Quad Concave Body Board Study

What works and what doesn't. Share design ideas, references and contacts for paipo board builders.
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bgreen
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Re: Quad Concave Body Board Study

Unread post by bgreen » Mon Aug 03, 2020 4:21 pm

If a tip sticks out 160mm and the distance between tips is 700mm that makes the board 380 mm wide (about 15"). Is that right?

PhillyViking
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Re: Quad Concave Body Board Study

Unread post by PhillyViking » Tue Aug 04, 2020 10:47 am

following are the closest boards I could find to your wings. Mostly the wide back. Except that instead of having distinct dorsal fins the entire board has some delta shape characteristics.
'
K. The paipo guys at Queens Beach in front of Kapiolani Park (near the Honolulu Zoo), Larry Godard Interview, mypaipoboards.org
paipo_guys.jpg
Paul Lindbergh Interview, mypaipoboards.org:
PL-wood-paipos.jpg
PL-wood-paipos.jpg (9.95 KiB) Viewed 333 times

My closest breaks are in New Jersey USA. They get a bit nip in the winter so I go south as much as possible. Be careful in the cold. I lost a lot of hearing in one ear to "surfer's ear". Of course those rock concerts didn't help.

I did get to surf in Norway a couple years ago so have had some exposure to the North Sea:
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CHRISPI
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Re: Quad Concave Body Board Study

Unread post by CHRISPI » Tue Aug 04, 2020 3:33 pm

bb5.jpg
My boards are the same as a wood Paipo but with soft buoyancy draped on shaped in a teardrop form. I could use plywood but it is too heavy and lacks the bouncy and strength of Airx foam. The photos I sent deform the true shape of the board.

PhillyViking
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Re: Quad Concave Body Board Study

Unread post by PhillyViking » Wed Aug 05, 2020 7:46 am

are your wings added on or part of the core airex core? Do you have any pics or dimensions of the core before adding the soft shell? Which of the airex foams do you use? Its an interesting candidate to address some of my pursuits:

* stringerless boards with just the right amount of flex and damping with stress distributed evenly
* More durable boards especially for travel

The Body Board world starts with soft foam and tries to control flex as an afterthought with rods and mesh close to the outer layer. I like your approach that starts with flex control.

Atlantasurfer on this blog made boards with Home Depot plywood for flex control and adhered soft foam on top for buoyancy and shape. viewtopic.php?f=4&t=681&hilit=black+betty It worked amazingly well but is heavy. He got flex like an alaia.

CHRISPI
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Re: Quad Concave Body Board Study

Unread post by CHRISPI » Wed Aug 05, 2020 3:06 pm

The wings are part of the core with added layers of cloth after shaping. Very easy to press form rocker and fin angle I put in about 2 degrees in my fin pitch. My supplier is East coast fibreglass supplies I mostly use Airex PVC C70, also 3D core material but is very resin rich and a bit heavy but exceptionally strong, I want to try Aramed honey comb core but it looks difficult to lay up I have also tried extruded polystyrene but can’t get the correct density in thin sheets very light and cheap but fragile in the low density form. I am using 2 sheets of 5mm x 1.09m x 1.02 about £25.00 a sheet , can make a second board out of the off cuts .so £ 50.00 for 2 cores .

CHRISPI
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Re: Quad Concave Body Board Study

Unread post by CHRISPI » Wed Aug 05, 2020 3:18 pm

You can change twist and bend flex by adding layers of cloth down the core spine. I feel flex in a board is desirable

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Re: Quad Concave Body Board Study

Unread post by PhillyViking » Thu Aug 06, 2020 1:25 pm

I am trying to build flex into my board as well. I have done a lot of mat riding where you really work shape shifting. You actually turn by twisting the mat (nudge the rail upward on the opposite side of the turn ). The floppier the mat, the more suction to take you down the wave during take off... etc. My goal is to make a board that has the best of mat and board behaviors. At 67 I am feeling the need for a leash (NA on a mat) and need some harder turning ability for certain conditions than i can perform on a mat. But I want the mat experience hence my interest in flexible, finless boards.

This next one will be a skinned HD EPS core. I am changing my plan for this board a bit as I think about composite fundamentals. I was going to build all my tensile strength in the bottom epoxy/ fabric layer and just adhere cork directly to the deck to address compression only. I was influenced by Tom Wegener who only builds strength on the bottom of his newer cork boards.

I have now realized that Tom Wegener has the constraint of only working with wood and cork in conjunction with an EPS core. He asserts that wood on the deck is prone to cracking compared to the bottom because of the tighter radius of bending. But the consequence is he needs more wood on the bottom than if he allocated less wood overall top and bottom or better yet in a multi layer sandwich .. that is the lesson of plywood. So I will put some epoxy/fabric between the eps core and cork deck. I only need enough on the deck to address break/bend forces .. the cork will handle compression. In theory I will need less glass by making a sandwich. On conventional builds there is typically more glass on top then bottom. But that's to handle compression from our bodies, not for tensile strength

This will also address Rodndtube's comments that I need to be concerned with downward as well as upward forces applied to the board, e.g. a big wave lips that hammer down from above. In this way I can do a layer at a time .. first the bottom and then decide 4 or 8 oz on top once I can evaluate the flex of the just the bottom. Its temping to use some unidirectional strips for fore-aft stiffness in particular but I just do not have a way of knowing how much I need and it should be the first layer adhered to the core.

I wonder if given Wegener's constraints, that he might do better to make a thin internal structure with 2+ smaller thicknesses of wood veneer closer together in a sandwich with foam, cork or other less dense material. That way he would avoid the tighter radius encountered if he placed the wood on the deck. It seems Ski, Wakeboard, Skateboards builders are doing more with composite materials and sandwiches than we are in the surf world.

I am now am using a higher density EPS sourced from Greenlight (NJ, USA) that they call Cfoam. Its somewhere around 2 rather than 1 pound density. It is noticeably stiffer and is less likely to tear during shaping.

I am trying to understand composite fundamentals. Lets say I wanted a board that was two inches thick to get the desired buoyancy and shape. Which is stronger: a thin inner sandwich structure to handle all the flex surrounded by less structural material or to spread the stiffer materials out in the entire thickness of the board. I think the latter. Am I correct? If i was using EPS I might want to get the thickness sliced into e,g, 3 thin sheets and glass in between them. In my case I would use 1/4" cork on the top and bottom of that for compression concerns. So maybe three sheets of 1/2" EPS sandwiched with fiberglass and thin (1/4") cork on the outside.

Another case for internal structures. We often overly glass travel boards in particular to protect against compression dings. In doing so we trade off flex we might have wanted. If we separate compression vs tensile strength concerns we can use skin materials like cork or soft foam to absorb compression and right size the amount of flex control in the internal structure. I am not saying that a paipo might not get broken in half in transit or in the surf but it is far more likely to get dinged. Has anyone actually broken a paipo (sponges excluded) in half?

Thanks for the material sources.

CHRISPI
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Re: Quad Concave Body Board Study

Unread post by CHRISPI » Fri Aug 07, 2020 12:43 pm

Layered and veneered structures get stronger with concaves , it’s so easy to press form layered shapes .there are so many types of skin layering to try out .With polyethylene , cork ,etc it’s easy to change a shape or add to after testing

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Re: Quad Concave Body Board Study

Unread post by PhillyViking » Sat Aug 08, 2020 11:25 am

What adhesive do you use to adhere PE etc. to the internal sandwich structure? The BB builders use heat welding for plastic to plastic but its harder to find an adhesive for plastic to epoxy/fiberglass that is effective but not nasty. Epoxy gets a mixed review at best. Barge contact cement seems to be a candidate .. the newer formulation might be safer?

I am interested in the detailed steps of your pressing process. I have been using vacuum bags for some of my epoxy projects but do not like that I end up creating a lot of waste from the throw away peel ply and bleeder cloth. I am trying to find ways of being eco sensitive.

It strikes me that some of the high density PVC foams (airex or divinycell) could be heated up then thermo pressed with or without an exact form. Maybe as simple as using a heat gun then mechanically pressing before it cools. The epoxy / fabric could then be hand layed up with detailed shape added to the outer material by hand (no vacuum). I like using cork where you use PE etc. but the approach is the same. I will try using cork in the internal core structure in the future but in the mean time I just use it on the outer 1/4-1/2" skin.

I can see doing an internal core sandwich structure with High Density Foam / Fiberglass as you describe, surrounded by thicker sheets of EPS and then cork on the skin. In that schedule, the cork can be adhered to the EPS with PU adhesive and the EPS with the structural sandwich using epoxy. Detail shape could be realized in the outer EPS and/or cork. The internal structure could be very very basic in shape and could be used in a variety of builds once the process is established.

Alternately, since we need some float anyway maybe just use HD EPS for the internal structure sandwich instead of even higher density PVC. The HD EPS might need to be thicker than then the PVC foam? Thats where the PVC might shine: you can go thinner. But as I said above, do we need to go thinner if we want to add float anyway. I am not clear on the science of how foam thickness would impact strength if the same three layers of glass was used otherwise (glass-1 - foam - glass-2 - foam - glass-3) . My understanding is that thicker foam layers makes it stronger. Am I correct?

Are you exposing your HD foam/Fiberglass structure on the bottom of the boards? If so, maybe I should not be referring to it as being internal. However, its still as if its internal in my thinking but maybe there is a better term. May I should just call it the (thinner) structural sandwich in contrast to outer layers used for buoyancy and shape.

Do you make an exact form to press against or use other approaches? I see people bending material over a 2x4s etc. Harry Akisada , see https://mypaipoboards.org/interviews/La ... dard.shtml has a great example of pressed veneers with complex channels albeit with wood. I see clever approaches to bend wood against objects without an exact form but have a harder time visualizing doing the same with HD foam with pre-cured epoxy/fiberglass in process. Of course vacuum against an exact form is the sure way to go but making an exact form for a one off is a lot of work.

If you are using a fiberglass / foam layer on the bottom then the concaves would add stregth. But, there would be less strength added if the concaves were added to a thick soft foam bottom.

CHRISPI
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Re: Quad Concave Body Board Study

Unread post by CHRISPI » Sun Aug 09, 2020 3:30 am

I used to use contact glue but it is difficult to lay up large pieces, after some testing I now stick the pe with laminating epoxy it has the same adhesion as contact glue but gives time to move the pe around before it sets, with contact glue if you make a mistake its bad news. For the core lay the centre first normally with one layer of 6 oz cloth, with extra strips or patches over areas that need strength .lay batons underneath to set rocker concaves etc use waits to set the shapes. After the shape has set I clean the rails to size finish with 45 deg bevel and lay 6 oz cloth top and bottom. Best way to understand how strong core structures are is to lay up samples and test them by twisting, bending, pulling and crushing them.

PhillyViking
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Re: Quad Concave Body Board Study

Unread post by PhillyViking » Mon Aug 10, 2020 10:51 am

Your shaping against batons makes sense especially since you are using two thin foam sheets to make the initial sandwich. If I have it right then the initial lay up is foam bottom, 6 oz glass middle, and foam top. Weights are used on top to push the thin flexible sandwich against the batons. The key is that the epoxy/FG is in between the two foam layers so is not going to adhere to the weights. Likewise, peel ply etc is not required.

I imagine that compared to bending wood , bending thin foam sheets does not take much pressure. This would seem much easier to execute then what ever Harry Akisada had to do to bend wood to a complex shape. Am I right that I should expect the thin foam to bend more easily than even wood veneer? I assume that once that initial center core sandwich is completed, the outside FG layers can be layed up without additional use of the batons. One layer of 6oz in the core is sufficient to hold shape until the outer FG layers are added for final strength in a subsequent step.

I really like your approach. I would just leave the outer FB layer on the bottom exposed and then add EPS on top for float and then 1/4" cork on the top of the EPS for comfort and compression concerns. Oh, I just realized the problem would be that the any concaves pressed to the center core would be reflected on the top of the initial sandwich core. That means any layers added to the top of the initial sandwich will not lay flat. How do you deal with that?

Solutions:

1.) Do you weight your PE deck to the core and then shape the reflected contours on the top of the PE deck. Its hard to imagine getting the PE to drawl into the contours of the core if not flat just using weights. A vacuum would work well for that and could be used without a lot peel ply since the there still is not epoxy on the outside in that step.

2.) Level off the top surface of the core using a small amount of expanding foam that could be sanded down to a flat surface or even use it to adhere the EPS other outer material in one leveling/adhere step.

3.) Leave the internal core surfaces flat and in my case add a layer of cork on the bottom that would accommodate shaping concaves or other complex features .. 1/4"-1/2" of cork would handle anything I might want to do on the bottom that is not flat. This approach would lend itself to changes to be made after testing in the water. Cork could be easily added, removed, shaped. Titebond and sand paper are the only items needed for change. In my case, cork on the bottom would add some relative weight but on the other hand I would not need to use innegra on the bottom for compression concerns. Cork does a great job absorbing compression but is not abrasion resistant like innegra for an outer layer, especially for the bottom. So I could take a hit on the cork bottom but not run it up to the sand on a beach break.

Thanks for your response. I was on a similar track of thinking but you are helping me clarify my own plans.

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