That’s what I’m talking about. Boardroom quality.
Thanks sharkcountry, the posts on this topic from you and your brother over the years have been very informative.
Good to know on the deck only, makes sense with a higher density foam. I like the idea of cut laping the bottom and doing a wood deck inlay. It’s probably a lot easier to fair out the edges of the wood that way. For the balsa skins, I assume you’re just taking 4” wide strips and taping them together and bonding them to the foam?
Haven’t looked much into flax but it seems to be quite popular these days. Let us know how you like them once you’ve had some time to test them out.
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Incredible boards! Those are truly functional works of art. Makes sense to layer the rails to reduce weight, plus that much balsa would get pricey. Are you using 4-3” strips and splicing them together to get the full length or do you have 8’ sheets? Have you done less than 1/2” rails or have you found that to be the right thickness? For the wood skins are you using 1/16” or veneers? I assume if you’re mixing cork and wood you would need at least 1/16” to match the cork thickness. For the bottom skin are you using a rocker table? What the typical vacuum level you use? I read from some of Berts posts he recommended ~6inHg for 1lb and ~17inHg for 2lb. He also said a 1:1 resin to fabric ratio, do you find that to be a good starting point? Also, are you sealing your cork for rails/skins?
Sorry for all the questions!
Those are some interesting thoughts, i’ll need to digest those a bit. The shape memory alloys concept is really thinking outside the box haha. Could have at least stuck with shape memory polymers, metal in surfboards seems wrong.
I wonder if the flex in a bodyboard allows it to match the contour of the wave since they’re usually pretty flat. You could probably reduce the rocker to account for the flex but it would be challenging to figure out where to remove rocker and where to keep it since it’ll be dependant on where it’s flexing the most which changes as foot placement changes. Not worth the trouble.
So you prefer longitudinal stiffness in the center as opposed to the perimeter? I was thinking some torsional flex would be better for when the board is going from rail to rail.
Flex is also heavily influenced by the shape of the deck- flat deck flexes more than a domed deck. Bert Burger 101. For me flex is such an elusive and unquantifiable quality that I really try to get the performance qualities from the board’s shape. Especially rocker and bottom contour.
See George Gall’s comments to me about torsional flex in the first Hot Seat link I posted above.
Regarding variable stiffness, that is what surfboard “foil” is all about. Thick (stiff) in the center/middle. Thin (flex?) in the nose and tail.
Yes, I only have 4” and 3” wide Balsa and now it is mostly 3” wide and 36” or 48” long. I have used most of the thinner wood, but I have a lot of 1/4” and thicker wood that I could resaw to 1/8”. I think 1/8” thick is best for strength, but for a denser foam, 1/16” is fine. We started using the 1/16” because we were wrapping the wood around the rails. We weren’t doing the wood perimeter rails. I think we used the Marko molded blanks back then and they were at least 1.5lb, maybe even 2lb foam. Then we started using foam from Home Depot and Lowes. That foam was lighter. Lowes foam was too light and it would dent over time.
I tape them together with a thin and narrow masking tape once I have them cut to fit the board. I tape all the seams and put the tape on the underside against the board when I vacuum them to the board. I do that because I was having problems removing the tape and it was ugly. I did a solid color lamination to hide that. I use a roll of paper to make a template of the Balsa skin to get it as close to the shape as I can even though I cut the wood before taping it all together. Sometimes I laminate the deck first, then I fair out the edge of the Balsa after it is vacuumed on. A wide pin line will cover that if it isn’t perfect.
I like Flax because it is faster than making a wood skin, but the flax I have is not made for surfboards and it isn’t user friendly. It was very inexpensive though, and prefect for testing with. Shaper Supply sells a flax for surfboards, but I got enough for several boards 8’ long for about $20 on Amazon. It is more like a heavy canvas, but I’m betting it is very strong. It did require a lot more resin than I normally use. The board is definitely heavier than if I did a Balsa skin, but it has Flax on both sides. I don’t mind it though because it is a 8’ longboard and the extra weight is good for that shape and size. I don’t like longboards, but I’m having trouble popping up after hip replacement, and the longer boards help. I made an 8’-6” earlier, but I’m hoping that this 8’ board will be short enough to have more fun. I hope to get back to my short boards before the summer swells start to show.
If I knew how to vac bag the lamination, it probably would be much lighter, but I have not tried vacuum laminations. I’m too lazy to learn, and too cheap to buy all the necessary extra material you end up throwing away like peel ply.
I will say that on my boards a deck with a Balsa skin is much more dent resistant those without the Balsa. In time I will see how the Flax works out.
Verdure’s technology seems to be gaining popularity with a couple brands having their boards build by them. Technology – Verdure Surf
They use bendy ply, I assume poplar as their rail reinforcement so they aren’t super stiff. Interesting that they do a thick skin on the bottom and cork on the top with neither sandwiched. It is similar to Tom Wegener’s boards https://youtu.be/SxyPcbvLeCE?si=_bJATyTXSd4DrsPu
Seems hard to believe no glass or even epoxy on the exterior will hold up over time. I believe Verdure is using an oil based sealer from Osmo.
Agreed, deck convex and concave affect flex.
I had a 7-6 closed-cell foam Morey-Doyle that I bought in January 1981 for riding my crowded breaks. Ended up being my most “fun” board to ride.
Flex was undeniable for steep take-off and hard lean turns and cutbacks — some incredible parallel to the surface, hard, half-circle bottom turns and re-entries. Did not affect down the line riding because there was no circular acceleration or steep drops involved.
Didn’t care what others said. That board was a blast to ride. Would buy another identical one in a heartbeat.
Need to be expertise becasuse the max centrifuge force in hard core attraction like “the rotor” is 1.5g. No way you take 1.5g lateral without strong harness. F1 pilot can take up to 4g lateral in what they called hard turns, use specific seats and restraint suits. I do some circuits turns in claaseB car with a pro pilot, far less speed than F1 but i was littearly crush in seat can’t breath each turns. No way i experiment this on my surfboards or fast speed gybe on my slalom windsurf !
When you turn prone on a bodyboard you push with your body on one side and pull with arm other side when initiate turn so you create rocker curve that help turn. When you stop twist board you have projection from the board comeback to shape. You know your board is dead when you have no more projection.
My (past) calculated and George Gall’s measured Gs.
As a high school football player (18 years old), I could leg press 600 lb vertically — multiple times per set. I weighed 152 lb.
Sorry as a mechanical engineering teacher i use SI units. So 21mph= 9.39m/s, 10 feet= 3m, centrifugal acceleration a=9.39^2 / 3=29.4m/s^-2 centrifugal force F=ma, for a 80kg guy F=80×29.4=2352N, more or less 235kg force. So you say a board take 235kg each (good) turns? But you can dings most surfboards in shop racks by just thumb push. You say a surfer push 235kg with legs each turns ? I always think i have powerless legs don’t know i can do this, never have legs fatigue even when surf 3 hours 10 turns by waves. Shoulders pain for sure but legs, never.
now i windsurf, standard speed GPS at jibe 25 noeud = 12.8m/s radius 4 m, a=41m/s^-2, F=3000N so i push 300 kg, while i change feets position and jibe sail and repeat this 100x per hour 2 or 3 hours a day.
Formulas are good but i think there is a problem in this reasoning.
George Gall’s measured G-force data from a hard bottom turn/cutback indicated 4Gs. That more than substantiates my circular acceleration calculation of 3Gs.
a = v^2/r
BTW in Imperial Units, 30.98 ft/sec = 21 mph.
10 ft (r) x 96 ft/sec^2 (a) = 960 = v^2
Square root of 960 = 30.98 ft/sec (v) = 21 mph
BTW what is minimum compressive strength of a properly glassed deck? Contact patch of 2 human feet (inches^2)? 450-600 lb divided by contact patch (square inches) = psi?
Further what is the contact patch of 2 human feet placed under a 450-lb to 600-lb load?
No extra load, average footprint surface area for one size 9, male foot is 28.7-30.1 sq inches (my foot size). Multiply by 2 for total contact patch. Assume 29 inches^2 x 2 = 58 in^2. 450-600 divided by 58 = 7.75-10.3 psi for no extra load contact patch.
Deepo Matthews has been making boards without fiberglass for many years. He uses bamboo and now he adds teak for accents. He uses an epoxy for the glue.
Paulownia is great for boards, but we noticed that it is a little heavier than Balsa.
I was texting with Tom maybe 10+ years ago about his hollow Paulownia boards that didn’t have fiberglass or varnish. He used oil as a sealer like the old Hawaiian solid wood boards. I guess he doesn’t do that anymore.
BTW these are a couple of the many G-force turns I have made (surfboard, bicycle, motorcycle, street-rigged mountainboard) over the years. Street-rigged mountainboards were where I learned about the impacts of circular acceleration and the effects of flex on board performance.
That cambered, 8-ply, 0.5” maple deck flexed significantly with circular acceleration.
Interseting, when i was young research student i worked in a university team at extensometer gauge use protocol in dynamic test. Main sponsor was aeronautique industrie but start by inserted gauge rosace in a skateboard deck, record deformation and deduce mechanical constraints, to develop protocole. When turns in board use we never had forces over 2x rider weight. Max was from the best rider, at flat transition at bottom of bowl, he put a pump that give him far more speed than us, maybe that’s why he was better.
Is it recommended to use slow cure epoxy for applying skins? I use fast mainly so that if I need to touch up my folds at the nose and tail it’s gelled enough that it holds. Seems like slow is the way to go so I have more time to get the board in the bag but I wasnt sure if there were any downsides. Any issues with non brightened epoxy? I usually use clear since I do a lot of pigmented lams. Although, maybe pigmented lams are OK with brightened epoxy.