tape - and run some dyed water down each to test the difference. "On paper" there should be a difference, but only testing will tell.

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RE: waxing hull...or sanding? - 11/7/2009 4:54 AM

Ron Olson

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Todd, that sounds like the same tape that we use at work called Nittoflan. The stuff is a shocking $62.00 a roll. I got a 5-finger discount on a full roll and sent it to Don Ferrette to try out but never heard if he tried it or not and any results if he did. It might be worth trying on the JAE .12 'rigger. As long as it doesn't get too hot it will peel off easily, we put it through some severe stuff. I'm talking hot as in around 600 or more degrees. It also has a "grain" in it so use a sharp X-acto or razor blade when cutting across the roll.

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RE: waxing hull...or sanding? - 11/7/2009 2:11 PM

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the discussion in here is getting a lot better,,keep it up guys

and my opinion here is waxing..

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