Messages

1

Sessions / Re: Small Day in Waikiki

« on: July 10, 2013, 10:35:19 AM »

What band was playing the music?

Brittni Paiva: http://www.amazon.com/Four-Strings-The-Fire-Within/dp/B002VTBH0K/ref=ntt_mus_dp_dpt_1/190-5615107-3998558
https://www.youtube.com/watch?v=StnVHAvpP8I

2

Sessions / Re: Small Day in Waikiki

« on: July 08, 2013, 11:12:53 PM »

Nice.. What board were you on.

DJ

If anyone could pick out a board from Naish's past catalog, I thought it would have been DJ: 9'6" Hokua.

I like to surf as early as safe. In the summer, that's far earlier than sane people are willing to wake up. Even though it doesn't show it, there were plenty of people waiting outside hoping Surf News Network hadn't lied to us. Of Course, no matter what the conditions, we're always blessed with beautiful scenery.

3

Sessions / Small Day in Waikiki

« on: July 08, 2013, 12:41:53 AM »

Just bought a GoPro. Here's my first attempt at a video:
20130629_Paradise

The waves were small and slow, but I did my best to have fun.

4

Technique / Re: High stroke rate inefficient?

« on: June 14, 2012, 01:52:18 PM »

You're still applying the reduction in drag as a negative number, essentially saying you can have negative drag. That's what supplies your increase in velocity without an external force. If it were possible we'd have perpetual motion and mass drivers that could accelerate infinitely.

Following your logic, I go from high drag (hull compressed in the water and force applied) to low drag (no paddle force applied) and velocity increases. When does that stop? Velocity would increase without limit except perhaps light speed.

Forces are vectors. They have magnitude and direction. I'm defining the paddling forces as positive, and drag as negative.

5

Technique / Re: High stroke rate inefficient?

« on: June 14, 2012, 11:16:06 AM »

Ehrawn, that is really interesting stuff. It’s scary that I think I understand it. The chart really helps illustrate your point.
I know you said the numbers you used are BS, but if I understand it correctly …Velocity increase is .0025 and it last one tenths of a second. So in the real world the velocity increase is so small and it is decreasing by the time the blade is out of the water. 

I didn’t put any dimensions on there for a reason. I chose those numbers to keep the lines close to each other on the graph and make it easier to see. My point was, when coaches talk about letting it glide after the stroke for a more efficient paddle, people think they have to pause to maximize that effect, like the OP’s estimate of 3 seconds. While there will be a slight increase in velocity as the board rights itself to a more streamlined position, like Bill stated, drag will decelerate you and if wait too long for your next stroke, you’ll have to exert more energy to get back up to the same velocity.

6

Technique / Re: High stroke rate inefficient?

« on: June 13, 2012, 11:53:14 AM »

Let’s try this again:
Newton's 2nd law states that the sum of the Forces is equal to the change in momentum:

Note that momentum is conserved in a system. Unless acted upon by an external force, velocity will be constant.
Now, take two states for a system:
1) A force is applied to propel the body forward through the water, which also disrupts the natural buoyant forces, putting into a position where drag is increased. The net sum of these forces is defined as positive, resulting in positive acceleration. For the time period while the force is applied, velocity is thus maximum at the conclusion of this period.
2) The force is no longer applied. Buoyant forces restore the body to its least resistive position in the water: drag forces are reduced from state 1.
Since mass is constant, acceleration decreases from state 1 to state 2. However, since momentum is conserved at any point in time and mass is held constant, the change from state 1 to state 2 can result in an increase in velocity. I threw some BS numbers into Excel (see attached).

Yes, acceleration is negative after you release. Yes, righting the board as you recover slows you down less on the recovery. However, at the transition from release to recovery, you can have an increase in velocity.

7

Technique / Re: High stroke rate inefficient?

« on: June 12, 2012, 11:03:21 PM »

Ummm, no.

Even if there were less drag, the only way to increase the velocity of something is to apply a force. And your paddle can't be at the catch at maximum velocity since the boat will be decelerating throughout recovery. Maximum velocity occurs just before recovery starts.

I'm sorry if it sounds like I'm arguing against your experience but what you are describing is not physically possible. High school physics and Newton's Laws of Motion will tell you that.

We're saying the same thing, Bill.

Sum of the forces = mass times acceleration. Forces can be positive and negative. If a force becomes less negative (in this case drag) acceleration increases.

8

Technique / Re: High stroke rate inefficient?

« on: June 12, 2012, 08:24:58 PM »

I think there might be a missunderstanding of what is meant by "glide." Watch a sprint video of  an OC. Here's an example:
NCOCA Outrigger Sprint Regatta #1 - OC1 Men's Open 250m

It's easier to see with oarsmen:
Redgrave Pinsent 2- final Atlanta Olympics 1996

As you pull, your boat/board will sink down in the water. On the release and recovery, it will pop up and run. That's glide. The acceleration isn't due to some magical force, but, because there is less drag on your boat/board as it lifts, you'll see an increase in velocity. Your paddle needs to be at the catch at maximum velocity to keep your speed up.

9

Gear Talk / Re: oxygen for long hold downs

« on: August 10, 2011, 11:31:08 PM »

Pilots train to find a HEED in an emergency. Surfers could too.

http://en.wikipedia.org/wiki/Helicopter_emergency_egress_device

10

Random / Re: What's for dinner?

« on: July 11, 2011, 11:44:23 PM »

kailua pork

? Maybe kalua pork?

Okinawan sweet potatoes (from the state fair, cooked last night after the kids went to bed), spinach salad and a grocery store roast chicken...busy Monday.

11

Sessions / Frontside Roundhouse!

« on: July 10, 2011, 11:46:02 PM »

So I'm still a pretty novice surfer- only been on a standup board for a couple of years. I made it out to my usual spot in Waikiki this morning. I missed the most of the south swell, but, thankfully, I missed the wind, too. A couple chest-high sets rolled in, but mostly waist high this morning. I was a little inside when a slow rollin' wave made its way through the pack. Me and one of the regulars were in the right position to catch it. He backed off, so I took a couple strokes and dropped down the face. It wasn't that steep, so I got a mellow bottom turn and a solid cutback. I was headed back up the face toward the peak, with my weight on my heals. I started to get to where it looked like it would break so shifted onto my toes…only there was nothing to press down on.  The wave jacked up and I was staring straight down the face. I thought for sure I was about to dive head first, but the wave curled over and knocked the nose of my board forward a little. It was just enough to push a little weight onto my paddle, and allow me to dig my fins in for my first roundhouse. Sure, the timing was totally an accident, but this was the first time my instincts took over. This was definitely the biggest thrill of my morning.

12

Gear Talk / Re: Wow! That's different.

« on: July 07, 2011, 09:40:35 AM »

never seen that on a long board

Directional stability; to make a 10'10" board paddle like a touring board

I'm not sure it's a long board any more. This looks like Naish's attempt at a hybrid board. Big clue are the holes in the deck for the tiedowns. It makes since that they would try this with the narrower Nalu since it will run better than a wider Mana.

13

Random / Shark Jumps a Surfer

« on: June 23, 2011, 07:14:19 PM »

http://www.orlandosentinel.com/multimedia/os-fla360-shark-jumps-surfer-20110623,0,3357331.story

14

Gear Talk / Re: carbon flex technology from hockey sticks

« on: June 21, 2011, 12:16:35 PM »

Bill, to confirm, you loaded the paddle from the ends and got it to buckle. It's very possible that you are right about the thickness of the small dia section of tube. The other possibility that the taper really didn't do much to change the stiffness of the shaft.

I agree that a lot of flex is not ideal, for the very reasons you discussed. Instead of trying to make the paddle shaft flexible near the blade, what I was trying to say is that it needs to be less stiff, but stiff nonetheless. Of course, that could be a moot point given what you talked about the joint between the shaft and the blade since we still don't have any manufacturers using monocoque construction.

15

Gear Talk / Re: carbon flex technology from hockey sticks

« on: June 21, 2011, 10:28:07 AM »

We essentially are paddling with "wet noodles" since paddle shafts are uniform in stiffness along the entire length. The free body diagram of the paddle as a force applied at the handle (mostly down), your bottom hand (pulling back) and a reaction force on the blade face (forward). This means the most flex would be right at your bottom hand (~3'). If you moved the max flex point closer to the blade (~10"), you should have less total bend in your paddle. This would mean less energy waisted bending the paddle and more applied to the water.

The question is how you would do this. You don't want more bend, like SeargentFL said, but you can't increase the outer diameter of the paddle shaft since it's limited by the average person's hand size. You could get the same effect of the taper by doing other things, though: change the weave for a higher bending stiffness, decrease the ID on top by adding more layers, etc.