How currents affect pumping

How does a current affect pumping. Lets say you are pumping through a current going one direction, and youre going against that current. Does that mean you are losing the speed of the current, and that you need to make up for that speed to keep the foil from stalling? IE, with no current you need say 10kmph to not stall a foil, if you add 5kmph current against it, does that mean you need to pump the equivalent of 15kmph on flatwater just to go 10kmph against a 5kmph current?

Whats the difference between pumping against a current versus against the wind? Is it the same principle or different?

Would you choose to pump directly into the current to get to the channel asap, or would you go cross-current like you would pump cross-wind instead of directly against the wind?

What happens to your foil when youre going with or against a current, anything special scientifically?

Yes interesting. I got told by a windsurfer that the 15knt wind was only 10knts due to currnet of the incoming tide. I thought yeah only for the very short length of water where my board isn’t up to planing before getting up on foil - wingfoiling not pumping.

cross current conditions are interesting. Several times I’ve been pumping out at just above stall speed and as soon as I turn 90deg the foil stalls out. Cross flow over the foil doesn’t seem to work very well at slow speeds.

In general, you could probably think of pumping into or with a current as running either against a treadmill or with a treadmill (or imagine a people mover like at the airport). The running feels the same and takes the same energy but you either move much slower or much faster depending whether you’re going against or with.

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so you would say cross current is worse than against the current directly?

I would think current impact is primarily to do with with water flowing over your foil. Let’s say you need to be moving at 6mph through the water to generate enough lift to get up on foil. So if you’re going straight into a 2mph current, you have that extra water flowing over the foil so you’ll generate lift at 4mph speed over ground. If you’re going with the current, you’ll generate enough lift at 8 mph SOG. Current at an angle would impact that relative to the direction I guess. How that effects pumping which brings in vertical movement in the water column? Not sure, hurts my head to think about it TBH. :grin:

I foil in a very rippy bay with at least a 3-4kn flow and pumping with the direction of flow is super difficult. Have to keep moving very fast and near flawless with your pumps. Made harder because the rip creates turbulence and unpredictable bumps.

The same spot blows mostly onshore and if the wind is up then you have no chance pumping into the wind with that rip.

Also do some dockstarts and dockstarting against the flow is super easy, and really hard with the flow.

What happens to your foil when youre going with or against a current, anything special scientifically?

I don’t think anything magical. It is only the transition between static and flowing water. The place I foil you kick off a wave and are not in a rip (ie no effect on your speed) and moving at ~12mph over the ground. When you hit the rip, you are moving at ~12mph over the ground, but suddenly your foil is only doing ~8mph through the water and you are at near stall.

(Sailing in England you become acutely aware of the difference between water speed and ground speed with all the tidal currents.)

Pumping with the current seems hard because at 10 kn pump speed plus 5 kn current suddenly there is 15 kn of air resistance (assuming no wind).

Anyone know what the breakdown is between drag from a typical foil setup vs typical air resistance drag?

So pumping in current - once your up and riding in it - is neutral. Your speed in the water is the same - so you cover more ground if your going with it and less if your going against it. The extra air resistance is negligable.

Even the change in speed over ground is MOSTLY irrelevant - becuase the current is doing the same thing to the speed of the wave. The wave has the same relative change in speed so if your chasing bumps its not drastically different.

It does some funny things on takeoff. For catching waves taking off against the current is great - if you can stand on the bottom. In big current i can even stand in one spot ant just hop and go and not paddle and im up and foiling while covering very little ground. I’ve even had spots where im almost foiling in place on the current then i kick out and rocket out at mach 3 in the current. Also you cover less distance on the wave so you get more time to do your deal then when you come off foil the current is taking you back to your take off.

Current going with the wave sucks, its the worst. Borderline uncatchable. Also you cover more downwind/downwave distance faster so less fun.

Theres also some funny stuff in scenarios where you move through differences in current - like longshore current thats different on the inside and outside. You’ll be up and riding downwind in light current then ride the wave in and hit a heavy rip in the direction of the wave and all of a sudden your foil speed throught the water drops quickly (because your momentum doesn’t change) and all of a sudden have to pump like a monster.