Arch wrote:Yes and no. Boats do move up and down through the stroke cycle, displacing more at one time than another, and just like with speed, the mean displacement is not directly proportional to the mean drag. More variance for the same mean displacement produces more drag. So caustic's idea is that by holding bodies in bow after the release you produce more sinking of the boat at that point in the cycle, made up for later in the cycle. I'm not sure that's right. A quick motion of body out of bow inevitably involves some vertical component which is compensated by motion of the hull, so you may end up with more up and down motion by moving too quickly. On the other hand, as caustic also points out, it's all a compromise like everything in rowing. In the absence of well-confirmed models, we go with what experience says works. I'm with Kit on the Australian approach. It seems best to me in the absence of hard data.completeIgnorance wrote:I don't understand the argument about increasing wetted surface after vertical acceleration is finished. Doesn't a boat (displacement hull) simply displace the weight placed upon it? So, by saying, "sitting in the bow increases wetted surface area", are people stating that somehow the mass has increased just by its positioning? Doesn't the stern lift when the rowers are positioned in the bow? Thus, reducing the wetted surface area in the stern? Wouldn't wetted surface area only increase if the hull was designed improperly?
I think it really does kinda boil down to preference
. The thing you can noticed when you see rowers, especially elite ones, is that when they catch the boat, you do see it lift out of the water a little bit, and when they release, it drops down. In terms of idealities, you want that rise and fall to be as little as possible, because that's energy moving the boat in a direction you really don't care if it travels - up and down, not forward. Now, the boat rise at the catch is pretty much not horrible - the boat sits a bit higher, and there's less overall wetted surface area on the entire shell (because some of the weight of the rowers is transferred as force on the blades, which is why the boat rises).But, sooner or later that weight force that is translated into propulsive force on the oars is going to stop, because the rowers must stop rowing, and that means that that will move that force of weight back to the boat, which is why is settles down in general at the end of ever stroke. BUT, if that weight settles down ahead of the designed COG, you not only have the entire boat dropping back down, but now you're doing it in a fashion that puts a dry portion, the bow, into the water, and at the highest speed point of the boat, meaning the highest friction.
And as it rises back out, water resists this rise a tiny bit through surface tension. some of this excess motion is unavoidable, but the effort isn't to eliminate it, but to reduce it as much as possible. Less bow dive means less increased friction at the finish, less water sticking to the hull as it rises out, smaller wave that radiates from the impulse of the drop/rise.