Long board/short board

[Broosta]

All else being equal shortboards will not accelerate faster, that is a myth which is based on the mistaken idea that the thrust which drives a board is constant, regardless of board and rider weight, which it isn't, it is directly in roportion to rider and board weight. In many situations a heavy board will accelerate faster. .. .

I beg to differ, a shortboard can accelerate faster than a longboard because it has less mass. This means in realistic terms that when a surfer pumps the board in order to go faster, the board with less mass will respond quicker to the forward thrust of the riders pumping action.
Why else do pros use lighter boards?
Its all to do with enertia and momentum. An object with a smaller mass can accelerate and decelerate faster. Fact.
Why are race cars made lighter? Ditto push bikes, motorcycles, anything bassically which is built for faster accelleration and speed!

Yes in some (not many) situations a heavier board will accelerate faster. Such as taking off on a big wave when the wind is offshore and so the heavier board will drop faster due to its greater mass making better use of gravity to overcome the wind resistance. But a smaller board will have less wind resistance so could drop faster regardless.
Optimum set up for fastest drop in the strong offshore wind situation would be heavy small rider on a heavy small board. IE the combination with the overall densest matter will drop down the wave faster.
But in every other situation a lighter/shorter board will accerate faster.

[Broosta]

if it helps, two skiers of 65 kilos, one on a pair of 165s and one on a pair of 185s, the one on 185s will go faster.

that is all.

The skier on the longer skis must then be experiencing less friction, in spite of having potentially moe ski in contact with the snow. Would you say that the skier on shorter skis is slower because he can't carve long lines and produces friction with short turns? Or is it the case that if both skier just head straight downhill then the guy on longer skis is faster?

This could be because the longer skis are less influenced by the bumps, same as bigger wheels on a skateboard are faster as they roll over uneven ground better.
And/or the skier weighs 'an amount' which will exert 'an amount' of downforce on the skis which cause the skis to sink into the snow 'an amount' which in turn slows the skier down 'an amount'. Longer skis will spread the weight over larger area and so sink into snow less. Less sinking into the snow means faster skiing.

But this is only because snow has far less friction than water...

[GowerCharger]

yep, a longboard will plane easier due to its higher volume, but once planing a shortboard has MUCH less drag so will be faster, the difference is that to remain planing a shortboard must be worked harder and kept in the steeper parts of the wave whereas a longboard will happily keep going through the flattest sections.
Just look at windsurfers, 10 years ago a "racing" board was pretty much the longest board you could buy, but with advances in technology and technique, and the fact the pros only go where the wind is good, they only use shortboards because they are much faster as long as the power is there to keep them on the plane.

[Roy Stewart]

All else being equal shortboards will not accelerate faster, that is a myth which is based on the mistaken idea that the thrust which drives a board is constant, regardless of board and rider weight, which it isn't, it is directly in roportion to rider and board weight. In many situations a heavy board will accelerate faster. .. .

I beg to differ, a shortboard can accelerate faster than a longboard because it has less mass. This means in realistic terms that when a surfer pumps the board in order to go faster, the board with less mass will respond quicker to the forward thrust of the riders pumping action.
Why else do pros use lighter boards?
Its all to do with enertia and momentum. An object with a smaller mass can accelerate and decelerate faster. Fact.
Why are race cars made lighter? Ditto push bikes, motorcycles, anything bassically which is built for faster accelleration and speed!

Yes in some (not many) situations a heavier board will accelerate faster. Such as taking off on a big wave when the wind is offshore and so the heavier board will drop faster due to its greater mass making better use of gravity to overcome the wind resistance. But a smaller board will have less wind resistance so could drop faster regardless.
Optimum set up for fastest drop in the strong offshore wind situation would be heavy small rider on a heavy small board. IE the combination with the overall densest matter will drop down the wave faster.
But in every other situation a lighter/shorter board will accerate faster.

You are correct in saying that a lighter board and rider combination will accelerate faster due to muscular effort than will a heavier setup (because the force is equal in both cases but the mass being driven is not), but keep in mind that most of the force driving board and rider is from the wave lifting board and rider upwards, imparting gravitational potential energy to them, and that amount of this force is proportional to mass. A wave can lift board and rider very quickly from trough to crest, however a rider willl take much longer to lift his own weight from trough to crest without wave assistance. . . . the rider simply doesn't have as much grunt as the wave. . . . even a small wave can lift just about any weight. The amount of energy which the rider can impart is proportionally a small part of the equation and is fixed in quantity, whereas when a heavier board is used, the wave is automatically applying more energy., making muscular rider input less of a factor.

None of your examples of race cars, bicycles etc being built light for speed are relevant, because in all those cases the driving force is constant, whereas in the case of board and rider the majority of the driving force is due directly to mass, and is proprtional to mass.

My contention is that for any given board and rider weight there is a similar speed and acceleration potential, and that this potential can be realised by optimising the thrust/drag ratio.

I agree that in a vertical drop the densest possible setup will drop the fastest (all else being equal) because it will experience the least friction. . . and also I agree that unless the board is at least as dense as the rider, such a setup will entail a very tiny board, however in reality a big heavy board can have very low drag during a drop, because it has similar frontal area to a shorter board, and thus a good thrust'/air drag ratio. . .

[Roy Stewart]

yep, a longboard will plane easier due to its higher volume, but once planing a shortboard has MUCH less drag so will be faster.

Incorrect, because what you say only applies to noseriding boards. . . . a tailriding longboard is able to reduce and minimise wetted surface area as speed increases, thus reducing drag. . . getting the best of both worlds so to speak. Windsurfing is a different case altogether.

[el_timmo]

so I'm sure that all of these rocket (or surfboard) scientists are helping you a hell of a lot, but I just want to say.... why don't you just try them out, forget the physics of it, and see which one you like more?

[GowerCharger]

Incorrect, because what you say only applies to noseriding boards. . . . a tailriding longboard is able to reduce and minimise wetted surface area as speed increases, thus reducing drag. . . getting the best of both worlds so to speak. Windsurfing is a different case altogether.

no its not incorrect, you are talking nonsense, a planing shortboard has less drag than any longboard regardless of how much you can reduce your "wetted area" or whatever you think. thats obvious to anyone. whose ever surfed both.
im done with this topic its just getting silly and pointless now.

[drowningbitbybit]

its just getting silly and pointless now.

Yup.
The biggest factor will always be how steep and fast-moving the wave is. Shortboarders will generally be on a steeper part of the wave and will therefore move faster QED.

[tomcat360]

if it helps, two skiers of 65 kilos, one on a pair of 165s and one on a pair of 185s, the one on 185s will go faster.

that is all.

but what if, it's a deep powder day, and the guy on 185s has skinny skis, and the 165s are big old fatties?

now, who would be going faster?

But simplified, you are on the right track.

nice to see another skiier

[Roy Stewart]

Incorrect, because what you say only applies to noseriding boards. . . . a tailriding longboard is able to reduce and minimise wetted surface area as speed increases, thus reducing drag. . . getting the best of both worlds so to speak. Windsurfing is a different case altogether.

no its not incorrect, you are talking nonsense, a planing shortboard has less drag than any longboard regardless of how much you can reduce your "wetted area" or whatever you think. thats obvious to anyone. whose ever surfed both.
im done with this topic its just getting silly and pointless now.

Firstly, the speed which a surfboard can reach depends upon the thrust/drag ratio, not just the actual amount of drag produced.

Secondly, you can't prove anything about the drag produced by longboards and shortboards simply by saying that "It's obvious to anyone", this is clearly a fallacious argument.

Thirdly I suspect that you are comparing generic noseriding longboards with shortboards, and thus are using one of the slowest surfboard types ever designed as your yardstick. This is understandable because that's all you are likely to have access to, but realise that longboard designs exist (mine for example) which are much faster, and which use horizontal underwater wing area to reduce friction and wetted surface area on the bottom. Underwater lifting surfaces have a much better lift/drag ratio than planing surfaces, so we use them to minimise the planing surface as speed increases. There are several other important speed increasing design elements which we use also, including increased mass.

Fourthly, I have achieved speeds of over 30mph on average head high beachbreak waves using boards over ten feet in length.

[Brent]

Without wanting to dip my toe in this murky pond...can anybody then explain why my 5'9" fish is the fastest board I've ever owned. Hmmm, Hydrodynamics. Worth reading up about.
I think what Roy is trying to say is a falling body will fall faster if it's heavier, but to say a heavier body will accelerate faster (when subjected to the same energy source as a lighter one) is simply bad science.

Lets imagine you're pushing a car in your driveway, same driveway, same pusher. What's going to move quicker...a mini or a ford pickup?

That really should be the end of this thread.

[Roy Stewart]

Brent,

You want to end the thread, that's crazy it's an endlessly fascinating subject, and we really haven't even scratched the surface of it. . . . .why end it, those who ae interested should be allowed to discuss it surely ? After all, no one is forced to watch the thread!

Of course it is the kind of subject which can at times make the head hurt a bit, so perhaps it should be taken in small doses.

By the way, do you have any idea how fast you have gone on your fish?

[Roy Stewart]

I think what Roy is trying to say is a falling body will fall faster if it's heavier

No I'm not saying that, I am saying that the thrust which surfboard and rider experience is directly proportional to mass. . . . .

but to say a heavier body will accelerate faster (when subjected to the same energy source as a lighter one) is simply bad science.

Obviously that's nonsense, but I haven't heard anyone on this thread suggest such a thing. . . . remember that the energy source is proportional to mass.

Lets imagine you're pushing a car in your driveway, same driveway, same pusher. What's going to move quicker...a mini or a ford pickup?

You still seem to have missed the point that the energy which drives the board and rider is proprtional to the mass of the board and rider.

It's one of the wonders of surfing, start to appreciate the awesome consequences of it.



That really should be the end of this thread.[/quote]