Hi Roy,
Yeah, the difference in fall energy is a fraction of a km/h - but still there. I think it's obvious that a heavier board gets its' advantage from it's significantly greater momentum.
A heavier board needs more energy to get it to that same speed... But fortunately there's far more energy made available than any board can harness, thanks to the wave itself. What I *didnt* put in before was the contribution the forward motion of the wave makes to energy storage (and subsequent velocity). That is going to be in the same order as the air drop factor itself I reckon, but can be tapped repeatedly over a ride (assuming it is in a position to do so - velocity, weight, etc).
Perhaps the people who say the momentum advantage is neutralised dont understand the relationship between velocity and momentum? If you understand that and play with the equations (even a small bit) its pretty obvious, I think.
And yes, a heavier board (all else being equal) is
always going to have a momentum advantage. I seem to recall mentioning this on Sways once... I forget and cant find the post
I'll be happy to eat those words if someone can prove otherwise... But I can't see that happening.
IMO it's easy for novices to skip over the significant of design expressed by Cd. It's important to remember that the Vt equation is formed by two linker sub-equations. And that every component of those sub-equations is equally important... Almost! Most of the variables themselves are built from other equations, but luckily the desired result for each of those is already well established (like gravitic acceleration on earth or the density of air). The same isn't as true for Cd! The drag coefficient is very difficult to calculate and is usually obtained through testing, rather than calculation.
Cd is always a value between zero and one (at least on this planet
). And because Vt is such a small number it has significant weight in the equation results. A small variance of Cd has a big impact. I used a constant value of 0.2 for this round of testing, which is a fairly low value and in the range a surfboard probably has.
Interesting comments re the tunnel fin. I suspect that tuning foil and careful mounting in relation to how the board travels/rides would be quite important.
RoyStewart wrote:Thanks for all your careful thoughts and calculations, it's really a great relief in a way, and a nice change from fighting off the rabid wolf packs !
No worries
Physics is the search for truth. Not a wrestling match between individuals
... Although sometimes you would think otherwise if you watch some physicists "debating".
Yeah, muscular input is interesting. It will, again, come down to energy transfer, storage and release I think. The more easily a board can be thrown around the more energy can be sent its way by the rider. Think of the difference between cutbacks on the two - very fast on the light board and more drawn out on the heavier. But a lighter board cannot hold on to potential energy like a heavier board can so it needs to recharge more often. A trade-off. Sometimes maybe a big one. Not sure how measurable it will prove tho.
Another design factor I'd like to discuss is the cooncept of "true area of contact"... Given two apparently identical surfcraft with the same surface area being wet they will not necessarily experience the same amount of drag. A good example is where one is highly polished on the bottom and one is not... This area can be counter-intuitive and I'm not sure anyone really has it nailed down yet - claims to the contrary. Obviously features like concaves also come into this too.
Hi Rich,
I don't think anyone is missing those points (at least, I hope not). But it sometimes helps to think about things in a static sense before adding more variables.
The calculations, etc discussed above necessairly simplify things a bit to identify the maximum effect of gravity, acceleration and momentum... And ideal situation, if you like. Because the wealth of physics available tells us there are certain basic truths about the world. And one of these is energy transfer, storage and release.
I think a good rider can use a really good cutback to to end high up on the face and reenter the curl. And they *are* using the potential energy in their body to store more energy in their board and boost it up there where they can then recharge using the wave enrgy (via gravity).
Anyway, just my 2c... Interesting discussion!
-doug
