Author Topic: Fin Box repair  (Read 10345 times)

scottg

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Fin Box repair
« on: June 29, 2014, 03:13:50 PM »
I am looking for a different take on a recent post about the damage I have to my fin box.  I have followed the recent post here:

http://www.standupzone.com/forum/index.php/topic,23360.0.html

But I did not think my questions would pertain, or be discussed if I added them to that post.  If my questions are redundant, I apologize. 

I have similar damage to my board.  I know I should replace the entire fin box, but I had an idea.  My fin box is still more or less in place.  It is slightly bent to one side, and I plan on bracing it up before the first repair, but it is not damaged in a way that will affect the track of the board.  I bought the board used and it has already been repaired once.  I am in Georgia and the mountain rivers are not kind to glass boards.  That is another reason I am hesitant to do a really nice repair.  I know this is not the last time this is going to happen.  My idea was to cut out one "corner" area at a time (corner being the outer corner of the fin box) as much as necessary (in this case about 1-2 inches out from the corner of the fin box), and just simply fill it with q-cell, and glass over it.  Then do the other corners, probably after the first corner has set and the fin box will not move.  This would keep me from removing the box all together, replacing the foam, re-routing, and installing a new box, and hoping that I get the thing straight.  I would like someone to tell me why this is a bad idea.  And keep in mind.  I expect this to happen again.  And this will be my first time repairing a board like this.  BTW, It is a 12' YOLO foam core fiberglass touring board.

Dwight (DW)

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Re: Fin Box repair
« Reply #1 on: June 29, 2014, 05:59:11 PM »
1st thing you should consider, is the disaster of allowing your board to gain more water weight with a half baked repair that will fail again, and again.

In that other thread, do what Bajasurf said and never worry again about failure.

scottg

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Re: Fin Box repair
« Reply #2 on: June 30, 2014, 07:09:50 AM »
OK, OK.  I give.  It might even be easier.  I am getting the foam today. 

scottg

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Re: Fin Box repair
« Reply #3 on: June 30, 2014, 05:02:41 PM »
Alright.  I have bitten the bullet and cut out the box as shown in the photos.  The previous repair was done so badly, I had to cut out a huge piece of the tail.  (looks like the person used fiberglass resin and burned a lot of foam)  So it leads to a new question: My hole is 4"deep, by 6x17 inches.  My research today (based a lot on boardlady.com) would say that a great product to fill the hole would be Divinycell.  I agree, but the stuff costs a fortune.  Would anyone suggest filling the hole with EPS, then routing a new hole for the fin box that is surrounded by 3/8 Divinycell?  Also, my router would not go deep enough to make the whole cut so I had to use a crude saw to get the rest out.  Will I be able to fill the gaps by inserting the foam block in the cut out hole with Q-cell and West System 5:1 or would there be a better way to insert the EPS?

juandoe

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Re: Fin Box repair
« Reply #4 on: June 30, 2014, 05:36:56 PM »
I would fill it with polyurethane foam and proceed per Boardlady.  In fact, that's what I did but my hole wasn't quite as large.  I reinforced a Chinook box with Divinycel and glassed the whole thing in.  If you use the Chinook box, cut off 1/8 inch or it will be a little deep.  Unfortunately, I read DW's recommendation a little late.   The other trick I picked up here was to stuff the box with playdoh before glassing it in. Kept resin out and was easy to clean out.  I have now done a grand total of 1 fin box so I am no expert. 
« Last Edit: June 30, 2014, 05:46:09 PM by juandoe »

scottg

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Re: Fin Box repair
« Reply #5 on: June 30, 2014, 06:25:13 PM »
I have seen a few threads on PU foam and I cannot get a good +/- on the stuff.  Sounds good and easy.  I have used the stuff enough on my house projects and I cannot imagine that it could be less structural than EPS.  I will look into it.  Right now I know nothing about it when it comes to this technique.  I assume it will not heat up the EPS in the board?  I have also had experience where it can stay in a liquid form if sprayed on too thick.  But in the case of home repair, I have never tried layering it to make sure it cures.  I would need someone to comment on whether or not there could be an adhesion problem with multiple layers, and any more feedback on PU foam would be appreciated.  I would love to be able to go to Home Depot and fill my hole for 5 bucks in ten minutes!  Something makes me think it is too good to be true.

Dwight (DW)

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Re: Fin Box repair
« Reply #6 on: June 30, 2014, 06:58:09 PM »
I'd fill the hole with EPS, then add core-cell for setting the finbox. Core-cell is better than Divinycell. Watch this video   its a chinook box install

Some guys cut corners and use Last-A-Foam and some even use plywood to shore up finbox installs.

I'm no expert on the spray foams. Never had much luck with them.
« Last Edit: June 30, 2014, 07:02:40 PM by DW »

scottg

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Re: Fin Box repair
« Reply #7 on: June 30, 2014, 07:54:29 PM »
I have not seen good reviews on the Last A Foam.  I agree.  Core cell is a new one.  I hope it costs less!  At any rate, I think the EPS route might be the way to go, but I still want to find out if the pu foam might work.  It is appealing enough to see if any other people have experience with it.

juandoe

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Re: Fin Box repair
« Reply #8 on: June 30, 2014, 08:39:56 PM »
The polyurethane foam I used was not the hardware stuff but the two part marine foam similar to this
http://boardlady.com/materials.htm

Another option would be to glue in a chunk of EPS with the PU foam.  At least you could avoid voids.  My repair is in a 1 lb EPS Infinity raceboard.  It is clearly stronger than the original.  My finbox was simply epoxied into foam with a layer of carbon over the top.  I hit a tree limb on flat water and crunched it into the foam. 

TallDude

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Re: Fin Box repair
« Reply #9 on: June 30, 2014, 09:05:25 PM »
I think the Gorilla Glue works fine. It sands fine too. It has a foaming property as it cures, so it will fill even 1/4" voids. It's not clear. It has a little yellow color to it, so you would see it on a clear glass job. Like DW said, glue or epoxy a block of 1.5 or 2# EPS in there. Then use some stronger foam as a cassette at the fin box. I was taught to leave a little bevel groove in the foam around the edge of the fin box. Gives the resin a little key to strengthen the glass lap on the box.   
« Last Edit: June 30, 2014, 09:07:00 PM by TallDude »
It's not overhead to me!
8'8" L-41 ST and a whole pile of boards I rarely use.

peterwSUPr

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Re: Fin Box repair
« Reply #10 on: July 01, 2014, 04:25:37 AM »
I would glue in a chunk of EPS to get it back to being a foam blank, and start the finbox install from there.  Here are a few thoughts on your install.  (BTW, I've built probably 20-25 windsurfers and have not had failures without massive impacts where the box breaks too).  Only one SUP so far though.

Make sure your fit is good with the EPS block, and fill any gaps with thin slivers of foam,  An airgap here or there will not kill you on such a large fix, but meltdown will.  As I mentioned on another thread if any part of your board starts to feel warm due to resin exotherm, have a bag of ice ready to put on it, it will cool things and help prevent problems, but if the bottom of your hole is in a thick area and well insulated from the surface, it may still not be enough if your resin kicks fast, so don't flood huge areas.

I have a deep router bit that I modified from a long one used for cutting edges.  We cut some crude slots into the non-cutting tip and it works great for routing into soft foam.   A drill bit might be sufficient, and would be longer than a typical router bit (for foam use only!)

You don't need to fully wrap a Chinook box in high density foam.  The box itself is strong, but your EPS is not.  You want to extend the area where the forces are applied.  The only reason to wrap a box would be to extend the depth deeper.  On the race board I just made I was not too worried about lateral loading, but I did drop in some 1/4" carbon wrapped corecell laterally, across the front and back area of the box, deeper than the box and maybe 4 or 5 inches wide.  Then I routed the hole for my finbox through those.  An impact pushing the tip of the fin back will try to push the finbox down at the back, but there is now a "U" shaped thing helping to support the back of the box and distributing the load.  It also helps with lateral loading.  Try light poplar plywood if HD foam is not accessible.  If the board is thin at the tail, if any part of your repair can bond to the glass on the deck of the board, that will add a lot of strength.

Hope that helps,
Peter

Dwight (DW)

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Re: Fin Box repair
« Reply #11 on: July 01, 2014, 04:50:28 AM »
Here is an image that shows the simple way I do it.

http://instagram.com/p/ikAzzLRUoJ/?modal=true

You're looking at a block of Divinycell 1.5" deep x 3" wide x 12.5" long for a 10.5" long Chinook box. I've since switched to Core-cell.

The finbox hole is routed after hot coat. The box is wrapped in one layer of carbon, then stuffed in hole. Ground flush after it hardens. Some guys top cap the box, some don't. I think top capping it is almost worthless. Top capping is only important for half-assed finbox installs set directly in EPS.


scottg

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Re: Fin Box repair
« Reply #12 on: July 01, 2014, 05:25:07 AM »
Excellent info.  I appreciate all the help.  My biggest fear is going to be the gaps.  I think I am going to drop a block of EPS in the hole and fill the gaps as much as possible with more EPS as suggested by peterwSUPr.  I would love to use the Gorilla Glue if that would really work, but I was planning on using West System 105/205 and some Q-cell to make a putty.  I am worried that it will heat up, but I might have no choice.  I am going to try and get a better hole this afternoon, but I am scared that I will just keep making the hole bigger and bigger.  I am working in a 60 degree, dry environment.  I guess I could throw a bag of ice under the board, and then on top of the work piece after I finish if that seems to work.  I would worry about condensation though even if there is a plastic barrier.  Boardlady stresses a dry environment. 

Dwight (DW)

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Re: Fin Box repair
« Reply #13 on: July 01, 2014, 07:35:38 AM »
I would love to use the Gorilla Glue if that would really work,

Gorilla Glue works great and is used by lots of shapers on EPS blanks.

Make sure you buy slow kick epoxy. Then no worries.

I've used EPS beads as filler. Crumble some foam. Fills big voids easier than Q cell.

Just stick to slow kick epoxy and be stress free.


scottg

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Re: Fin Box repair
« Reply #14 on: July 01, 2014, 08:29:19 AM »
Sounds good.  I hope to get the EPS in today.  Thanks for all the help.  And I hope to use a little of everyone's suggestions.

 


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