You can get there from here.

for some reason i can't sleep tonight. probably b/c i'm thinking about too many things. well here's one of them for ya.

warning: rowing and physics on a collision course. proceed with due caution.

for the last two years, every major race i've been in has been plagued with headwind conditions. both boats i've been in for those two years have been highly affected by the wind. so i've been thinking rather seriously about what the wind does and how to beat it.

in a lightweight boat, everyone is affected roughly the same amount by the wind. that isn't to say that two crews rowing just as well as each other will be able to handle it the same. i know that i am not as strong at the catch as most rowers. especially when the loading increases (headwind) my power output diminishes dramatically.

the common solution to this is to clam up the oars. the inside arc of the handle is shifted a centemeter away from the pin, and the outside arc is shifted 1 cm inward. inside lever is longer. outside arm of lever is shorter. voila. lighter load. side effect is that the handles row a cm further out from the pin. minor issue in a sweep boat. a little more annoying in a scull, but acceptable in a pinch.

my question is, what else can be done to solve the lightweight problem? specifically, when two crews who weigh the same race each other in a headwind, how does one maximize the performance of the weaker crew?

i must begin by looking at the behavior of the boat at the catch. forget everything you know about rigging. mike davenport was right most of the time in the nuts and bolts guide to rigging, but glossed over a couple of major issues about the arcs, almost to the point of being incorrect.

here's my take. the outside arc should be optimized for rowing the most mechanically efficient stroke in the water. the inside arc should be optimized for maximum comfort for the rower. somewhere in between the two is an oar (which i remind you should be straight), and a pin (which must be stationary). the inside arc is much a matter of personal preference. i will concern my self with the blade.

i may express the kinetic energy of a moving boat as T = 1/2 m*v^2. m is mass. v is velocity. grab a high school physics text to follow along. then there is the work-energy theorem. meaning it takes some amount of work W to achieve the change in kinetic energy to accellerate the boat. so from a constant speed (since the wind slowed both crews down the same amount on the recovery), it takes some work W to get the boats up speed by the release. work is defined as W = F*d where F is the force applied and d is the distance that force was moved. for the motivated: there's a dot product in there. project everything in the direction of the boat's motion. details. but what that does is allow the rower to more gently take the catch. the blade grips the water faster because the blade need not be moving as quickly to catch the water properly. there is also very little wasted energy from the blade to the water because the steep angle of attack generates against the back of the blade to lock it in place like an airplane wing. again, details. but this is why we row steep catch angles, okay?

so now there's a secondary benefit to putting all this pressure on the blade at the catch and not moving it very far. by the time the oar swings toward the perpendicular, where it moves the boat most directly, the body has been given time to build more force against the handle. biomechanically, the middle third of the stroke is also the most powerful. however, in a fluid sense, the perpendicular third of the stroke is very wasteful. once the blade's angle of attack lessens, it pulls away from the boundary layer behind it and generates the large vortices of water we see as puddles. very simply, any energy given to puddles is lost and does not go into the motion of the boat. we usually do not worry about this very much, because it is fairly small compared to other more pressing technical issues. minimizing the energy in a puddle is really a matter of establishing a faster lock on the blade and rowing a steep catch angle.

i've taken you through this newtonian look at the drive because it's the way the rowing community usually thinks about it. i think there is a better way. instead of thinking about the forces and angles individually, let's look at the stroke from an energy standpoint. we may do this easily since the rower and the boat each move only in one dimension. (it doesn't really matter that they are the same.) at the catch, a rower puts some amount of pressure on the footstretchers, and [apart from their own accelleration,] just as much pressure bow-ward on the oar. we may assume the rower is stationary at the catch. the handle is moved through some distance toward the bow until the release. integrate the force over the bow-stern distance the handle has traveled, and you find the amount of work that went into the stroke. the energy from this work must go somewhere. as discussed, some of it goes into the puddles, but most goes into propelling the boat forward. regardless of angles or rigging or anything else, the boat takes on the energy put into the handle. this is good because we have simplified the whole problem down to one dimension in space.

going back to the strong and weak lightweight crews, i will note that the wind slows the boat down further than normal. ergo, the catch is heavier than normal, even when clammed. the stronger crew will respond to the heavier (slower moving) load more favorably than a weaker crew, who would respond better to a faster moving load. ah, wait. more physics here. T = 1/2 m*v^2 = F*d = W. abstractly, v^2 and F server the same purpose. there is a constant multiplier between them. energy may be added to the boat either by pushing harder on it or by moving it faster. both have the exact same effect. the slight of hand i will suggest is that a weaker crew must be allowed to keep the boat moving, while a stronger crew may simply push it harder.

the difference happens at the catch. in a headwind, when properly clammed, i THINK (although i have not measured) that the load is heavier at the catch than normal, and consequently lighter at the release (otherwise it wouldn't be properly clammed). so the solution is to lighten the load at the catch where the handle is moving very slowly, and firm it up towards the release where the handle speed is higher. so now it's simple rigging to accomplish this end.

to shift the loading, the first solution i think of is moving the footstretchers abow. catches must come faster, but in a headwind, that's not as serious an issue. it may also be desirable to shift the loading from the outer thirds to the middle somewhat. this would be accomplished by smaller blades or wider spread. smaller blades would be more forgiving at the catch and allow the handle to continue moving for the price of slightly larger vortices in the water. a wider spread would diminish the catch and release angles for a faster/lighter stroke, but again at the price of larger vortices. short catch and release angles would also demand a quicker change of direction at the ends, an enemy to a smooth fluid stroke, but perhaps one that lightweights could more easily get away with.

so there's the musing for tonight. i promise you, it took a lot longer to type than it did to think about.

andy