thats exactly what was happening beading up…goin faster…so is it the sanded waxed finish or the finish coat buffed and waxed faster…i think the finish coat with the wax…wadda ya reckon?
Tough to say, depends on your needs.
With a surfboard, you need to easily get past that planing barrier, somewhere between 9-15mph before you can go on your merry way. Once you past that, acceleration is comparatively lowdrag.
In bigger waves, the barrier is of course, higher.
In 12’ + waves, that barrier can be around 17-22mph, that you MUST get past before the board unwets.
So the first barrier, the lowest speed you need to unwet length drag off your board, and plane solidly off the tail, is the one that is most important for most peeps.
Sanded 6-800, in the direction of water flow.
wax is supposed to go on the bottom! i was putting it on the deck…oops…that wasnt funny,carry on.
Greg, your theory that a longboard will top out in speed due to a larger wetted surface area is incorrect, because there is no rule that says a longboard must have its bottom touching the water. All you have to do is hang on the tail and stick that nose out in space and ‘presto!’ you are riding a low wetted surface area board. Longboards top out only if they are noseridden, which maximises surface area.
yeah that opens my eyes with the lenghth speed ratios and weight…never really thought of it that way…my tow boards sometimes testing them in med 6-8ft and they wont go cause of weight and length super slow no turns…they start to move at 30ft and still feel like they need more speed which is the way i like it when its big the board to feel like it can handle a lot more speed then the wave has… when its small i like it to feel maxed out speed…leed .Ill go the 6-800 with the wax for small board thanks
Sorry Cheyne,
Wax has been proven to be slower. Use the 600 to 1200 grit, sanded fore and aft, and if you really want to move out, polish the board with something which is water soluble and lowers the surface tension of the water. Coconut oil is excellent for this, and will last 30 to 40 minutes.
You may have noticed that your boards felt faster after being polished with wax if they had previously had grit or wax particles, or even dried salt on them. Any tiny imperfections bigger than the grit found on 400 grit sandpaper will slow you down, and often you can’t see them. A waxed surface is still slower than the surface preparation mentioned above.
roy i had to laugh when i read your reply to greg about wetted surface area ,
what greg said was entirely true ,while your comment had an element of truth , i think its classic , coz you always make statements in such a way , that they can be backed by a law or principle of physics…even if they are rather ambiguous…
the only problem i saw with your response roy ,
wind resistence…
you start sticking that much board up at high speed and the air will catch it…but maybe we can explore that one , on another thread…
back to rough/smoothe surfaces…
laminar flow is rather slow…
if you look at the speed of a bead of water running across your board , thats about the speed of laminar flow, water can only flow so fast when its in direct contact with a surface…
once the flow goes turbulent , it can now move way quicker…
anyone ever been laminating a board and this happened???
you push resin around with your sqeegee , if you push a blob onto a dry area , coz the resin has direct contact with the board it moves slow…
but what about when the board is wet , you do a quick turn with your sqeegee and you get a blob that moves lightning fast , usually flying off the board (beware bystanders),because its resin on resin , not resin on board…
to really get the point across would require a series of lengthy examples and an examination of the laws that apply ,
which i dont quite have time for…
if i had to choose between 2 polished surfaces,
i would choose cut & polish over wax and polish,
a finely scatched surface will be faster than a surface that has scratches filled by a wax , leaving a smoothe surface…
rough is faster …you can still have a rough surface that looks shiny…
something that looks smoothe to us , can still look pretty rough to a water molecule under pressure…
regards
BERT
Nice comment Bert.
One observation my wife and sister-in-law made last weekend. Pulling the kids on boogie boards by the leashs: they were much faster on wet sand than in the shallow water (I think those ideal wet sand conditions were fleeting). Still kids had a blast and laughed when flying off in a “slow spot.”
Scientist are now looking into ways of pulsing small electrical currents in surfaces to reduce drag.
Most man-made methods of reducing surface drag are water soluble; most biological methods are not (going by memory, I’ll have to check this).
Hello Bert,
I am glad that you are smiling, that’s got to be all good!
However your statement that it is ‘entirely true’ that longboards ‘top out’ in speed due to a large wetted surface area is itself clearly untrue for the following reasons:
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A longboard, or any board, need only have a small part of the bottom in contact with the water.
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In the case of a longboard with a horizontal lifting fin, the board is sometimes able to surf with the bottom completely clear of the water, and in such a case it has potentially less drag than any conventional shortboard.
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The speed of a board is determined by the force propelling it, less drag. Since a heavier board attracts more gravitational energy than a light one, a heavier board is able to have more wetted surface area than a light board without losing speed.
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It follows from (3), that boards which have a large bottom area, and are very light, are likely to be very slow unless the bottom is kept out of the water.
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Currently, so called ‘Performance’ longboards are typically lightweight boards with a large bottom area, and are thus slow boards unless their bottoms area is kept substantially free of the water.
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These so called ‘Performance’ longboards are designed to be noseridden, and this riding position guarantees that most of the bottom of the board is in contact with the water. This kind of board is thus subject to high drag in proportion to it’s weight and is therefore slow.
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Heavy longboards which are able to be surfed with low wetted surface area are thus always going to be faster than lightweight longboards with high wetted surface area, and they are able to be as fast as any smaller board and rider combination with a similar weight to drag ratio.
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Bert, you raise the possible problem of wind resistance with large area boards which are surfed substantially free of the water. The following points apply to this question:
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Wind may be used to develop aerodynamic lift, which enables the board to lose wetted surface area by lifting itself free of the water.
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This aerodynamic lift enables a significant reduction in drag and thus an increase in speed.
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Aerodynamic lift is easy to achieve, because wind flowing up the face of the wave does so at the same angle as the wave face itself thus allowing the natural trim angles of the board to function as appropriate angles for aerodynamic lift. In other words, aerodynamic lift occurs naturally if there is free board area available.
Regards, Roy
here ya go roy , so called performance longboard, with the bottom kept substantially free of water…
yep roy im stumped , lost for words …i just cant refute logic like that …
regards
BERT
Roy,
That would depend a lot on bottom curve and the wave your riding. I designed a rocker years ago called pinacle rocker that reduced wetted surface. Yes it did work but on fast steep waves shorties were still faster. So much depends on the waves.
Cheyne,
I’m living in Arizona, surfing in CA and FL whenever I can, traveling a bit, working in a chemical plant, and snowboarding in the winter.
I know you weren’t talking to me, Roy, and much as I’d like to stay clear of this, some of your points demand a response.
Quote:
- Since a heavier board attracts more gravitational energy than a light one, a heavier board is able to have more wetted surface area than a light board without losing speed.
Surely you’re not saying that gravity pulls heavy objects faster than it pulls light ones? Remember Galileo & his iron balls? 9.8 m/sec/sec no matter what the weight.
If your primary point is about the drag across a wetted surface due to water adhesion, make it without the erroneous assumption that heavy objects fall faster than light ones.
Moreover, drag coefficients through water have more to do with contour & release point than with overall wetted surface. You’re mixing sciences to where you’re muddying your point.
Quote:
- These so called ‘Performance’ longboards are designed to be noseridden, and this riding position guarantees that most of the bottom of the board is in contact with the water. This kind of board is thus subject to high drag in proportion to it’s weight and is therefore slow.
Actually, ‘Performance’ longboards are the high-rockered, multi-finned variety designed for squared-off turns and scoring points in a system designed for shortboard competitions. They do probably move more slowly through water - in a pure, unweighted, straight-line analysis - than do ‘noseriding’ longboards but that would be more due to the rocker, hard rails, and multiple fins all conspiring to create more drag than a board with flatter rocker, softer rails, and one fin. Ironically, although the area of potential wetted surface could well be identical with these 2 boards, the one with more de-facto wetted surface (the noserider) would have much lower drag coefficients than the ‘performance’ one and would move faster despite its greater true wetted surface (and obviously regardless of respective board weights).
If one just stands there doing nothing cruising down the line of a mellow pleasure point wave (for example), a flatish noserider type board is quite “faster” than my 9’0" Harbour Simms “performance” thruster longboard that has little glide ability. But when I surf the Simms actively (pumping carves for example) in a decent wave, it’s much faster than the old classic boards. (I find the 7’4" single-fin spherical revolver 1969 shape board to be even “faster” of course - damn that board is great fun! )
I have a feeling that despite their length, Roy’s boards surf more like a performance longboard (off the tail, not much board in the water) than a traditional longboard.
Let me add a very little bit, as an licensed civil engineer and my recall of fluid mechanics (University of Hawaii, about 1975).
At low speeds, the molecules immediately next to a surface, move with the surface, but the velocity distribution varies with the distance from the moving surface. Prantl’s Law. At low speeds flow is laminar, and there is a boundary layer that is dragged along with the moving surface. The BL gets thicker with the length of the moving surface (surfboard) until at some speed or distance the flow becomes turbulent. Once turbulent flow happens, the boundary layer no longer thickens, in fact may become thinner, so you’re not dragging along an increasingly larger mass of water with you. Cheyne, this may be useful in consideration of speed versus length.
Now, a roughened bottom (most experimenters have used closely graded sand) will induce turbulent flow much sooner, so the rough surface can be faster IN THE RIGHT CONDITIONS. As discussed above, this happens at different speeds for different hulls.
I believe all the necessary research has been done, but few of us have broad enough experience to be aware of it, or access it. You have to locate data that is applicable to your situation, that is, the data have to be from something that is “dynamically similar” to your application of interest. Generally, the velocity and length ratios between model and application have to be of the same proportion. Calculate the Froude number for this, whether it’s for bottom roughness considerations, or flow around fins (another thread that was beat on quite a bit lately).
My little brother was a competetive sailor for a while, and mentioned that some sailors were into sanded bottoms, etc. But stop, these guys race courses that are miles long, and a very small percent difference in hull speed means a big lead at the end of a race. For surfers, rides are a few tens of seconds long, at best, and a major difference to a sailor (2 percent) isn’t gonna mean squat to a surfer.
In sum, most of us are gonna use polished bottoms for several reasons, among them being that 1, they sell better off the shop racks; 2, they don’t get as filthy as sanded bottoms; 3, the speed differrence between polished and sanded is very small, something most won’t use/appreciate/feel.
Hello Benny,
No I was not saying that a heavy object falls faster than a light one. A heavy object will fall at the same speed as a light one (friction excluded), but it the heavy object will have a greater kinetic energy and momentum than a light object. Thus if two boards of different weight are travelling down the same wave slope, but they both have the same wetted surface area, then the heavier board will go faster because it will experience proportionally less friction. If the friction experienced by both boards is the same, then it will have less effect on the heavier board because the heavier board has more kinetic energy at any given speed than the light board.
So as you can see I was not making any erroneous assumption about heavy objects falling faster than light objects.
You state that drag coefficients have more to do with contour and release points than overall wetted surface area. This is also untrue. More wetted surface area will create more drag (all else being equal) To say that drag is more to do with contour is to pretend that wetted surface area is of no consequence. Hydrofoil design and catamaran design have shown that a reduction in wetted surface area will reduce drag. Of course the shape of the hull is also important! The point about reduction in wetted surface area was made first on this thread by Greg Loehr.
Neither of the longboard types you mention are designed for minimum wetted surface area at speed, and both the noseriding type board and the ‘performance’ type longboard are very slow. The noseriding board is slow because noseriding is slow due to high wetted surface area. The ‘performance’ style longboard is slow because it is designed for slow tail pivot turns, and also because it is usually a compromise board which is also a noserider.
Both of these longboard types are also slow because they have a lot of surface area in proportion to their light weight.
Tomatdaum,
Your chart of allowable roughness is very interesting. Tank tests which were done at around the time of the Rainbow II challenge for the One Ton Cup in the early '70s indicated that a 400 grit sanded finish was the fastest possible bottom finish. I was surprised to hear that a 600 or finer finish is used by windsurfers, until I read your allowable roughness information. It seems likely that the 400 grit finish would actually fit neatly into the chart, because the speeds of the old IOR One Tonners was very slow. It was probably the case that the tank tests which came up with the 400 grit information were carried out at speeds of 5 to 10 knots.
As I design my boards to ride on a progressively smaller area of the bottom as they accelerate by projecting the nose area out of the water, the fastest surface I can achieve could be a sanded bottom which graduates from 400 grit in the nose area through to 1000 or 1200 in the tail and fin zone.
Thanks for the useful information!
Hello Honolulu,
I didn’t know that the velocity to length ratio of a hull was a consideration when calculating the fastest bottom finish. It is a difficult factor to apply for craft which alter their waterline length during use, but could be helpful for submerged fins. I hope to be able to learn a bit more about this theory.
It seems that your scientific attitude took a slight nosedive at the end of your post when you said that an increase in speed of 2% won’t mean ‘squat’ to a surfer. A 2% increase in speed means two extra yards after 100 yards has been travelled. An extra 2 yards can mean a lot to a surfer who is racing a long section, it can mean the difference between making the wave or not making the wave. Evaluation of the usefulness of a 2% speed increase is something each individual surfer can choose to make, or not, but it is not necessarily the case that it means nothing.
As Cheyne and others have noticed, a faster bottom surface can be felt by the rider. The human body is a remarkably sensitive instrument. I can easily tell the difference between a freshly sanded and oiled bottom, compared with one that has not been touched for months. Unfortunately this feeling is difficult to translate into data, but it is real.
Regards, Roy
i wasnt even gonna bother arguing the point with roy…but the call that a light longboard is slow ,well that comment was off the planet…
if you were going to launch a longboard into the air , do a complete 360 and then land again ,what would be the first prerequisite for being able to perform such a move???
i rest my case…
regards
BERT
Being a novice I ask:
Are surfboards going faster than laminar?
HerbB
Bert,
If you read what I wrote carefully you will see that I did not say that ‘light boards are slow’.
What I actually said was that a board which has a high surface area to weight ratio will be more affected by drag due to skin friction than a board with a low surface area to weight ratio. This is because a heavy board has more kinetic energy at the same speed than a light board, and also because a heavy board is propelled by proportionally more gravitational energy than is a light board. Thus if the two boards have the same surface area in the water. the heavy board is less affected by skin friction.
This does not imply anything about the actual weight of the board, as it is the surface area to weight ratio which is relevant.
It would be also true to say that if two lightweight boards of the same weight are riding a wave, then the board which has the least surface area in the water will be less subject to drag from skin friction than the other.
I don’t see what 360’s have got to do with it. I was talking about skin friction.
Regards, Roy
PS My post was in response to GReg Loehr’s assertion that longboards ‘top out’ in speed more than shortboards. I was pointing out that this is not because of their length, but because of the current state of longboard design.I offered a reason why longboards need not be subject to high skin friction drag, but also pointed out that lightweight longboard designs are subject to relatively high skin friction drag when surfed from the nose.