I just shaped a 7’0" X 18"T X 22-5/8" X 18-7/16N" X 2-7/8" (with an 11" square tail) Egg/Mini Simmons quad.

I used the McKee system but his formula is for short boards, guns and longboards so I had to do my own figuring to extend his formula for a shorter wider tailed board. Even his longboard formula stops at a tail width of 17-1/2" so I had to extend his formula with my own math to figure out where to put the fins. After making the board it looks to me like the back fins were a bit to close together.

Here is where my fins ended up.

Front fins are 12-1/4" from the tail, 1-1/8" from the rail.

Back fins are 5-5/8" from the tail and 8" between the fins. (my 6’1" mini that’s 18-3/8" @12" came out 6" from tail and 12" between back fins)

Could some of you experts do your own math based on my boards dimensions and tell me where you WOULD have placed your fins?

Obviously I will be able to adjust performance with fins but I’m just wondering if I’m in the ballpark as far as my final placement goes.

McKee adds 0.75" between the rear fins for every inch of tail width at the point where his chart stops (17.5 tail). That makes the spacing between the rear fins come out to 12.4".

I don’t get how you concluded 8" between the rear fins was right when his chart shows 8.75" for a 17.5 wide tail.

My tails are wider than 17.5 too. This is how I do it.

Thanks for the help Dwight, guess I did to many bong hit’s before I started. I have no doubt my back fins are to close together yet I’m still a little lost when it comes to deciphering his tables. Using the Muti-System formula the placement for the back fins on a 7’0 would be 5-5/8". Ok, I got that much right. Now using the provided width between back fins update table you must input the tail width and the distance from the tail used for the back fin.

So I have an 18" tail and back fins are at 5-5/8" from tail.

Now the updated shortboard table shows that a tail @ 17-3/4" with back fin @ 5-1/4" should have a spacing of 8-3/4"

The update table also shows that a tail 1/4" narrower (17-1/2") with the same tail distance the spacing would be 8-9/16" ( a difference of 3/16")

So going in the other direction I get to my boards tail width of 18" so I add the 3/16" difference and I get 8-15/16" for the proper spacing. Obviously no where near the 12-1/4" you would use.

After reading a little more on the Mckee website I read a passage where Bruce suggests that as a rough guide he places the back fins around 2" off the rails. Checking my board I see that if I had placed the fins @ 10" apart I would be right on the 2 inches from the rail he suggests. So in the end after my calculations using the provided tables I got a figured of about a 9" gap (somehow I must have swapped 8" for 9" in my rush) for my board, and after the 2" from the rail suggestion I get a 10" gap between fins and on top of that you say you get a 12-1/4" gap between fins.

I’m not sure where you get the .75" increase per foot number or if your looking at the longboard formula or the shortboard/gun formula?

The longboard formula only shows an increase of 1/2" to 5/8" for every inch of tail. (but I’m not shaping a longboard)

The shortboard formula shows and increase of 3/4" (like you suggest) for every inch of tail.

So using the shortboard table a board with a 17" tail and fins placed 5-3/4" from the tail the distance between fins is 8-3/8". So adding an inch to the tail to get my boards 18" and then adding the 3/4" gap per inch of tail like you suggest gets me 9-1/8".

See why I’m a bit confused? I’ll just stick with the 2" from the rail as my guide but I still don’t see how you ended up with a number of 12-1/4"?

I have limited experience with the McKee but after surfing a few boards using it my preferred layout is the Hanalei Fin Systems quad setup. It is based off of measuring distance from rail rather than a mystic graph of space between fins etc. Some prefer McKee, I prefer this way. Worth considering if you are working on another quad at some point. The two are totally different though, keep that it mind.

A basic guide to how it all works together (as well as downloadable pdfs showing layout) is at:

My .02 is that the little adjustments from the probox system let you tweak it around after the fact which is extremely beneficial when you’re a garage hack like me! Lets me find the sweet spot on each board, cuz I don’t know where it would be until after a few surfs!

Have fun with your quad! No matter what you will no doubt be able to get used to however it surfs and hey, you made it and it will catch waves, the rest is gravy… how much fun is this…!