View Full Version : Accurate tuttle fin head dimensions

18th February 2009, 01:13 AM
I have purchased a tuttle fin the is not fitting exactly. I realize that I can use soap or other tactics to determine the areas that are not fitting perfectly. However, I also wanted to use a more empirical approach to determine how best to mod the fin to fit. The brass inserts may not be in the right location.

I also have a deep tuttle that I would like to modify to a regular tuttle and wanted to ensure that I get it right the first time. You know: measure twice, cut once.

I have searched the web for drawings with dimensions and found only one so far (here http://www.home.umk.pl/~skoter/jaws/articles/finbox_tuttle.gif). The trouble is that the width shown is wrong and so I'm forced to question the remaining dimensions.

Does anyone know where I can find a dimensioned drawing of a tuttle box and/or fin head?


18th February 2009, 04:22 AM
Hi sauls,
The other dimensions are pretty close.
The thickness of the Tuttle fin head is 0.620" -0.624"/15.748-15.8496 mm on the original Larry Tuttle drawing (which I am not at liberty to divulge)
The Skoter dwg. needs to be corrected.
The length of the base (at the fin root) is 6.136"-6.140"/155.8544-155.956 mm.
Larry Tuttle measured the upper corners in a different way than on the Skoter Dwg.
The vertical dimension (from the base of the fin head) to the sharp junction at the back end of the fin is 1.250"/31.75 mm.
The vertical dimension from the base to the sharp junction at the front of the fin base is
2.00"/50.8 mm.
Both the top corners get a 0.25" radius from the sharp junctions.
The front and rear angles on the Larry Tuttle drawing are 80 deg. from the base at the wider root side. This is 10 deg. off perpendicular.
The distance between the drilling for the brass barrel nuts is 4.135"-4.140"/105.029-105.156 mm (centered on the top of the fin base). On the deep Tuttle the hole of the shorter end of the fin base is 0.491"/12.4714 mm from the junction of the rear angle and the top angle.
The center of the barrel nut cross drillings is 0.50"/12.7 mm below the top surface of the fin root.
If you modify the Skoter Dwg. with these numbers you will have your own version of the original Larry Tuttle design.
The Deep Tuttle uses all the same widths and angles, it's just 18 mm/0.7086 taller than the std. Tuttle.
If you make your own drawing and send me a copy (not of the forums please) I will check it against the original Tuttle design and make corrections as required.
Best I can do and still maintain my credibility with both Starboard and Larry Tuttle.

18th February 2009, 04:23 AM
Hi S

Not that this answers your question (I see Roger has done that) - but after using a few boards, and adjusting fin heads to suit - I think the fin boxes are often distorted during placement in the boards: for example an iSonic 122 2008 - the box was compressed down its length, hence bulged in the middle and required the fin head ends trimming to sit flush; conversely a CA SL58 2006 - the box was slightly compressed in the sides, once sanded down the fin head sank too deep!

This is for stock and 3rd party fins - so, most likely the boxes are the problem.

So - bottom line: whether or not the fin heads are accurate, they'll probably still need to be custom fit to the board.

Regards - Martin

18th February 2009, 05:02 AM
Thanks Roger.

I noticed he has the front and back angles wrong too.


18th February 2009, 07:04 AM
A couple of clarifications.

The 0.7086 higher than a std tuttle, is that measured perpendicular to the root of the fin or perpendicular to the top surface?

radius on the corners between the sides and the front/back edges?

Any idea on the proper drilling for the barrel nuts or will that depend on whether you're using std or metric?

I can't seem to get the Deep Tuttle dimension from the back to the first bolt hole to work out (you said 0.491, I get 0.514). Are the holes in a different location than the std Tuttle box?

Thanks for the Great Reply Roger!!


18th February 2009, 11:16 AM
Hi Saul,
The 0.7086" "addition" is measured perpendicular to the top surface and is parallel with the top surface.
1/4" (0.250") radius on the upper corners and on the front and back corners.
The cross drilling for the barrel nuts needs to be a size that makes the OD of the
barrel nuts a light press or heavy push fit in the fin head material.
No, the top of the Deep Tuttle drawing drawing suggests 0.724"/18.3896 mm from the front junction of the front taper and the top.... then 4.135"/105.029 mm between the hole centerlines.......0.491/12.4714 from the rear taper junction with the top to the center of the rear hole.
Spacing is the same as the std. Tuttle box (actually just extended up 18mm).
Centerline of the front barrel nut cross axis is 0.472/12.0 mm down from the top and the clearance drilling for the fin screws is 1.260/32 mm deep.
As far as where the hole in your fin box is, vs where Larry Tuttle meant for them to be
in the Tuttle fin head that's something you may need to alter.
I've used a rat tail (round) file to slot many boards to get the angle down to the barrel nuts right. Just use a large dia. fender washer with a good large dia. rubber washer under to seal the slot.
Several boards have had the fin screws coming out of the deck at pretty crazy angles.
Good engineering practice would have the fin screw holes counterbored concentric and
perpendicular to the clearance hole down to barrel nuts.
Hope this helps,

28th August 2010, 04:32 AM
Hi Roger,

do you also know what the dimensions of the fin box should be?

Especially the width of the box (dimension around 15.816.0 mm), should how much wider than the fin head?

28th August 2010, 10:15 AM
Hi Cholo,
The fin head dimension (from the original Larry Tuttle (Water Rat) drawing is 0.620" (+0.000 -0.004)
so the tolerance range is 0.6160"-0.6200" which according to my inch/metric conversion program
give the metric dimensions as 15.646mm - 15.748 mm.
So if the fin head width is 15.748 mm max and it is supposed to be an nice snug "push fit" I would guess
that the fin box width would ideally be about 15.75 mm.
Hope this helps,

28th August 2010, 11:49 PM
Hi Roger,

thanks for the fast answer, but I think now I am more confused.
the fin head width is 0.6160"-0.6200", or 0.620" -0.624" like you wrote above in Feb. 2009?

From what you say it seems that the fin head was defined in detail by Latty in a mechanical drawing, but he didn't make the equivalent drawing for the fin box (board side)?
What's most important is the connection, the detailed fin head drawing is not so useful...


29th August 2010, 12:14 AM
Larry, of course, not "Latty", too much hurry...

What I wanted to say: "the detailed fin head drawing is not so useful", without the detailed drawing of the slot on the board (fin box).

29th August 2010, 08:17 AM
Hi Cholo,
My mistake in the previous post. I got the tolerance backwards.
The Larry Tuttle drawing gives the fin head "thickness" (the dimension that fits in the slot and need to be parallel and close tolerance on both the fin and the fin slot in the boards is:
0.620" -0.000 +0.004, so what I suggested in Feb. 2009 is correct.
Max fin head dimension is 0.624" (15.8496 mm) and the min. fin head thickness is 0.620" (15.748 mm)
There fore the slot in the board should be 5/8" (0.625") (15.875 mm) if you allow 0.0010" clearance to get the fin down into the slot.
So, based on the Larry Tuttle drawing, the size (width) of the fin slot would be 15.875mm or 0.6250" minimum.
Sorry for the error.... my laptop battery was dying and I got in a hurry.
Hope this helps,

29th August 2010, 05:35 PM
Hi Roger,

so, roughly summarizing:

fin head width (mm) = 15.80 +/- 0.05

fin slot width (mm) = 15.875 -0.000 / + ?

The problem is that all Deboichet Custom (I have 2008 SL4's made by UFO) have fin head width of 16.05 / 16.10.
Old Starboard tuttle boxes were much wider than that and I even used mylar spacers up to 3x 0.3mm (!) in order to have good fit. That was also happening for other board brands. Now I have changed for a new isonic and the deb's simply do not enter the fin slot, which is around 15.8 mm.

My big question mark is whether to work the fins or the board.
Considering that I'll keep the fins for many years and will buy more deb's soon, and that I'll change the board every one or two years, I would prefer to enlarge the board fin slots to 16.15 mm.

But, if fin slots (Starboard and others) from now on will always be 15.8/15.9 mm wide (as Tuttle drawing), maybe I should consider to work all my fins, once for good? (with no possibility of return...)

What is your suggestion?


29th August 2010, 08:31 PM
Hi Cholo,
The obvious answer (to me anyway) would be to open up the fin box on your iSonic, and continue to use your fins that fit all your other boards.
I just received a 2010 iSonic 121 WC and I noticed immediately that the fin box is not the std. Cobra box
we have seen for the last 10 years.
Obviously they have redone the interior mold for the fin boxes on the new iSonics, and my guess would be that they spec'd. the original Larry Tuttle design dimensions.
So, we may see better (closer to Larry's original desin tolerances) quality control on all Starboard fin boxes, but then again maybe only on the "hand crafted" high end, very expensive iSonics.
Enlarging the interior of a fin box, already installed in a board, is a lengthy hand work process unless you have a fairly large milling machine and some very special very long end mills and a way to swivel the
cutter to the front and rear taper angles.
So, working the fin heads down seems the logical way to fix this issue.
Maybe a better way to go would be to make up side shims for your other boards, and then epoxy the
shims into the fin boxes to decrease the interior width.
This is something you could do in a pretty straight forward manner, without any large precision tools required.
You could cut off the head on a broken fin, and carefully tap a couple of holes and grind/file/sand it to the correct width/length/depth, and use it as a "master" to "cast" the shims into the fin boxes on your other boards, then work down all your fin heads to this spec. The tapped holes could be used to "pull" the master plug out of the fin box after the epoxy slurry you use to hold the shims in place has cured.
Hope this helps,

30th August 2010, 12:19 AM
Hi Roger

actually I made a mistake in the slot width measurement of the isonic (I removed the caliper from the slot before reading, therefore I got smaller values!), the right value is more around 16.0/16.05 mm.
Anyway, I can only measure the beginning of the slot, the feeling is that deeper in the slot the thickness is getting smaller.

So I take even more happier your suggestion of leaving the fins as they are and work just a little bit, with sanding paper, the board slot.

By the way, what is the slot width you measure on the 2010 isonic 121 WC?


30th August 2010, 09:41 AM
Hi Cholo,
I'll have to get some precision tools and measure the new iSonic 121 fin slot.
I can use an adjustable parallel to measure at least half way down in the box.
I'll try to do that in the next few days and let you know what I find.
I would make it a priority, but Hurricane Earl is bearing down on my "hideaway" in Cape
Hatteras, so that gets my main focus until Hurricane Earl gets past the Outer Banks of
North Carolina.
As far as "sanding" your fin box, I think you will be at it a very long time.
Perhaps get a file and be able to remove more material, and right where you need to remove it.
Another option would be one of the tiny wheel air driven belt sanders and make some sort of guide
so you simply widen the slot, not put tapers in it and goof it up.
Hope this helps,