Importance of fin Placement?

Normally when we set fins se follow a formula (Some just guess)

I made a down sized shortboard were we maintained the volume with a shorter thicker board however with a rail simular to his standard shortboard, Basically the volume was hidden in the center while maintaining his standard rail.

Since I went 4" shorter I set the front fins a 1/4" back.

We thought we had produced the magic carpet for those shoulder high glassy fall days we get in south orange county in the fall. It was a complete failure.

My rider came back and was very displease and said our experiement was a complete failure. So I check out the rocker, foil, outline. bottom contours and finally looked at the fin settings. Form there I asked about drive? The surfer said it had no drive and was a slug. Did I cave? No I did not!

 

We took the board to the sanding room and re-routered the fin boxes and set the 1/4" further up.

5 surf sessions later the rider told me he had 5 solid session and the board had so much more drive and speed. Also being shorter than his standard by 4" made his surf sessions very lively.

The funny thing for me was it was only 1/4" difference in the front fin placement.

Now keep in mind I don’t thing most surfers are this senitive? He has surfed the world over and as been sponsered by some big players in the industry.

 

The lesson I got from this is when downsizing a shortboard fin placement should not be drasically changed.

 

Here’s a photo of the cosmetics after the correction (Not pretty) however it works.

So know we will make the board in a space suit. (It will be documented)

4" shorter

Same rails

1/16" increased thickness

1/2" wider

Center Point 1" forward than standard.

Rocker constrained

Material XPS

Stringers Parabolic

Cloth (New Technology)

Resin EPOXY

Method: VACUUM

Projected weight: - 5 pounds

 

Core: Combo XPS + other

Glass: New Technology Space suit

Stark Industries: Ironman testing

 

Photo of mistake corrected:

 

Did you move the rear a 1/4" as well over your normal placement or did you leave that alone? 

I just re-did my fin placement table that I use and found that I was unknowingly designing boards for myself that I expected to ride a certain way around a fixed fin placement.  That is subtle tweaks of a given design for a fixed length but never moving the fins position.  Once I changed my chart it threw off my known expectations of what I thought I was going to accomplish.

For me aside from all the subtle interactions of foil, rail shape, construction, outline, bottom shape, etc. the rocker and the fin placement as well as the toe, cant and fin shape have been the most critical for performance.  Now I'm almost starting over for a known design in that I'm unsure if I can reach the design goal. 

The current board in question is a good wave board.  I added an 1/8" more tail rocker but moved the front fin placement 1/4" forward.  Not a good combo for what I expected the board to do.  I'm going to remove the fins, glass-ons and put in boxes.  My gut feeling is the new more forward fin position is good but more tail rocker is going to require larger fins.  Board turns better rail to rail but doesn't have the bite I was looking for during cutties.  I'd rather put larger glass ons but I'm having a hard time getting templates I'm familiar with. 

In the future I'm thinking of cutting the tabs of the box fins and glassing them onto the board just so I can get the templates I want. 

I adjust my fin placements with a linear formula similar to the one Brewer uses. It works great for guns and step up boards, However I have found that my standard fin placements for High Performance shortboards works for my downsized models better than trying to adjust.

What I will do now is continue to use my formula however will not use it in reverse.

For example I set my fins for advance surfers with the following:

Back fin: 3.5"

Front fins: 11.25" 1/4" toe 7 - 8 degree cant 1.25" front rail

In the case I described I had set the front fins at 11.0". The back fin was a standard setting. Putting the front fins on a 1/4" forward change the whole dynamic of the board.

There is a trend amongst the better surfers to ride shorter boards (Slater Trend). It’s actually pretty cool because it’s making people more open to a wider range of boards which is good for the board builders.

I think where I went  wrong is that normally when I make a 5’0" HPSB for a Grom I will set the fins at 3.25" back and 10" front and cut a 1/4" off the base and it works perfectly. That was a liner adjustment. However I have found that for a grown experienced surfer you don’t want to change his fin set up from his standard shortboard. Just adjust the volume distribution and reduce the length with a slight increase in width. The center needs to be pulled forward as well. I’m sharing a formula. However I’m sure many will disagree. I work very closely with my guys who surf from Santa Cruz to Puerto and all over INDO so the feed back is priceless. Once we know the board is shaped well we can proceed with the Space suit.

I’ve set the fins for 4,200 boards and never have I had such feed back as I received from my experimenting. Having good surfers to work with really helps you develop your design theories.

 

 

O.K. thanks for sharing and explaining.  I can see what your getting at.  I only have myself and a few riders that I've tried to educate to bounce theory and practice against.  Some surfers are very technical and know what they are talking about some are technical and don't have clue.

My take on those shorter wider designs is front foot/back foot.  Front foot is the lower entry drive, extra width is to compensate for the reduced volume for paddling and glide.  Back foot is hpsb.  I've gone away from trying to make a better hpsb to work in crappy waves to this "new" design push.  So the first few I did I did the same as you and reversed my fin placement chart for a shorter board.  Boards where too sticky off the back foot. 

So reducing length was compensated by the reduced entry rocker but the tail, except for an increase in width, had a similar rocker to a 4" longer hpsb.  My back foot isn't 2-4 inches further back so why should my fins be further back. 

I think that if you take a good surfer that wants the board to snap and carve a certain way you'll see he will be standing in a sweet spot.  Something about the relationship of his back foot to the fins to the distance to the tail tip is more critical than people realize. 

It kind of clicked for me after watching a short video of Darren Handley talking about Mick's boards.  He didn't want to talk about exact details only that after getting a design refined did they start making subtle alterations to his fins position and cant to really dial the board in. 

Thanks again, gets the mental gears turning.

good reading and can relate to alot of what you are doing and saying....I tinkered with diff placements for ages with my quads but after settling on set placemnets for specific designs, I have not altered them for a few years and am just making performance adjustments with fin templates mostly....obviously the boards shapes will always be modified to suit the surfers needs but I am super confident with my fin placements, slight adjsutments to tail rocker and bottom contours etc can be made with total confidence and no uncertainty ...but 99% of time using FCS so can fine tune fin templates and can make adjsutments from board to board for customers (with cant and toe) as needed too....

or just go finless, its easier but harder...... 

Back in the 6-fin thread ACE made a comment about his fin placement system relating to the fin cluster as a unit and moving it as a whole rather than fronts vs backs.  Maybe if you had moved the rear fin back 1/4" to keep the same spread with the fronts your rider wouldn’t have felt such a big difference.  

nice thread Surfding, thanks for sharing

In the end we have the right formula for these shorter boards we are building.

It's so cool to hear what others are thinking or doing on this subject.

DHD does make some magic boards. My son is friends with Mick so I have held a few boards of his.

Most of my fin setting logic is based on surfer feed back.

However the feed back is only valid if the surfer knows how to surf?

http://www.surfline.com/video/locals/huntington-beach_2375

 

Like Ace commented earlier, I always assumed that it was the cluster that moved and not the individual fins. The side fins can be manipulated with toe and cant, but in relation to the other fins their orientation stays the same. Otherwise the flow of water is changed too drastically. Then again…I really don’t know how to surf. At least not like those guys. If there is a formula, I’d sure like to see it. Proprietary info excluded.