epoxy vs. Poly

[tomcat360]

hey doug, would you be interested in making a video of you jumping on your board off of a truck

I wanna see what happens! (a EPS/epoxy, that is)

[Roy Stewart]

That's nothing !

I have driven a 2 tonne 1971 Dodge Ambulance up my 12 foot balsa pintail. . . . reversed up it using it as a ramp (fin down) and drove right off the back of it. There was a little bit of damage though.

[Sweet!]

[dougirwin13]

Tomcat,
My current epoxy board isn't up to that :) My next will be. It might be a few months, but if you remind me I'll take some footage with my phone's video camera (up to 2 megapixel).

Roy,
I am not surprised - I have seen your boards before (snappies anyway). Any more 17' action on WMV mate?

-doug

[Roy Stewart]

HI Doug, I think I have another clip somewhere, will have a look.

[dougirwin13]

Thanks. I like the olosurfer clips you have posted so far. The music is good too.

-doug

[Roy Stewart]

I found the clip, here's the short version:

http://www.olosurfer.com/movie_theatre.html

The clip is called '17 footer September 05'

We are also uploading a longer version (more waves, 58megabytes, bigger screen, different sounds) which I will post a link to when it's done.

The clip was the first session I had on the big board after fixing it, so I hadn't ridden it for 18 months, hence a few awkward moments.

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[dougirwin13]

Cool. Thanks for that.

Had to laugh at some of it. :) You riding 17 seconds and some guys on thrusters try to catch the wave... And can't. hehe!

Non-surfing friends of mine even enjoy watching those.

-doug

[Baratacus]

I have a question about the epoxy/eps foam boards. I know a lot of people are down on them because they are lighter weight and have more bouyancy than a traditional Polyurethane foam board w/stringer. They tend to bounce around more on the wave and lack the inertia of the heavier boards to plow through chop. I understand this and how it would impact a surfer weighing under 200lbs. I'm 6' and 240lbs. I bring enough weight with me to plow through any chop I come across. My issue is that I need at least a 10' P.U. board to float my weight properly. The thought of being able to ride a 9'4" to a 9'6" preformance long board really appeals to me. Does anone know what kind of dimensions (thickness/width/length) I would need with an EPS foam board and epoxy resin?

Thanks

[dougirwin13]

Uuumm... Once a board is moving it's buoyancy doesn't matter. The true wetted surface matters (friction physics).

But for paddling, duck diving, etc there most certainly IS a difference.

But you are asking how much :P

There's an excellent technical discussion on the Swaylocks Forum about this whole subject called Can we put the eps = extra float myth to rest once and for all?

You'll notice plenty of numbers bounced around but no one really comes up with a simple rule of thumb.

It all depends on the density of the foam being used.

Rebuild you poly board out of lighter EPS but make it 1/5th of and inch thinner. It won't be too different, but it'll float you better. You should easily be able to loose 6" off a longboard.

But there'll be repercussions. the change in length will necessitate other design changes (in terms of planshape, rocker profile and the various surface contours).

Had enough :)

-doug

[Roy Stewart]

Uuumm... Once a board is moving it's buoyancy doesn't matter. The true wetted surface matters (friction physics).

Mostly true, but to be precise what happens is that as a board accelerates it gains lift from the bottom surface, which starts to replace lift from water displacement, however there is still some significant lift from displacement happening unless the board is going very fast, so buoyancy can still be an issue when surfing relatively slowly. .. . it even happens that surfboards can sometimes ride waves at 'displacement' speeds without planing and then buoyancy is definitely providing most of the lift.

[dougirwin13]

Sure. But the place between displacement and "skimming" is a fine line.

For example, various bottom shapes have different places where they release. Same with rails.

So I am generalising just a little again... For the same reason as other times - the level at which I think other readers on here understand the concepts.

I recall some interesting discussion you, myself and a few others had on Sways regarding board size, true area of contact and physics. Got really interesting. It was around about here, if I recall correctly.

Fine discussion!

-doug

[Roy Stewart]

Doug, you are an archaeologist, I can see that. it was an interesting discussion alright

Now regarding your assertion that the line between displacement and skimming is a fine one, one assumes that you mean that surfboards typically make the transition from displacement to planing very quickly. If that's what you were saying then I agree, except to say that it depends upon the surfboard hull type.. . . . a 17 foot olo board with an even rocker and a pintail has a long transition between dislpacement and planing, in fact it's often hard too pick when the board is planing or surfing at displacement speeds when riding slowly. . . whereas my 11'9" which hasa wide nose with lots of rocker generates so much lift from the bottom so quickly that it just bounces up onto the plane very readily.

Bottom line is that buoyancy can be an issue while surfing, not just when paddling

[Baratacus]

I completely understand where you guys are coming from and I really apreciate the discussion. You both make very valid points. I've been surfing in this area for about 20 years and there are a wide variety of breaks to choose from. I prefere the long board here because you can walk it to compensate for the change in the conditions and the shape of the wave. But when a wave starts to peter out or I need some speed after climbing to the lip I need bouyancy. Thanks for the links to the other topics and I'll get reading up on them right away.

edit:
wow, its amazing how many people have trouble understanding bouyancey. On a longer board, a 10lb saving in weight can be a big deal. I still don't know if it would be worth the extra money for a EPS board, when I could get the same increase in bouyancey by creating a thicker or maybe a wider board. I'd be creating more drag and making the board even heavier though... damnit Jim.. I'm a surfer not an engineer!

[Roy Stewart]

By the way, making the board heavier will, all else being equal, increase the thrust/drag ratio, so the board will be faster.

.

[dougirwin13]

Roy,
Archaeologist? Me? Thanks - I wish. LOL Just have a good memory for interesting conversations.

You are right, of course. I suppose we all tend to speak from the paradigm we are most familiar with. Yes, I am talking boards in the 5' to 11' range with relatively modern rails, flat/concave/double-concave bottoms and somewhat modern rocker. Hull or V type bottoms and more round rails also change things. Not to mention rocker type and progression. Those designs tend to transition fairly quickly to planing. And I would guess more suddenly than the olo style, hull bottomed boards.

With the notable exception of your own boards I think that's the case with 99%+ of the boards on this forum.

By the way, making the board heavier will, all else being equal, increase the thrust/drag ratio, so the board will be faster.

Provocative as usual!

Warning for the casual reader! A large number of people on Swaylocks disagree strongly with this, so you might want to be careful about blurting this one out to your local shaper/designer.

Roy - Personally I think something of a communication breakdown occurs on Sways when you bring this one up. I reckon that there's misunderstanding about what you are calling speed and what other people are calling speed. Then emotions come into play and things degenerate into a flame war.


Baratacus,
I tend toward the engineer/physics mindset The upshot, for you, is that you can get the same buoyancy from a shorter, wider, thinner epoxy board because you can use a less dense core material to get the same flex and durability. But some other changes will need to be made to compensate for those dimensional changes.


-doug

[Roy Stewart]

Roy,
Archaeologist? Me? Thanks - I wish. LOL Just have a good memory for interesting conversations.

You are right, of course. I suppose we all tend to speak from the paradigm we are most familiar with. Yes, I am talking boards in the 5' to 11' range with relatively modern rails, flat/concave/double-concave bottoms and somewhat modern rocker. Hull or V type bottoms and more round rails also change things. Not to mention rocker type and progression. Those designs tend to transition fairly quickly to planing. And I would guess more suddenly than the olo style, hull bottomed boards.

With the notable exception of your own boards I think that's the case with 99%+ of the boards on this forum.

By the way, making the board heavier will, all else being equal, increase the thrust/drag ratio, so the board will be faster.

Provocative as usual!

Warning for the casual reader! A large number of people on Swaylocks disagree strongly with this, so you might want to be careful about blurting this one out to your local shaper/designer.

Roy - Personally I think something of a communication breakdown occurs on Sways when you bring this one up. I reckon that there's misunderstanding about what you are calling speed and what other people are calling speed. Then emotions come into play and things degenerate into a flame war.

Hi Doug,

Yes apparently emotions do get in the way now and then but it is nevertheless an indisputable physical fact that heavier surfboards have more thrust due to the fact that they have greater gravitational potential energy, and also that larger heavier objects (larger scale objects) which rely on gravitational potential energy for thrust (as surfboards do almost entirely)have a better thrust drag ratio and attain higher speeds, because drag is proportional to surface area which increases with the square as an object is scaled up, whereas thrust, which is based on mass (and thus with volume if an object is scaled up) , increases with the cube.

This is why larger gliders go faster than smaller gliders.

As for me having a different idea of speed from certain swaylockians, you may be right, some of them think that speed is a kind of style, but I am still working with the theory that speed distance divided by time, and am currently measuring speed using gps and expressed in kmh.

[Roy Stewart]

You are right, of course. I suppose we all tend to speak from the paradigm we are most familiar with. Yes, I am talking boards in the 5' to 11' range with relatively modern rails, flat/concave/double-concave bottoms and somewhat modern rocker. Hull or V type bottoms and more round rails also change things. Not to mention rocker type and progression. Those designs tend to transition fairly quickly to planing. And I would guess more suddenly than the olo style, hull bottomed boards.

With the notable exception of your own boards I think that's the case with 99%+ of the boards on this forum.

\

You should say "with the notable exception of SOME of your boards. .. . . . some of my longer boards, (the ones with wide noses and a lot of nose rocker ) leap up onto the plane very quickly indeed. .. . a 27 inch wide nose with a high rate of rocker curve produces a lot of lift at paddle in to takeoff speeds. . . . as you can see in this clip: http://www.olosurfer.com/VortX.wmv

Thanks for a great yarn

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[dougirwin13]

Hi Roy!

Yes apparently emotions do get in the way now and then but it is nevertheless an indisputable physical fact that heavier surfboards have more thrust due to the fact that they have greater gravitational potential energy, and also that larger heavier objects (larger scale objects) which rely on gravitational potential energy for thrust (as surfboards do almost entirely)have a better thrust drag ratio and attain higher speeds, because drag is proportional to surface area which increases with the square as an object is scaled up, whereas thrust, which is based on mass (and thus with volume if an object is scaled up) , increases with the cube.

Not sure I'd say thrust - surfboards don't have a motive source of their own. They harness that of the wave - a small bug I have with the modern shortboarders :)

I think the disagreement is probably keyed to the interpretation of the words people are using. Recently I have started pointing people to Lesson 1: Describing Motion with Words in an attempt to reduce these kinds of misunderstanding.

I think you are talking about Velocity, as opposed to Speed. All those horizontal and vertical zig-zags that modern shortboards do have more speed, no doubt about it. But their velocity is far less than my current 9'6"... Which is less again than, say, one of your 17'ers!

Sorry - I am a little bit of a physics/engineering geek :D

This is why larger gliders go faster than smaller gliders.

Larger wing area per mass allows greater lift. That is no guarantee of greater Speed, tho. A small, heavy glider may reach a greater speed... Partly because it will fall faster (as in an aerobatic glider)! But that doesn't necessarily give it a greater velocity (as in cross country and soaring events), where larger wings are a decided advantage.

For an interesting summary of the energy conservation/expansion behind gliders check out Problem Ten on the Physics 105 - Final Examination.

So two of the factors in a glider are lift and energy conservation (and how that conserved energy is finally expended). Neither guarantees Speed but can be easily used to guarantee a higher Velocity. And I think bigger boards certainly have higher Velocity... And Momentum!

I quite like the FAI site for gliding, BTW.

Same thing?

As for me having a different idea of speed from certain swaylockians, you may be right, some of them think that speed is a kind of style, but I am still working with the theory that speed distance divided by time, and am currently measuring speed using gps and expressed in kmh.

Speed, Velocity, Momentum, Inertia and more. I don't know if you can isolate variables out to the granularity of a GPS (around 10 meters) and expect to argue things out convincingly with all comers. Some will consider the windy path of a modern shortboard to mean that it has travelled further in the same amount of time.

I know that some Swaylockers have an understanding of Speed and Velocity which is well grounded in Physics. A few well beyond my own.

Personally I prefer the higher Velocity and Momentum of a bigger board in most cases...

You should say "with the notable exception of SOME of your boards. .. . . . some of my longer boards, (the ones with wide noses and a lot of nose rocker ) leap up onto the plane very quickly indeed. .. . a 27 inch wide nose with a high rate of rocker curve produces a lot of lift at paddle in to takeoff speeds. . . . as you can see in this clip: http://www.olosurfer.com/VortX.wmv

Aaahh... Tunnel fin. nice little clip. Thanks, I always enjoy them. Yep, I see what you mean. Funny, sometimes it looks as if the front half is planing and the back is displacing :D

Thanks for a great yarn

Likewise! Its always interesting and I always enjoy your clips. So do my wife and kids (esp ones like Glide Street).

Cheers!
-doug

[borneng]

I was never good at physic when I was growing up. And I just hate the fact that being familiar with it would probably mkes it easier for someone to learn surfing. You have to understand it to be able to execute it.

This is the part I drag myself into learning. I could probably be the idiot about this but that's how I feel really.

But hey, that's just me. A crazy woman.