This new carbon fin doesnt go all the way in up front, its fine at the back. Is it just a matter of sanding the top of it bit by bit until it fits ? Normal tuttle fins fit fine, its just this deep one that sticks short. Oddly the front end goes all the way in if pushed in angled forward then comes back out when straightened.
Appreciate any tips.

If it will go all the way in when tilted forward, then it doesn't sound like there is a problem with the depth, but you can easily measure this with a vernier caliper in order to be sure.

The "depth" of the box should never be the limiting factor, instead it is the front and rear face of the fin head that should fit tightly against the box, and these two surfaces should define both the rake and depth position of the fin.

Like SurferKris said, get the steel ruler out and measure the fin head and the front of the tuttle box depth. I have had an older deep tuttle fin that topped out in a newer "deep" tuttle box, with similar results. It would always relocate to the same bit of fin head sticking out past where it should be, even when i tried to start it in on a different angle. If that's what it is, then the solution is to take off some of the fin head with a hacksaw or file. It's the tapers that should carry the load.

if the tuttle box is deeper than the fin head at the front then you have to lightly (and I mean lightly) sand the fin where it gets friction marks from going in the box. When sanding just make the friction mark disappear, no more than that. It might only be a few strokes with the sand paper and it's gone. Then retry fitting it each time. It's very easy to take too much, so if it gets close, but not quite there, then do the bolts up and see if that gets it the rest of the way there. It's far better for it to be a bit tight than for it to be loose.

Dont just force it.... a ruler is your friend

Given it fits flush one way, then the other, but not both at same time it is NOT a depth problem. it is the fin being too long front to back. Like how you can fit a square into a smaller square hole if you put in on the diagonal, this will fit on the diagonal (front or rear properly seated but never both) and that's what it is doing to you.

so u need to sand either the front or rear without changing the angle. Block not hand sanding, so you keep good flats

At some point in the last few years, big slalom boards would no longer take oversized Tuttle fins. They would take a deep tuttle of a certain size, this had something to do with being foil ready, as the top is also used to support the fin/foil, where as before the top never touched.

I have three such deep tuttle fins, I will measure it for you. The guy that's makes fhot, called them foil box ready or something like that. I am pretty sure all new deep tuttle are made to this new spec.

How that helps. If that's the problem then top needs to be trimmed.

I can't see how it is depth if it will set front all the way in then wants to rotate all the way in at back and front pops out. It is deep enough at front and rear (as the front can go all the way in under some situations)

as I said - but have never heard said to me - it's a length issue not how deep you are putting it in.

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Mark _australia said..
Given it fits flush one way, then the other, but not both at same time it is NOT a depth problem. it is the fin being too long front to back. Like how you can fit a square into a smaller square hole if you put in on the diagonal, this will fit on the diagonal (front or rear properly seated but never both) and that's what it is doing to you.

so u need to sand either the front or rear without changing the angle. Block not hand sanding, so you keep good flats

What Mark said. I've had to sand down most of my tuttle fins, whether deep or not. They'd usually do exactly what you describe before sanding. I often also had to sand the sides. Always made me a bit nervous, but never ended up being a problem.

As others have said, its not a depth issue, but probably the fin head is slightly too long for the box.

The worst ever match I've had was an AHD foilboard and AFS foil, same company. I spent about an hour sanding the foil head a bit by bit, you dont want to over do it. I gave up and took it down to the shop I bought it from. The owner got out his Vernier callipers, measured both, the foil head was 1mm to long. Thats a massive amount considering both were from the same factory.

The shop owner said the best swap for a tatty old sail he had was for those Vernier calipers

Because the fin can rock back to front, there could be a hump in the middle of the fin box hole. Get the ruler out and measure front , middle and back of fin and hole. Hate to be sanding the fin when there is a lump of resin in the hole. I'd also check if the bottom of the box is too tight. Could be a drop of resin down there on the side.

If one end or the other goes all the way in, I'd be sanding a little off the length. Maybe measure really accurately and compare to fins that fit. Having said that, the difference is probably so small it won't show up on a ruler.

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Imax1 said..
Because the fin can rock back to front, there could be a hump in the middle of the fin box hole. Get the ruler out and measure front , middle and back of fin and hole. Hate to be sanding the fin when there is a lump of resin in the hole. I'd also check if the bottom of the box is too tight. Could be a drop of resin down there on the side.

Yeah, you could be onto something there, either that or the top of the fin head has an odd shape, like the cut down starboard foils do?


I'm struggling with the idea that the fin head is too long for the box. If that were the case then the fin head would be jutting out along the whole length and parallel to the bottom of the board. The tapers will always meet square with each other. Fixing it would require sanding all of the taper/s back, and keep the angle of the taper correct. As random as some fin manufacturers can be when they box their fins, I've not ever seen a fin where the length of the base was too long, shorter yes, but never too long. nor are the taper angles ever wrong. They seem to get those two measurements right at least.

I've seen length too long a lot. and had to sand to sand the end down.
But it should always sit square, something's not right.

Box and fin should have straight edges, if there are convex curves, the fin can rotate. There should be a solid connection on the top and bottom at both ends, this keeps the fin square in the box.

If anything slightly concave ends are best.

Wrap sand paper around the ends, draw it back and forth to keep the profile the same. Take a tiny bit of each end. I'm sure you will find it goes in a little further.

Wrap sand paper around the ends, draw it back and forth to keep the profile the same. Take a tiny bit of each end. I'm sure you will find it goes in a little further.

Imagine bread being to long for the toaster, you can always get one end or the other in.

^^^ good analogy

I think length but just to be safe take a couple mm off the very top of fin head first. If it still does the same thing, then its length.

Dear all, many thanks, you gave me the confidence to get the sandpaper out once the ruler found the problem. The front end of the fin was 5mm deeper than the front part of the box. Rear end was fine. It was misleading to wonder why the front end would go in alone, it seems the tilted angle of insert for that hid the depth fault. Shaved it off with fine paper and block. 5mm was alot. Well past the carbon cover and into the white core. Fit is now perfect.

note, the problem was the fin, not the box - I checked it out with another deep tuttle (a mates foil) before going to work.
For info : This is a new ready to foil box, the fin is older (but in new condition).

Another happy customer.

Five!!!!!

Can you try another deep Tuttle to see if the issue is the box or the fin? Box may need love rather than fin.
Get some yellow red or pink bright kids chalk and rub it on the fin head and in the box - get a good amount on there, then try to install the fin and wiggle it slightly when its just shy of being seated as far in as you can get it. Pull out the fin and you will see where the fin rubs on the box-or not. The parts rubbing hardest are where you need to relieve with some sanding. Be gentle- go easy, don't use very coarse paper- use a sanding block so it stays flat (or a curved block for inside the leading and trailing edge of the box). Sand a bit try again repeat as necessary. Try not to sand it out of shape so that it has high spots that will rub on the box and wear it thin. Im with Mark most likely the overall length is the culprit, but if there are any bumps voids or fat spots they will show using the chalk trick.