Quad fins for a Nugget

General Discussion
1

I am in the process of modifying a McCoy Nugget for multiple fin options.

To avoid vandalising a hand shaped board, I bought a popout Surfboardagency FX All Round Nugget 6’6 x 21 1/4  x 2 7/8  (47L).

The boards is a thruster setup and I want to add a single fin box and additional quad rear plugs. The general idea is to allow the board to be surfed exactly as designed (thruster), but also as single fin or quad or 5-fin setup.

I have worked out where I want the rear quad fins to go: 16.6cm from tail and 12.0cm from stringer (that’s where the rear tip of the fin should end up).

I decided to use the ‘Golden Ratio’ due to absence of any real knowledge about fin placement. Already built into the board is the convergence point to which the front fins point. I think the rear fins should also point towards the same point. I then devided the distance between the stringer and the lines from the front fins by 1.618 to determine where to place the lines to which the rear fins will be aligned. 200mm nails, strings and a lawn make it easier:

 

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The shadows in this photo show the distances to the stringer at the nose:

 

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I then divided the distance between front thruster fins and rear thruster fin by 1.618 to determine where to put the fins along the strings.

There are 2 possible versions and this version looks more balanced:

 
 

 

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This is my favorite fin set up for a domed bottom.  Rears are staggered sizes and put out on the rail, not inboard.  Very loose and lively, with plenty of drive.  Good for soft/slow conditions, but will also hold in faster conditions.  More carve than snap.  

 

 

 

 

 

 

 

 

 

 

This setup works, too, but it’s not nearly as loose/lively.  Better in more powerful conditions.  

 

 

 

 

 

 

 

 

 

 

I ran this board as a singlefin (only) for 6 months, including the use of the Starfin.   It’s pivoty, but not drivey at all.  I would only run it that way if I was surfing powerful conditions.  

5

Oh, and I don’t know what that core is like, but if it’s light density EPS you might want to install HD inserts out of Dcell or PU prior to installing the boxes so they’ll have something to hold onto.  

6

Thanks, gdaddy!

I’m actually leaving the install to a professional. I bought the board and negotiated a price including the modifications. They told me that I cannot buy FCS2 inserts and equipment unless I am a ‘licensed installer’ or something like it. I hope the guy knows what he is doing, but chances are he does. If the fins rip out, that’ll be a lesson learned for next time.

I decided to start with the FCS II Performer PC Carbon Quad Set (large) plus the FCS II Performer Centre (large). That way, I will not need to use a key to switch fins. http://www.surffcs.com.au/…/fcs-ii-performer-centre…

The centre fin box at 10’’ is just long enough to allow the snap-in FCS2 Performer fin to sit where the original thruster centre fin used to be, and the front of the box is far enough forward to place a Gullwing Fin in the recommended position 18.5cm from the tail. I hope the tail is thick enough to fully accept the box without sanding any off it. I usually use one of Roy Stewarts polycarbonate Gullwing Fins, with or without the BLEF bumps. But for this board, I might go back to using the snap-in Gullwing fin that came with one of my Zots. I want to change fins while in the surf, and also have another Franken-McCoy in the family. With a bit of collaboration from other McCoy afficionados a complete change of fin setup in the surf will be possible.

I have not been able to find clear instructions for quad fin placement, except the McKee tables. The attached photo shows where I think McKee would have placed the fins, compared to my placement. The other difference to the McKee recommendations is that the distance to the stringer at the nose of the board is a bit larger. That is dictated by the already installed front fins, and my conviction that all 4 fins should point to a common conversion point.

Here are some measurements for those who might want to modify a Nugget to Quad themselves. The McKee recommendations are in brackets behind:

XF Nugget 6’6’':   

Tail width at 12’‘:         43.6cm       17 + 3/16’’

    Front fins distance from tail:         29.2cm   11+1/2’’  ( 28.7cm McKee )

    Front fin distance from rail:  Measured perpendicular to stringer (not shortest distance):  3cm

    Front fin cant:   5deg

    Front fins distance from stringer and from each other:  rear of fin 18.5cm;  front of fin 18cm from stringer;

    Rear centre fin distance from tail: 8.6cm  (8.8cm McKee)

    Final rear quad placement values chosen by me:

        16.6cm from tail  (13.3cm McKee) ; using 3degree cant boxes.

        12.0cm from stringer.   (10.4cm McKee)

        Rear fin projection line 5.2cm from stringer at nose ( McKee: 2.86cm)

        Front fin line 8cm from stringer at nose  (McKee: 6.985cm); this was of course already built into the board by the placement of the front FCS2 plugs.

 

 

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I made a few cardboard dummy fins during the attempts to work out where to put them. This photo includes the centre fin box and the snap-in centre fin in the original thruster position:

 
 

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More views with dummy fins (the cant is rather random, just cardboard and duct tape):

 

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These three views show the other possible option that can be obtained by dividing the distance between front and rear fins by 1.618.

I don’t think it looks like it would work well, except maybe to make it feel like a twin fin:

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your rear quad fin boxes are quite a bit too far forward.   Put them about an inch further forward than the rear of the existing center box.

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I agree with Keith Melville. The rear fins need to be set back more than the pictures you show.

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I would move the centre finbox forward to be inline with the back edge of the smaller fin box which then allows you to try a gullwing fin further forward which is the best position in my opinion.

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Thank you, Keith Melville and Sharkcountry.

If the rear quad fins are too far forward, would will be the unwanted effects? I assume it would be something like the tail sliding out in larger waves, like some surfers say of twin fins?

Would the effect of a small-ish nubster fin cancel out the effect of the rear quad fins being too far forward?

 

14

That’s a good point. However, I don’t even find my 7’1’’ Zot and 8’ SF Nuggets too stiff with the Gullwing fin in the 18.5cm from tail position, and the 6’6’’ Nugget will be at the shorter end of my quiver.

My first priority is to make it possible to surf the board with thruster configuration as originally designed. An original McCoy Gullwing fin will be able to go a bit more forward than the snap in versions. The fin box needs to be this far back to allow the rear fin to be in the original position.

15

the unwanted effects of those fin boxes in the wrong place include kidney stones, occasional sleeplessness, snoring, sneezing, muscle cramps, bloody stool, and of course spinning out on bottom turns and lacking drive (of all varieties).  No, a nubster fin would not prevent all of the above. 

Your mileage may vary. 

16

Oh dear! I’m suffering from most of these afflictions already, I’ll be doomed if I ride that board , it is certain to exacebate the situation.

I may call the shop tomorrow, and if the installer has not picked the board up yet, then I’ll get it back and re-assess. If it’s too late, and I cannot find a pleasant use for the fin boxes where they are, then maybe I’ll install a few more too far back and too close to the stringer, and use it as a bad example. Or as an immunisation: If I can learn not to wipe out on that board, I’ll be ripping on a proper one!

17

I cannot vouch for the accuracy of the diagrams etc, but it does not seem completely off to me:  Some Quad fin options and effects shown: 

http://store.magicseaweed.com/blog/page/5/

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I don’t agree 100% with the Magic seaweed page. I think rear fins closer to the rail loosen up the board, same for having them clustered together. Too close and there’s a lack of drive. Your turns will be more pivot like.

Read this article and all the comments. http://www.surfline.com/blogs/talking-design-the-board-blog-with-rusty-preisendorfer/rusty-looks-back-at-the-history-and-evolution-of-quads_38953/

One quad setup that I really like is the Alexander Gemini layout. Don’t have the numbers so you’ll have to look it up. Rear fins spread apart from the front and about half the distance between stringer and rail, almost no tow or cant. Boards fly and they turn great, feel solid like a thruster with the advantages of the quad. We have several of the Geminis, so I just copy the layout from one of them to a similar sized board I make. For looser boards, I use Robin Mair’s quad layout.

For another option look at what Greg Griffin does. I ride his 5 fin boards and have ridden the newer super short 3 fin that some people call a fang tail, or felix the cat tail. The 3 fin is definitely something you need to try.

I use probox fin boxes and they allow me to change the cant and I can move the fins about 3/8" fore or aft. It allows for a lot of fine tuning, or just changing things up for fun.

19

Some images for you. Also… a lot of times you’ll see the rears call for “X” inches from the rail. With more rail curve that places the fins further in towards center, so you have to look at a lot of variables. I like to generalize it and make the rears “X” inches a part or percent from the stringer versus rail. The shot of the Rusty board is kind of what seems popular for a quad/thruster layout.

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20

Well, you guys have done it…I did get the board back today before any changes were started.

Back to the drawing board!