Optimum Pumping Techique

It happenes, allowed or not, in all competitive fleets. Regardless of the right or wrongs, I'm interested in understanding the theory of how to do it well.

Graeme, Windsurf pumping is more like a bird flapping it's wings than rowing isn't it?

As I said earlier, I think the optimal frequency is related to a Strouhal number of around 0.2, but I'd be amazed if the RYA haven't funded research into it.

Don't get me wrong Rupert, I'm not advocating pumping. But it happens legally in some classes, and seems de facto allowed in others. Therefore someone must have researched the science of how to do it well, measuring the performance deltas of different techniques.

Hmmm, interesting thoughts and a complex subject. Time to do some digging.

I think its a complex thing and not something that can be boiled down to a straightforward number. Pumping in the traditional sense, i.e just pulling in an armful of sheet, doesn't generally work well unless you were sheeted wrong in the first place.

Depends on the sort of kinetics that you want to do, point of sail and circumstance.
There is an engineering side to it related to natural frequencies, which in turn is a function of mast stiffness, staying, sail shape (square top to triangular). How light / responsive the boat is also plays a part.
I'd take issue with Graemes statement that windsurfer's rigs are more responsive that (carbon) dinghy masts, as even unstayed dinghy masts are a lot stiffer in terms of % deflection vs length than windsurf masts, and nat frequency is a function of (stiffness / weight)^0.5. Windsurf masts are just pumped much quicker 1:1 by proper athletes!.
Also, a lot of what you do in a windsurfer in the light, esp downwind is predicated on having a UJ i.e. paddling the rig through the air. Upwind stuff and well powered downwind is a lot more jerky though, and I think as much to do with unloading the feet as flapping the rig. NB jimbos technique at WSF showed that the board was rocking side to side a lot, the pros would have the board at a constant level of heel.

As for the kinetics, upwind in most boats hiking or trapping when powered some kinetic bounce works well in waves to "unload" the rig and rudder as it loads up going into / up a wave. Done well it can also steer the boat, cutting down on rudder use. This would all be counterproductive in a steady state i.e completely flat water environment. In light airs you don't do this as you are not trying to shed a little power as the rig loads up.
Coming out of a lighter airs roll tack or gybe, or flattening after initiating a steer due to heel, you are generally fanning the sail, and looking to have a component of wind associated with the roll, i.e. from the beam especially at the top of rig. So the boat is rolled flat sheeted appropriately over the course of maybe 2-3 seconds, with the sheeting adjusted appropriately as the roll ends. Out of a roll tack you'd sheet in a bit to compensate for the rig no longer thinking its reaching. Depends a little on how much apparent you've generated.
Downwind, to initiate surfs on proper waves you'll  generally have heated up to build speed to catch the wave, then its juts a matter of sheeting to catch up with apparent as it comes forward, then steering and sheeting to maximize length of ride / avoid sailing into wave in front. So really thats just sheeting, albeit sometimes you have to sheet in quickly if its a fast surf.
The more dynamic / transient stuff is more on the reaches in the choppier stuff where again you can bounce the boat over a wave. Drop maybe a foot of sheet and and catch it whilst bouncing on the boat. Really transient maybe 0.5 seconds. You aren't really sheeting per se, but its a little transient burst that can get you over or onto a wave. Like the upwind stuff, its not "rowing" in a dinghy as such as if you just did it continually on flat water you'd be slow, as the recovery from the burst more than negates the burst itself, but pays for itself if it gets you a surf or pops you over the wave in front. So very skillful.
Its noticeable to me that on say a Zero, despite having a much stiffer lighter rig and hull than the laser, the (small) square top sail sheds so much power dynamically that the transient stuff is if anything less effective than the laser with triangular sail. The upside is that the square top is dynamically smoothing the ride upwind when powered so you don't need to be so physical as in a laser if you don't want to be.

The finn techniques downwind look like they are very much predicated on being able to rock the boat and sheet 1:1, not quite windsurf style UJ articulation but nearly. It looks fussy to me but no denying its skilful and atheletic, one thing is for sure it creates a vast amount of disturbed air near or downwind.

Two points.

1) Yes Peaky a lot like a bird flapping it's wing

2) Dan I didn't mean the efficiency of the rig, I meant being a rig free of being fixed in one plane, it is able to be moved more flexibly than a dinghy, the key thing being the ability to let the front go infront of the back in order to scoop more air into it which can then be fanned just like peakies bird. It's a fact most windsurfing rigs are crap for pumping, which was why I used to design and build my own with a tighter leech, those floppy leech things were hopeless.

I had a think about it and I've worked out a little basis for an equation those who like these things could consider applying to dinghy pumping.

If B = the boom length,
and V = the velocity of the boat in metres per second. (not the wind speed, imv it's the created wind we're looking for at these low speeds)

Then a simple equation to give an idea of the optimum pumping rate given the refresh period, R,

would be R = B/V

It's a start at least.

Using a laser as an example. Boom length = 2.76

at 5 mph = 2.2352 mps

Then the optimum refresh time would be 1.23 secs. between pumps.

Edited by iGRF - 07 May 18 at 3:50pm