As someone who completed a degree in marine engineering it's amazing to hear people start talking about the physics of surfing! I feel its crazy how little people know about whyyy these things work. Keep it up, loving the videos!

Flat bottom contours are overly discounted in today's surfing world. They work, are neutral and pretty forgiving. Trackiness of concave bottoms can be reduced with soft transitions leading into the rail. Rails and rocker are very important aspects to consider along with bottom contour. Pro tip: don't try to put every bell and whistle into your (custom) board. Focus on what you want, the kind of waves you usually surf and how strong of a paddler you are. This was a great video depicting how bottom contours work and the effect they have while riding.

Perfection! I absolutely love these videos. The strong effort to tie in science-based principles to surfing is such a breath of fresh air. I've always loved that about all the videos and podcasts you've done. Thanks for another amazing video.

20 years of surfing. Never have I been schooled this well. thank you!!!!!

I've shaped surfboards with all concaves. I've been lucky with the double concave for speed. The single to double to V for various conditions and the single for "lift" and stability. Is a never end thing with this hydrodynamics.

Thank you for the clear explanation. Well done 🤙🏽

This is fantastic. Theres so much hocus pocus when it comes to surfboard design. Clear and informative, well done!

another outstanding video. honestly, if the Oscars had a surf theory category...

Please do surfboard recommendations (specific models) for levels. Love the vids!!

As you mentioned in your last example, I have a fish type board that has a single to double concave with slight "v" at the tail. These contours are subtle, almost imperceptible, even while using a straight edge for reference. The board is absolute magic.

An exceptionally appropriate planshape you've chosen to use in the examples👍

the main aspect many people dont understand is the possibility putting more rocker on the rail than in the center by choosing right bottom contour combo.

I’m a beginner shaper/upcycler. This video is incredible, thanks so much! I experimented with concaves/channel bottoms on my most recent upcycle project. Watching the vid helped my understanding a lot. Adding the Vee in the tail may have been a detail I missed.

Awesome video! Love how your channel is able to fuse surfing and physics. Its much needed for the sport. Keep on making great videos !

all right in the paper, but in practice things change, concave can be slower, disastrous for the rocker, have a windy effect on the paddle and before gliding, especially on medium-length boards and in dirty and rough conditions. Even channels can ruin an entire board made to perfection, such as generating too much speed. The most important thing is definitely the rocker and then (unfortunately) you need to experiment and modify the board countless times to make it work really and well, it would be too easy to get results from the theory, which still remains a good starting point.

this was simply amazing

Great video!

Hi Will, I love this series! Very informative and makes the science easy to understand. One thing I hear shapers talk about and miss in this video is how convex to single to vee creates a flatter center rocker for paddling and increased rail rocker for turns. You don't mention that in this video, do you think this effect is insignificant compared to the ones you mentioned about weight distribution during speeding up on your front foot and turning off your back foot? Or is it all one and the same?

This video is phenomenal thanks so much

Amazing work guys! keep it up!

Great video.very informative.

Surfboards spend most of their time moving on a rail but you mostly talked about how boards act when moving flat like when going straight away from the wave.

Man this video is so good!

Ahead of their time, the Campbell Bros introduced a reduced center fin with long- based, low-aspect, very canted side fins aligned to "deepen" its double concaves and channel flow rearward when pressured. Check out cutback master Taylor Knox on 5 fin Bonzer in Mexico for proof.

Sorry you've got this concave thing wrong. Put a concave bottom board bottom up on the racks. Lay a straight edge on the centre line at the deepest part of the concave so its running nose to tail. You'll see the straight edge teeters on the apex of the rocker. Now rotate the straight edge, you'll see when the edge is at a diagonal to the stringer it'll be mostly in contact with the bottom. This diagonal path is the fastest way for water to move across a rockered concave. This is how concave creates lift when a board is in trim. Water is being displaced rapidly toward the outside rail. The lift on the outside rail in a turn is how concave creates drive through turns when the inside rail is weighted.

Awesome!! 🤙🤙

I personally run a single to a triple then back to single into a quad with slight double v off the tal.

Been following this series, I build my own boards, and also try to search for scientific papers to support my designs, while also being a bit mad and innovating, following my personal theories while there is no scientific research for surfboard design. altough I agree to the theories presented on other videos, I don't agree 100% with this one, you are forgetting a lot of factors on this one, adding a concave just modifies a surfboard so much, you are adding more than removing something. You might be adding wetted surface area and rocker. Also doesn't the redirection of water create drag? Therefore the concave by redirecting water creates drag, giving that the fins are giving the surfboard the directional stability/velocity and preventing from it spinning out?

👍 now let's talk about entry belly, to flat, then concave ... I'm stuck on mini simmons boards 😁

what would be a good shape for a river wave? perhaps for someone who hasn't surfed but has skate/snowboarded for 20+ years and would like to be very technical very quickly and should be able to adapt to surfing very naturally. I'm talking about the various waves in the st.Laurent river surrounding the island of Montreal.

Nice one!

i shape my own boards and these vids are very informative! (it is a single concave all the way through) for speed in smaller waves.

I love bottom contures..

thanks for sharing

More knowledge bombs!

I have a board which has flat bottom contour from nose to chest area (When your lying face-down and paddeling) and transitions gradually to a double concave in the middle of the board (No single concave before the double) then it transitions to a Vee at the tail end. I do not know what does that do for the board or the rider or how the board will behave in the water. It's a 6'6" x 21 x 2.75 Egg shaped board. I still haven't tried it because we are still on strict quarantine. It's still wrapped in it's packaging. It's my 1st board. Been riding rentals. Would appreciate it if you could tell me what to expect with that kind of bottom contour. Most boards start with a single concave then gradually transition to double but this one, from flat, goes to double right-away. Please do share if you have tried a board like this. Thank you and best of luck to your channel. :)

Does fin box filler a necessary for a 5 fin boxes board?

Hey, im thinking of making my own shortboard 6'0 34L what do you think the best bottom contour is?

i love EVO shape ;)

Bob Mctavish did not invent the Vee Bottom...…..Midget was months if not years in front of the pack. Bob was documented riding them BUT he did not invent the VEE Bottom.

Brilliant, quick dirty...

Rode a really weird board the other day that held a line with a lot of speed but just would not turn. I guess it must have had a deep single concave....

Do some specific models please.grovler.all around....

concave is hard to shape, a machine has to do it. flat bottom is fast, round bottom is slow and flat bottom with tail lift works the best. V bottom spins out and slows the board down..

🤩🤗💛💛💛🤗🤩

Everything they say is backwards from what it really is. A convex bottom surfboard does a high line way better than any other board as long as the rail is not too hard or Sharp. When the waves are larger and bumpier the board should have a convex bottom. You get more speed and control. I'm very flat weak waves concave is better but again only to a certain size. There are so many other variables like thickness in foil that have to do with this but I don't understand how big wave Surfers don't have convex bottoms under big wave boards for paddling they should have convex not only in the middle but toward the rail with downrails that are full and you'll have a lot more maneuverability

can you make the video easy to understand I don't think I understood one thing

The what? The oonderside. Oh, the oonderside... gotcha

Good video