Wow it’s February already!
We’re on a concave deck kick this last few weeks and we wanted to try to create a concave deck skim style board. We liked the concept of creating the bumpy-lumps as an addition to the exterior of an existing shape. BUT, as we noted that takes some extra care in protecting the bumpy-lumps with carbon tape or something. That area will become prone to dings, but there is something else that has to be considered. We didn’t really enumerate it when we talked about the design considerations on the concave deck surf style wakesurf board. We’ll start this discussion with a picture.
This is jumping way ahead, please foregive us for being so convoluted here, but we think it will make more sense. In the picture above, what we’ve done is glue some bumpy-lumps to the wakesurf core foam and then used a 3 mm sheet of divinycell H80 to the deck side. You can see the bumpy-lumps forward around the front foot area. We wanted to test a few things, one is that we have effectively molded a deck skin. We can apply a higher density foam over the complex shape underneath, providing protection to the raised areas, but also can you guess what else it achieves?
Did you guess stiffness? Yeah! Remember how we talk about the flat panels on your car doors, where the manufacturer puts in curves or indentations to stiffen up that area? Skinning these bumpy-lumps increases the stiffness using that same property. That is such a great use of the bumpy-lumps, but it also introduced another issue.
It’s stiffer in that area, but what about the areas right at the ends? Yeah, not as stiff. So, much like channels that abruptly end, that transition from bumpy-lumps to flat create a weak spot, in effect. Well not weak, but the areas just on either side of the stiffness increase will recieve disproportionally more bending forces and no doubt if this board were to break, it would be just short of the bumpy-lumps.
Now we did compensate for that, there is a small patch of carbon fiber under the skin, but what we wanted to convey is every design change has some ramifications! We also really like the idea of the additional of bumpy-lumps as a means of adding stiffness to a concave deck skim style board.
So lets get into the build of this concave deck skim style board. We mentioned in yesterday’s post that we wanted to work with both some H60 divinycell and H80 divinycell. The H60 is a green color and is also a 4 pound density foam. We use our template to trace the outline on the foam. We should also note that Divinycell comes in flat sheets. It is thermoformable into curves and shapes. Most manufacturers don’t bother, alothough that would be a vast improvement to the finished product as the core foam would be shaped, just like with surf style boards that shape the core from a blank.
We use a jig saw to rough cut the outline and then a sanding block to bring the outline down to shape. We’ve also cut a slight angle into the outline to make shaping the rails easier. Now if we were making a standard skimmer, the shaping would mostly be done at this point. We’d round over the deck side along the outline and then laminate it. We know, crazy simple, huh? Step 1 cut. Step 2 sand. Step 3 laminate. Step 4 sell for a profit. Ok ok ok, not quite that simple, but these are pretty easy to construct and the general shape is a reflection of that. We are probably going to work on adding some light concaves to the bottom to see how those work on this shape. It will complicate the build process, but we are thinking might increase the performance some. We’ll see!
As you saw in the very first photo, our plan for this build was to make a skinned concave deck skim style board, we used a lighter weight wakesurf board core foam with the H60, so now we want to increase the durability of the deck by skinning with a heavier weight H80 3 mm skin. The divinycell H8o is color coded, if you will, with this grey color. The H80 is a 5 pound density skin. We trace the outline, but cut generously as we’ll be matching the bottom and the deck skin and then rounding it all off when we finish shape the rails.
Here we have cut both pieces in preparation for the build process. That’s where we’ll leave it for today. Come back again as we load all of this onto the skimmer rocker bed and create the project in the very first picture of this post!
We really appreciate you following along!