Quick question about quad fins placement. I’m shaping a 6’3" x 20 (14.25" tail) round pin quad for over head surf (for context).
I notice that basically everyone uses 1/4" toe in for the front fins and most use 1/8" toe in for the rears. Why? Is there a reason?
Why use parallel fins, with 3/16" toe in? Is there an argument against parallel fins?
gracias!
Most of the quads I’ve seen pop up recently have been doing all the fins at the same toe-in angle. More advanced shapers have figured out that fin clusters work similarly to the front wheel alaignment on cars. If the front wheels on your car turned exactly the same on the left and right, you would burn through tires really fast. The leading set of quad fins travel through a different arc than the trailing fins do. A quad fin cluster should have different toe-in angles to keep drag to a minimum allowing the board to rotate through a turn with very little resistance. Another way to think about it is to look at the 2+1 longboard fin configurations, the center fin is straight providing drive and stability while the side fins are toed in to rudder the rail line and rocker into a turn. Quads work similarly, the leading fins rudder the board into a turn while the trailing fins help with stability and drive. The trailing fins should always be straighter.
Byron
I notice that basically everyone uses 1/4" toe in for the front fins and most use 1/8" toe in for the rears. Why? Is there a reason?
Too much of a good thing.
Makes for a more predictable response. Many are made so that the fins point to the same location, which happens to result in that setup. Many ways to set them up, but its likely a good place to start - good all round setup.
IMO, they are still less predictable than three,center fins are great stabilizers. But 4 are faster on rail.
Here’s how I do my quads. The trailing fins are bigger for drive, the leading ones rudder into the turns. 8 degrees cant on the leading, 6 degrees cant on the trailing, 3/16 toe in on the leading, 3/32 toe in on the trailing…Byron
Sorry to go on & on, but this is also important; I use center foiled fins on the trailing fins and flat inside leading fins. This helps keep the cluster stable and from tracking weird…Byron
We’ve had the best result with 80/20 foils on the rear fins, and flat sided foils up front. I agree that the rears should be toed less,or at least for most boards. On the quad fishys best feedback is 3/16ths toe up front and 1/8th in the back. The cool thing about the quad is it’s giving shapers something to sink their design teeth into once again. There also seems to be more margin for error…meaning they still work toed 1/4…or 3/16ths, or 1/8th or 3/32s whatever on the rears. It’s really gonna come down to where you surf,and how you like your board to ride. If I knew I was going to J-bay and would be riding my quad fish on the manageable days…I’d set my rear fins near parallel or 1/16th just to clear sections. Oh and I’d pull the tail in a bit as well.
Think of it like an aircraft. The main wing is the Front Fin, and the horizontal stabilizer is the rear fin on each side. The main purpose of the stabilizer is to try and keep the main wing at a certain angle so it can generate lift.
As you keep increasing the rate of turn, the angle of attack grows more for the rear fin than the front, because of the toe-in. So, the rear fin stalls first, while the front fin is still providing lift. This stall creates the needed drag to keep the front fin providing lift. If the rear fin does not stall first, both can potentially stall at the same time, and you spin out. Of course, you can push the board hard enough and to a big enough angle that both fins are stalling at once, but the rear fin (if the same area) will still produce more drag and try to rotate the front fin back into a non-stall angle. The rear fin keeps you from over-rotating and spinning out.
Does this make sense? It’s kind of the way the thruster works, but think of having a thruster center fin on each side of the board…
If I am wrong, please correct…
JSS
Yes makes sense… sorry to hijack this thread but I want to throw in a question as I’m planning on experimenting with on a quad setup.
The quad setup I’m planning to experiment with is:
Leading fins toed-in 1/4"
Leading fin template similar size to a twin fin (larger surface area) and single foiled
Trailing fins parallel and much closer to the stringer (maybe 3" or 4" from stringer)
Trailing fin template to be a smaller surface area and foiled symetrically (i.e. Like a thruster centre fin)
The concept is to be a hybrid of a Quad and a thruster… the purpose of the design is to provide the manouverability of a quad with hold and drive of a thruster particularly when going from rail to rail.
Planning on using Probox so that I can have options for the fin positions of the fin cluster.
Thoughts?
-Cam
Bulkley sets up his Quad shortboards that way with the rear fins being 2 + inches from the rail and has real good results with it. Says it keeps some power in the board with the fins being more underneath you.
The toe-in of a fin makes it easier to initiate a turn as the fin is pointed into the forces of resistance instead of against them .More toe-in is good for slow waves and less is good for lined up ones. You as a designer decide on what you are looking for and that deternines the toe-in. At higher speeds less toe-in is needed and will enable higher end speeds. Size of fin, use of area-template, and placement-forward-back, tilt and toe-in create the design of the fin system .
thanks for that concise insight Sunsetpoint.
that really helped me understand what is going on.
a lot of times these threads get so over the top
that i either get lost or don’t want to sift through
all the posts for the simple explanation.
Sunsetpoint’s assesment of fin turning dynamics is abosolutely right. I try to explain things as simply as possible, but it can be hard to put theoretical concepts into words. For me personally, I’m 6’0" and 195lbs, so I run my toe-in straighter for drive and I angle my cant out a bit more to let the board roll onto the rail easier. I have the size and weight to hold my board on rail, so I don’t need the fins to help initiate the turn as much. That is why I run 3/16" toe-in on my leading fins as opposed to a 1/4" toe-in.
Byron
gracias hombres!
so much useful info in here!
This is all great information and timely for a couple of recent projects I’m putting together. I’m trying to get a grasp on the front-to-back placement of the quad cluster and the cluster dimensions as it relates to the length of the board. I realize that the planshape and fin template is a factor in this decision as well. Let’s take a fishy outline at 5’8" and stretch that outline to 6’0", 7’0" and even 8’0". If we are using a baseline of quad placement of Rear @5 3/4" and Front @11 1/2 on the 5’8" how do you adjust for increasing the length of the board?
Outline in all cases is something like 17x 21.5 x17, Fin Template=Rainbox/LokBox PT Quad (speed-dialer-ish)
Any thoughts or input appreciated on this.
Tom S.
Where do you get your fin placements from and why do you chose this template ?
My mistake, let me rephrase without mucking up the discussion with junk:
I’m trying to get a grasp on the front-to-back placement of the quad cluster and the cluster dimensions as it relates to the length of the board. I realize that the planshape and fin template is a factor in this decision as well as the type of surf (small beachbreak)
Let’s take a fishy outline at 5’8" and stretch that outline to 6’0", 7’0" and even 8’0". Outline in all cases is something like 17x 21.5 x17.
Any thoughts or input appreciated on this.
Tom S.
From 6’ to 7’ i would move the fins about 1/2" to 3/4" forward
For quad fin placement, Bruce McKee has some great info at http://www.mckeesurf.com/…mckee/fingraphic.htm, with the formulas available at http://www.mckeesurf.com/…n_direction_data.pdf.
For a quick look at how different aimpoints in relation to the nose effect the toe, I wrote a program that does the calculations for you, taking board length, tail width, fin size, etc, into place. Check out the calculator at http://www.kainoalani.com/design/toecalc.html. Feel free to reuse it on your own site.
Ah yes, fin direction in the end is simple… If your front fins are at 4 degrees toe in and a thrusters rear fin is at zero then your rear quad side fins are at the degree of the sweep of the arc… in the middle generally at 2 degrees.
When Bulkley emailed me to ask why I have my back fins away from the rail etc… It goes like this… If a thruster setup has a balanced hold with the tail fin so far from the rail, then why shouldn’t a quad have the tail fins somewhere in between. There is a relationship between tail width at 12" up and the width between the rear fins, thus I produced a formula for this. Tail fins too close to the rail…, too much hold. Tail fins too close to each other, not enough drive. My distance between back fin, according to tail width, you will find, reduces a time lag in redirecting the boards back onto the straight line between turns. Eliminates the feel of the board staying on one tack and gives a ‘Thruster’ like recentralizing feel rather than a need to throw the tail across from one turn to the other normally associated with having all the fins close to the rail.
when I started making the Quads way back. I placed the fins according to how the boards looked and felt to ride. Some of my previous formulas had all the fins moved further forward for Round Pins etc to compensate for differences in tail area etc..
The M5multisystem formula's fin positions are now pretty much to the millimeter of providing a nice balance of hold, fluidity and drive.. You can move the positions around a bit but I found that the distances between the front and the back fins are like a nice standard Commodore car but you could shorten or lengthen the wheelbase according to taste. I ended up placing the front fins where a Thruster had them so that people would have less excuses not to try one..the M5 having a Thruster built in.
Jefferey's Bay 1992, Tom Curren Search 2, Searching for Tom Curren and Ultimate Sessions all feature Tom riding a 6'11" Mckee Quattro with bigger back fins than front (what I thought was 'Formula One' at the time). All the biggest barrels and bottom turns. All on a four-fin.. No one knew, no-one told... check. <a href="http://www.mckeesurf.com/brucemckee/quattro.htm">http://www.mckeesurf.com/brucemckee/quattro.htm</a> for proof and <a href="http://www.mckeesurf.com/brucemckee/multisystem.htm">http://www.mckeesurf.com/brucemckee/multisystem.htm</a> for all the formula info and downloads.. Welcome to a parallel surf world. <a href="http://www.mckeesurf.com/brucemckee/indexfiles/fotos/surf/currenjbaybig.jpg">http://www.mckeesurf.com/brucemckee/indexfiles/fotos/surf/currenjbaybig.jpg</a>
Great info Bruce & Griff. Nothing like a primary source to get accurate research 