leong

28 minutes ago, Jim Snyder said:

Sorry, I still don't buy the "locked paddle". I'm willing to call it an "apparently locked paddle" but physics would argue otherwise. The only way to avoid the equal and opposite  reaction is paddling in a medium that offers total resistance in a boat that is capable of zero friction.

The punter would find his "punt rod" or whatever he calls it useless in your 100 knot current, wouldn't he? When they turn upstream, the hundred knot current would capsize both of them.

I'm thinking of taking up punting now.

Yes, the locked paddle is only an approximate lock. The bigger the paddle the closest to a lock if you have a good stroke.

Yes, the punter couldn't push the pole fast enough to push off the bottom going downstream in a 100 knot current.

>>the hundred knot current would capsize both of them.

This is a hypothetical situation for the purpose of a hint. So forget capsizing.

Anyway, I think your answer is that the paddler would win the downriver race, right?

Now use physics to answer the upriver race. Hint: think of the power exerted to move the boats.

2 hours ago, Jim Snyder said:

Ok I'll bite. The current shouldn't matter in either direction but this would be a stupid brain teaser if I weren't missing something. It reminds me of the stupid argument that it's possible to plant a paddle in one place in the water and propel a boat without any backwards paddle motion with respect to water.

Okay, first let's get the "lock the blade" out of the way. See this video.

With regard to the race, I'm not sure if your saying that it will be a tie between the punter and the paddler in either direction or that the same boat will win in either direction? Hint: Think about this: Suppose the river current is 100 knots. Going down-river the paddler will travel at 105 knots ground speed (100 knots free from the river plus the 5 knot paddling speed). Do you think this applies to the punter too?

End of hints.

Time for a brain teaser:

Puck the punter and Paddy the paddler can both propel their respective small craft at 5 knots in still water. They decide to race in a river flowing at 4 knots.

Who will win the upriver race? Why?

Who will win the downriver race? Why

Punting

Hey Bob,

Roger and I used to take a long round trip paddle almost every week between Manchester Harbor and Milk Island. Speakin' of old paddling partners, I wonder where Marjorie is.

I now paddle or sail almost everyday for six months each year in SE FL. I'll be back to "America" by mid May.

Leon

4 hours ago, Phil Allen said:

Take home is that Neanderthals (who weren't our ancestors to be precise) likely colonized islands that could only be reached by some sort of watercraft.

 

Actually, we share about 2% of the DNA of the Neanderthals. It accounts for our excellent forward stroke and Eskimo rolls.

On 3/27/2018 at 5:36 PM, Alex Debski said:

"Kayaking is an absurd form of long-distance ocean travel. All the big muscles in the body are useless."

 

Someone didn't learn about torso rotation. When it really counts!!!

Even arm paddling uses fairly big muscles; i.e.  shoulders, biceps and triceps. I think he means paddling is not a high force exercise like in weight lifting .

Of course paddling faster increases the force exerted, but you eventually reach your maximum available horsepower (since power equals force times speed). The drag force increases exponentially at or above hull speed. Even a world class sprinter putting out his maximum of 300 watts of power to go at 13 knots is exerting a force of under 16 pounds.

Thanks, Jane. I just ordered it.

My Pentax waterproof camera finally died. I'm looking to replace it with an inexpensive waterproof camera. This Lumix model doesn't have a lot of features like GPS, but I don't care. Any first hand knowledge on this camera?

15 hours ago, Brian Nystrom said:

A brave woman doing amazing work, especially considering she was holding her paddle upside-down and backwards.

I reported this paddle-position anomaly here several years ago. I'm on the water almost everyday (either paddling or sailing a small craft) in southeast Florida and the anomaly persists; i.e. anecdotally, 80% of paddlers here hold their paddles as you describe. If it was random it would be 50%. Even when I correct someone they often they revert to backwards after they land and relaunch. Perhaps there's a thesis topic waiting for some Ph.D. student in the psychology of ergonomics and/or perceived paddling hydrodynamics.

https://paddling.us3.list-manage.com/track/click?u=783950cb0b5631ae167c815a6&id=7d9a4bc8aa&e=c16e7dc81e

9 hours ago, Brian Nystrom said:

 

Pick your paddling partners carefully!

Hmm, it's not that I refuse to paddle with anyone who would paddle with me, but the way it works out, I mostly paddle alone. Nevertheless, I did choose myself carefully and if I fail a roll I usually use a paddle float for a re-entry and roll.

Because of impedance mismatch I don't think you'll get anywhere near the 6dB to 9dB of gain that the link indicates. Besides, as Ed indicated, the height of the antenna is the main contributor to range. Once I did a radio check from Plum Island with my handheld and the CG station in Boston said I was loud and clear.

10 hours ago, Pintail said:

You meant <purling>, Leong?  ;^)

Sir Christopher, you’re usually correct, but probably not this time. The definition of purling has to do with knitting; it's not the surfing term meaning the bow has submerged under the water while sliding down the face of the wave. I’m in good company spelling it pearling.

-Leon

On 11/10/2017 at 3:58 AM, Paul Sylvester said:

At the moment he realized he might have trouble should he have tried to slow the boat or speed up to get more in front of it?

 

My guess is speeding up would have lifted the bow and prevented the pearling (bow diving).

After capsizing like that most NSPN members would have rolled up and continued surfing.

"A well-designed sea kayak paddled by a competent, prudent individual may be the most seaworthy craft afloat."

-Yachting Magazine, April 2001

A surfboard is pretty seaworthy, too.

http://www.sun-sentinel.com/local/palm-beach/fl-reg-capsized-boat-rescue-20171030-story.html

I paddled though the Jupiter Inlet twice. Sometimes it’s quite an adventure.

About twelve years ago I met Gene for the first time while I was tuning up my roll at Walden Pond. Gene was there in a sea kayak. Because he had never paddled in the ocean, I convinced him to meet me at Lanes cove a few days later and our friendship began. He soon joined NSPN.

Within a few months Gene had mastered a reliable roll. Gene, several others and I met weekly to paddle from various put-ins on the north shore. Several years later Gene started to slow down. We both assumed it was due to normal aging.

But about seven years ago Gene was diagnosed with cancer (a fairly rare blood disorder called Multiple Myeloma). For sure that accounted for his slowdown.

In many ways Gene is a hero. Through many years of chemo, blood transfers, broken bones, two complete hip replacements, etc., he kept paddling whenever he could and made the best of it. What more can a sea kayaking hero do? He clung to life as long as he could. Unfortunately, the cancer finally beat him.

RIP Gene (aka Chip)

-Leon (aka Biff)

1 hour ago, leong said:

Correct. Obviously the paddle is moving, but not much. A wing paddle locks better than a flat Euro paddle which locks better that a GP paddle.

>> I cant' believe I've gotten sucked into this.

Resistance is futile.

I think the center of rotation (pivot point) is close to the center of the paddle. Say half of paddle length is 100 cm. Thus the top of the blade is ~ 90 cm from the center of rotation. Thus the bottom of the blade moves ~11% faster than the top of the blade (100/90).

Correction: I think the center of rotation (pivot point) is close to the center of the paddle. Say half of paddle length is 100 cm. Thus the top of the blade is ~ 80 cm from the center of rotation. Thus the bottom of the blade moves ~25% faster than the top of the blade (100/80).

6 hours ago, Jim Snyder said:

Without this compensation the boat would slowly grind to a halt like a pendulum if the paddle never went back faster than the boat went forward.

 

Correct. Obviously the paddle is moving, but not much. A wing paddle locks better than a flat Euro paddle which locks better that a GP paddle.

>> I cant' believe I've gotten sucked into this.

Resistance is futile.

1 hour ago, mhabich said:

In the video the end of shaft/top of blade may be stationary wrt the water, but the blade below the water is moving through the water, since the paddle pivots about the top of blade. 

I think the center of rotation (pivot point) is close to the center of the paddle. Say half of paddle length is 100 cm. Thus the top of the blade is ~ 90 cm from the center of rotation. Thus the bottom of the blade moves ~11% faster than the top of the blade (100/90).

6 hours ago, rfolster said:

That was a confusing point for me since I have always understood that there should not be any velocity of the blade.  Isn't the blade to remain stationary with respect to the water and the boat pulled passed it?

That's called locking the blade. It's theoretically not possible but this how-to video shows how to almost do it.

3 hours ago, Jim Snyder said:

I think that's how we want it to feel but in reality unless the water was in a sense a solid, this is not possible.

Exactly. But a larger blade will move a larger mass of water and thus does not move through the water as fast. From a mechanical efficiency standpoint that is a good thing, because the kinetic energy of the water is lost. However, there is a trade-off. It also reduces your cadence and that may be a bad thing. That’s because, according to Hill’s Equation, there is an optimal cadence where human muscles can put out their maximum power. So that’s one reason people use smaller blade paddles and, perhaps, GPs.

On 9/16/2017 at 6:57 AM, rfolster said:

Blade Velocity = 4 knots (based on average paddling speed instead of using some incomprehensible time vs distance in nanoseconds or something like that)

Rob,

Note that the blade velocity should be with respect to the water, not with respect to the moving boat. If it's with respect to the boat you have to subtract the boat velocity to get the velocity with respect to the water.

6 hours ago, rfolster said:

 

I think an issue I have with your time assessment is that all other things are to remain equal.  I am specifically referring to your love of power and work.  In order for your formula comparison to be accurate, the same amount of work needs to be performed at each calculation.  If you apply the same amount of work for the steady-state boat to increase the stationary boat by the same 0.1 mph per stroke, it will never increase its speed since you will loose the .1 mph between strokes.  However, even with that aside, if we were to say that the boat could accelerate to 5mph using your formulas, the time it would take to accelerate the stationary boat to 5mph would be more like 50 seconds based on 5mph (final speed) /.1mph (per stroke).  This would change your average acceleration per stroke to 2.78*10exp(-5) [mph/sec squared] to which I contend is not comparable to the acceleration while paddling since it is half the speed.

 

I made up some example numbers for this. My point was to show that while you are paddling, each stroke must accelerate the boat. I included the comment  because someone (outside of this thread) said that, in steady state, you're not accelerating.  I'm not trying to equate the work of startup vs.steady state or even the average acceleration. When I paddle fast it's quite noticeable that I pull very hard at the start of the catch. That results is a short burst of acceleration. But I just (based on my guess of 0.1 mph and 0.5 secs) computed the average acceleration. Nothing more, nothing less.

On 9/13/2017 at 3:56 PM, leong said:

didn't mean this quote. How do you remove it?

Rob,

Your calculation for M (mass of water) and V (blade velocity) is unnecessary if all you want to do is compute the ratio of velocities for the conservation of momentum approach.

To compute the percentage change in velocity for two different boat weights you perform this divide
(MV/245)/(MV/240)

Because MV cancels out the result is

240/245 ~ .98 (a 2% decrease in speed)

But perhaps you’re onto something; i.e. your values of M and V result in a very small kayak velocity (~ 0.67 knots as you calculated). That would mean that the contribution of momentum to accelerate the kayak is trivial compared to water drag.

However, I think the problem is that your value for M (which you express as weight = 41 pounds) is wrong. With each stroke your paddle is imparting momentum to some theoretical volume of water. And if you know what this theoretical volume of water is you can calculate M.  But how do you what is the theoretical volume of water in the conservation of momentum equation? It’s a complex problem in fluid dynamics. But if your estimate of M is reasonable then you’ve shown that drag is the more significant part of the slowdown with increasing weight.

I am aware that the answer I gave is an overestimate of the total percentage of slowdown just due to the momentum argument; that’s because it doesn’t account for the slowdown due to just drag. But the Guillemot Kayaks link I gave does use a conservation of momentum argument, just like I did.

-Leon

2 hours ago, leong said:

Note: if the velocity is (east = 3 knots, north = 4 knots) you're moving in the northeast direction at 5 knots.

1 hour ago, lhunt said:

 "The GPS will always try to keep you on the current line whether it's the original line or a newly computed line."  Probably Leon meant "keep you on the correct line" or something like that.

Ha ha, yes. I probably meant the correct current line. My head hurts!

PS

Note should be: if the velocity is (east = 3 knots, north = 4 knots) you're moving at 36.9 degrees at 5 knots.

Note above should have be: if the velocity is (east = 3 knots, north = 4 knots) you're moving at 36.9 degrees east of north at 5 knots.