A slippery topic
The Slipperiness of “Slip”
Slip has been a buzzword around boathouses lately, and like most things that enter the rowing and sculling lexicon suddenly, there’s a lot of misinformation about it - everyone wants to seem as though they know something about it and very few of us are willing to admit it when we don’t, so half-baked ideas abound. This post does not aim to be the final word, but rather to explore the most elementary basics of slip as a primer on the least we should know and a revelation of how much we all do not know.
To begin with, and perhaps most importantly, we should acknowledge that there is more than one type of slip. Coaches and athletes alike, though, toss the word into conversation as though everyone is talking about the same concept when in fact they aren’t. Most commonly, when someone says “slip” without defining their terms, they’re talking about slip at the catch, which is roughly defined as the amount that the blade moves between the time that it touches the water at the catch and the time that it begins to propel the boat. More precisely, it encompasses how long/how far/how much catch angle is “lost” between the blade entering the water and the blade having 20 Newtons of propulsive force on it, but 20 Newtons is not a lot, and presumably the force will rapidly increase thereafter, so for the layperson forget 20 Newtons and just focus on the interval between “in the water, not yet loaded” and “in the water, loaded/connected and propelling the boat. As a coach, I have no means of measuring newtons at hand, but I can see connection and load. This form of slip is comparatively easy to get one’s head around, and it conforms readily to the corollary idea that more slip is undesirable and less slip approaches optimal. It is very common, then, for folks who think that this is what we are always talking about when we are talking about slip, and so we fall into the idea that more slip is bad and less slip is good. Likewise, if there is slip at the catch, there must also be slip at the release, with the mirror image definition that slip at the release would be defined as how much the blade moves in the water after it has ceased to be loaded and is no longer propelling the boat. In this case, the blade is still in the water and is literally putting the “brakes” on the boat.
Neither of those types of slip, though, is always or inevitably what your coach is talking about when she uses the word. Oftentimes, what the coach is talking about is a more general and universal concept of slip, by which we mean how the blade moves in the water relative to the start and finish lines between the catch and the release. This is a more difficult spatial concept, and it cannot be as readily labeled good/bad or desirable/undesirable. In this context, slip is both necessary and inevitable, and is to be judged better or worse solely on the basis of whether the blade moves substantially toward the starting line (undesirable), a few centimeters toward the finish line (better), or substantially toward the finish line (optimal). Multiple factors are involved in determining this: catch timing, power application, release timing, as well as catch and release angles and the overall degrees of your arcs. Interestingly, it appears that the most reliable way to get more positive slip of this type is to set your footstretcher closer to the stern in order to steepen your catch angle. Presumably, a steeper catch angle allows the momentum of the boat to carry the blade further toward the finish line as it enters the water, and assuming that your power application and release are in order such that the boat is running well, your blade will emerge from the water substantially closer to the finish line than it was at the moment of the catch. Certainly it is measurably true that winning boats tend to have positive slip and that boats with negative slip are rarely winning crews.
For more information on this topic, I refer you what Valery Kleshnev, Volker Nolte, and Mike Purcer have written and presented on these topics.
