Surf Simply's Question Time: Why are side fins toe'd in towards the center?

[@davidgough3512]

If you've ever steered a boat with a rudder, toe-in is pretty simple and obvious. When you bury the right rail, the right fin's toe-in acts as a boat's rudder would, set to make a right turn. (Meanwhile the left fin is being lifted out of the water so it loses influence.) This is true regardless of foil and lift. The "cant" or tilt of this rudder presents a more perpendicular surface in relation to the water while banked over so that the ruddering can maintain its effect. Whatever foil is added to the fin only serves to enhance the primary effect of a turned boat rudder. A toed-in side fin will quicken the turn even with a straight foil. BTW a thicker fin with a rounded leading edge is faster, holds better for its size and produces less turbulence.. something to consider for trailing quads and center fins. So sand those knife edges off your fins; they'll be less likely to "hum", they'll be faster and they'll be safer!

[@SurfSimply]

Wow David thanks for this insight, it’s all very interesting indeed!

[@davidgough3512]

@@SurfSimply back at ya! I lived thru the short board revolution so my knowledge is broad but shallow haha. Appreciate your scientific approach! Foil, angle of attack, lift, concaves, channels, edges, release etc are indeed mysterious, fascinating, magical and huge in their effect. Like you, I look forward to more research and design because I don't think we're anywhere near complete in surfing evolution.

[@natews7104]

Ah ha, that’s how “side bites” help tighten a carving turn radius, compared to single fin only - the rudder effect of the canted side bites steer the tail around. Brilliant explanation, thanks.

[@SurfSimply]

I agree David, I’m hoping that in the future particular with wave pools, we might be able to set up some testing equipment and finally get some real data on some of these theories.

[@oiysh]

I was hanging on the edge of my seat thinking you would have a theory for how thrusters work , ahh but no. You made some good points especially abou AOT. Quite variable. Transitiong too. One thing for certain is a thruster is slower than a single fin in a straight line. So there is a drag element. Perhaps more deflection is occuring rather than lift.

[@filipepapa]

One more great video of yours! In fact there’s an interesting point over there about if happens stall or not when it’s changed the stagger angle from 3-7° to 0°, because as hardly as I think it would stall there is a chance of having cavitation in high velocities and angle of attack on the upper fin (the one closer to the face wave, with higher aoa). The stall phenomenon is more often held by airfoils in airflow stream and not in water as it’s density is way higher. Moreover, this extreme conditions of high aoa may happen in very short instants naturally (as the surfer does a sharp turn or snap) with or without the stagger angle and from that I don’t think the implementation of this stagger angle was made to avoid these conditions as the surfer does turns for both sides. I do think they were made to make the board rails more attached to the wave face, thus combining the lift from the fins and the rail to keep the surfer on the wave face in the power zone in a more comfortable configuration (having more lateral flow under the board) and avoiding pearling in hollow waves. After all these implementations were all made by empirical testing right? I just wish there were more researches in this area of study...

[@finfoil8544]

Very good video! What is often overlooked is that assymetric side fins need more toe-in than symmetric ones. The more camber a fin has, the more toe-in it needs to compensate for it's negative "neutral angle" (angle of 0 lift) which typically requires around 2deg extra toe. Id rather see boards having the symmetric toe-in value in their boxes so that fin builders can compensate for the additional toe-in due to camber built in the fin.

[@tonybeatbutcher]

Once again, very interesting. real good info fr shapers.

[@bfazenda1]

As always, great to see and hear! It all comes across very clearly. In my mind, the 'Bernoulli lift' is best described as a 'pressure differential' between top and bottom of the foil (i.e. difference between p_above and p_below), rather than high pressure underneath and low pressure above, but that's detail. [You need new pens :) ]

[@larryhawes9322]

I have a question re: pressure differences and lift as a hydrodynamic function instead of an aerodynamic function? Water is not compressible whereas air is. Does water flow faster across a surface creating a low pressure area? It does with air but m not sure the same principles apply with water? When water is redirected there is a force applied in the opposite direction but not so sure about pressures like a wing because water behaves so much differently than air given the same foil shapes..

[@yasu4303]

Very cool video. Fin cant seems like the natural follow-up video, but I'm really dying to better understand hulls vs planes. The hull seems so undesirable, yet my hull pig is amazing, and the whole Andreini following swears by them. What's going on down there? Thanks!

[@davidgough3512]

In boats, round hulls are faster, but in surfing will lose plane without a constant long-running wave.. hence their cult-following at point breaks. A single center fin and soft-wrap rails allow the board to "find" its place in the curves and suction of the wave, rather than forcing a lot of fin and rail water-displacement ( "gouging") to "drive" the board.

[@fedorsmith]

Great video. Is there empirical evidence about what happens when you angle the fins out? I'm sure shapers have tested all sorts of configurations, just curious. I would assume frequent stalls and tail spins.

[@markelliott9987]

can confirm. surfed a board with fins toed out, the board constantly wanted to spin out and almost wanted to shoot me off the back of the wave. turning was pretty much impossible , could hold a line once you got use to it.

[@nicmellone7831]

Love your vids! I am super curious about what different surfboards are made from and why! How has surfboard material changed through time? What do you think the future will hold? Are there more than just wood, epoxy, or fiberglass? Thank you so much!!!

[@nicmellone7831]

Ooo, also maybe the inside part of the surfboard, like open vs close cell foam or the possibility of more sustainable materials in the future? :)

[@davidgough3512]

@@nicmellone7831 love to hear "sustainable". Oh for the day when surfers become the environmental "Gandalfs" of the planet haha! Nontoxic, durable, biodegradable. Same goes for wetsuits. Some are literally molding foamlike blanks from live mushroom mycelia , which is then dried. Imagine GROWING your next surfboard.

[@alexisbernier2075]

Great vids, that covers it up for the toe in but what about the angle of the fin? That should come in to play with the lift and the fin template that is used. Normaly from 3° to 9°.

[@torquejetboards1507]

I am a manufacture of Jet boards, electric powered surfboards. We are finding that having the fins toed out helps with much harder turns at high speeds. We are usually not riding waves and are on flat water, so there is no wave water pushing up sideways under the board. We use a jet like a jetski to propel us forward. What would be your thoughts on this?

[@woodman1701]

Toed out at the front?

[@paulcombes3782]

Please do not ride your jet board thingy near me ...🙂

[@paulinouye945]

Aloooha!what is the magic behind single fins on Longboards ,brah? Mahalos!

[@woodman1701]

I believe he be better just trying out different types of FCS fins and knowing that if you turn the fin inward at the front it’s gonna turn harder. Straighter it is stiffer it gets. However the real question is what happens if you reverse the left and right fins? I’ve tried everything except for actually reversing the side fins. I’ve even tried fins with no foil at all that were just flat fins and they actually were pretty good.

[@ezvibe8310]

Could this be the reason groveler type boards tend to have less aggressive tow in vs high performance boards?

[@davidgough3512]

I'm guessing that designers balance design components to compensate between outline, rocker fin configuration wave size(speed) and performance levels. Like using more rake or less toe-in on a rockery, curvy outline, or vice-versa. So it depends on the rest of the design. A short curvy groveler may indeed require less from toe-in to initiate turns.

[@ezvibe8310]

As you mentioned, there are likely other design features that come into play with fin tow in angle. Surf conditions and surf goals may factor in too. When i look at a board that has aggressively towed in fins and or rocker, my basic sense of physics tells me that board will not paddle efficiently, it will induce drag. However, my goals at my mushy, local break are different from the guy who is charging pipe or some other place that has real waves. thanks for your insight

[@nicolekelly8645]

I just LOVE these vids! Science 💕

[@MrYannickVincent]

Thanks, that was very interesting! One Question: So why exactly are Keel Fins not angled in and what would that provide, more speed and less maneuverability?

[@davidgough3512]

Originally the fish was a way for a kneeboarder to handle steep fast hollow waves in a wide outline.(No room to place knees and flippers within an actual narrow pintail singlefin). Each keel is designed to work with it's side of the tail like a single-fin pintail, like an old-school pipeline board would have. Keels are large for their depth, so when running flat, toe-in would have them fighting each other in a "snowplow" of drag, turbulence and wiggle-waggle. We're talking racing tubes here, not a series of S-turns.

[@patrickfitzgerald6073]

What about fin profile? They're generally flat on the inside side and curved on the rail side. How does that relate to what you talked about here?

[@SurfSimply]

Hi Patrick, we made a Surfing Explained video that discusses the reason for the foiled shape of a fin: m.kzbin.info/www/bejne/mJiYoZZ7mtVqY6M

[@patrickfitzgerald6073]

@@SurfSimply Thanks for the reply! I'm still not sure the connection between the fin profile (bernouli's law) and the angle of fin boxes is quite clear to me, but thanks for giving me a place to start to think abut it.

[@sushimamba4281]

Does the toe-in also create drag, especially if the toe-in angle is increased?

[@brianspinelli5728]

yeah i'm pretty sure, thats why when toeing in the fins there's a trade off between speed and manuverability

[@MrRobinski]

Tow in and fin splay angle also affecting each other aren't they?

[@SurfSimply]

Absolutely Troy, and the cant also!

[@jasontroy3911]

Keel fish fins are straight and double foiled....if your fins are that straight and single foiled it feels like you have the parking brake on......ask me how I know

[@brett7794]

So what you're saying if my center fins on my quad are 80/20 then they are going to slow my board down compared to a 50/50 foil? I'm so confused

[@finfoil8544]

Exactly, extra camber (asymmetry) requires extra toe-in because their neutral angle (angle of 0 lift) is negative.

[@afloatfish]

Love the content

[@DylanTheVillan]

Why provide an image of a bonzer for the thubnail if you’re only going to talk about thrusters

[@Hoptropolis]

This is weird, after listening to the podcasts you imagine what people look like!!

[@SurfSimply]

Did Harry fit your imagination or were you surprised?

[@Hoptropolis]

@@SurfSimply Pretty much fit the bill, dark lanky Brit!