hi!
I´m about to build my third foilboard in xps and due to the higher density it adds more weight to the final board than EPS. To reduce weight I was plaining with the idea of making a few chaneels of hollow interiar to get down to about the same weight as EPS or lower.
might be a stuped idea or it might not. I use xps because it is easier to get in right size where I live. no or no go? what is your opinion?
Hello Dun,
Welcome to the forum. You’d have to do the math (volume of foam removed x density of foam = reduction in weight) and see if it is worth it and decide if there will be a compromise in strength of the core, if it will need to vented, etc. I take it you have to add some even heavier HD foam to support the mast box/connection?
I made some ‘racing’ parts for a sailboat where I drilled out this and that and carbon fiber-ed this and that to remove weight and in the end I only saved maybe 2 oz (60g) and they were more of a pain to finish, but I do get to say they are made from ‘drillium’…
What is your XPS foam density?
yes I hear you! since the board is pretty thick. about 13cm at thickest parts there is a lot to be removed so on a good day i could maybe get down 1/3 of the total xps weight with is 30g/liter in density. epes i think is about 20g/L
will use a pvsfoam around the foilinserts and probablu not hollow board at that point. maybe do two channels in both side of the board
and thanks for the welcome!
20 g/L is not a foam density I would use for Surfcraft builds.
XPS needs some surface prep before glassing. Higher density insets for box installations would be helpful. What is the volume of your board design?
If your board was 60 liters volume the difference between one made with 20 g/l vs 30 g/l foam is 600 g.
i get it to be 650 g for a 65 liter board if i do my calculation right. 65 liter xps blank would be 1950g and 1/3 of it is 650g. not much but everything counts like Dave Gahan sings:)
I chambered a stringerless 8’ XPS board I made years ago. It is the only board I have ever broke in half. The break was where a chamber was. The board lasted several years, but it broke paddling out and I don’t recall getting hammered by the lip. One thing I did wrong was I didn’t stagger the holes, I did holes straight across several sections. It may have lasted longer if I staggered the holes. I really liked that board, but it was a good learning experience.
thansk for the input! I do not get what you mean with stagger the holes? my foilboard will probably be thincker than your longboard, but still you make a point. might not be worth the risk of breaking it.
I cut rockers slices then glue them up the smae way they make balsa boards. I made chambers like they do when they make Balsa boards, but I just drilled out holes across several pieces instead of staggering where the empty spaces would be. I think it is possible to cut out some of the foam. My impression is that foil boards don’t get the same pounding because they float on the wings.
yes you might be right and I will not do any jumping with it. only surf waves. I might give it a go anyway;)
Wouldn’t adding cavities defeat the purpose of using XPS (closed cell), because any leaks would let the cavities fill with water?
I’d love to do a dual density blank. Higher density on the deck and rails. Lower density in place of a center cavity.
Two different densities of XPS foam? Difference in densities?
If the surface area of low density foam in your center cavity is large, you are likely to get significant pressure dings (leading to delamination). Low density XPS has low minimum compressive strength that pressure dings easily.
Long ago, a Sways member glued wood sheets/veneer over a an XPS skeleton with XPS rail strips.
Found the old XPS skeleton/rails with poplar skins thread. Unfortunately, the pictures are no longer there.
I found the idea of XPS boards here: Clay Island: Waterproof XPS Board Build – Update After 2 Years of Use
But he uses XPS because it’s closed-cell, so he doesn’t have to worry about pinholes or dings waterlogging the foam.
If the board has hollow cavities, then we still have to worry about them flooding due to dings/pinholes.
So why would hollow boards need to use XPS? Once we’re committed to being watertight (cavities), then it shouldn’t matter if we use EPS?
My dual-density foam idea is: use the lowest-density XPS board (DuPont Panel Core 20 is the lowest I’ve found), 24kg/m^3 for the majority of the board volume. Then use denser XPS board, maybe 50kh/m^3, on the deck and rails for impact/dent resistance.
Basically, it would be a lot of work to save 10-20% of the board weight, but if someone is already using a 3D CNC mill to cut their board blanks, then it shouldn’t be terrible. If someone is hand-cutting their blanks, then build the whole blank out of denser XPS, then cut out the center section, fill with lower density XPS, with a thin layer of denser xps on top:
Salomon bleuboards were hollow with xps skins. Good board, light but like all xps boards had delam problems here and there.
Go for it, it’s what firewire do now and many others. I mostly only do sandwich deck and reinforced rails nowadays for all, add lot of durability. Becarefull to add enough buckling strengh to bottom.
What happens when you ding your board with internal cavities.
EPS soaks up water…
DuPont Panel Core 20 is specifically sold for composite core. I’m not sure what the surface treatment is, but if dupont is marketing it for that application you’d hope they have solved delam issues?
What happens when any EPS board gets dinged and soaks up water?
Adding cavities makes it even worse. Maybe add a vent plug (like SUPs often have), that doubles as a drain plug for the cavity?
