Longboard fin box

[benjl]

Hi guys

I tried to fit my new single fin in to the sup yesterday but found that the back of the fin raises up when I screw down the front. Is this normal?
It's a Naish board so won't have a crappy box with out of spec tolerances.

I'm not used to single fin boxes but just seems that the fin doesn't feel super stiff only being screwed in at the front instead of a futures or typical fcs design that in used to with thrusters.
The fin sits flush in the box until I screw down the front and then the back lifts.

[jaffa1949]

Odd, that.
Most longboard fins for a centre box should have a brass or stainless steel pin that is horizontal at the other end of the fin from the screw. The pin fits into a groove in the box then screwing in the fin shouldn't raise the other end!
The fin shouldn't feel loose as the forces of surfing could move it around in the box .
Some fin boxes have a number of slots where the square wash for the screw goes in they are also where you put the pin into the groove, if the pin is situated in one of those slots then a tightening of the screw would raise the rear of the fin!
Picture of fin please

[Big H]

Loose fins I shim with tape....masking tape if just barely loose, duct tape if more space, one or two layers to get it done. That fin looks like it is a loose fit and the front end is getting pulled down rather than the back sticking up; shim it on the sides and under a bit and you'll get a tight fit and should be level.

This is the idea; I used to use plastic grocery bags but found that tape is easier and 2" wide tape is almost exactly perfect when you lay tape right down the bottom spine then fold around on both sides.

[oldmansurfer]

Here is a youtube that shows and explains how to install a fin

[benjl]

Thanks Jaffa, it's a standard looking longboard fin with the square washer and pin that gets screwed in the front through the washer.
I watched a video on YouTube of how to slot the washer in to the rails in the box and followed that? Here's a pic of the fin, under the plastic piece of packaging it's just a standard looking longboard fin

[oldmansurfer]

It's odd because the pin that holds the back in is right there where it pops up? Maybe there is damage to the track in that area? At any rate I don't think it going to make much difference in performance but if you want it looser then put the fin forward

[benjl]

Do you think perhaps the fin is poorly cast?

[Big H]

It is not that the back is popping up, but the front is being seated too far down because the box is loose; the effect of the front seating too low is that the back end will stick up a bit. Shim and it will be level.

Not all fins are created equal; some fit tighter than others in the same box. Boxes as well; depending on the installation, can be pinched in the middle via a poor installation or sightly wider than other boxes for whatever reason.

[oldmansurfer]

It is not that the back is popping up, but the front is being seated too far down because the box is loose; the effect of the front seating too low is that the back end will stick up a bit. Shim and it will be level.

Not all fins are created equal; some fit tighter than others in the same box. Boxes as well; depending on the installation, can be pinched in the middle via a poor installation or sightly wider than other boxes for whatever reason.

That seems like a lot of play in the area where the pin is. If the front is going to far down then that still shouldn't raise the back where it is pinned into the track. The pin should be the fulcrum of rotation for the fin and since it is in the rear then it shouldn't be moving much unless the pin is way too small and the track is way too big. Perhaps though the entire base of the fin is meant to be sticking out when it looks like it was made to not be sticking out . In other words shimming it will make it stick out evenly and perhaps that is how the fin was meant to be?

[benjl]

It's just that if I don't screw it down then the fin sits flush so it seems as though it should sit flush?

Interesting points though, I might have to take it to a surf shop and see what they think as I don't think I have any shims or washers to try space it out

[Big H]

It's just that if I don't screw it down then the fin sits flush so it seems as though it should sit flush?

Interesting points though, I might have to take it to a surf shop and see what they think as I don't think I have any shims or washers to try space it out

Tape Ben....shim with tape. Or a plastic bag like the video. If one layer of tape or plastic is not enough then go with two, then three. It works.

[Big H]

It is not that the back is popping up, but the front is being seated too far down because the box is loose; the effect of the front seating too low is that the back end will stick up a bit. Shim and it will be level.

Not all fins are created equal; some fit tighter than others in the same box. Boxes as well; depending on the installation, can be pinched in the middle via a poor installation or sightly wider than other boxes for whatever reason.

That seems like a lot of play in the area where the pin is. If the front is going to far down then that still shouldn't raise the back where it is pinned into the track. The pin should be the fulcrum of rotation for the fin and since it is in the rear then it shouldn't be moving much unless the pin is way too small and the track is way too big. Perhaps though the entire base of the fin is meant to be sticking out when it looks like it was made to not be sticking out . In other words shimming it will make it stick out evenly and perhaps that is how the fin was meant to be?

There is a surprising amount of variance in fin boxes and in the fins themselves, esp. when dealing with handmade fins and fins from different manufacturers.

[Big H]

Do you think perhaps the fin is poorly cast?

It looks like a chinese generic to me so yes, probably, but not that it matters much since it's pretty normal even with bigger names. I have shimmed FCS & True Ames fins to get a better fit, as well as a couple of fins that I got from locally manufactured sources. I have had the same fin fit perfectly in one board and be loose in another. It seems like that is just the way of things.

[waikikikichan]

McDonald's straw I've found to work the best. Cut around an 1 1/2" and lay across the fin slot. Then push fin down onto it.
You might want to check the location of the brass pin against other fins. Seems a bit low, which maybe the reason why it needs to rise before contacted the top of the box

[benjl]

Fascinating ideas! I checked it tonight and there is definitely play between the bass but and the tract. Not sure if the brass but is too low / small or the Tract is too large but I can lift the back of the fin up and down about 2nm.

Are you able to draw me a diagram wkk?

[waikikikichan]

Depending on the fin's depth, you might have to cut the straw anywhere from 1 1/2" to 1 3/4", but just so it doesn't poke up out of the box too much.

IMG_0538.JPG (39.07 KiB) Viewed 2754 times

IMG_0539.JPG (63.81 KiB) Viewed 2754 times

IMG_0540.JPG (78.96 KiB) Viewed 2754 times

[jaffa1949]

Just goes to show, if fin boxes and fins were dimensionally consistent we wouldn't have these amazing fixits.
Dead credits cards work too!

[benjl]

Well I took the sup for a spin in the weekend, wkks method definitely secured the fin in the box (now can't get it out) although still had the back of the fin raising up.
I was in a shop before and they gave me these fcs shims? Ever seen these before?

I also found out the hard way that this board was a very optimistic purchase.. Haven't been able to stand for more than 4 seconds yet and neither have any of my mates who also surf. I'm sure I'll get there but the choppy and windy seas haven't helped learning! Need a lake. Decided to also buy an inflatable 10'0 today so that I can cruise around the harbour or go with mates etc.

Also got the knack of doing it in a moonboot! Haha. Surprisingly it feels quite supported and ok, the moonboot is actually quite bouyant even when drenched. I'm supposed to get it taken off on the 28th Dec so should be back to fully surfing in April!

[benjl]

Well I've tried the shims and tried wkk's method but the back end still sticks out about 2.5mm above the box. I've now got
The fin pretty firmly secured in the box but just can't get the back flush.
I was wondering if it's due to some rocker in the back of the board / fin box which would make it slant downwards a few mm's the further back it went on the board?

[waikikikichan]

Stop worrying about it. it's usually one of two things
1) It's just a tall base. Look at the photo of my orange fin,it's shorter from pin to the top. The shims will not help the fin from sticking up.
............ OR.......
2) The thickness of the board way back there is super thin and the box is shaved down as it matches the curvature of the tail. That's why the Futures fins center is 1/2" depth versus the sides at 3/4" depth.
If it doesn't shake or move, then it's fine.