Fins position and toe in

General Discussion
1

Aloha everybody,

I am shaping my first shortboard which will be 5’4x19’1/4x2’2/4. I chose the thruster fin position for my first surfboard but I have some questions as I am a bit confused. In some article, they say toe-in is about 1/4 inches. But if I applied McKee formula I have more than 1/4 inches as toe-in. Could you tell me if I am applying well the formula and good fin placement or should I go with standard 1/4 inches toe-in. What is the impact of high toe-in value more than 1/4 inches?

By applying this formula according to McKee’s table chart, I have:

HBF distance from the stringer to rear lateral fin, given by McKee Chart. So at 27,1 cm (10-11/16"), so I have HBF=38,8/2-2.54 = 16.86cm (6.63 inches)

LT: Surfboard lenght=5’4=162.56cm. d = fin lenght = 11.5cm. a= FIN DIRECTION COMPENSATION (giving by McKee chart)

So to calculate the fin toe-in, I applied this formula:

LBF=(LT-DFT-d)*((HBF-a)/(LT-DFT))+a

At the end I have LBF=15.52cm. So toe-in = HBF-LBF=16.86-15.52 = 1.34cm (0.52 inches)

Regards,

Eric.

2

I have noticed quite a few boards I have had in for repair (popular brands) that are using cant of over 10 degrees, sometimes upto 12 degrees (from horizontal using a level to flatten out the concaves) seems pretty extreme, but it seems that around 10 degrees is becoming fairly normal these days.

Would be nice if someone could chime in?   Yorky… are you there?

3

Hello Eric-

I think your board is too short and maybe too wide for the McKee formulas to work as posted.

Does the top half of this sketch picture look like your current plan?

I can see where the toe-in is extra large due to the McKee toe-in angle being based off an offset from the stringer.

What is your tail width at 12"/30.5cm from the tail?

I am not an expert, I just think McKee layouts are fun to draw while drinking coffee…

4

1/2" sounds like too much

5

I am not following your math but 1/2" toe over a 4 1/2" fin is stupid.

You would have realized that as soon as you layed it out on your board.

Here’s how I (and many others) do it.

Mark your rear dot.
Measure 4 1/2" up the stringer and place your front dot 1/4" (or 1/8" or 3/16 or whatever toe you want) closer to the stringer.

You can also measure 9" up the stringer, double your toe and put a dot there. This probably helps make your lines truer.

Alternately, in a recent thread, Mako explained marking toe in relation to the nose. I have heard that lots of folks do it this way too. Mako’s write-up is really good, you should look for it.

6

Hi J.Randy, yes, your sketch look likes my board. My tail width at 12" (30,5cm) is exactly 40cm (15,75 inches).

So you think I should forget about Mkcee formula for my board and go for: 

Central fin from the tail 3-1/4" (8,3 cm), front fins distance from the tail 10-11/16" (27,1cm) and toe in 1/4". Does it makes sense?

Thanks alot for your help.

 

7

Aloha Crisp, thanks for your reply and advices. I gonna look for Mako’s thread about making toe. If you have the link under your hand it will appreciate. I wrote to JRandy about my new fins placement.

8

You’re welcome…

Here’s the thread:

http://www.swaylocks.com/forums/fin-placement-eff-up

9

Yeah that’s the way I generally do it too, ChrisP

10

Eric, I am glad the picture was good. I was hoping it would help the discussion. Since I do not make or ride shortboards I would look to the others for the exact numbers. The only number that did not seem ‘realistic’ from your math was the toe-in.

Here is the basic diagram from Greenlight:

 

 

 

11

I’ve mentioned my method for setting the toe in on my boards.  This morning I was setting some boxes so I snapped a couple of pictures.  First I decide where I want my rear dots.  Next tear off a sheet of masking paper.  First I align the edge of the paper to a rear dot, smooth out the paper and I sight down the board and find the toe in I desire for the curve of the rail and the rocker of the board.  I spend a lot of time on this and make sure I get it right.  When I am happy I put a stick pin through the paper into the stringer near the nose.

 

 

I double check everything then I lay down my square and measure up and make my front dot.

 

 

Now I just pull the stick pin, flip the paper and put my pin back through the same hole in the paper and into the same hole in the stringer and now I can create a very precise mirror image on the other side of the blank.  Is this the way a production shop does it, of course not, but is is a very precise way I can get it right every time.   To me, the method of measuring a toe in based off of a distance from the stringer is a recipee for a big screw up.  If you are measuring that way you’d only have to be off the tinyest fraction and it would wind up looking like a major screw up when sighting down the board from nose to tail.  Also the length and curve of the board and the desired turning and drive characteristics you are after are affected greatly by your fin placement so I would not recommend picking an arbitrary toe in like 1/8th inch or whatever some website says measured from the stringer.  Let the shape of the board show you the toe in.

Hope this helps someone out.

PS:  It really looks bad if your fins are going different directions when the board is sighted from nose to tail.  Something to think about if you’re trying to get your dots proportional by measuring from the stringer.

 

12

Hi JRandy, thanks so much for the diagram. I was wondering if the basic diagram from Greenlight can be applied for any kinda of board lenght, I mean fins position measurement.

13

Mako, that is so damn helpful!