Hello,

my fanatic gecko 133L fin "wobbles" in its seat despite I tight the screw a lot. I can notice some movement.
I knwow this should not happen, but which are the real effect?

Pleople that tried my board said "it is very stiff in water,difficult to start planing,". The gecko should be a super easy to plane board, do you think the wobbly fin is the reason?

Thanks

Regardless, I would fix the wobble. Is it a fin box defect ?. If it's not, then loose fin is easy to fix with some electrical tape. You will then be able to test if it's the cause of the fault.

It will cause spin out big time depending on how loose it is.

The plastic from a ice cream container is what i use if the gap is big.

If the gap is small the outside cardboard from a notepad works well.

If the gap is really small a bit of paper works well.

Put it down the side of the fin so cut pieces a bit shorter than the fin box size.

Put enough tape around the base or cut a shim out of a sheet of plastic.

Thanks mates, and by the way do you think this would be the reason of the "difficult to get planing" despite the board nature? Like a stiff board in water?
I cannot test it soon to verify, unfortunately

You really can't overcome even slight wobble from a fin at any kind of high performance level. It will probably affect early planing and will ultimately just break the box.

The first thing to eliminate is the possibility of a cracked box. That's unlikely but it's really bad if it happens. Inspect the box for cracks with a bright flashlight. Try other powerbox fins (I assume it's a powerbox) in that box and see if they're loose too.

Next, you may be using too long a fin screw, so that it's bottoming out in the fin's housing before the fin is fully secured in the box. If the fin without a screw goes in solid but wobbles when you tighten it, then that's likely the issue. Use a shorter screw or more washers between screw and the little indentation on top of the board.

If the fit is only slightly loose then using automotive spray paint is a good way to build up the surfaces gradually, a layer at a time. It's pretty durable and won't leave residue the way tape would. There's product called "sandable primer" which is ideal for this.

Awalkspoiled's suggestions are all great.

If it is neither a broken box nor a screw that's too long, and you choose to use tape to eliminated the wobble, I'd use clear packing tape. You may need more layers than with electrical tape, but it's less likely to scrunch up or leave sticky residue.

lucab, to clarify: When you say fin wobbles, is it when you wobble the fin with your hand ?. Or is fin wobbling (oscillating) when you are planing ?

boardsurfr: I have never noticed residue with electrical tape (a slight discolourisation on the base ?). Maybe its the stuff I'm using and I've had pot luck ?. I like this electrical tape because it squeezes in place and locks the fin into the box. It can also remove it when putting fin in a different board with a different toleranced fin box (and either more tape, or no tape as required). But, I'll keep your tip in mind next time.

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jn1 said..
boardsurfr: I have never noticed residue with electrical tape (a slight discolourisation on the base ?). Maybe its the stuff I'm using and I've had pot luck ?. I like this electrical tape because it squeezes in place and locks the fin into the box. It can also remove it when putting fin in a different board with a different toleranced fin box (and either more tape, or no tape as required). But, I'll keep your tip in mind next time.

It's quite possible that you are buying different tape in Oz than the stuff I buy in the US. I use electrical tape for the mast, and it sometimes leaves a bit of residue. Does not matter much on the mast since I'll put new tape on next time I use it, but could possibly be an issue in fin boxes. Temperatures also seem to affect electrical tape more than packing tape. On the colder days (~ 10 C), the electrical I use can get quite stiff, and sometimes does not stick well to the mast. But electrical tape will require fewer layers, and can be easier to put on and take off, so if you're using the same fin in different size boxes, it could have a clear advantage.

Yes the gecko is a great board. Depends on how severe the wobble is. Does the board feel light? If so, report back once the wobble is fixed.

It may certainly play a role with planing as it's the side load from the fin which provides lift and speed!

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jn1 said..
lucab, to clarify: When you say fin wobbles, is it when you wobble the fin with your hand ?. Or is fin wobbling (oscillating) when you are planing ?

boardsurfr: I have never noticed residue with electrical tape (a slight discolourisation on the base ?). Maybe its the stuff I'm using and I've had pot luck ?. I like this electrical tape because it squeezes in place and locks the fin into the box. It can also remove it when putting fin in a different board with a different toleranced fin box (and either more tape, or no tape as required). But, I'll keep your tip in mind next time.

Hello, it is moving in the slot parallel to board rail direction looking at the board from the tail move side to side. It is few mm travel but it is noticeable

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Manuel7 said..
Yes the gecko is a great board. Depends on how severe the wobble is. Does the board feel light? If so, report back once the wobble is fixed.

It may certainly play a role with planing as it's the side load from the fin which provides lift and speed!

My fear is that the wobbling translates in continuos change of the planing trim, resulting in hard to plane or entering and exiting from the planing continuously

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lucab said..

Manuel7 said..
Yes the gecko is a great board. Depends on how severe the wobble is. Does the board feel light? If so, report back once the wobble is fixed.

It may certainly play a role with planing as it's the side load from the fin which provides lift and speed!

My fear is that the wobbling translates in continuos change of the planing trim, resulting in hard to plane or entering and exiting from the planing continuously

There could be lots of things contributing to a board sticking to the water.
- the wobbly fin
- size of fin
- mast base position
- boom height
- type and size of sail
- trim of sail
- position of footstraps

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John340 said..

lucab said..

Manuel7 said..
Yes the gecko is a great board. Depends on how severe the wobble is. Does the board feel light? If so, report back once the wobble is fixed.

It may certainly play a role with planing as it's the side load from the fin which provides lift and speed!

My fear is that the wobbling translates in continuos change of the planing trim, resulting in hard to plane or entering and exiting from the planing continuously

There could be lots of things contributing to a board sticking to the water.
- the wobbly fin
- size of fin
- mast base position
- boom height
- type and size of sail
- trim of sail
- position of footstraps

Water in board due to a cracked fin box .

Time for pics

If it is moving a few mm in the box its extreme....

Or do you mean at tip of fin?

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Mark _australia said..
Time for pics

If it is moving a few mm in the box its extreme....

Or do you mean at tip of fin?

At tip of fin, of course

Make sure screw is not too long. Could be you are bottoming out .and not fully tightening the fin in the box. Something to check.

The Gecko boards should have a powerbox for the fin?
This box is conical in all aspects and fin should not be able to wobble at all.
So either the screw is bottoming out or the top of the fin-head is reaching the top of the box (which it shouldn't do).

I'm now thinking screw also.......
Easy way to check the screw too, Lucab

Wash the bolt hole in the fin well, scrape it out with a stick or wire etc, sand in the bottom could be enough to cause the bottoming issue.

Now force the fin into the box hard. Turn the board over but don't have it resting on the fin (or it will just move on you)

Drop the screw lightly into the hole so its sitting on the barrel nut. Not sitting on the the fin base, it needs to sit on the brass nut in the fin.
The screw washer should now only be sitting about 6-8mm above its seated position. ie: how high it is sitting now is how far it will go into the fin when you screw it in.

If the screw is too long, or even if it is correct but the yellow rubber washer is missing that can easily be enough for it to bottom out in the fin before its pulled the fin into the box.

I sometime count the turns until bottoming out with the fin out of the box, then count when it's in. If they are close the the same you need a shorter screw.

Screws that are too long are a big problem, unless you check the fin for looseness there's no way of knowing if it's in properly. A screw the right length with damaged/ dirty threads is worse. You know it's the right length, so don't bother checking when it goes tight. Nowadays, I hold the fin, so I can feel it being pulled into the box, and watch the washer squashing out.

On all my fins I drill a 5 mm hole about 5 mm deeper than the nut . Then tap the hole . That way I can use a slightly longer screw that goes all the way through the nut . All my fins are powerbox and only have one nut so I want it as solid as I can get .
In case anyone wants to know , on fin bolts , one turn of the screwdriver is 1 mm in bolt length . It's a way of calculating how far your threading into the nut . Minus the lead in chamfer which would be about 2 mm.
Thats enough from me .

If its finbox fit I've used shims cut from monofilm ( old dead sails) before or the old coke/beer can which is .1mm thickness aluminium to fill the gap and stop powerbox fins from going too far in the box and with tuttle to take up the play between different fitting/sizing finboxes
Also as above drill the scew holes 5mm or so deeper into the fin to accomidate a longer screw from bottoming out .A 5mm drill bit is fine for M6 thread or 1/4" (rare now) threads ., tapping it deeper is best after this but if its only g10/glass/carbon the screw can form its own thread just dont force it all the way in at first and screw it in and out a few times until it goes all the way in .

And then I'll add - Lucab you need to do all this and be 100% sure.

Then - if its still loose after the bolt is NOT too long and then if still loose you made shims and THEN if still loose we may have a cracked box which is serious.

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Mark _australia said..
I'm now thinking screw also.......
Easy way to check the screw too, Lucab

Wash the bolt hole in the fin well, scrape it out with a stick or wire etc, sand in the bottom could be enough to cause the bottoming issue.

Now force the fin into the box hard. Turn the board over but don't have it resting on the fin (or it will just move on you)

Drop the screw lightly into the hole so its sitting on the barrel nut. Not sitting on the the fin base, it needs to sit on the brass nut in the fin.
The screw washer should now only be sitting about 6-8mm above its seated position. ie: how high it is sitting now is how far it will go into the fin when you screw it in.

If the screw is too long, or even if it is correct but the yellow rubber washer is missing that can easily be enough for it to bottom out in the fin before its pulled the fin into the box.

Thanks Mark, I have changed the bolt to a 5 mm shorter and the issue seems very contained now.

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Imax1 said..
On all my fins I drill a 5 mm hole about 5 mm deeper than the nut . Then tap the hole . That way I can use a slightly longer screw that goes all the way through the nut . All my fins are powerbox and only have one nut so I want it as solid as I can get .
In case anyone wants to know , on fin bolts , one turn of the screwdriver is 1 mm in bolt length . It's a way of calculating how far your threading into the nut . Minus the lead in chamfer which would be about 2 mm.
Thats enough from me .

This is a very good hit!

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ggf said..
If its finbox fit I've used shims cut from monofilm ( old dead sails) before or the old coke/beer can which is .1mm thickness aluminium to fill the gap and stop powerbox fins from going too far in the box and with tuttle to take up the play between different fitting/sizing finboxes
Also as above drill the scew holes 5mm or so deeper into the fin to accomidate a longer screw from bottoming out .A 5mm drill bit is fine for M6 thread or 1/4" (rare now) threads ., tapping it deeper is best after this but if its only g10/glass/carbon the screw can form its own thread just dont force it all the way in at first and screw it in and out a few times until it goes all the way in .

Today I will test this, definitively it is not only a matter of screw but the slot box is slightly larger than it should be

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Mark _australia said..
And then I'll add - Lucab you need to do all this and be 100% sure.

Then - if its still loose after the bolt is NOT too long and then if still loose you made shims and THEN if still loose we may have a cracked box which is serious.

Hi Mark, I would exclude the cracked box. Changing the bolt improved a lot, with few "old sail shims" I am sure I will fix it

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Imax1 said..
On all my fins I drill a 5 mm hole about 5 mm deeper than the nut . Then tap the hole . That way I can use a slightly longer screw that goes all the way through the nut . All my fins are powerbox and only have one nut so I want it as solid as I can get .
In case anyone wants to know , on fin bolts , one turn of the screwdriver is 1 mm in bolt length . It's a way of calculating how far your threading into the nut . Minus the lead in chamfer which would be about 2 mm.
Thats enough from me .

Why not drill a bigger hole then you wouldn't have to tap it
youve been lucky if the threads you've put in the fin line up with those in the bolt
But more important why do you only have one nut!

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Ben1973 said..

Imax1 said..
On all my fins I drill a 5 mm hole about 5 mm deeper than the nut . Then tap the hole . That way I can use a slightly longer screw that goes all the way through the nut . All my fins are powerbox and only have one nut so I want it as solid as I can get .
In case anyone wants to know , on fin bolts , one turn of the screwdriver is 1 mm in bolt length . It's a way of calculating how far your threading into the nut . Minus the lead in chamfer which would be about 2 mm.
Thats enough from me .

Why not drill a bigger hole then you wouldn't have to tap it
youve been lucky if the threads you've put in the fin line up with those in the bolt
But more important why do you only have one nut!

You leave the nut in while doing this , then the thread lines up and you don't have to knock the nut out . If I was replacing the nut i would drill a 6.5 mm hole .

Select to expand quote

Imax1 said..

Ben1973 said..

Imax1 said..
On all my fins I drill a 5 mm hole about 5 mm deeper than the nut . Then tap the hole . That way I can use a slightly longer screw that goes all the way through the nut . All my fins are powerbox and only have one nut so I want it as solid as I can get .
In case anyone wants to know , on fin bolts , one turn of the screwdriver is 1 mm in bolt length . It's a way of calculating how far your threading into the nut . Minus the lead in chamfer which would be about 2 mm.
Thats enough from me .

Why not drill a bigger hole then you wouldn't have to tap it
youve been lucky if the threads you've put in the fin line up with those in the bolt
But more important why do you only have one nut!

You leave the nut in while doing this , then the thread lines up and you don't have to knock the nut out . If I was replacing the nut i would drill a 6.5 mm hole .

That works, I read as you only had one nut and were using the same one in all your fins.