Glass over boxes just remind me of a brick shithouse built on less than solid ground. All of the glass over boxes that I know of just have a tiny bit of glue attached to soft foam supporting the underneath of them. Does capping them really compensate for this sort of foundation?
I woud say, Yes
some designs require glass over and some dont
Maybe it’s just me who has problems with glass overs after install.
Have you won the best avatar yet?
I use a lot more resin/chopped fiber mix to hold them in than just a bit of glue. I set in the box dry, mask around it, remove the box, fill the hole with resin/chopped fiber, put the box in, remove excess resin around the masking, and then clamp them down. For eps, I use Gorilla glue (you must clamp with this). Many production shops do only use a little bit of resin, or more often so much that they melt massive amounts of foam away. Nobody knows until I get them in for repairs and pull the box out. Unless it’s something like an FCS plug or center box where I can do layered filling, I never use epoxy because of the melting risk.
Structurally, if the finbox has a large enough flange with cloth over it, it’s essentially part of the skin. The flange will provide enough resistance in side loading to keep the box in the correct position. However, this depends on the size of the flange and how soft the foam is. That’s why if you use enough resin/glue, the soft foam factor is gone. Adequate sized flanges are those like on lok-box and o’fish’ll boxes in my opinion. I don’t consider foam to be structural, although many finbox designs are just set in it without cloth over them. Using wood strips around centerboxes or setting “plug” type boxes in D-cell are much stronger if the use conditions warrant it.
PeteC knows.
But check this. I am impressed that I was able to find it.
Honestly I don’t know why anyone would use any other fin system other than Probox!! very simple system very dependable and very strong! So many fin set up posabilities!! In EPS or PU Lay a couple layers of 6oz cloth in your cavity let it kick than install box as normal!!! No glassing over!! Glueing in a fin box???
CG
Honestly, I don’t know why anyone would be anything other than a Presbyterian. …
(Not picking on you Chris, just making a point)
Great idea Greg!
…in my opinion ALL systems are prone to fail due to a low density foam and a hard plastic inter relation
and actually ALL fail
people see less fails with Probox or Lokbox because the simple reason that arent massives and very rare to see some outside USA
lot of boards using Futures (old ones more prone to fail) had 1 or more of the boxes lose
even Speedfins
FU s are pretty good and the installation resist several impacts (put in a stringer, less when put in the foam) if you have a “fuse” type of adjusting tab
What’s the point???
Considering all the available systems out there which are few! Probox gives you the most advantages as far as set up and versatility and strength all in one!! For me It’s a pretty simple decision! Unless you surf on the freeway your going to have a pretty hard time breaking them! You can use your FCS fins in them and several others with little modification to fin base. I don’t work for Probox just have tried them in many diffrent boards for over 3 years and surfed them in many conditions on several diffrent parts of the planet>
So that said again why use another system???
There is already plenty of material/debate in other threads about the pros/cons of various fin systems. A very specific question was asked at the beginning of this thread, and Im sick of seeing any fin system related thread turn into a “debate” about which is best and why. Bump one of those threads to the front page if you want to discuss it. They are there…
Wow Sensitivity!!!
I’ll give my 2 cents on the “Specific Question”!!
It dos’nt matter what type of fin system you use unless you anchor it putting some cloth over the top is not going to do anything!! There is so much load force on a fin that you will blow out glue or adhesive what ever!! I have been fixing boards for 35 years and making my own boards. I have seen all kinds of fin system blow outs. If the H pattern is adheared to the deck on an FCS you have no anchor for example. I like lining any system cavity first with some layers of cloth especially EPS. When I first started using EPS it was suggested on this forum to use Marine adhesive that was a bad move!! to rubbery and flexy I had never used EPS before and was woried about thermal melting, Now it’s a couple of layers of cloth first then fill it! Reguardless of the fin system you choose or use I think this is the best way to go!!
CG
Does capping them really compensate for this sort of foundation?
Ask futures or lokbox and they’ll tell you yes. Ask others and probably no. Ask guys that use really big fins, and no/yes.
It all depends.
Resisting Torque is key. Some fins apply more torque, as do some surfers and some waves. Tie in your box to the deck glass and youre golden.
FUs are almost always adhered to a wood stringer. They are also bigger so you get a bigger root relative to fin size.
Failure modes are really important and you didnt mention what problems you are having so Im generalizing.
Not surprisingly, this has come up before. Not surprisingly, being an engineer (civil) and surfer, I’v jumped in before… but here we go again.
The force exerted on a fin has to be received, for lack of a better word, by the foam/glass structure below it. The more you can spread out the force, the lower the stresses on the underlying materials. But know tha just like building an idiot-proof or snap-proof board, there is always a wave, rock, situation, or idiot who will blow the whole thing apart.
Adding milled glass or short fibers to the resin used to anchor the fin box DOES NO GOOD. The limiting factor is still the AREA over which the bond is made and it makes no difference how strong the glue is. This misconception comes up time and again, dammit, you think someone would get over it by now.
The H-pattern of wood strips is a small step in the correct direction, but all things are only as good as their weakest link. where is the weakest link in the H-pattern? I think it’s at the joint between the box and the wood strips. The joint area is quite limited and in turn the H-strips won’t distribute much force. Still, a small step in the right direction. Labor intensive, it’s not likely to catch on.
Wider flanges on the box are good, they distribute fin forces. Glass over a box is good, it distributes fin forces. Example…the first three Futures boxes I ever installed on a board made for a demanding little cutie… well she ran over someone and tore one whole fin and box right friggen out. Of course she wanted me to fix it, and it was a clean blow-out and likely would have been and easy repair. But the wife stepped in, went nuts and the whole deal went up in smoke.
Glass over your fin box installs. It’s easy, quick, and helps as much as anything else, certainly more than some of the ideas I’ve seen here.
I won’t argue too much. My solution was for one pound foam and I found it firmed up the box considerably. So maybe a medium step. But as you say, they are all going to fail if you hit them right.
BTW, I’m a CE too. Mostly hydraulics/hydrology. Structures was a snooze for me.
As I noted here before, one little addition on the ProBox and even Futures is to use a 3/8 inch tube with saw type notches on one end and do like the FCS installs and put in a couple of H pattern holes filed with resin and bonded to the deck and bottom of the box. OTOH, more weight, more chance for melting foam, more trouble.
Just use smaller fins.
Thanks Charlie and Greg for adding to my comments on the flanges and glassing over. I’m an ME, so I deal with stuff on a lot smaller scale than you CE’s. I really think that the flanged designs in boxes were a step forward. The reason I use chopped fibers in poly is because it simply makes a really gooey mixture rather than a cabosil or other thin filler. For me, it’s easier to fill with this. Also, I’ve repaired many flanged side boxes that took front/rear impacts and the boxes were completely knocked out. So cleanly that I reused them. This was obviously a lack of anchoring. On side loading, I agree that increasing the anchoring doesn’t do much.
For really low density foam like 1 lb, template routing out a cavity and filling with the 2 lb pour foam, then routing for the box would be an easy thing to do. I’m using this stuff alot as I encounter more and more areas of melted foam in eps boards around boxes during repairs.
Another reason for glassing over boxes in eps is foam expansion when heated. I’ve been seeing quite a few eps boards with gaps around the boxes. These have been relatively dark boards and the heated eps starts pushing the boxes out. When it cools and the foam shrinks, a gap is left. Glassing over as much as possible will hold them in a bit better.
Adding particulates (milled fibers, cabosil, micro-balloons etc.) or fiber does accomplish an
advantage… it improves fracture toughness and fatigue resistance of the resin/epoxy. As
far as improving the strength of the box install, definitely not. I cant imagine too many boards that last long enough where fatigue comes into play.
Amen! This statement goes a loooooongggg way. forgotten too often
I’m in agreement with most of what Honolulu said.
Glass over systems are stronger because it adds loan-bearing surface area. Adding surface area to the sides of the box (concaves, ridges, bumpouts, etc…) all spread the load. Through-the-board systems are stronger, as well.
The glass over the box/plug supports the top of the box. By this, I mean that the stress on the box under normal surfing conditions is lateral, where one side of the box is pushed into the board and the other is lifted out. The glass over the box helps hold the box down on one side and helps hold it up on the other (as long as the glass is bonded well to the box). The same can be said for end-to-end impacts… the glass over the box holds it down on one end and up on the other.
I think additives make the medium stronger, as somebody said here already… but it’s the bond of that medium to the foam that matters most. Ideally, you’d want the resin to soak into the foam a bit… scratches or perforations might improve the bond between the foam and the resin.
I really like it when the engineers on here back up what we’re doing at Coil, however implicitly. We put more fiber than anyone else over the flange, and we get a pressure bond to boot. Not to mention that the box is hooked to the deck on a lot of our boards. Solid install also gives better feel to the fins, or so a lot of riders report. At least a couple of you have seen or ridden 'em also.