Rusty breaks down the ingredients for a perfect four-fin: QUADROPHENIA: PART ONE

I came across this article on surfline and it was a lot of good information.  I recently shaped a quad and had to really dig for most of the information that is in this article.

 

QUADROPHENIA: PART ONE

Rusty breaks down the ingredients for a perfect four-fin
Posted: **11/10/09**  |  Visits: **6339**



&nbsp;&nbsp;|&nbsp;&nbsp;Comments: **22**&nbsp;&nbsp;|&nbsp;&nbsp;<a href="http://www.surfline.com/blog/entry.cfm?id=38677#storycomments">View Comments</a>
Four fins are faster than tri fins.

Four Fins are looser than tri fins.

Four fins ride the barrel higher and tighter than a tri fin.

They drop in easier.

They come out of the gate quicker.

Accelerate on cutbacks.

Do better airs.

Can be ridden shorter.

Draw new and different lines.

Josh Kerr is one of the half-dozen or so of the ASP World Tour who regularly experiment with quads.

So why isn’t every surfer on the planet riding one?

It’s all Hype?

Different strokes?

Media?

The pros don’t so I won’t?

Maybe shapers don’t have it right…yet?

Perhaps if there were a ubiquitous effort, a Manhattan Quad Project,
the design would evolve at a faster rate and all would enjoy the
benefits.

Sorry, somebody has to win a major friggin contest on one first.
(Biggest win? CJ won the Body Glove Surfbout on a quad in '07.)

So at this point, who seems to like them and who doesn’t? And why?

Typical first impression of a quad is this: fast and loose, but not
confident without something directly under the back foot. It takes a
few sessions to trust the setup – and run with the positive attributes.

The lack of an auto-centering sensation seems to be a common complaint
from most detractors. Without a center fin, a lot of surfers miss the
instant feedback from the back foot and the ability to do quick
adjustments. With quads there is an information gap in rail change that
varies widely depending on fin (rear especially) position.

Backhand performance is also a concern of 3-fin loyalists. Going
heelside, the rider delivers more power through the rear foot and
specifically the heel. Visualize foot angle and where the energy is
going…for most surfers pretty much in line with the rear fin, three
inches and change from the back end.

Early days of the 3-fin, I’d put rear fins way back on some rider’s
tail blocks. It was necessary to do this to keep more powerful,
rear-foot surfers from blowing their tails out on acute direction
changes. Occy’s were set at 2 3/4" and some of Tom Carroll’s trailers
were as far back as 2" from the end of the board. As rockers and
outlines evolved, the rears crept up to 3 1/4" to 3 1/2" on an average
shortboard.

If a rear fin on a tri is moved up an inch or two from the placement
most people are used to, the board loses drive, hold, and moves the
pivot point further forward. A surfer would have to completely readjust
his rear foot placement. Same holds true with a quad.

Which leads to probably one of, if not the single most important detail
in designing a 4-fin surfboard: fin positioning. Not weird-ass tails.
Not crazy bottom contours. Fins. How big they are, outlines, and foils.
Where they are, their relative positioning with respect to each other,
cant and nose vector.

Jamie Sterling is a fan of quads in the barrel at Teahupoo 'cause they go fast and hold at speed. Photo: Tyler Cuddy

Early on I took a fairly simplistic approach to it.

Early quads were an attempt to add drive and control to twins. In 1980/81, Twins were de rigueur.
Since 1982/83, tri-fins were most surfers’ experiential basis. In my
mind, I’m starting with a tri-fin. So I took the rear fin on a tri, and
was theoretically splitting it in half. The more the rider wants the
feel of a tri, the further back and closer together I’d keep the fins.
If a rider was after more of a twin-fin feel, I’d move the rears
towards the rail and the front fins.

My common middle ground: for argument’s sake, a 6’2" tri-fin has fronts
at 11" and rears at 3 1/4". A lot of designers go half the distance on
a quad, so that would put the rears at 5 1/2" and the same distance
from the rail, about 1 1/8". In my humble opinion, I feel this is a
little on the neutral side. I split the difference on distance from the
tail (tri vs. quad: 2 1/4"), which would be 3 1/4" plus 1 1/8"…or 4
3/8". Easier math: 7’ board. Fins at 12" and 4" on a tri. Half the
distance is 6". Split the difference, 5" for a quad. On average, I try
to keep my rears about 2" in from the rail. That’s a generalization. It
becomes a more complicated depending on tail width and board length.

Fin size: Fronts are similar to tri-fins, perhaps slightly
smaller. Rears: profiles similar to fronts reduced approximately 10% in
overall area. You can adjust drive by swapping out rears with different
aspect ratios. More upright fins for tighter arcs. More rake to add
length and draw to turns.

Foils: Your preference on fronts…your favorite tri fin fronts
are a good starting point. If you are a fan of cambered fins – stay
with them. If you prefer flat-sided fronts, you will probably like them
in the trailers as well. Smaller, weaker surf; flats are probably the
go as they react a little quicker and provide instant feedback. Bigger,
more powerful surf – most prefer cambered or dual (full) foil
trailers. Less prone to cavitate and let go. Some prefer full-foil
trailers in everyday surf, citing more “feel”…smoother, cleaner, etc.
Not as fast.

Cant on rears: Typically, I halve the angle of the fronts. It
can vary according to intended use. Smaller softer surf; a little more
cant will add some lift and looseness. Conversely, less tilt will
increase speed, hold, and drive.

Nose vector (line towards nose): I typically point all four fins
to approximately the same place, which depends on board length and type
of surf the board is intended for.

Another shaper’s insight into quads and fin positioning: Bruce McKee
has done nearly 30 years of homework for all of us and he’s quite happy
to share it here.

Why not chuck a quad in the back with the rest of your quiver? Photo: Tyler Cuddy

So back to…why aren’t more surfers embracing this design?

I suspect that there were probably a lot of takers that might have had
a go early on before a lot of work had been done. They may have had a
less-than-satisfactory experience and shared it with others that may
have at one point been interested.

Some of it may be due to negative stigma. The print media. In an
incredibly myopic and disappointing “Surfboard Issue” last year the
polyurethane/polyester tri-fin was declared the winner and still champ
in a fizzling technology push.

Thankfully, we have the Internet.

Search and you will find. There are quite a few board builders offering
quads. Even Simon Anderson himself rides and enjoys quads and has
several models in his product line.

My suggestion is that if you are interested, search out a builder who
embraces the design and has a solid history with the setup. It’s not as
easy as just sticking four fins on a board.

More often than not when I let someone demo a quad they are pleasantly surprised.

+++

Check back later this month for “Part Two: A History of Quads,” with words from Simon Anderson, Jeff Clark and more.

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BONUS ANSWER TO A COMMENT FROM LAST MONTH:

Last month’s blog on tails, we received a question in response to the Simon Anderson story:

So Rusty - did you build a thruster later that same night? –Munga

Rusty answers:

I tripped on the experience for a couple of days, wrestling with the
thought, was it the board or the surfer? My mind said it was 90% Simon.

After a few days, wtf, I stuck a trailing fin on my favorite twin. My
first surf on the jury-rigged tri-fin was in decent surf but it was not
nearly as good as Blacks on that day I watched Simon. First impression:
board was noticeably slower but had a tentative short burst of speed
out of turns on the better waves. It felt like the parking brake was on
but when I drove off my back foot hard enough the board would come back
up to the speed it had as a twin…just briefly, and as soon as I let
off, it would slow down again.

I shelved it.

The next board I made myself after the twin to tri-conversion was a 4
fin round-tail. It was a super fun board. It had the speed of a twin
but with more drive and a bigger sweet spot. I vividly remember it
doing swooping cutbacks at full speed, almost effortlessly. I rode it
for a few months.

So, I’m working on my 2nd board ever and I am really considering making a quad. I’m in love with flying down the line and I was told from someone else that I should really shape a quad if that’s what I’m into.

But, my concern is that I’m a front footed surfer and from what I’ve been reading there is a lack of control without the trailer fin. Do you see an issue with front footed surfers not being able to off pull moves that are totally back foot oriented any more than if they were on a tri fin thruster? Or even making big backside bottom turns.

 

A quad setup is ideal for a front footed surfer but you can increase control by moving the back fins closer to the tail.  I would take a look at the quads that you like now and see the placement on those boards (if there are any that you like).  I have noticed that there is an adjustment period when switching to a quad but it’s something you will figure out.  One sugguestion I have though is that if you want to fly down the line you probably want to make sure to decrease the cant on the rear fins to add drive.  On the last board I shaped I chose specs similar to the biscuit for fin placement and the board didn’t have much drive.  It needed heaver surf to get going.  After spending a ton of time trying to figure out what was causing the problem I came to the conclusion that it was the fin cant and toe-in on the trailing fins that was causing this.  The toe-in on the biscuit had all 4 fins toed in 1/4".  If I were to shape the board again today I would reduce the toe-in on the rear fins closer to 1/8" toed in and keep the front 2 at a 1/4".  I would also suggest Probox to adjust the cant.  I have switched to probox since.  This would increase drive, speed and hold.  Just a sugguestion but you have to take into account the surf you are going to be riding the board in as well and cater to that.

I edited this because it was totally unclear

I agree that there’s an adjustment period when switching from thrusters to quads… especially if all you ever ride are thrusters. But if you have a wide variety of boards in your quiver, and ride them, it’s a pretty steep curve… mostly timing. But then again, I’m a quadophile.

In terms of control, I’d hesitate to move the fins back too far. The margin of error is small, and you can get pretty stiff quickly. With the Probox fin system, you can move the fins just fractions of an inch, and feel the difference. I’d be more likely to change tail shape first, before adjusting fin position, if control is what I was after.

Not sure what you are saying about cant and “tow,” but taking into consideration the surf size/speed/shape is very important, increasing cant for smaller, weaker surf, and reducing it for faster, more powerful surf. This is not a commercial, but Probox lets you make those adjustments with the twist of an allen key.

99 of my last 100 surfs have been on a quad or twin. There's a reason for that. The day I rode a thruster again I was missing the extra speed inherent in a centerfin-less setup. Felt a little sluggish but I'm sure as there is an adjustment period to go from a thruster to quad, the same is true for quad to thruster. For now I'm sticking with quads and continue to refine them to suit my style.

I like the way Rusty thinks...

~Brian

www.greenlightsurfsupply.com

 

Probox quads are the go for me.

"The lack of an auto-centering sensation seems to be a common complaint from most detractors. Without a center fin, a lot of surfers miss the instant feedback from the back foot and the ability to do quick adjustments. With quads there is an information gap in rail change that varies widely depending on fin (rear especially) position."

 

I think Greg Griffin’s 5 fin has the advantages of a quad, more fin area on the rail where it is most efficient at picking up energy, and a small center to address the above mentioned issues.  Greg calls it a supercharged thruster.  I’ve also heard it said they are quads with a training wheel.  Most people who try them like them.

I have to agree with the Probox way. Perfect for quads. Drivier inserts for those Big walled up days when all you want is something to make sections and a little more cant for the “everyday” stuff.

Onto board shape. Wider tail with some type of cut out, swallow/fish to help give it more bite in the back. It seems like a lot of quads are shorter and wider. Any issues with a slightly bigger shape? 

Rusty is great. All of his blogs on surfline are excellent and have taught me much about my equipment. My first Quad has just arrived and I will let you guys know how it goes when I get a chance to put it in the water.

 

okay, am i the only one that got lost when he started talking #'s ???

he lost me at this sentance: "I split the difference on distance from the tail (tri vs. quad: 2 1/4"), which would be 3 1/4" plus 1 1/8" " ...

can anybode fill me in?

What I think he means is that he doesn’t really like the simple quad formula of the rear fins being set half the distance between the front fins and the tail - it places the fins too far up for his tastes

He tries to get a more thruster feel by noting the measurement that the rear fin would be if it was a thruster - this will always be substantially further back.

Then as a compromise he then places the rears half way between the simple quad formula and the theoretical thruster position - this shifts them back a bit. I suppose he has developed a strong intuition of where fins should be on a thruster and he is using it to act as a guide to quad placement.

this sound right everybody?

That is exactly what he is saying.  He was explaining that the formula for the thruster was pretty much figured out and in this case it would be “fronts at 11” and rears at 3-1/4"."  The common formula for a quad is half the distance from the trailing edge of the front fin to the tail.  In this case that would put the trailing edge of a set of quad rear fins at 5-1/2" (half of the 11" to the trailing edge of the front fins).  He prefers to split the difference between the standard formula for the quad and the standard formula for the thruster.  So he takes the distance for a thruster rear fin, subtracts that from the distance for a “standard” quad (in this case 5-1/2" - 3-1/4" = 2-1/4").  He then takes half of that distance to find the mid point and places the rear fins there.  Using this example it would be 1-1/8" (half of 2-1/4") up from the thruster setup or 1-1/8" back from the quad, depending on how you want to look at it.  This would place the set of rear fins 4-3/8" from the tail.

 

Split Thruster anyone? afoaf?

One thing that puzzles me about quads is the extra fin area that most people use.

The fin area of MR twin fins is almost identical to a medium/large thruster set. Plus some thusters use a smaller rear fin.

Quads often have quite large rear fins. The result is more overall fin area and more fin area towards the tail compared to twins and thrusters. Is it possible that quad rear fins are often moved too far forward to compensate for too much rear fin area? Or maybe the tri fin setup is more efficent than a quad and needs less fin area.

The last time I tried to place rear quad fins was a mess. First I marked in placement for single, twins and thruster, then drew lines between all the back fin dots plus the centre of the tail. I figured the rear quads would be in the middle between those placements somewhere! My best guess was on a line half way between the rear thruster fin and twin fins. The line was about 45 degrees between those fin settings. It works well, but very close to McKees formula.

 

 

" One thing that puzzles me about quads is the extra fin area that most people use. "

 

  me too !!!

  lately , after a lot of trying different template fins of mine , i find i am often  using fcs 'gs' or 'M.R.TX'-sized fins in mine , in up to head high surf. i use a fifth 'TX' sized one [in the back , thruster- setup  plugs] sometimes, when it gets a bit bigger / hollower.

 

  seems to work for me.

 

the next quad-setup boards i ride  will definately be narrower in the tail and narrower overall ...the Walden 'CD4' i have been riding since feb/march this year is a fat arse , low rockered board  ! [fun when it's a bit fat / flat , a bit sketchy when hollow !

 

 [i still want to quad setup my island 6'3 and my orange stub 6'1/2" ]

 

   cheers

 

  ben

 

 

 

Hey Lynchy,

What is that Rusty Quad doing, is it alive? Love to hear some feedback here.

Wouter

i’ve been thinking about doing a fin placement study for one of my design projects at school. Im just starting shaping so i would use a bunch of board ends with different fin set ups and different lengths apart.

why not just a bunch of boxes?

or some adjustable one…