Wakeskate prototype

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#1

Hi everyone, my name is Logan and I would really like your help. I’m working on a bi-level wakeskate. Its essential a skateboard on the water. It endures wakeboard impacts and speeds. A bi-level is two boards: a 9-ply maple concave top deck that looks much like a skateboard deck but it much bigger & a bottom deck build much like a wakeboard but with a PU rail.

A bi-level is made by Ronix Company but it lacks in a few areas that I feel if improved would greatly enhance the performance. I have the Top deck specs laid out and there is not much wiggle room for change. The bottom deck is where I am running into issues; and that’s why i’ve come here for some much needed and greatly appreciated help.

My main problem is weight and strength. Bi-levels now are way too heavy; around 14 lbs. The top deck and pieces to connect the boards weight 7.5 lbs. To get the total board weight to the ideal amount of 11.5 lbs I need the bottom deck to weigh in at around 4 lbs. The size of the bottom deck needs to be 39" long X 15" wide in the middle, with 12" (tip/tail) Thickness can be 1/2" - 1".

After scouring the web I’ve decided to go with a vacuum bagged foam core sandwich construction with a PU side rail. After taking a look at the engineering aspects my brain has begun to melt.

So my questions are:

What foam core (or any core for that matter) could withstand the core crush of wakeboarding/wakeskating? And how thick should it be?
(I was thinking Dyvini H80 around 3/4" thick) There will be milled out indents where the board attached in 4 places about 3/16" deep X 2" x 3" on the bottom of the board.

What laminates should be used? weight? weave? CF or FG? <mixed?
(I was thinking CF and FG mixed on the top and bottom but have read the loads would be unequally distributed between the two & cause failure versus all CF.)

What should the laminate layup angles be to provide the proper torsional and directional stiffness?

I tried to look all this up for the last week or so but it just seems the more I learn, the more questions I have to answer. Just any pointers in the right direction would help and advice from experience on what you think would be strong enough materials and the weights associated with those.

#2

Sounds like you have a pretty good start on how to go about this. As you’ve identified the layup schedule of the skins is going to be the big question. I think that you’ll find that no one here is going to be able to give you all the answers you want. Ultimately there are two ways to get the answers you need:

  1. Higher an engineer to do the calculations for you and give you a layup schedule. Not sure what your budget is but it would be worth looking in to as your part is fairly simple and it might be cheaper than you think.

  2. Trial and error. This is a very common way so go about it for projects like this especially if you aren’t scare of breaking a few. You would want to start off with a few assumptions. In this case you have a final weight you are trying to achieve. Working from that you have a proposed core that would weigh around 1.14lbs [(39*13.5-.75) volume in inches divided by 1728 (cubic inches per cubic foot) * 5 (density of H80 foam)] Add to this the weight of the rails which I have at around 1.5 pounds based on .5 inch wide rails using a fairly low density urethane (1.1 g/ml)

These added together gives you a core weight of 2.64 pounds with out any inserts. This leaves you with 1.4 pounds for your laminate to reach your 4 pound goal. Assuming a laminate with 50% resin by weight this only leaves you with .7 pounds or 9 ounces for actual reinforcement. Which would only be enough for around 1 layer of 9oz cloth on each side. I couldn’t say for sure but I think you would find this to not be strong enough.

#3

Thanks for running the numbers as I was a bit off.

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