I’m well on my way with board number 3. This time its a 1l’3" semi-tandem for my son and myself. I was wondering how I should install a standard longboard finbox into 1 lb. eps foam. I would think that I would need extra support around the box. The only two ways I could think of were to either “post” the box to the deck by drilling holes that went from the bottom of the fin box to deck and filling them with resin, or to inset a piece of plywood beneath the balsa and route through it when I put in the box. How should it be done?
3 ways I know of are:
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route out an area larger than you fin box and insert higher density foam into that area
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place thin wood strips on each side of of the fin box vertically and longer than the fin box (there are pics of this in the archives)
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same as 1 but insert wood
my understanding is that you are reinforcing against side torque not vertical stress. i.e. reinforce the sides not the top of the box.
#2 wood look something like attachment
Its not the picture I was thinking of but here is a good picture the process. The post also has web site that shows the complete process.
[URL]http://www.swaylocks.com/forum/gforum.cgi?post=206535;search_string=eps%20finbox;#206535[/url]
Since you are using only 1 lb foam you will need to tie into the skins of the board. From my sailboard-building days the strongest method was to build a “cassette” out of the fin box and insert it into a slot that is all the way through the board. Trouble is this method is so strong that if you hit an object hard enough, your box, fin, and tail will break off (all in one piece, at least).
Next method is to tie into just the bottom skin. This can be done using a 1/4" pvc foam sheet inlay where the box will go. We used a router set at the proper depth to get the hole for the sheet. Cut a hole for the fin box as you normally would, seal the inside of the hole with some 5 minute and pot the box.
Lastly, just some heavy glass patches around the fin area will be okay. Figure about 24 ounces total, then pot the box as usual.
HTH,
George
I just route the hole and then drill three holes through to the deck. Tape over the holes when sinking the box and add some glass patches around the fin box area on the bottom. I’ve never had any problem with this method in surfboards. Now sailboards are a whole different story.
GL
What size holes to to put through to the deck?
Hey Waaahoo,
the third 1-1/8 inch diameter holesaw tool for the FCS install makes great holes for that type of method. I’ve done that for quite a few stringerless PU blank/poly resin boards. Never did it on epoxy. That tool is the hole saw with the grit on it. The important thing is that there is no pilot drill. The diameter of the saw is the same at the width of the hole for the box as well which is the lightest/strongest configuration.
HTH,
George
Like George said …
Thanks guys but I don’t know what diameter the third fcs hole saw is. I’m guessing 1/4 inchish?
Half inch d-cell all the way around. I glue together the d-cell ‘box’ first with 5-min epoxy. Then lam in the plastic box with a layer of glass & epoxy. Route out your hole in the EPS at 2" x 11.5" instead of 1" x 10.5"…lam the whole works in with another layer of glass wrapping under the box w/the d-cell.
If you do it ahead of time, and you’re bagging on skins, just make a 12" x 2" piece of d-cell using 5-minute epoxy to glue it all together. Route your EPS & lam in the d-cell plug. Bag on the skin, then route through everything to set your finbox like normal (remember where you put the d-cell!).
Thank you guys for all the help! In the future I could see doing some hybrid solution between 4ests and Ben’s approach. I could maybe surround the box with some nice wood and have it turn out very nice. Since I had already started this board I went with the: presaturate the eps with resin, put an extra patch of glass under (and eventually over), then put in tap holes filled with resin that go to the bottom of the deck. I think that I managed to include just about every solution 
Thanks again for all the help!
I use about 3/4"
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Thank you guys for all the help! In the future I could see doing some hybrid solution between 4ests and Ben’s approach. I could maybe surround the box with some nice wood and have it turn out very nice. Since I had already started this board I went with the: presaturate the eps with resin, put an extra patch of glass under (and eventually over), then put in tap holes filled with resin that go to the bottom of the deck. I think that I managed to include just about every solution
Thanks again for all the help!
I’ve used the glass under box approach, basically folding every layer of cloth on the bottom into the slot for the box, plus adding a layer under it. It’s a mess to do, but it’s strong. So far this has worked well, hitting rocks with the fin at full speed and having the board fly off the roof of my car doing 50mph after not strapping it down(I was in a hurry and forgot). The board hit the asphalt then kept going and hit a fence. The fin broke at the screwhole, no damage to the box or board around the box except for some scratches where the fin pin was (the pin bent).
regards,
Håvard
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hitting rocks with the fin at full speed and having the board fly off the roof of my car doing 50mph after not strapping it down
Thats the kind of strength that I’m looking for!