Why would a fin crack at ferrule ?

That's normally caused by hitting some thing. I do see slight damage at the tip. Tip going backwards, causes front of base to move down, If it's only resin in the box holding the barrel nut, that will give way. My solution there, is sticking it back together with 5 min epoxy. Then grinding hollows on both sides of the join and repair with layers of fibreglass. The worst part is sanding it back to fit the box

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Imax1 said..
Would it be wrong to say because it's a Select fin ? I'm surprised it didn't clean rip itself out of its head.

Not wrong at all, unfortunately.

Have you checked screw length, too long they will push on the top of head with nothing pushing back. Alternatively instead of widening the holes in your board, you should have made sure the nuts where free to move. Wd40 helps. That way the screw may have cleared the composite section instead of making a groove where the thread is, or maybe it would made it worse...

With the fin out of the box, count the turns until it bottoms out. The when it's in the box make sure you are not using more turns.

Dissenting opinion-

The barrel nuts may have been rotated. Would explain both situations, just as much as the finbox holes in wrong place would be an explanation (and I find the latter far less likely as they're all the same in a moulded product made in the thousands.... unlike a fin where the nuts can rotate)

I'd check a few other fins and I would almost bet the hole filing was not needed.

The head on many fins is moulded on, so the screw hitting the moulded-on part will make it crack off, just like that. That is the screw not being straight due to the barrel nut being rotated, and it pushed on the moulded crap part thats not as strong as G10

ANY new fin, screw long bolts in and rotate the nut to perpendicular before (careful) trial fitting. (Easier than the screwdriver slot in the barrel nut)

Forget how many turns of engagement, measure depth with a kebab stick or similar from the board bearing surface to bottom of fin hole, figure out how far the hole goes past the barrel nut and cut bolts to that length minus say 3-5mm - accounting for the rubber washer thickness of course.

I have fins with so much use its crazy, and no corrosion has expanded them and screwed up the fin head. When you look at BOTH issues it wasn't corrosion, it was a wrong angle on the screw.

I do things a bit different. Any fin I use I knock out the nut and drill the screw hole 7.5mm , at least 5mm deeper than the nut. That way I can use a bolt all the way through the nut with space to spare. It kinda matters to me because I'm a one nut powerbox guy. That's a 12mm nut not the 9mm. Ps, I've never ripped a nut out. And I have tried. I use 55cm pointers .
On another point , is Tuttle better than Powerbox ?

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Imax1 said..
I do things a bit different. Any fin I use I knock out the nut and drill the screw hole 7.5mm , at least 5mm deeper than the nut. That way I can use a bolt all the way through the nut with space to spare. It kinda matters to me because I'm a one nut powerbox guy. That's a 12mm nut not the 9mm. Ps, I've never ripped a nut out. And I have tried. I use 55cm pointers .
On another point , is Tuttle better than Powerbox ?

The hole on most fins goes 5mm past the barrel nut. Cut the bolt to only go to bottom of barrel nut and it is like 8mm thread engagement, more than any normal nut.

Sik.

I hand fit bolts for all custom boards all the time.... and/or do the depth so the new board matches their old boards with no special screws, cos I'm a good bloke.


Tuttle is better

Unless i've gotten so good at hitting the bottom that i don't even notice it anymore, i'm pretty sure this one didn't hit the bottom.

The marks on the tip are from resting in wet sand on beach and the sail moving it around i think.

The ferrule has some thin green / corrosion layer on it but it fits well, was not stuck in there and could rotate.

Screw length is good.

The fin came with used board.

The holes were definitely on an angle before. Top of screw pointing backward. The filing job was done before going out with this fin and returning with the damage.

I re-enacted the fin extraction process, and i feel i may have ID'd an operator fubar.
You see, we got 10 amazing early season sessions.
After that I felt like i'd aged 20 years and could hardly stand up on the beach while attempting to tap / wiggle the very tight fitting tuttle out of the deep tuttle box.
A kind of fight or flight type system kicks in in me, and it's gear or me, my back.
I gave up wiggling, tapping, pulling and discovered a pleasant cantilever action by thudding the tip of the fin, on the trailing edge, toward the nose of the board, a nice push at the end and out she swivelled.
Home for apre sailing by the fire, yeeha!

Examination of my process shows that the top edge of the fin, would have been getting bashed out on the top of the box.

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Imax1 said..
I do things a bit different. Any fin I use I knock out the nut and drill the screw hole 7.5mm , at least 5mm deeper than the nut. That way I can use a bolt all the way through the nut with space to spare. It kinda matters to me because I'm a one nut powerbox guy. That's a 12mm nut not the 9mm. Ps, I've never ripped a nut out. And I have tried. I use 55cm pointers .
On another point , is Tuttle better than Powerbox ?

I can relate to that. I have found a big variation between fins as to how far in the hole has been drilled. And then there is the variation between boards. So many of my fins have specific screws sitting in them, and one board has even more specific screws sitting under the footstrap velcro. When the fin is a little loose and tightening the screw is not helping... disaster can ensue. If I'm unsure I count the turns (actually half turns, ie wrist movements).

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remery said..

Imax1 said..
I do things a bit different. Any fin I use I knock out the nut and drill the screw hole 7.5mm , at least 5mm deeper than the nut. That way I can use a bolt all the way through the nut with space to spare. It kinda matters to me because I'm a one nut powerbox guy. That's a 12mm nut not the 9mm. Ps, I've never ripped a nut out. And I have tried. I use 55cm pointers .
On another point , is Tuttle better than Powerbox ?

I can relate to that. I have found a big variation between fins as to how far in the hole has been drilled. And then there is the variation between boards. So many of my fins have specific screws sitting in them, and one board has even more specific screws sitting under the footstrap velcro. When the fin is a little loose and tightening the screw is not helping... disaster can ensue. If I'm unsure I count the turns (actually half turns, ie wrist movements).

The 6 mm screws we use make it easy for us. One turn is exactly 1 mm depth into the nut. You definitely want to go all the way through the nut . Especially the smaller 9 mm nuts . Take away the chamfer both sides and your lucky to have 5 mm of solid thread. Flog it out with sand and the fact that brass is bad for thread strength , it is important to have healthy nuts , especially with a one nut powerbox . Why don't they always use the stronger 12 mm nuts ? It's no heavier or expensive. Saying all that , I slightly oversize my tapping hole on my nuts. It's still better to partially strip a nut than break a finbox. I have never lost a fin due to nut failure. And I've tried . If your screw is 5 mm longer past the nut there is a good chance that the fin will kick back , strip the nut , and the fin still hangs on. If you only do 5 turns into the nut you have no chance. I have replaced many bent screws and stripped nuts after crash testing. Cheaper than loosing a fin. And you can still get home.

Nice to make boards so theyre all the same screw length too

The OP's crack could be the result of what structural engineers call insufficient edge margin.

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Imax1 said...... it is important to have healthy nuts...

Absolutely agree! Wait, what was the topic again?

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Shifu said..

Imax1 said..
Would it be wrong to say because it's a Select fin ? I'm surprised it didn't clean rip itself out of its head.

Not wrong at all, unfortunately.

And i can second that experience ,Twice.
2 swims bcoz of this. Exactly.