Why do I feel less balanced and more tippy when I’m stopped than when I’m moving? I guess one answer is that when my paddle is in the water I’m basically enlarging my boat’s footprint, making it easier to balance. I’m guessing there is more to it.
How does this boat balancing issue relate to balancing a bicycle stopped vs moving or standing on one foot vs hopping on one foot.
Maybe this is too nerdy but it’s something I thought about recently as I was trying to become comfortable in my new boat.
And some boats feel more stable
at speed. Depends on the hull surfaces.
Yes
You are correct. And if you feel it tipping get that paddle in the water!
loose hips don’t sink ships
– Last Updated: Dec-10-09 8:47 PM EST –
Your abs are stiff/locked and your are using your head or arms/paddle to "get back 2 center". Use your hips ie:lift/lower a BUTT/hip.You will never be tippy after you can go all the way to the cockpit rim, by using ONLY your hips.
Yup
V-bottoms often “want” to sit to one side or the other at rest, and can feel twitchy when centered.
Whitewater kayaks can feel like they
have little stability at rest, and they also spin more easily if not moving relative to the water.
At speed, they feel somewhat more stable, but are harder to spin, especially some longer “old school” kayaks. I have an old kayak with flattish bottom and flattish sides that, at speed, will bullet right through an eddy if I don’t start a spin a bit in advance.
Law of Conversation of Linear Momentum .
Take a physics course … or try a waveski …
A Kayak is Not a Bicycle
A bicycle relies on the gyroscopic forces of the spinning wheels for much of it’s stability; the rest comes from the continual steering inputs that you give it with the handlebars. The kayak has no spinning wheels (except possibly for those above your shoulders!). It uses the forces inputted via the paddle (and rudder if you are using one).
“Law of Conservation of Linear Momentum”? What the heck is THAT!?
Yes, no gyroscopic effect, but the water
passing over the surface of the kayak may provide restorative forces, especially if some surfaces are flattish.
The bow is plowing through water
so the water on both side of the bow is effectly holding the boat upright.
When practicing heeling drills
– Last Updated: Dec-11-09 2:06 PM EST –
students have a tough time stationary.
They fell much more stable when underway.
Just why I am not sure.
A trough is a trough..the canoe or kayak displaces the same amount of water when still or underway..there is something else going on.
So far this is the best I found
http://www.boatdesign.net/forums/stability/stability-speed-29023.html
pretty whimpy gyros…
…on a bicycle. Mine, at least. No - it’s the steering input and inertia forces more at work on a bicycle. We do a thing called “slow race” with motorcycles all the time, and I do it for practice on the bicycle too. The idea is to see how slow you can go without putting a foot down and still maneuver a closed course. Some might recognize this as Trials competition. If you can find some gyro effect to take advantage of (such as the heavy flywheel in a trials bike) it does help - but in the end, it’s all about balance, control, inertia, force (other than gyro), and geometry. One has to go pretty fast to get any significant gyro effect from a lightweight bicycle wheel, but we still do just fine at moderate speeds.
If you think gyro force is a bigger deal in bicycles than all the other, think about the bizarre practice of upright bipedal walking. We make multitudes of minute adjustments without even thinking about it - or we tip over.
I think that is also the case with narrow boats. The big differing factor would be fluid dynamics rather than the mechanical forces of the bicycle (wheel geometry against road surface, rake/trail of frame, etc). Water flowing over a surface will cause either pressure or vacuum (think of an airplane wing), but either way it will inhibit changes in attitude. If the forces (p or v) are greater, the stability will be greater. You can increase the forces with velocity and make stability increase (to a point).
momentum
Conservation of momentum is that mass times velocity before a collision is equal to mass times velocity after the collision.
Tippiness of a boat has little to do with collision physics.
Thanks for that link KM
Great info
Because
You’re a novice/beginner and not intermediate as your profile shows ? Or you’re just trolling us along. Seat time, I’m sure, will correct that. Discussing it, will not.
Wow!
Someone asks a legitamate question and they get called a troll? Bashed for calling themselves an intermediate? There is always one in a crowd.
Have you been paddling w/ Duckheads?
Every time I paddle with those guys, I lose my balance when we stop.
It’s probably related to that pipe and bottle they pass around.
Common problem
On flat water I feel much more tippy at rest. When paddling in rougher conditions we normally are more stable when pulling, When hutting and both our paddles are out of the water we stand a better(worse )chance of getting bounced out of the canoe. It is also a factor of the canoe(or kayak)…
At a race I will stand up for the National anthem In Randy’s Minn2. I will not stand up in a J-boat or other race boat.
Charlie
Real phenomenon
Why are you bringing the OPs experience level into this? Dynamic stability is a real phenomenon. Yes, seat time will make one able to use it to one’s advantage, but there’s nothing wrong with discussing the physics behind it, is there? This is a ‘Discussion’ forum after all.
Some thoughts
– Last Updated: Dec-12-09 2:51 PM EST –
The links above were interesting, although I think there was some misinformation on the boatdesign.net thread. In particular, I don't think dynamic pressure, drag or vorticity on the hull surface while underway play any significant role. The moment arm of the resulting torques would be too small (or zero) and so could not provide restoring moments of any magnitude. The conservation of linear momentum theorem isn't really applicable, as there are external forces being applied.
It's much more likely that the off-axis forces (buoyancy and thrust, both) of the paddle in the water are used by the paddler to provide the restoring moments while underway in a tippy hull. Looking at other (better) paddlers, I think we are all unconsciously rocking side to side while paddling forward, essentially falling slowly, i.e. rotating, from one side to the other.
The change in direction (from one direction of falling to the other) is no doubt helped by the swing of the paddle to the next stroke, along with torso rotation and movement of the CG of the torso to the other side of the boat. If you sit in a motionless boat and mimic the paddling sequence, while providing no forward momentum, the boat will feel more stable, I think.
If I’m in a tippy boat and need to stay still, I typically take a couple of slow strokes forward, a couple backward and then repeat, to idle in place, so to speak. So I guess I'm saying that I think paddling is more like walking than a bicycle, inasmuch as walking can be considered a controlled 'falling-forward'.
As an experiment to see if hull forces actually play a part in this (seeing as I dismissed it out-of-hand above), I would try the following: Take a motionless kayak with a couple of sandbags in it, tilt it 15 degrees and time how long it takes to come to rest. Then I would do the same thing while towing it at constant velocity. If dynamic hull forces play a part, then the oscillation time will be reduced, and should probably vary with the square of the velocity, i.e. it will be very easy to see. I'll put that on the list of experiments to try in the water channel I'm building.
You could approximate this by giving an empty kayak a shove after deflecting it to one side and seeing if it stops oscillating faster than after a stationary oscillation test. If anyone gives this a try, it would be great to hear about it (my paddling season is over).
Cheers, Carl