Help with Fin Box in 1lb EPS

I am installing a 10.5" Fins Unlimited box in 1lb EPS using RR epoxy w/ Slow hardener. I have searched the archives for days trying to figure out the best way to install the box. I have read many different ways and a lot of them do not mention which type of hardener they are using. Every one seems to agree on a tight tolerance fit to keep the resin pool down, therefor the heat down. From there I am not sure which way to go, pour in steps, use ice, ect. or if I can just proceed as normal with the slow hardener. Any help would be appreciated.

have you reinforced the area around the box at all? high density insert, stringer, etc???

I will be routing into the stringer for the box install, if that is what you mean, but no inserts or anything like that.

did you make a router jig for the box?

build a nice, close tolerance jig that you can use to route a perfect hole using a pattern routing bit.

(probably not this exact bit…you’ll want more cutting depth)

test the accuracy of the jig and the routing process in scrap foam before you go to the finished blank so you gain some confidence.

make sure you make small passes with the bit, especially over the stringer so that you don’t get any radical “bite” with the router.

as for the epoxy…you’re on the right track with the slow…if you’re using a close tolerance hole for the box you won’t be able to do multiple pours like you can with a probox install where there’s a gap you can pour in to…instead, you’re going to fill the box with resin and sink in the box…pressing down hard to force out the excess resin. wipe all this resin away and then place a piece of wax paper over the box, so that you can weight it down to make sure that it doesn’t “float” up out of the cavity.

regarding exotherm…user Mahana and his brother have a cool trick where they use icepacks over and under the box to keep the resin relatively cool as it cures so that it does not overheat, eat in to the foam and compromise the strength of the box.

set up the board with the tail on a table or surface…lay down an ice pack, put the tail down on the ice pack with the box area centered over the ice…pour in the resin, push down the box, wipe off the excess, put down the paper, put down another ice pack and then put some weight over the whole thing to keep that box packed down.

perhaps someone will follow up to confirm or deny what I’ve advised here.

I’d be concerned about a fin box in 1 lb with no high density inserts. The stringer will protect it fore/aft, but if you get a good lateral hit, or even just the lateral pressure from a big fin (what size fin is going in?) being turned hard, the 1 lb will give. Everyone I know working with 1 lb is using high density inserts.

How thick is the stringer? If it’s thick enough it might be resisting lateral forces

At the very least you’d want to dig out a hollow under the bottom glass to create a resin flange. Use a big pan head screw to do that. Then lateral force will be transferred to bottom glass.

I would strongly advise an insert in 1 lb foam, but it sounds like you've already lammed it. Afoaf's advice is all good, I'd add to cap the box with a patch over and if the bottom glass isn't 6 oz or more, put a patch down before routing the slot. The stringer and the bond between the top of the box and the glass is going to have to take most of the loads - the 1 lb will ''give'' easily. If your tail is thin enough that the box touches the deck that would help a lot.

if the board is already lammed, what about this:

- route for your fin box as normal. tight fit per afoaf.

- then, "route" 2 slots perpendicular to fin box route. say 2" from each end. 1/4" thick that go past the box 1"-2" on each side and go all the way to but not through the deck lam. you might need to start with one of those drywall cutout router bits or a small drill bit then scrape out the last bit of foam by hand.

- mix up some resin with lots of chopped glass, and fill in the deeper perpendicular routes let it kick.

- then do your fin-box on top of that as per instructions on this thread

what i'm hoping will happen is that you will get a bond with the deck that spreads the load out wider than the box without doing a full "H" pattern like FCS which would add a bunch of weight.

thoughts anyone? viable? stupid?

You Swaylock's guys are SMART! (at least when you agree with my opinion) :)

For the OP, there's all kinds of fancy ways you can brace it up if you want to spend the time. John Mellor will come on here in a while and show his sideways stringers, and or you can do the old sailboard trick of partial stringers alongside the box, and I'm sure there's more....

Wow, this is getting rather good. Thanks for the help everyone. The board will have a rather big fin, 8.5"-9". I had no idea about putting inserts in, oh well. Afoaf seems to have the heat issued cured for me, and I did not even know I had the density issue so its just a bonus.

The board is glassed with double six bottom and triple six top. The stringer is 3/16" so not much help there. The tail is to thick for the hope of the box coming close to the top glass.

I like all the ideas so far, guess I will wait and see what else pops up and what everyone thinks and make a decision.

If it comes down to it would a glassed on fin be a more simple fix.

learn to do boxes...there will be more of them in your future...you can really change a board up by moving and changing fins.

I forgot the cloth for the box...

 

The 3/16'' stick and double 6 bottom are going to help. IMO cap it with 2 layers (one barely bigger than box, another larger), don't sand all the cap off, and it should be OK 'til you hit a rock.

You still can do an insert after the fact. Route out an oval 1/2" to 3/4" larger than the box that goes almost to your deck.Knock out last few beads with a screwdriver. Cut out and insert using some Poly foam,xps,d-cell,corecell,etc. Gorrilla glue it in place. Route out for your box and then epoxy it in. No need to worry about exotherm now. Sand flush then add a patch of glass over the box and insert.

CJ

Ya know, cj's right, you can still do the insert. A little more trouble now, but if you use 6 lb foam it'll be strong as.

Lebowski,

 

   Your project sounds like it's AAALLLLLOOOOOOTT more interesting than what we got going on.  Not to mention the only surf here is on the internet!  Good luck with it.  Post whatever you end up doing, and if you took pics along the way it would be awesome. I really like the oval insert idea BTW.

 

  Oh,  If you need something bigger than the 8' while your working on this one I can email you my garage code.

 

Shane,

 

"Why do I get all the reterms, hmmmmmmmm."

I was thinking you could take a Sawzall blade or jigsaw blade and scribe out two slots that go all the way to the deck - like the H pattern FCS does. Just create to slots that extend the plane of the sides of the routed out hole all the way through to the deck glass. The slots will only be as thick as the width of the blade, but it will help support the box with little extra weight.

I appreciate all the input on how to fix the 1lb problem. I am having a hard time convincing myself to modify my current board for the fins sake. I have no problem putting on a glass on. Starting to sound easier than any other option. This is only my third board and it came out much better than I anticipated so the thought of routing out an oval in the glass and foam just makes me queasy. The H pattern sound more doable but I still believe the glass fin on would be a better option for me, no modifying of finished board and now worries of heat. I now know if I ever do another 1lb board an insert is the way to go, I have some left over Biofoam scraps that are kinda greenish, wonder it that would work and have a little greenish oval design? Thanks to everyone for all the input.