Author Topic: Heavier Boards Faster?  (Read 23219 times)

PonoBill

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Re: Heavier Boards Faster?
« Reply #15 on: November 02, 2010, 08:59:22 PM »
Doesn't really work like that. This would require a really long post, I guess I'll write it as a Ke Nalu article. The core of the reason is that while displacement limits (the point where the hull starts to push over the bow wave) do mount rapidly as the hull speed is reached, drag also rises pretty quickly with speed. The curve is more hyperbolic than hockey stick. More weight, more hull in the water, more drag. The relationship of weight to hull speed is well known, especially in the scull and kayak worlds where folks have done lots of hydro testing.

One more addition to the long list of articles I've promised myself to write.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

kwhilden

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Re: Heavier Boards Faster?
« Reply #16 on: November 02, 2010, 09:54:10 PM »
Bill,
What doesn't exactly work like what?  Please explain.  I'm pretty sure that I disagree with you... LOL :)
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PonoBill

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Re: Heavier Boards Faster?
« Reply #17 on: November 02, 2010, 11:36:55 PM »
What doesn't work is the idea that at cruising speeds the weight doesn't matter. The Residual Resistance issues are less important at lower speed but the Frictional Resistance remains important. that's a function of wetted area, velocity squared and some coefficients that don't much matter. Wetted area increases with weight. I wish it wasn't so, but it does. Plus paddling is always a matter of accelerating the full mass of the vessel and it's load. Friction slows the craft, paddling applies force to accelerate the craft enough to regain speed lost between strokes. F=MA. If you think through the physics you realize that there IS no such thing as paddling to maintain speed.

Also, in race conditions the ability to accelerate above hull speed is not tied to weight to any great degree, other than higher frictional resistance at higher velocity. The Residual Resistance factors have a lot more to do with displacement to length ratio, the beam, the distribution of volume along the hull and the shape of bow and stern than they do weight. and of course the amount of power the paddler can apply. More weight makes it harder to accelerate, of course.

Really, way too long. I started to reply in detail but it's going to take hours to put it all together. I'll do an article and then you can disagree.
« Last Edit: November 03, 2010, 12:06:08 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

refthimos

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Re: Heavier Boards Faster?
« Reply #18 on: November 03, 2010, 11:27:30 AM »
Have to agree with Bill here.  The idea that there is really a "cruising speed" at which a heavier board is faster than a lighter board doesn't work for me.

SUP and uphill cycling (climbing) are similar in my mind in that while there are a number of factors involved in determining speed (e.g. aero drag, road resistance and dragging weight uphill for climbing, aero drag and hydro drag for SUP), there is one factor for each that really determines speed: for climbing it is how much weight you are dragging uphill, and for SUP how much hydro drag you are encountering).

Intuitively, you know that if you are riding a bike uphill, it is going to be a LOT tougher if someone sticks a 50 pound weight on the bike.  You aren't just "cruising" along when climbing on a bike, each pedal stroke is a mini-acceleration and in between a mini-deceleration.  You are constantly changing speeds, even if imperceptibly. Power meter and cyclometer data consistently bear this out.

Well SUP is similar, in that you are not just "cruising" at a constant speed... You are accelerating your board every time you take a stroke... if you think you are just "maintaining" speed, you're fooling yourself, because if you simply "maintained" speed during your stroke, you would eventually slow to a stop, because you're board is ever so slightly decellerating in between every stroke (and really, probably towards the end of the stroke as well, depending on how efficient your stroke is).  So a lighter board is going to be a lot easier to accelerate, and pull forward through the water, in order to "maintain" speed.

Now if you think that the added momentum of a heavier board is going to help you during the "glide" while your paddle is out of the water, I have a pretty good feeling that is not the case.  I can't say I have empirical evidence to back it up, but I would be shocked if the additional hydro drag created by the heavier board did not more than offset any momentum advantage.

Continuing with the cycling analogy, it is well accepted that the combined weight of bike and rider are really what matters when determining power to weight ratios...  In other words, a light bike will make climbing easier, but taking 10 pounds off your bodyweight (while maintaining the same power output) will have approximately the same effect as losing 10 pounds from the bike (and probably a lot cheaper!).  The point is that you have to consider total moving weight.  Same thing with SUP.  Do you really feel that you would be faster if you strapped a 30 lb weight to the center of your board?  I sure as heck don't.

Six Feet and Glassy

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Re: Heavier Boards Faster?
« Reply #19 on: November 03, 2010, 12:10:43 PM »
I remember reading an article about golf balls.  Seriously!   :D    It said that golfers who said they "had to" have softer balls ( :D) actually couldn't perceive differences in hardness when the logo on the ball was hidden and they were wearing earplugs.

They were judging the "softness" of the ball by what they were hearing.

I have a feeling the same is happening with SUP race boards.  We hear the board donging like a bell weirdly and it just doesn't sound "good".  The more solid sound of a heavier board makes the board "feel" better.

But as mentioned, I think while we're "feeling" better, we're also working harder and going slower.

More weight, whether it's in your butt or built into the board, displaces more water.  And more board under water means more drag.  And the drag is on top of the added weight you're pulling to begin with.  So adding weight to a SUP rider or board is like adding weight AND going up a steeper hill with a bike.
Ken

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Re: Heavier Boards Faster?
« Reply #20 on: November 03, 2010, 12:13:29 PM »
... Can't wait for Pono Bill's article.  Dunno if I'll understand it, but still...Can't wait!   ;D
Ken

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kwhilden

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Re: Heavier Boards Faster?
« Reply #21 on: November 03, 2010, 12:25:16 PM »
To be perfectly clear, let me re-state my opinions.

1. At racing speeds, lighter boards are faster than heavier boards, all else being equal. I think everyone agrees with this.
2. At cruising speeds, and all else being equal, a heavier board *may* be faster depending on the conditions and the paddler.

Why might it be faster? The answer is the same as your argument that a lighter board will be faster:

Quote
You are accelerating your board every time you take a stroke... if you think you are just "maintaining" speed, you're fooling yourself, because if you simply "maintained" speed during your stroke, you would eventually slow to a stop, because you're board is ever so slightly decellerating in between every stroke (and really, probably towards the end of the stroke as well, depending on how efficient your stroke is).  So a lighter board is going to be a lot easier to accelerate, and pull forward through the water, in order to "maintain" speed.

I agree that boards are constantly accelerating and decelerating throughout the paddle stroke and recovery. But you're fooling yourself too if you don't think momentum also is a factor. Consider the extreme case of a board/paddler that has no weight whatsoever. It would decelerate to a complete stop extremely fast the moment the paddle left the water because of friction. So would a heavier board be more resistant to frictional deceleration because of its greater momentum? Would a heavier board hold it's speed better after the paddle leaves the water?

Imagine a situation where you are paddling directly into a small wind chop. Every wave slows you down. Would extra momentum from a heavier board help you paddle through chop more efficiently? I think perhaps it might, but we really should test it on the water. I think there is a good chance that under cruising conditions without chop, the extra momentum may be a benefit as well in certain situations. Again, this should be tested... we're only talking theory here.




« Last Edit: November 03, 2010, 01:11:54 PM by kwhilden »
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rkdjones

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Re: Heavier Boards Faster?
« Reply #22 on: November 03, 2010, 12:58:47 PM »
Wetted area is related to weight so this would argue for lighter being faster.  Acceleration is worse for heavier boards, whether that is a change in speed or height (climbing a hill).

I can see only one argument for the efficiency of a heavier board, probably only valid for relatively flat water and displacement boards.  Unlike bicycling, a board slows between strokes, and each stroke brings it back up to speed.  A lighter board does slow down more.  I think that the turbulence created by the paddle is related to the speed of the paddle relative to the water, so paddling wastes the most energy to turbulence when the board is going its slowest.  If the light board drops speed more between strokes, loss to turbulence in paddling will be greater.

I don't know if this argument really holds any water, but it is the only one that makes any sense to me.

Robert

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Re: Heavier Boards Faster?
« Reply #23 on: November 03, 2010, 01:00:46 PM »
I'm on a 44 lb SUP now. And so far have not had much trouble keeping up with other paddlers (in flat water).

I know that when talking about weight with on a hydrofoil (SkySki or AirChair), many riders think they need the lightest possible ski out there. But what many of them need is high performance... and durable. I imagine this comes into play with a SUP too. As long as the performance is high enough to be acceptable, and the thing is tough as nails, then a certain amount of weight is acceptable.

I've already made one repair in my epoxy board, which undoubtedly would have taken on water had I not fixed it right away.
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kwhilden

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Re: Heavier Boards Faster?
« Reply #24 on: November 03, 2010, 01:27:40 PM »
I did a quick calculation on the increase of wetted surface area from a fiberglass to a plastic SUP. Let's assume it's a 14' x 30" SUP, and that the glass board weighs 25lbs and the plastic board weighs 50 lbs. The extra weight causes a 1% increase in wetted surface area (~0.35 square feet increase). Since drag is linearly proportional to wetted surface area, the increase in drag is 1%. Seriously folks... how many people would notice that? I'm sure that racers would notice it, and enthusiasts that like to paddle hard, but the average paddler, it's probably a non-issue compared to everything else.

For casual touring, perhaps a plastic board that weighs 25 lbs extra won't affect performance in any measurable way. I've done a lot of multi-day touring in plastic sea kayaks that weigh 65lbs vs. 45 lbs for fiberglass, and it doesn't make the kayak slower in any appreciable way at touring speeds.

I like Airjunky's comments.  A little extra weight might be worth it if it also comes with increased durability. It depends on your use.






« Last Edit: November 03, 2010, 01:30:50 PM by kwhilden »
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refthimos

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Re: Heavier Boards Faster?
« Reply #25 on: November 03, 2010, 03:34:10 PM »
First of all, I love these kind of discussions.  This is a relatively new sport, and I am relative newcomer to it at that, but it's cool to be involved in these kinds of debates when SUP design and theory is still in its relative infancy.  And some of us agree with others but everyone in a respectful manner.  Very cool.

With that said, I have no way to verify your calculation that adding 25 lbs of weight increases drag only 1%, but it just "feels" like that is not accurate.  If I go from my current weight of 195 to 220, and am unable to increase paddling strength, it just "feels" like I am not going to go only 1% slower.  Similarly, if I stick a 50 lb weight on my board, am I really going to be slowed only 2%?  100 lbs, 4%?  OK at some point we are going to sink this board! Haha.

I don't disagree that the engine is BY FAR the most important thing in the equation.  I used to race against guys that could ride away from me on a 40 lb bike, my 16 lb carbon fiber rig be damned.  Same would go with SUPs.  And I could see where a hypothetical "weightless" board+ rider would not be as fast as a board+rider with "some" weight, but I still think the correct thing to consider is not board along, but board+ rider, and even a 100 lb female is putting enough weight on the board to avoid the "weightless" situation described.

I have two roto-molded sea kayaks, and I chose them based on durability and price.  And selection, which is largely a result of the first two variables (manufacturers make many more roto-molded yaks than they do fiberglass or kevlar because that is what the (almost entirely recreational) market is looking for).  But I don't think they are as fast as a lighter kevlar boat.  Agreed that the difference is not so significant that a novice will paddle like a pro losing 20 pounds from the yak, but yes there would be a difference.

Heavier SUPs can be the right choice because they are cheaper, offer a greater selection, are more durable, can be repaired, etc., but not because they are faster.  I think.

pdxmike

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Re: Heavier Boards Faster?
« Reply #26 on: November 03, 2010, 04:17:54 PM »
I think this is a great topic, too.  PonoBill mentioned that this has been discussed before--probably referring to this recent thread:

http://www.standupzone.com/forum/index.php?topic=9003.0

Anyone who hasn't read it should, because there were a lot of interesting points made on it, too.

Maybe the subject needs a whole book, rather than just an article.  The book could make the NY Times Bestseller List for both Friction and Non-Friction. 

pdxmike

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Re: Heavier Boards Faster?
« Reply #27 on: November 03, 2010, 04:22:38 PM »
.
Heavier = more wetted surface=more friction.
I've heard that same equation before, but expressed slightly differently:  "The more cushion, the more pushin' ". 

Mitchell

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Re: Heavier Boards Faster?
« Reply #28 on: November 03, 2010, 10:14:58 PM »
One thing i am trying to find out is if there is a BALANCE of the weight where you will have an optimal momentum with the least amount of pulling effort.

The reason i say these sort of things dont necessarily apply to outrigger and surfski and other styles of paddling is because they are using boats that are WAY more efficient in the water and already have amazing glide and extra weight would only make you pull harder.

But in our case stand up boards are these big flat things (to a certain extent) that sit in the water and are affected greatly by the water, or more so than the very fluid dynamic shaped outrigger boats.

Now you say that a heavier board is more board in the water thats just the way it is. But what if one board is double the weight but has a design that lets it be 2 times as buoyant? Im not sure if this is possible but wouldnt that give it the same amount of wetted area but a possibility of greater momentum.

What i am trying to see is if newtons law applies to aid us in the fact that "something in motion wants to stay in motion" and over time saves us more energy than having to deal with "something at rest wants to stay at rest" if that makes sense...

Who knows. I wanna read the article and try to come up with some calculations for myself and post them and see if people could throw things that i did not take into account at me and see if we can all come up with a definitive answer to "is lighter ALWAYS better?"

blueplanetsurf

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Re: Heavier Boards Faster?
« Reply #29 on: November 03, 2010, 11:33:34 PM »
.
Heavier = more wetted surface=more friction.
I've heard that same equation before, but expressed slightly differently:  "The more cushion, the more pushin' ". 
LOL - pdxmike, you are a comedian!

My first unlimited board was a 18' Bark that I bought used from my friend Herbie Titcomb who did not like it because he thought it was too heavy.  It weighs 44 pounds and is a bear to move around but I kind of like the way it feels in the water (but not the way my back feels getting it into and out of the water).  It takes more power to get it going but once it moves, the momentum keeps it gliding, think of a heavy flywheel.  A lighter board will accelerate faster and easier but also decelerates faster.  A heavier board can also be an advantage in windy/ bumpy conditions, where a super light board can be harder to control.  In the right conditions, the Bark is a fast, competitive raceboard despite the weight and I did well with it in many races.  I used it in the 2009 Molokai race, see picture, and finished in 6:15.
I have to agree with the others though, that most of the time, lighter is better.  Using the example used before, think of two boards that are exactly the same size and shape, but one is twice as heavy.  If you put them in the water, without standing on them, the boards will displace as much water as they weigh.  The metric system works well here because 1 liter water weighs 1 kg.  If a board weighs 10 kg it will displace 10 liters of water to float.  If it weighs 20 kg, it will displace 20 liters.  So, the lighter boards will float higher in the water, displacing less water= less resistance through the water.  You can't make the heavier board "more bouyant" without increasing the wetted surface, thats just basic physics.
That said, spending big bucks to save a few pounds is probably not worth it for most paddlers.  The paddle is a different story as you have to lift it up out of the water hundreds of times and even a few ounces will make a noticeable difference.
Robert Stehlik
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Hawaii's SUP HQ
http://www.blueplanetsurf.com

 


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