That’s correct too
Unfortunately, last time I used that example (a couple of years ago), everyone claimed it was not applicable. Well, it is applicable. It's nice to see that some people understand the basics.
Great discussion
while I was aware of the vector arithmetic involved in ferrying and relative motion in general, I did not have an intuitive sense of the side pressures on the hull.
GBG already answered it, but the answer to my question is thus that it doesn’t matter (except upon entry of fast current etc) because there is no difference in pressure from one side to the other. What does matter while paddling, however, is the difference in pressure between the upstream and downstream ends, making corrections from the downstream end much easier.
Another bullseye
Still, it's worth saying that most fast-water ferries are across small swaths of current, so most of the time, you will need to put quite a bit of effort into either resisting or at least *planning for* that initial "blow around" of the bow as you enter the flow, and also because in these cases, a good portion of the run will take place while your boat still has momentum (in other words, while it is still in the process of being accelerated by the current, and that's explained by
FORCE = MASS x ACCLERATION again).
This principle I've been trying to convey is about what happens after that acceleration stops.
I meant when “in” the current flow; more
You answered it by answering no heel is necessary.
I disagree because that answer ignores (at least) water friction, but I suppose we've been ignoring that for this entire exercise.
Suppose you are side surfing in a hole, stationary versus the earth in all directions. Does it matter whether you heel upstream or downstream?
Suppose you are jet ferrying across an upstream wave face that extends across the entire river, as below a river-wide ledge. Does it matter whether you heel upstream or downstream as you jet ferry?
Suppose you are upstream ferrying across a strong current when sitting near the stern of the canoe. You are an effective switch paddler or even using a double paddle (i.e., equalized paddle forces on each side). Will your bow tend to be blown downstream or just stay at the same angle?
Still Not There
"I disagree because that answer ignores (at least) water friction, but I suppose we've been ignoring that for this entire exercise."
We are not ignoring water friction. When talking about ferrying across broad stretches of flow (very unlike your two examples here), friction of the water only comes into play in terms of limiting your boat's speed as it moves *forward through the water*. It sounds to me like you are still envisioning sideways movement of the water impacting the hull or passing by the hull from one side in situations where there is no counteracting force to make that possible, such as my example of ferrying across a big river like the Mississippi (though this principle is easy to see even on very small rivers). In your examples below, friction with the water is what will flip you if you don't lean properly, but as described in each answer, that's an entirely different situation.
Note that in the example I've been using, you can be out in current of any speed that you wish to use as an example, so you are definitely "out in the current flow". One key difference, though, is that in the absence of an external driving force applied to the boat (see below), you cannot ferry straight across a current that moves faster than your maximum paddling speed. Once the current is faster than the fastest speed you can paddle, you direction of ferrying will have some downstream component. Once you have a powerful driving force such as surfing, you can "hold your own" in currents much faster than you can paddle, thereby avoiding downstream drift.
What I'm trying to explain can only make sense after getting a handle on the basic concepts of relative motion, and to try to figure out why the various non-ferrying facts I've mentioned (which also involve understanding relative motion) can't be ignored. But I'm open to questions.
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"Suppose you are side surfing in a hole, stationary versus the earth in all directions. Does it matter whether you heel upstream or downstream?"
YES! In this situation it does, but in this situation there IS a driving force pushing your boat against the current and that force is not related to the water itself (as it has to be). Dare I confuse the issue and point out that the source of the force in this case is gravity? Anyway, in this case the motion of the boat relative to the water really IS sideways. You'll flip in an instant if you don't lean so that the "approaching water" (now, this term is talking about water velocity relative to your boat) hits the bottom, not the side of the hull.
However, see the very bottom of this post, because the more ideal the surfing wave, the more straight through the water the actual direction of travel relative to the water (not the river bottom) will be and the less lean will be required. Don't be fooled by the fact that any sudden veering action leading to an angle that's farther away from an upstream heading will produce a momentary acceleration (indicating unbalanced forces), and you'll have to lean pronto when that happens.
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"Suppose you are jet ferrying across an upstream wave face that extends across the entire river, as below a river-wide ledge. Does it matter whether you heel upstream or downstream as you jet ferry?"
Again, yes it matters, and once again, your boat is being pushed against the current by an outside force (and again that force is gravity, just as with all surfing situations), not by pushing against the water with your paddle in a standard power stroke. In this case, if your boat's heading is somewhere to the left of straight upstream (so you are ferrying to your left or toward "river right"), gravity holds you on the low portion of the wave and the water passes under your boat on a diagonal from forward-right to rear-left (relative to your boat), so you have to lean to the left, lifting the right bottom side of your boat to face that oncoming current.
Even in your examples, everything can be explained by relative motion. It's just that the relative motion between boat and water are very different in your two examples than in the one I've been stressing so far.
Just to stir the pot and confuse the issue even more, in that situation of surfing a river-wide wave to ferry all the way across, the diagonal motion of water beneath the hull will become almost nonexistent if the low spot below the wave is broad that the ends of the boat are not in any slower turbulent zones. On a really good surfing wave, the boat would basically be shooting forward against the water at the same speed as the current in the same manner as a surf-boarder on an ocean wave. And that example could be duplicated with a model car riding on wheels. YOu'd have a conveyor belt that runs over a hump and into a trough before rising and leveling off again. A non-powered toy car, placed in that trough as the belt moves, would be held in place by gravity and thus the faster the belt traveled, the faster the car would go (boats do this when surfing as well). If the car were placed in the trough on at some kind of angle away from straight ahead, it would shoot off at a right angle toward one side. The motion relative to the stationary ground beneath would be on a diagonal, but the motion relative to the conveyor belt (like the water in a river) would be directly forward! Most waves I've seen like the one you describe are not all that ideal, but even so, a boat that ferries under surfing power is normally going a lot closer to straight ahead *through the water* than diagonal.
And my third, stern heavy example?
I added a third, stern heavy canoe example by later edit. You may not have seen it. I think your answer would be instructive.
I think “relative motion” is completely irrelevant to the OP’s topic, but I’m still saving that opinion for later because I think your elucidation of the issue has been generally instructive.
Friction is slightly relevant to ferrying because a drifting canoe will not drift at current speed. It will drift slightly slower.
Your responses to my two surfing examples aren’t completely clear to me, as you seem to be saying heeling (leaning) downstream is necessary to counteract a gravity force or a water friction force – which is it? We agree, I’m sure, that the surfing canoe isn’t moving downstream because of gravity, but the question is about what necessitates a hull heel. Perhaps it’s to counteract a different force phenomenon: differential current speeds in a wave/hole resulting in differential Bernoulli pressure effects on different sides of the hull.
I may be oversimplifying
and I have missed much of this discussion, but I disagree that the forces on both sides of the boat are equal during a ferry. They may be consistent, but they are not equal. The force on the upstream side of the boat has to be great than on the the downstream side of the boat to cause the boat to move sideways when the paddler is doing a forward stroke. If the forces were equal, the boat would move straight forward. Vector analysis explains the motion, but good paddling stills applies, which means raise the side of opposition (upstream side), paddle on the downstream side of the boat, and correct at the downstream end.
Acceleration can’t stop during a ferry either, or your lateral motion will stop and you will begin moving downstream.
right !
Acceleration can’t stop during a ferry either, or your lateral motion will stop and you will begin moving downstream.
the action begins and ends there.
all other analysis and products thereof are secondary for not directly related reason or actions.
for example, in swifter rivers flows or at John Wayne State Park, a secondary move may be pinning the bow into a current then driving forward with a stern propulsive ‘directional’ move while edging.
Ok but these movements support the initial bow entry propulsive motion.
or a downstream eddy turn …
Both sides of the coin.
I don't know if this will help or confuse even more, but both sides of this debate are correct. Here goes my try.
Relative motion is true both to you and the boat AND to the observer standing on the shore.
Imagine you paddle to the middle of the lake to do some night fishing. You do not drop an anchor. During the night the lake magically starts to flow, very slowly at first and constantly picking up speed until the observer on the shore tracking you with GPS sees that your doing 2mph. There are no waves or hydraulic features, just flat water moving at 2mph. To you in the darkness, you're still sitting still and the fishing is good.
Later, before daylight you decide to paddle back to shore, you do a perfect bow draw to turn 180 degrees and start your power strokes. The resistance on the paddle is the same as starting up on flatwater and the same bow wave. Once you're paddling at your cruising speed of 2mph, you do any corrective stroke you would do while traveling that fast. I don't think I would try a bow draw for a correction, but use a stern pry or draw since it's easier in the eddy end of the canoe. Now you notice that strangely, the bow wave seems a little larger (like it would be when traveling 4mph) and your strokes have to be quicker also to feel the same resistance on the paddle. The boat is traveling at 4mph through the water even though the observer on shore sees your boat standing still.
You mistakenly think you're going in the wrong direction. Do any stroke and lean that you would while traveling at 4mph on flat water to turn 180 degrees. You want to make up some lost time and increase to your top paddling speed of 5mph. Now the observer sees that you're in fact doing 7mph. The resistance on the paddle and the bow wave is consistent with your experience of 5mph.
You suddenly realize that your original heading was correct and do a bow jamb to turn 180 degrees. You dump your canoe in the darkness because you were actually doing 7mph and didn't lean. Only your momentum carried you over during that snap turn. It was not due to any factor other than momentum, the same as it would have been on flat water while traveling at 7mph.
Sometimes relative is really relative for staying open side up.
My apologies to the forum. My statement about the bow jamb at 7mph is wrong. The current is 2mph thus the static pry is only good until boat and current have equalized at 2mph.
dig hole …
buncha thrashers …
OK - I got it wrong…
I agree that the lateral movement of the ferry is the result of “relative motion” (paddler paddling at an angle upstream + downstream current moving the boat downstream = lateral movement) and not the force of the water. I got it wrong when I said “If the forces were equal, the boat would move straight forward.” The boat is moving straight forward and is being carried back by the current. Much of this post has been about that, and I missed it again. It’s just so different from the way I thought a ferry works that I slipped back into old thinking.
I’m still struggling with the comment that the forces are the same on the upstream and downstream sides of the boat during a ferry. It would seem to me that the force on the upstream side has to be greater than the downstream side, and you should compensate by raising the side of opposition (the upstream side) during the ferry. So I went back and looked at my video above, and I didn’t see any leans during the ferries, although the ferries aren’t very long and the current is very mild. There are leans when I pass from slower into faster current, or vice versa, but that is a different situation. If we ever get any water I’ll have to play around with this some more.
Yup - another good example
of relative motion, and the fact that you need to make adjustments when there are different forces at the bow and the stern like a turning stoke or crossing an eddy line.
of course
the upstream has more force than the downstream…is why hull goes downstream.
eddy paddlers are mucking the ferry which is not eddy paddling, a ferry is distinct from leaving an eddy.
leaning or edging, is always present with capable eddy paddlers, river/stream paddlers.
in a sea kayak hull, edging is similar to counter steering in cycling. If one learns early, counter steering is ‘hardwired’ if not the basic turning technique is learnable if pursued like left foot right paddle …
paddling a sea kayak without edging is always evident with most beginners and on…but with the ferry eventually…and the longer the ferry …one considers edging maintaining course…then in doing that discovers the yak is moving faster with a hull curved rudder reducing drag.
whitewater ferries
Since the OP placed this post in the “whitewater” category, I assume that he or she is most interested in whitewater ferries.
Whitewater ferries are usually nothing like the relative motion involved with a ship traveling more or less at equilibrium with a large mass of moving water, such as a tidal flow.
Whitewater ferries are often done in current that is so strong that the paddler or paddlers cannot make it to an eddy directly across the river regardless of ferry angle, even when paddling all out. Conversely, it is not unusual for whitewater paddlers to ferry to a target eddy that is actually upstream of the eddy they exited. In these situations there is definitely movement of the boat upstream relative to the mass of flowing water, and the boat is in fact being accelerated against the water with every stroke taken.
I define jet ferries pretty much as Glenn does. These are quick ferries done across a relatively narrow tongue of fast current, typically at the bottom of a chute. Certainly, a well-formed wave face can be used to facilitate the ferry if present, and if one is the boat often gets ‘jetted’ across the current using no more than a stroke to enter the current and a static pry or draw. These ferries can require careful timing of a necessary change in boat heel from downstream to upstream (relative to the main current) as the boat enters the jet leaving the first eddy and exits the current into the second eddy.
For whitewater ferries it is almost always easier to increase the ferry angle than it is to decrease it. Many paddlers will start the ferry with a relatively conservative angle (little angle relative to the current flow) and allow the current to increase the angle as needed. It is usually much more difficult to execute a major angle correction after the bow has gotten blown downstream on a forward ferry, or the stern on a back ferry.
For major angle corrections, it is almost always easier to execute these from the downstream end of the boat since the current assists rather than hinders the correction. Well-executed stern pries are usually the most powerful correction strokes for an upstream ferry and a kayaker has an advantage since a strong pry and strong forward sweep is available on both sides of the boat.
There is a difference between correcting the ferry angle and maintaining the angle, and sometimes different strokes apply in each situation. Most whitewater single-bladed paddlers do not shift paddle grip, so for an on-side ferry powerful forward strokes with a stern draw component are usually used to maintain angle or for minor angle corrections. For gentler current an on-side static draw can often be used to maintain angle.
For off-side ferry a stern pry can usually be used for even pretty significant angle corrections, but at the cost of significant upstream momentum. Most whitewater single-bladed paddlers will maintain the angle of an off-side ferry by using primarily cross-forward strokes, unless the current speed is gentle enough to just use a static on-side pry. There is such a thing as a cross-forward sweep, but it is hard on the off-side shoulder.
Olympic Ferries
Rarely see a correction stroke from thees guys. Check out the onside ferry at 0:50 where he spins after going through gate 16 to set up an onside ferry over to the upstream gate at 17. Then there is an off side ferry at 1:00 between the downstream gate 19 and the upstream gate 20. These guys are amazing.
http://stream.nbcolympics.com/canoe-slalom-day-4
thanks Eck
wudda missed this…
ESP 7’s one move eddy turns are amazing…needs further analysis
the first paddler, the SA, is ripe for a shoulder dislocation. Benus, too slow, has the posture.
They continuously use that stroke I never learn.